National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

San Antonio Missions National Historical Park

Natural Resource Condition Assessment

Natural Resource Report NPS/SAAN/NRR—2016/1191
ON THE COVER

Mission San José at San Antonio Missions National Historical Park

Photograph courtesy of the National Park Service 
San Antonio Missions National Historical Park

Natural Resource Condition Assessment

Natural Resource Report NPS/SAAN/NRR—2016/1191

Kathy Allen

Sarah Gardner

Andy J. Nadeau

Anna M. Davis

Kevin Benck

Lonnie Meinke

Shannon Amberg

Thomas Walker

GeoSpatial Services 

Saint Mary’s University of Minnesota 

890 Prairie Island Road Winona, Minnesota 55987

March 2016

U.S. Department of the Interior

National Park Service

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, 

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Please cite this publication as:

Allen, K., S. Gardner, A. J. Nadeau, A. Davis, K. Benck, L. Meinke, S. Amberg, and T. Walker. 

20XX. San Antonio Missions National Historical Park: Natural resources condition assessment. 

Natural Resource Report NPS/SAAN/NRR—2016/1191. National Park Service, Fort Collins, 

Colorado. 

NPS XXX 472/132206 XXX, , March 2016 Month 201X (The Fort Collins Support Office will fill out this line for you)
iii

Contents 

Page

Figures...................................................................................................................................................ix

Tables..................................................................................................................................................xiii

Photos.................................................................................................................................................xvii

Appendices..........................................................................................................................................xxi

Executive Summary..........................................................................................................................xxiii

Acknowledgments..............................................................................................................................xxv

Acronyms and Abbreviations............................................................................................................xxvi

Chapter 1 NRCA Background Information ...........................................................................................1

Chapter 2 Introduction and Resource Setting ........................................................................................5

2.1 Introduction ..............................................................................................................................5

2.1.1 Enabling Legislation.........................................................................................................5

2.1.2 Geographic Setting ...........................................................................................................5

2.1.3 Visitation Statistics...........................................................................................................8

2.2 Natural Resources.....................................................................................................................8

2.2.1 Ecological Units and Watersheds.....................................................................................8

2.2.2 Resource Descriptions....................................................................................................11

2.2.3 Resource Issues Overview..............................................................................................13

2.3 Resource Stewardship ............................................................................................................21

2.3.1 Management Directives and Planning Guidance............................................................21

2.3.2 Status of Supporting Science..........................................................................................21

2.4 Literature Cited.......................................................................................................................23

Chapter 3 Study Scoping and Design ..................................................................................................27

3.1 Preliminary Scoping ...............................................................................................................27

3.2 Study Design ..........................................................................................................................28

3.2.1 Indicator Framework, Focal Study Resources and Indicators........................................28

3.2.2 General Approach and Methods.....................................................................................32

3.3 Literature Cited.......................................................................................................................37

Chapter 4 Natural Resource Conditions...............................................................................................39
iv

Contents (continued)

Page

4.1 Forested Riparian Corridors...................................................................................................40

4.1.1 Description .....................................................................................................................40

4.1.2 Measures.........................................................................................................................41

4.1.3 Reference Conditions/Values.........................................................................................41

4.1.4 Data and Methods...........................................................................................................41

4.1.5 Current Condition and Trend..........................................................................................43

4.1.6 Sources of Expertise .......................................................................................................53

4.1.7 Literature Cited...............................................................................................................53

4.2 Native Grasslands...................................................................................................................55

4.2.1 Description .....................................................................................................................55

4.2.2 Measures.........................................................................................................................56

4.2.3 Reference Conditions/Values.........................................................................................56

4.2.4 Data and Methods...........................................................................................................56

4.2.5 Current Condition and Trend..........................................................................................56

4.2.6 Sources of Expertise .......................................................................................................60

4.2.7 Literature Cited...............................................................................................................61

4.3 Upland Shrublands/Woodlands..............................................................................................63

4.3.1 Description .....................................................................................................................63

4.3.2 Measures.........................................................................................................................63

4.3.3 Reference Conditions/Values.........................................................................................63

4.3.4 Data and Methods...........................................................................................................64

4.3.5 Current Condition and Trend..........................................................................................64

4.3.6 Sources of Expertise .......................................................................................................73

4.3.7 Literature Cited...............................................................................................................73

4.4 Reptiles...................................................................................................................................75

4.4.1 Description .....................................................................................................................75

4.4.2 Measures.........................................................................................................................75

4.4.3 Reference Conditions/Values.........................................................................................75
v

Contents (continued)

Page

4.4.4 Data and Methods...........................................................................................................75

4.4.5 Current Condition and Trend..........................................................................................77

4.4.6 Sources of Expertise .......................................................................................................85

4.4.7 Literature Cited...............................................................................................................85

4.5 Amphibians.............................................................................................................................88

4.5.1 Description .....................................................................................................................88

4.5.2 Measures.........................................................................................................................88

4.5.3 Reference Conditions/Values.........................................................................................88

4.5.4 Data and Methods...........................................................................................................89

4.5.5 Current Condition and Trend..........................................................................................91

4.5.6 Sources of Expertise .......................................................................................................96

4.5.7 Literature Cited...............................................................................................................96

4.6 Breeding Birds........................................................................................................................98

4.6.1 Description .....................................................................................................................98

4.6.2 Measures.........................................................................................................................98

4.6.3 Reference Conditions/Values.........................................................................................98

4.6.4 Data and Methods...........................................................................................................99

4.6.5 Current Condition and Trend........................................................................................102

4.6.6 Sources of Expertise .....................................................................................................115

4.6.7 Literature Cited.............................................................................................................115

4.7 Resident Birds ......................................................................................................................118

4.7.1 Description ...................................................................................................................118

4.7.2 Measures.......................................................................................................................118

4.7.3 Reference Conditions/Values.......................................................................................118

4.7.4 Data and Methods.........................................................................................................119

4.7.5 Current Condition and Trend........................................................................................120

4.7.6 Sources of Expertise .....................................................................................................128

4.7.7 Literature Cited.............................................................................................................128
vi

Contents (continued)

Page

4.8 Aquatic Macroinvertebrates .................................................................................................130

4.8.1 Description ...................................................................................................................130

4.8.2 Measures.......................................................................................................................131

4.8.3 Reference Conditions/Values.......................................................................................131

4.8.4 Data and Methods.........................................................................................................132

4.8.5 Current Condition and Trend........................................................................................132

4.8.6 Sources of Expertise .....................................................................................................139

4.8.7 Literature Cited.............................................................................................................139

4.9 Fish .......................................................................................................................................141

4.9.1 Description ...................................................................................................................141

4.9.2 Measures.......................................................................................................................142

4.9.3 Reference Conditions/Values.......................................................................................142

4.9.4 Data and Methods.........................................................................................................142

4.9.5 Current Condition and Trend........................................................................................143

4.9.6 Sources of Expertise .....................................................................................................151

4.9.7 Literature Cited.............................................................................................................151

4.10 Water Quality .....................................................................................................................153

4.10.1 Description .................................................................................................................153

4.10.2 Measures.....................................................................................................................156

4.10.3 Reference Conditions/Values.....................................................................................158

4.10.4 Data and Methods.......................................................................................................159

4.10.5 Current Condition and Trend......................................................................................159

4.10.6 Sources of Expertise ...................................................................................................174

4.10.7 Literature Cited...........................................................................................................174

4.11 Air Quality..........................................................................................................................177

4.11.1 Description .................................................................................................................177

4.11.2 Measures.....................................................................................................................177

4.11.3 Reference Conditions/Values.....................................................................................179
vii

Contents (continued)

Page

4.11.4 Data and Methods.......................................................................................................179

4.11.5 Current Condition and Trend......................................................................................182

4.11.6 Sources of Expertise ...................................................................................................189

4.11.7 Literature Cited...........................................................................................................189

4.12 Soundscape.........................................................................................................................193

4.12.1 Description .................................................................................................................193

4.12.2 Measures.....................................................................................................................193

4.12.3 Reference Conditions/Values.....................................................................................194

4.12.4 Data and Methods.......................................................................................................194

4.12.5 Current Condition and Trend......................................................................................197

4.12.6 Sources of Expertise ...................................................................................................201

4.12.7 Literature Cited...........................................................................................................201

4.13 Dark Night Skies................................................................................................................203

4.13.1 Description .................................................................................................................203

4.13.2 Measures.....................................................................................................................203

4.13.3 Reference Conditions/Values.....................................................................................203

4.13.4 Data and Methods.......................................................................................................204

4.13.5 Current Condition and Trend......................................................................................204

4.13.6 Sources of Expertise ...................................................................................................212

4.13. 7 Literature Cited..........................................................................................................212

4.14 Viewscape...........................................................................................................................214

4.14.1 Description .................................................................................................................214

4.14.2 Measures.....................................................................................................................214

4.14.3 Reference Conditions/Values.....................................................................................215

4.14.4 Data and Methods.......................................................................................................215

4.14.5 Current Condition and Trend......................................................................................218

4.14.6 Sources of Expertise ...................................................................................................253

4.14.7 Literature Cited...........................................................................................................253
viii

Contents (continued)

Page

4.15 Hydrology (Surface and Groundwater)..............................................................................255

4.15.1 Description .................................................................................................................255

4.15.2 Measures.....................................................................................................................257

4.15.3 Reference Conditions/Values.....................................................................................257

4.15.4 Data and Methods.......................................................................................................257

4.15.5 Current Condition and Trend......................................................................................258

4.15.6 Sources of Expertise ...................................................................................................268

4.15.7 Literature Cited...........................................................................................................268

Chapter 5 Discussion .........................................................................................................................273

5.1 Component Data Gaps..........................................................................................................273

5.2 Component Condition Designations.....................................................................................275

5.3 Park-wide Condition Observations.......................................................................................278

5.4 Literature Cited.....................................................................................................................280

Appendices.........................................................................................................................................283
ix

Figures

Page

Figure 1. The Missions Unit of SAAN. ................................................................................................6

Figure 2. Location of the Rancho de las Cabras Unit of SAAN. ..........................................................7

Figure 3. Ecoregions surrounding SAAN park units (EPA 2011). .....................................................10

Figure 4. Exotic plant removal areas with the number of times each area has been treated 

since 2001 (NPS 2014b). .....................................................................................................................16

Figure 5. Change in mean annual precipitation (left) and mean summer precipitation 

(right) in the SAAN region between 1951 and 2006 (PRISM 2014)...................................................17

Figure 6. Projected change in mean annual precipitation in the SAAN region by 2050 

(left) and by 2100 (right) (Maurer et al. 2007) ....................................................................................18

Figure 7. Projected change in mean winter precipitation (left) and mean spring

precipitation (right) in the SAAN region by 2050 (Maurer et al. 2007)..............................................18

Figure 8. Projected change in mean winter precipitation (left) and mean summer

precipitation (right) in the SAAN region by 2100 (Maurer et al. 2007)..............................................19

Figure 9. Projected change in mean annual temperature in the SAAN region by 2050 

(left) and by 2100 (right) (Maurer et al. 2007) ....................................................................................19

Figure 10. Projected change in mean annual aridity (left) and mean spring aridity (right) 

by 2050, as predicted by the change in AET:PET ratio (Maurer et al. 2007)......................................20

Figure 11. Projected change in mean annual aridity (left) and mean spring aridity (right) 

by 2100, as predicted by the change in AET:PET ratio (Maurer et al. 2007)......................................20

Figure 12a. San Antonio Missions National Historical Park natural resource condition 

assessment framework. ........................................................................................................................30

Figure 12b. San Antonio Missions National Historical Park natural resource condition 

assessment framework. ........................................................................................................................31

Figure 13. Description of symbology used for individual component assessments. ..........................34

Figure 14. Cogan’s (2007) study boundary (yellow) relative to the park boundaries. .......................42

Figure 15. Forested riparian communities within the northwestern area of the Missions 

Unit (data from Cogan 2007)...............................................................................................................44

Figure 16. Forested riparian communities within the southeastern Missions Unit at 

SAAN (Cogan 2007)............................................................................................................................45

Figure 17. Forested riparian communities within the Rancho de las Cabras Unit at SAAN 

(Cogan 2007). ......................................................................................................................................46

Figure 18. Native grassland restoration sites at the Rancho Unit (left) and near San Juan 

Dam in the Missions Unit (right) (close-up aerial photos from Mitchell 2013). .................................57
x

Figures (continued)

Page

Figure 19. Extent of upland shrublands and woodlands in the northwest portion of the 

Missions Unit (data from Cogan 2007)................................................................................................65

Figure 20. Extent of upland shrublands and woodlands in the southeast portion of the 

Missions Unit (data from Cogan 2007)................................................................................................66

Figure 21. Extent of upland shrublands and woodlands in the Rancho Unit (data from 

Cogan 2007).........................................................................................................................................67

Figure 22. Major herptile sampling sites in SAAN at the Missions Unit (left) and Rancho 

de las Cabras Unit (right) (Duran 2004). .............................................................................................76

Figure 23. Species richness of reptiles in SAAN (data from Strecker 1915, Gallyoun et 

al. 2002, Gallyoun et al. 2003, Duran 2004, Dittmer and Fitzgerald 2010, Woodman 

2013, NPS 2014)..................................................................................................................................78

Figure 24. Texas is experiencing varying degrees of drought; Bexar county is circled in 

blue (USDM 2014). .............................................................................................................................84

Figure 25. Areas in the vicinity of SAAN where Strecker (1915) observed amphibian 

species (see Table 22). .........................................................................................................................90

Figure 26. Major sampling sites in SAAN at the Missions Unit (left) and Rancho de las 

Cabras Unit (right) (Duran 2004).........................................................................................................90

Figure 27. Scully (2006) sample sites in the City of San Antonio study unit during 2003-

2005 surveys of SAAN. .....................................................................................................................101

Figure 28. Scully (2006) sample sites in the Rancho de las Cabras study unit during 

2003-2005 surveys of SAAN.............................................................................................................102

Figure 29. Breeding species richness values from 2010-2012 in SAAN..........................................104

Figure 30. Number of breeding individuals observed during the Twedt (2013) surveys of 

SAAN from 2010-2012......................................................................................................................108

Figure 31. Resident species richness values from 2010-2012 in SAAN (Twedt 2013)....................122

Figure 32. Number of resident individuals observed during the Twedt (2013) breeding 

surveys of SAAN from 2010-2012....................................................................................................125

Figure 33. The location of SAAN units in the San Antonio River Basin. ........................................130

Figure 34. Locations of the water quality monitoring stations that are within, or in close 

proximity, to the SAAN units. SAR=San Antonio River. .................................................................134

Figure 35. The severity of drought in Texas 2011-2014...................................................................138

Figure 36. The San Antonio Missions Unit with water quality sampling locations 

(Meiman 2012)...................................................................................................................................155

Figure 37. Water temperature readings (Received from Joe Meiman, February 2015)....................160
xi

Figures (continued)

Page

Figure 38. Specific conductance in SAAN (Received from Joe Meiman, February 2015). .............161

Figure 39. Dissolved oxygen data for SAAN (Received from Joe Meiman, February 

2015). .................................................................................................................................................162

Figure 40. pH readings from SAAN, 2000-2012 (Received from Joe Meiman, February 

2015). .................................................................................................................................................163

Figure 41. Total phosphorous levels in SAAN (Received from Joe Meiman, February 

2015). .................................................................................................................................................164

Figure 42. Nitrate concentrations (Received from Joe Meiman, February 2015).............................165

Figure 43. Nitrate concentrations and monitoring well elevation (Received from Joe 

Meiman, February 2015). ..................................................................................................................165

Figure 44. Nitrite levels in SAAN (Received from Joe Meiman, February 2015). ..........................166

Figure 45. Total Kjeldahl nitrogen (TKN) (Received from Joe Meiman, February 2015)...............167

Figure 46. Total sulfate in SAAN (Received from Joe Meiman, February 2015)............................167

Figure 47. Chloride levels within SAAN (Received from Joe Meiman, February 2015).................168

Figure 48. Balcones Escarpment geologic uplift indicated in red letters..........................................170

Figure 49. Palmer Drought Severity Index for Texas (USDOC 2014).............................................171

Figure 50. Locations of ozone and PM monitoring stations relative to the two SAAN 

park units............................................................................................................................................181

Figure 51. Annual 4th highest 8-hour maximum ozone (O3) concentrations (ppb) at the 

Pecan Valley monitoring station (site 48-029-0055), 1999-2014 (TCEQ 2014a).............................183

Figure 52. Annual 4th highest 8-hour maximum ozone (O3) concentrations (ppb) at the 

Calaveras Lake monitoring station (site 48-029-0059), 1998-2013 (EPA 2014a) ............................184

Figure 53. Annual particulate matter (PM2.5) concentrations (weighted annual mean) at 

Pecan Valley (site 48-029-0055), 2007 - August 2014 (TCEQ 2014b).............................................185

Figure 54. Annual particulate matter (PM2.5) concentrations (weighted annual mean) near 

SAAN, 2008-2013 (EPA 2014a) .......................................................................................................186

Figure 55. The location of Tufa House (Mission San Juan) within SAAN, and the 

Stinson Municipal Airport. ................................................................................................................196

Figure 56. Day and night dBA measurements by frequency for 27 days at SAAN’s Tufa 

House sampling site ...........................................................................................................................197

Figure 57. Grayscale representation of sky luminance from a location in Joshua Tree 

National Park, California (Figure provided by Dan Duriscoe, NPS Night Sky Team). ....................206
xii

Figures (continued)

Page

Figure 58. False color representation of Figure 56 after a logarithmic stretch of pixel 

values (Figure provided by Dan Duriscoe, NPS Night Sky Team). ..................................................206

Figure 59. Contour map of anthropogenic sky glow at a location in Joshua Tree National 

Park, analogous to Figure 58 with natural sources of light subtracted ..............................................207

Figure 60. Levels of light pollution occurring in San Antonio and surrounding areas.....................210

Figure 61. Location of refineries near the SAAN Missions Unit. ....................................................211

Figure 62. Locations of vistas in the Missions (left) and Rancho de las Cabras Units 

(right). ................................................................................................................................................216

Figure 63. Composite viewshed analysis for the 22 vistas in the Missions Unit (left) and 

three vistas in the Rancho de las Cabras Unit (right).........................................................................217

Figure 64. Locations of photo points used to display non-contributing features along the 

entrance road (Vista 24).....................................................................................................................241

Figure 65. Extent of the San Juan labores in SAAN.........................................................................249

Figure 66 darker gray are the areas visible from the park vistas. .....................................................250

Figure 67. Landcover change from 2001 to 2011 in SAAN’s Rancho Unit and 

surrounding areas (MRLC 2014).......................................................................................................251

Figure 68. General location of SAAN and the San Antonio River in southeast Texas. ...................255

Figure 69 Surface hydrology features at SAAN. ..............................................................................257

Figure 70. USGS stream gauges in the vicinity of SAAN................................................................258

Figure 71. Period of record hydrography for daily mean discharge for USGS 08178565 

(USGS 2014)......................................................................................................................................259

Figure 72. Depth to groundwater for J-17 index well for period November 1932 to April 

2015 (EAA 2015)...............................................................................................................................262

Figure 73. Location of groundwater monitoring wells in relation to the Rancho Unit.....................263

Figure 74. Depth to groundwater levels for groundwater monitoring well USGS 

290802098232901 (USGS 2014).......................................................................................................263

Figure 75. Depth to groundwater levels for groundwater monitoring well TWDB 

6862104 (TWDB 2014c). ..................................................................................................................264

Figure 76. Palmer Hydrologic Drought Index (PHDI) for Texas. Graph was created and 

downloaded from time series data from the National Climatic Data Center (NCDC 2014). ............266

Figure 77. Description of symbology used for individual component assessments. ........................276
xiii

Tables 

Page

Table 1. 30-year climate normals (1981-2010) for the San Antonio Stinson Municipal 

Airport weather station near SAAN (NCDC 2015). ..............................................................................8

Table 2. 30-year climate normals (1981-2010) for the Floresville weather station near 

SAAN’s Rancho Unit (NCDC 2015).....................................................................................................8

Table 3. Non-native invasive plant species within SAAN receiving high or medium 

invasiveness rankings from NatureServe (adapted from NPS 2010)...................................................14

Table 4. GULN Vital Signs selected for monitoring in SAAN (Segura et al. 2007). .........................22

Table 5. Scale for a measure’s Significance Level in determining a components overall 

condition. .............................................................................................................................................33

Table 6. Scale for Condition Level of individual measures................................................................33

Table 7. Extent of forested riparian communities (in hectares) within park boundaries 

and within Cogan’s (2007) study area. ................................................................................................43

Table 8. Species occurring in the pecan-sugarberry forest (recreated from Cogan 2007). .................47

Table 9. Species occurring in the eastern cottonwood temporarily flooded forest alliance 

(recreated from Cogan 2007). ..............................................................................................................48

Table 10. Species occurring in the cedar elm-sugarberry/possum-haw/Virginia wild rye 

forest (recreated from Cogan 2007).....................................................................................................49

Table 11. Species occurring in the live oak forest alliance (recreated from Cogan 2007)..................49

Table 12. Native species in the seed mix for SAAN’s prairie restorations (Mitchell 

2013). ...................................................................................................................................................58

Table 13. Extent of upland shrubland and woodland communities (in hectares) within 

park boundaries and within Cogan’s (2007) study area.......................................................................64

Table 14. Native plant species found in all three of Carr’s (2003a, b) upland woodland 

and shrubland macrohabitats................................................................................................................68

Table 15. Species occurring in the Honey Mesquite - Granjeno / Prickly-pear species -

South Texas Ericameria Woodland (Cogan 2007). .............................................................................69

Table 16. Species occurring in the Chapparo-Prieto Shrubland (Cogan 2007). .................................69

Table 17. Species occurring in the Huisache-(Honey Mesquite) Woodland (Cogan 2007). ..............70

Table 18. Reptile species that were observed by Duran (2004) during the 2003 inventory 

of SAAN. .............................................................................................................................................79

Table 19. Relative abundance of reptile species captured with coverboard method 

(Dittmer and Fitzgerald 2011). ............................................................................................................80
xiv

Tables (continued)

Page

Table 20. Relative abundance of reptile species observed at the Missions Unit and 

Rancho de las Cabras Unit in SAAN between 2011 and 2012 (Woodman 2013)...............................80

Table 21. Reptile species with relative abundance in SAAN (NPS 2014)..........................................81

Table 22. List of amphibian species catalogued by Strecker (1915) in the San Antonio 

area. Locations are shown in Figure 24. ..............................................................................................89

Table 23. The amphibian species listed in Duran (2004) and Woodman (2013)................................91

Table 24. The relative abundance (number of individuals) of amphibians during 2012 

surveys at the Missions Unit and Rancho de las Cabras Unit (Woodman 2013). ...............................92

Table 25. Amphibian species abundance (NPS 2014). .......................................................................93

Table 26. Species richness values by habitat type and by season observed during Coonan 

(1987).................................................................................................................................................103

Table 27. Species richness values reported by Scully (2006) for both the units of the park 

within City of San Antonio and the Rancho de las Cabras units of SAAN (2004-2006)..................104

Table 28. Breeding species with the highest relative abundance values (# of birds/1000 m 

of transect) observed during each season for the San Juan Woods land tract in SAAN, 

1985-86. Species are arranged alphabetically, and not by overall abundance (Table 

modified from Coonan 1987).............................................................................................................105

Table 29. Breeding species with the highest relative abundance values (# of birds/1000 m 

of transect) observed during each season for the Espada Labores land tract in SAAN, 

1985-86. .............................................................................................................................................105

Table 30. Relative abundance for the 22 most commonly observed breeding bird species 

during Scully (2006) ..........................................................................................................................106

Table 31. Seasonal bird densities (birds/ha) for the San Juan Woods and Espada Labores 

land tracts at SAAN, 1985-86 1, 2 (Table reproduced from Coonan 1987).........................................109

Table 32. Seasonal bird species diversities (Shannon-Wiener Diversity Index, H') for the 

San Juan Woods and Espada Labores land tracts at SAAN, 1985-86 1 2 (Table reproduced 

from Coonan 1987)............................................................................................................................110

Table 33. Species richness values for resident species sorted by habitat type and by 

season observed during Coonan (1987).............................................................................................120

Table 34. Species richness values reported by Scully (2006) for both the units of the park 

within the City of San Antonio and the Rancho de las Cabras units of SAAN (2004-2006)............121

Table 35. The most abundant resident bird species in each season for the San Juan 

Woods land tract in SAAN, 1985-1986 (Coonan 1987)....................................................................122
xv

Tables (continued)

Page

Table 36. The most abundant resident bird species in each season for the Espada Labores 

land tract in SAAN, 1985-1986 (Coonan 1987) ................................................................................123

Table 37. Resident bird species and number detected during 10-minute surveys of 40 

randomly located point locations in SAAN during the breeding season (May-June) from 

2010-2012 ..........................................................................................................................................125

Table 38. Aquatic Life Use scores (ALU) are based on the points calculated with the 

metrics listed above to evaluate the benthic invertebrate sample to assess the condition of 

the aquatic habitat (TCEQ 2007). ......................................................................................................131

Table 39. The ALU and IBI values for aquatic habitat assessments (TCEQ 2007)..........................132

Table 40. Results of San Antonio River water quality monitoring, 2000-2002 (SARA 

2003). .................................................................................................................................................135

Table 41. Results of SARA habitat assessments (SARA 2005)........................................................135

Table 42. Results of San Antonio River water quality monitoring, 2003-2004 (SARA 

2008). .................................................................................................................................................135

Table 43. Results of San Antonio River water quality monitoring, 2012 (SARA 2012)..................135

Table 44. Total IBI score, integrity class, and attributes to those respective scores 

(reproduced from SARA 2005). ........................................................................................................142

Table 45. List of fish species by source and documentation in SAAN.............................................144

Table 46. IBI and integrity class summary for stations in SAAN, 1998-2002 (SARA 

2003). .................................................................................................................................................146

Table 47. IBI ratings for the SAAN fish community in river segments 1911 and 1901, 

2003-2004 (SARA 2005)...................................................................................................................146

Table 48. IBI scores for fish collected in 2010 in the San Antonio River in August 

(SARA 2010). ....................................................................................................................................147

Table 49. IBI scores for fish collected at three (segment 1911) stations in June of 2011 

(SARA 2011). ....................................................................................................................................148

Table 50. IBI scores for fish collected at three (segment 1911) stations in June of 2012 

(SARA 2012). ....................................................................................................................................148

Table 51. IBI scores for fish collected at three (segment 1911) stations in May and June 

of 2013 (SARA 2013b)......................................................................................................................148

Table 52. Texas Commission on Environmental Quality surface water quality standards 

for surface-water quality (TCEQ 2014).............................................................................................159

Table 53. Typical water quality from the Edwards Aquifer and San Antonio recycled 

water...................................................................................................................................................169
xvi

Tables (continued)

Page

Table 54. National Park Service Air Resources Division air quality index values (NPS 

2011). .................................................................................................................................................179

Table 55. Explanation of sound level values, for reference (Lynch 2009). ......................................194

Table 56. Percent time sound exceeds the given dBA level (Lynch 2009).......................................197

Table 57. Summary of sound sources identified during on site audible surveys in SAAN 

(Lynch 2009). SD = standard deviation.............................................................................................198

Table 58. Average maximum dB levels for aircraft overflights during Lynch’s (2009) 27 

day monitoring period........................................................................................................................199

Table 59. Discharge observations based on mean daily discharge for USGS streamflow 

gauges near SAAN (TIFP 2012, USGS 2014)...................................................................................259

Table 60. Annual estimated groundwater discharge data for Edwards Aquifer, 1934–

2012 (measured in thousands hectare-meters) (EAA 2013). .............................................................260

Table 61. Identified data gaps or needs for the featured components...............................................273

Table 62. Summary of current condition and condition trend for featured NRCA 

components. .......................................................................................................................................277
xvii

Photos 

Page

Photo 1a. The San Juan Acequia (above) and Espada Aqueduct (below) (Photos by 

Shannon Amberg, SMUMN GSS 2013)..............................................................................................11

Photo 1b. Espada Aqueduct (below) (Photos by Shannon Amberg, SMUMN GSS 2013)................11

Photo 1c. The church at Mission Espada (Photo by Shannon Amberg, SMUMN GSS 

2013). ...................................................................................................................................................12

Photo 2. Crested caracara (USFWS photo). ........................................................................................12

Photo 3. An example of a forested riparian corridor located along the Acequia de Espada 

(photo by Kathy Allen, SMUMN GSS 2013)......................................................................................40

Photo 4. The front-most vegetation is the invasive giant reed growing in the San Juan 

Woods (Photo by Shannon Amberg, SMUMN GSS 2013).................................................................51

Photo 5. Indian blanket (Gaillardia pulchella), a native wildflower, in a prairie planting 

at Mission San Juan (Photo by Kathy Allen, SMUMN GSS 2013). ...................................................55

Photo 6. Upland woodland at SAAN’s Rancho de las Cabras Unit (photo by Shannon 

Amberg, SMUMN GSS 2013).............................................................................................................63

Photo 7. Texas brown snake (Storeria dekayi texana) in SAAN in 2003 (photo from 

Duran 2004). ........................................................................................................................................75

Photo 8. Cover board used in the Rancho de las Cabras Unit of SAAN (Photo by 

Shannon Amberg, SMUMN GSS 2013)..............................................................................................77

Photo 9. Three amphibian species present in SAAN are shown from left to right; Rio 

Grande chirping frog, Great Plains narrowmouth toad, and the Blanchard’s cricket frog 

(photo by Duran 2004).........................................................................................................................88

Photo 10. An arboreal PVC-pipe, shown with green arrows, mounted on a tree trunk at 

the Rancho Unit; these were used in amphibian sampling efforts in 2012 (Photo by Kathy 

Allen, SMUMN GSS 2013).................................................................................................................91

Photo 11. The painted bunting, a South Texas specialty species whose breeding range 

extends into SAAN (Photo by Ronnie Maum, USFWS). ....................................................................98

Photo 12. Great-tailed grackle, which was among the most commonly observed species 

during Scully (2006) (NPS Photo).....................................................................................................108

Photo 13. Northern mockingbird, which was among the most abundant ground-dwelling 

insectivores observed in the Espada Labores land tract during Coonan (1987) (NPS 

Photo).................................................................................................................................................110

Photo 14. Brown-headed cowbird egg (mottled color), that has been laid in a chipping 

sparrow (Spizella passerina) nest (NPS Photo). ................................................................................111

Photo 15. Eastern meadowlark, a common resident species in SAAN (NPS Photo)........................118
xviii

Photos (continued)

Page

Photo 16. A northern cardinal, one of the most commonly observed resident species in 

SAAN (NPS Photo). ..........................................................................................................................124

Photo 17. From top to bottom, the largemouth bass, and channel catfish (photos by 

SARA 2014).......................................................................................................................................141

Photo 18. Red shiners are a native species species commonly observed at SAAN (photo 

by shiners that (SARA 2014).............................................................................................................143

Photo 19. Picosa Creek during the 2011 drought (NPS photo by Joe Meiman). ..............................150

Photo 20. Acequia de Espada at the Espada Aqueduct (photo by Shannon Amberg, 

SMUMN GSS 2013)..........................................................................................................................153

Photo 21. Aqueduct along the Espada Acequia (photo by Kathy Allen, SMUMN GSS 

2013). .................................................................................................................................................154

Photo 22. Gas flaring at the Calumet Refinery next to Acequia Park, south of Espada 

Dam (Photo by Shannon Amberg, SMUMN GSS, 2013) .................................................................177

Photo 23. Church at Mission San Juan (NPS photo).........................................................................193

Photo 24. Sound monitoring equipment at Tufa House (NPS photo). ..............................................194

Photo 25. View of Mission Espada (NPS Photo)..............................................................................214

Photo 26. Views of Vista 8 (State archaeological monument on site sign) from all four 

cardinal directions (NPS Photos by Greg Mitchell)...........................................................................219

Photo 27. Views of Vista 9 (Mission Concepcion Church) from all four cardinal 

directions (NPS Photos by Greg Mitchell). .......................................................................................220

Photo 28. Views of Vista 2 (Mission San Jose Church) from all four cardinal directions 

(NPS Photos by Greg Mitchell). ........................................................................................................221

Photo 29. Views of Vista 3 (Visitor Center) from all four cardinal directions (NPS 

Photos by Greg Mitchell)...................................................................................................................222

Photo 30. Views of Vista 4 (GPS mark washer north of Grist Mill) from all four cardinal 

directions (NPS Photos by Greg Mitchell) ........................................................................................223

Photo 31. Views of Vista 0 (Carsonite marker at acequia mile 3.3) from all four cardinal 

directions (NPS Photos by Greg Mitchell). .......................................................................................224

Photo 32. Views of Vista 5 (Mission San Juan) from all four cardinal directions (NPS 

Photos by Greg Mitchell)...................................................................................................................225

Photo 33. Views of Vista 12 from all four cardinal directions (NPS Photos by Greg 

Mitchell).............................................................................................................................................226

Photo 34. Views of Vista 14 (Mill Ruins) from all four cardinal directions (NPS Photos 

by Greg Mitchell)...............................................................................................................................227
xix

Photos (continued)

Page

Photo 35. Views of Vista 15 (Acequia Park Security Building) from all four cardinal 

directions (NPS Photos by Greg Mitchell). .......................................................................................228

Photo 36. Views of Vista 16 (in prairie near the dam) from all four cardinal directions 

(NPS Photos by Greg Mitchell). ........................................................................................................229

Photo 37. Views of Vista 17 (the dam overlook) from all four cardinal directions (NPS 

Photos by Greg Mitchell)...................................................................................................................230

Photo 38. Views of Vista 18 (End of Acequia Trail) from all four cardinal directions 

(NPS Photos by Greg Mitchell). ........................................................................................................231

Photo 39. Views of Vista 1 (River Rest Pavilion) from all four cardinal directions (NPS 

Photos by Greg Mitchell)...................................................................................................................232

Photo 40. Views of Vista 6 from all four cardinal directions (NPS Photos by Greg 

Mitchell).............................................................................................................................................233

Photo 41. Views of Vista 7 (San Francisco de la Espada Mission) from all four cardinal 

directions (NPS Photos by Greg Mitchell). .......................................................................................234

Photo 42. Views of Vista 13 (Espada Aqueduct) from all four cardinal directions (NPS 

Photos by Greg Mitchell)...................................................................................................................235

Photo 43. Views of Vista 19 (parking lot near the San Francisco de la Espada Mission) 

from all four cardinal directions (NPS Photos by Greg Mitchell). ....................................................236

Photo 44. Views of Vista 20 (grassy area near the aqueduct) from all four cardinal 

directions (NPS Photos by Greg Mitchell). .......................................................................................237

Photo 45. Views of Vista 21 (east of the original dam) from all four cardinal directions 

(NPS Photos by Greg Mitchell). ........................................................................................................238

Photo 46. Views of Vista 22, located at the center of the ruins, from all four cardinal 

directions (NPS Photos by Greg Mitchell). .......................................................................................239

Photo 47. Views of Vista 23, located at the high point overlook, from all four cardinal 

directions (NPS Photos by Greg Mitchell). .......................................................................................240

Photo 48. Views of photo point 24, located at the eastern most culvert along the entrance 

road, from all four cardinal directions (NPS Photos by Greg Mitchell). ...........................................242

Photo 49. Views of photo point 25, located near the middle point on the entrance road, 

from all four cardinal directions (NPS Photos by Greg Mitchell). ....................................................243

Photo 50. Views of photo point 26, located at the entrance gate of the Rancho Unit, 

looking northeast and east into the park (NPS Photos by Greg Mitchell). ........................................244

Photo 51. Views of Vista 10, portal located to the west of the Mission Concepcion Unit, 

from all four cardinal directions (NPS Photos by Greg Mitchell). ....................................................245
xx

Photos (continued)

Page

Photo 52. Views of Vista 11, portal located to the northeast of the Mission San Jose Unit, 

from all four cardinal directions (NPS Photos by Greg Mitchell). ....................................................246

Photo 53. Views of the San Juan labores from gates 9155 (left) and 9107 (right) (NPS 

Photos by Greg Mitchell)...................................................................................................................248
Appendices 

Page

Appendix A. Non-native plant species documented in SAAN (ornamentals excluded) 

(Halvorson and Guertin 2006). ..........................................................................................................283

Appendix B. Plant species documented in SAAN’s riparian woodlands/forests (Carr 

2003a, b) ............................................................................................................................................287

Appendix C. Native herbaceous species documented in SAAN’s old fields (Carr 2003a, 

b). .......................................................................................................................................................294

Appendix D. Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b) ............................................................................................................................................301

Appendix E. Reptiles identified in or near SAAN (data compiled from museum vouchers, 

Strecker 1915, Gallyoun et al. 2002, Gallyoun et al. 2003, Duran 2004, Woodman 2013, 

and NPS 2014)...................................................................................................................................312

Appendix F. Breeding bird species observed in SAAN from 1985-2012. ........................................316

Appendix G. Breeding bird species abundance by season for the San Juan Woods (SAJU) 

and Espada Labores (ESPA) land tracts, SAAN, 1985-86 (Appendix reproduced from 

Coonan 1987).....................................................................................................................................320

Appendix H. Relative abundance and distribution of breeding bird species observed 

during Scully (2006) ..........................................................................................................................323

Appendix I. Breeding bird species and the number of detections during 10-minute 

surveys of 40 randomly located point locations on San Antonio Missions National 

Historical Park (Table modified from Twedt 2013). .........................................................................327

Appendix J. Resident bird species observed in SAAN from 1985-2013...........................................329

Appendix K. Bird species and number detected during 90 area search survey visits to 40 

randomly located survey locations in SAAN during winters of 2010-2011 (n=30 visits), 

2011-12 (n=30 visits), and 2012-2013 (n=30 visits). ........................................................................334

Appendix L. Resident bird species and number detected during 10-minute surveys of 40 

randomly located point locations in SAAN during the breeding season May-June 2010 (n 

= 20 counts), 2011 (n = 30 counts), and 2012 (n = 30 counts)..........................................................336

Appendix M. Resident bird species abundance by season for the San Juan Woods (SAJU) 

and Espada Labores (ESPA) land tracts, SAAN, 1985-1986 (Appendix modified from 

Coonan 1987).....................................................................................................................................337

Appendix N. Relative abundance and distribution of resident bird species observed 

during Scully (2006) ..........................................................................................................................340

xxiii

Executive Summary 

The Natural Resource Condition Assessment (NRCA) Program aims to provide documentation about 

the current conditions of important park natural resources through a spatially explicit, multidisciplinary synthesis of existing scientific data and knowledge. Findings from the NRCA will help 

San Antonio Missions National Historical Park (SAAN) managers to develop near-term management 

priorities, engage in watershed or landscape scale partnership and education efforts, conduct park 

planning, and report program performance (e.g., Department of the Interior’s Strategic Plan “land 

health” goals, Government Performance and Results Act).

The objectives of this assessment are to evaluate and report on current conditions of key park 

resources, to evaluate critical data and knowledge gaps, and to highlight selected existing stressors 

and emerging threats to resources or processes. For the purpose of this NRCA, staff from the 

National Park Service (NPS) and Saint Mary’s University of Minnesota – GeoSpatial Services 

(SMUMN GSS) identified key resources, referred to as “components” in the project. The selected 

components include natural resources and processes that are currently of the greatest concern to park 

management at SAAN. The final project framework contains 15 resource components, each featuring 

discussions of measures, stressors, and reference conditions.

This study involved reviewing existing literature and, where appropriate, analyzing data for each 

natural resource component in the framework to provide summaries of current condition and trends 

in selected resources. When possible, existing data for the established measures of each component 

were analyzed and compared to designated reference conditions. A weighted scoring system was 

applied to calculate the current condition of each component. Weighted Condition Scores, ranging 

from zero to one, were divided into three categories of condition: low concern, moderate concern, 

and significant concern. These scores help to determine the current overall condition of each 

resource. The discussions for each component, found in Chapter 4 of this report, represent a 

comprehensive summary of current available data and information for these resources, including 

unpublished park information and perspectives of park resource managers, and present a current 

condition designation when appropriate. Each component assessment was reviewed by SAAN 

resource managers, NPS Gulf Coast Network staff, and outside experts, when appropriate.

Existing literature, short- and long-term datasets, and input from NPS and other outside agency 

scientists support condition designations for components in this assessment. However, in a number of 

cases, data were unavailable or insufficient for several of the measures of the featured components. 

In other instances, data establishing reference condition were limited or unavailable for components, 

making comparisons with current information inappropriate or invalid. In these cases, it was not 

possible to assign condition for the components. Current condition was not able to be determined for 

5 of the 15 components (33%) due to these data gaps.

For those components with sufficient available data, the overall condition varied. For featured 

components with available data and fewer data gaps, assigned conditions varied. Five components 

are considered of low concern: upland shrublands/woodlands, reptiles, breeding and resident birds, 

and hydrology. Two components (fish and water quality) were of moderate concern. Three 
xxiv

components were of high concern: air quality, soundscape, and viewscape. Soundscape and 

viewscape also appeared to show a deteriorating trend due to continued urban development. The high 

concern levels are primarily due to the urban land uses surrounding the park and are largely beyond 

NPS control. Detailed discussion of these designations is presented in Chapters 4 and 5 of this report. 

Several park-wide threats and stressors influence the condition of priority resources in SAAN. Those 

of primary concern include the presence of non-native invasive species and effects of urban 

development (e.g., habitat loss and fragmentation, pollution, hydrologic alterations). Climate change 

could also threaten many resources, as the San Antonio region is likely to become warmer and drier 

for at least parts of the year within the next century. Understanding these threats, and how they relate 

to the condition of park resources, can help the NPS prioritize management objectives and better 

focus conservation strategies to maintain the health and integrity of park ecosystems.
xxv

Acknowledgments 

We acknowledge San Antonio Missions National Historical Park staff for the technical expertise 

provided during scoping, through multiple stages of review, and via phone and email; specifically, 

Greg Mitchell, James Oliver, and Susan Snow. Gulf Coast Inventory and Monitoring Network staff, 

including Martha Segura, Joe Meiman, Robert Woodman, and Billy Finney offered logistical insight 

and critical review of interim documents. San Antonio River Authority (SARA) staff assisted with 

project scoping, data gathering, and document review. Ellen Porter of the NPS Air Resources 

Division provided guidance on interpreting air quality data. The NPS Dark Night Skies Team offered 

information and guidance on the preparation of the dark night skies component. Dan Twedt provided 

guidance on the breeding and resident bird assessments. Donna Shorrock, Intermountain Region 

NRCA Coordinator, and Jeff Albright, Natural Resource Condition Assessment Coordinator, 

provided program guidance. Thank you to all others who assisted the development of this document.
xxvi

Acronyms and Abbreviations 

ALU - Aquatic life use

CLI - Cultural Landscape Inventory

CLR - Cultural Landscape Report

CRP - Clean Rivers Program

dB - Decibels

DEM – Digital Elevation Model

DO - Dissolved Oxygen

EPA – Environmental Protection Agency 

GIS – Geographic Information System

gpm - Gallons per minute

GULN - Gulf Coast Network

I&M - Inventory and Monitoring

IMPROVE - Interagency Monitoring of Protected Visual Environments

IBI - Index of Biotic Integrity

NAAQS - National Ambient Air Quality Standards

NADP - National Atmospheric Deposition Program

NCDC - National Climatic Data Center

NFI - Noise Free Interval

NPS - National Park Service

NPS ARD – National Park Service Air Resources Division

NRCA – Natural Resource Condition Assessment

NST - Night Sky Team

NVCS – National Vegetation Classification Standard

PHDI - Palmer Hydrological Drought Index

PM – Particulate Matter
xxvii

SAAN - San Antonio Missions National Historical Park

SARA - San Antonio River Authority

SARIP - San Antonio River Improvement Project

SMUMN GSS – Saint Mary’s University of Minnesota, Geospatial Services 

SpC - Specific Conductance

SSF - Stinson Municipal Airport

TCEQ – Texas Commission on Environmental Quality

TDS - Total Dissolved Solids

TSS - Total Suspended Sediments

TWDB - Texas Water Development Board

USGS – United States Geological Survey

WCS - Weighted Condition Score

1

Chapter 1 NRCA Background Information

Natural Resource Condition Assessments (NRCAs) evaluate current conditions for a subset of 

natural resources and resource indicators in national park units, hereafter “parks.” NRCAs also report 

on trends in resource condition (when possible), identify critical data gaps, and characterize a general 

level of confidence for study findings. The resources and indicators emphasized in a given project 

depend on the park’s resource setting, status of resource stewardship planning and science in 

identifying high-priority indicators, and availability of data and expertise to assess current conditions 

for a variety of potential study resources and indicators. 

NRCAs represent a relatively new 

approach to assessing and reporting on 

park resource conditions. They are meant 

to complement—not replace—traditional 

issue-and threat-based resource 

assessments. As distinguishing 

characteristics, all NRCAs:

 Are multi-disciplinary in scope;1 

 Employ hierarchical indicator 

frameworks;2

 Identify or develop reference conditions/values for comparison against current conditions;3

 Emphasize spatial evaluation of conditions and GIS (map) products; 4

 Summarize key findings by park areas; and 5

 Follow national NRCA guidelines and standards for study design and reporting products. 

Although the primary objective of NRCAs is to report on current conditions relative to logical forms 

of reference conditions and values, NRCAs also report on trends, when appropriate (i.e., when the 

underlying data and methods support such reporting), as well as influences on resource conditions. 

These influences may include past activities or conditions that provide a helpful context for 

The breadth of natural resources and number/type of indicators evaluated will vary by park. 

2

Frameworks help guide a multi-disciplinary selection of indicators and subsequent “roll up” and reporting of data for measures 

 conditions for indicators  condition summaries by broader topics and park areas 

3 NRCAs must consider ecologically-based reference conditions, must also consider applicable legal and regulatory standards, 

and can consider other management-specified condition objectives or targets; each study indicator can be evaluated against one 

or more types of logical reference conditions. Reference values can be expressed in qualitative to quantitative terms, as a single 

value or range of values; they represent desirable resource conditions or, alternatively, condition states that we wish to avoid or 

that require a follow-up response (e.g., ecological thresholds or management “triggers”).

4 As possible and appropriate, NRCAs describe condition gradients or differences across a park for important natural resources 

and study indicators through a set of GIS coverages and map products. 

5

In addition to reporting on indicator-level conditions, investigators are asked to take a bigger picture (more holistic) view and 

summarize overall findings and provide suggestions to managers on an area-by-area basis: 1) by park ecosystem/habitat types or 

watersheds, and 2) for other park areas as requested.

NRCAs Strive to Provide...

Credible condition reporting for a subset of 

important park natural resources and indicators

Useful condition summaries by broader resource 

categories or topics, and by park areas
2

understanding current conditions, and/or present-day threats and stressors that are best interpreted at 

park, watershed, or landscape scales (though NRCAs do not report on condition status for land areas 

and natural resources beyond park boundaries). Intensive cause-and-effect analyses of threats and 

stressors, and development of detailed treatment options, are outside the scope of NRCAs. 

Due to their modest funding, relatively quick timeframe for completion, and reliance on existing data 

and information, NRCAs are not intended to be exhaustive. Their methodology typically involves an 

informal synthesis of scientific data and information from multiple and diverse sources. Level of 

rigor and statistical repeatability will vary by resource or indicator, reflecting differences in existing 

data and knowledge bases across the varied study components. 

The credibility of NRCA results is derived from the data, methods, and reference values used in the 

project work, which are designed to be appropriate for the stated purpose of the project, as well as 

adequately documented. For each study indicator for which current condition or trend is reported, we 

will identify critical data gaps and describe the level of confidence in at least qualitative terms. 

Involvement of park staff and National Park Service (NPS) subject-matter experts at critical points 

during the project timeline is also important. These staff will be asked to assist with the selection of 

study indicators; recommend data sets, methods, and reference conditions and values; and help 

provide a multi-disciplinary review of draft study findings and products.

NRCAs can yield new insights about current park resource conditions, but, in many cases, their 

greatest value may be the development of useful documentation regarding known or suspected 

resource conditions within parks. Reporting products can help park managers as they think about 

near-term workload priorities, frame data and study needs for important park resources, and 

communicate messages about current park resource conditions to various audiences. A successful 

NRCA delivers science-based information that is both credible and has practical uses for a variety of 

park decision making, planning, and partnership activities.

However, it is important to note that NRCAs do not establish management targets for study 

indicators. That process must occur through park planning and management activities. What an 

NRCA can do is deliver science-based information that will assist park managers in their ongoing, 

Important NRCA Success Factors

Obtaining good input from park staff and other NPS subject-matter experts at 

critical points in the project timeline 

Using study frameworks that accommodate meaningful condition reporting at 

multiple levels (measures  indicators  broader resource topics and park 

areas)

Building credibility by clearly documenting the data and methods used, critical 

data gaps, and level of confidence for indicator-level condition findings 
3

long-term efforts to describe and quantify a park’s desired resource conditions and management 

targets. In the near term, NRCA findings assist strategic park resource planning6 and help parks to 

report on government accountability measures.7 In addition, although in-depth analysis of the effects 

of climate change on park natural resources is outside the scope of NRCAs, the condition analyses 

and data sets developed for NRCAs will be useful for park-level climate-change studies and planning 

efforts.

NRCAs also provide a useful complement to rigorous NPS science support programs, such as the 

NPS Natural Resources Inventory & Monitoring (I&M) Program.8For example, NRCAs can provide 

current condition estimates and help establish reference conditions, or baseline values, for some of a 

park’s vital signs monitoring indicators. They can also draw upon non-NPS data to help evaluate 

current conditions for those same vital signs. In some cases, I&M data sets are incorporated into 

NRCA analyses and reporting products. 

6An NRCA can be useful during the development of a park’s Resource Stewardship Strategy (RSS) and can also be tailored to act 

as a post-RSS project.

7 While accountability reporting measures are subject to change, the spatial and reference-based condition data provided by 

NRCAs will be useful for most forms of “resource condition status” reporting as may be required by the NPS, the Department 

of the Interior, or the Office of Management and Budget. 

8 The I&M program consists of 32 networks nationwide that are implementing “vital signs” monitoring in order to assess the 

condition of park ecosystems and develop a stronger scientific basis for stewardship and management of natural resources 

across the National Park System. “Vital signs” are a subset of physical, chemical, and biological elements and processes of park 

ecosystems that are selected to represent the overall health or condition of park resources, known or hypothesized effects of 

stressors, or elements that have important human values.

NRCA Reporting Products...

Provide a credible, snapshot-in-time evaluation for a subset of important park natural 

resources and indicators, to help park managers:

Direct limited staff and funding resources to park areas and natural resources that represent 

high need and/or high opportunity situations 

(near-term operational planning and management)

Improve understanding and quantification for desired conditions for the park’s “fundamental” 

and “other important” natural resources and values

(longer-term strategic planning)

Communicate succinct messages regarding current resource conditions to government program 

managers, to Congress, and to the general public 

(“resource condition status” reporting) 
4

Over the next several years, the NPS plans to fund an NRCA project for each of the approximately 

270 parks served by the NPS I&M Program. For more information on the NRCA program, visit 

http://www.nature.nps.gov/water/NRCondition_Assessment_Program/Index.cfm.
5

Chapter 2 Introduction and Resource Setting

2.1 Introduction

2.1.1 Enabling Legislation

San Antonio Missions National Historical Park (SAAN) preserves the largest concentration of 

Spanish colonial era cultural resources in the U.S. (NPS 2000). It was designated a National 

Historical Park and signed into public law 10 November 1978, by President Jimmy Carter (P.L. 95-

629):

“In order to provide for the preservation, restoration, and interpretation of the Spanish 

Missions of San Antonio, Texas, for the benefit and enjoyment of present and future 

generations, there is hereby established the San Antonio Missions National Historical Park 

consisting of Concepcion, San Jose, San Juan, and Espada Missions, together with areas and 

features historically associated therewith.”

In addition to the four Missions, the original legislation included the Espada Dam and Aqueduct and 

portions of the Espada and San Juan Acequias (Amdor et al. 1994). The park boundary was expanded 

in 1978 to include more of the historic acequias and original Mission compounds (Amdor et al. 

1994). The Rancho de las Cabras Unit, which consists of lands historically associated with Mission 

Espada’s ranching activities, was acquired by the NPS in September 1995 (OCULUS 1998). 

2.1.2 Geographic Setting

SAAN consists of two distinct units: the Missions Unit and the Rancho de las Cabras Unit. The 

Missions Unit (Figure 1) is located within San Antonio, Texas (Bexar County), which supports a 

population of over 1.4 million people (USCB 2015). The Rancho Unit lies in a more rural area of 

Wilson County, near the town of Floresville, approximately 51.5 kilometers (32 mi) to the southeast 

of the Missions Unit (Figure 2). The park encompasses 389.3 hectares (962 ac) and includes historic 

landscapes, structures, and natural areas (Greg Mitchell, SAAN Natural Resources Program 

Manager, written communication, 22 September 2015). Missions within the park include: Mission 

San Francisco de la Espada (Mission Espada), Mission San José y San Miguel de Aguayo (Mission 

San José), Mission San Juan Capistrano (Mission San Juan), and Mission Nuestra Señora de la 

Purísma Concepción de Acuña (Mission Concepción). Both park units are situated along the San 

Antonio River (NPS 2001).
6

Figure 1. The Missions Unit of SAAN.
7

Figure 2. Location of the Rancho de las Cabras Unit of SAAN.

SAAN is located in the western climatic sub-region of the Gulf Coast and is characterized as 

subtropical, with mild winters and high heat and humidity in the summer (Segura et al. 2007, NPS 

2015a). Mean annual temperature in the San Antonio area is 21.0° C (69.8° F). The annual mean 

high temperature is 27.1°C (80.8°F), with an average of 110 days above 32.2°C (90°F) (NCDC 2015, 

Table 1). The average low temperature is 14.9°C (58.8°F) with freezing temperatures (0° C or 32° F 

or below) occurring on average only 14 days per year (NCDC 2015). Mean annual high temperature 

around Floresville (near the Rancho Unit) is slightly higher than in San Antonio, while mean annual 

low temperatures are over a degree lower (Table 2). Mean annual precipitation in the San Antonio 

area is 77.5 cm (30.5 in) with one peak in early summer and one in fall (NCDC 2015, Table 1). Mean 

annual precipitation near Floresville is slightly lower at 73.8 cm (29.1 in). Thunderstorms are 

common during the late spring and early summer months, sometimes bringing heavy precipitation in 

short bursts or isolated events (NPS 2001). Precipitation in winter months arrives typically as light 

rain, drizzle, or even fog; snowfall is rare (NPS 2001). SAAN is located 225 km (140 mi) from the 

Gulf of Mexico and, as a result, is sometimes affected by tropical storms and hurricanes, producing 

heavy rainfall and occasional tornadoes (NPS 2001). 
8

Table 1. 30-year climate normals (1981-2010) for the San Antonio Stinson Municipal Airport weather 

station near SAAN (NCDC 2015). Jan Feb Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Annual

Average Temperature (°C)

Max 17.4 19.7 23.4 27.4 30.9 33.6 35.0 36.4 32.4 28.1 22.6 17.9 27.1

Min 5.2 7.4 11.0 14.9 19.6 22.6 23.1 23.4 20.8 15.8 10.1 5.3 14.9

Average Precipitation (cm)

Total 4.4 4.6 5.9 5.5 8.7 9.5 5.3 6.4 7.2 9.5 5.8 4.8 77.5

Table 2. 30-year climate normals (1981-2010) for the Floresville weather station near SAAN’s Rancho 

Unit (NCDC 2015). Jan

FebMar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Annual

Average Temperature (°C)

Max 18.0 20.1 23.6 27.6 31.0 33.8 35.3 36.1 33.1 28.7 23.6 18.9 27.5

Min 2.9 5.1 9.1 13.3 18.6 21.6 22.7 22.4 19.4 14.2 8.9 3.7 13.5

Average Precipitation (cm)

Total 4.0 4.5 5.1 5.4 8.6 7.7 6.3 5.4 7.8 8.5 5.6 4.8 73.8

2.1.3 Visitation Statistics

Over the 10-year period from 2004-2013, SAAN received an average of just over 1 million visitors 

annually, with a peak around 1.56 million in 2009 (NPS 2015b). The park provides free tours of the 

missions and a museum of artifacts from the time period (NPS 2013). The Visitor Center at Mission 

San Jose regularly shows a film on the native people of south Texas during the 18th century. Nearly 

13 km (8 mi) of paved trail stretches along the San Antonio River between Mission Concepción and 

Mission Espada, allowing visitors to enjoy the scenic beauty and natural resources of the park (NPS 

2013).

2.2 Natural Resources

2.2.1 Ecological Units and Watersheds

The Missions Unit of SAAN lies within the Environmental Protection Agency’s (EPA) Texas 

Blackland Prairies Level III Ecoregion. According to the EPA (2010, p. 7), this ecoregion is

“...distinguished from surrounding regions by its fine-textured, clayey soils and 

predominantly prairie potential natural vegetation. This region now contains a higher 

percentage of cropland than adjacent regions, and pasture and forage production for 
9

livestock is common. Large areas of the region are being converted to urban and industrial 

uses.”

Griffith et al. (2007) states that less than one percent of the region’s original grassland vegetation 

currently remains. Within the park, these former prairies are now old agricultural fields or scrublands 

(Cooper et al. 2005).

The Rancho Unit lies in the East Central Texas Plains ecoregion (Figure 3) also known as the Post 

Oak Savanna or the Claypan Area. The EPA (2010, p. 7) states that

“this region of irregular plains was originally covered by post oak savanna vegetation, in 

contrast to the more open prairie-type regions to the north, south, and west... Many areas 

have a dense, underlying clay pan affecting water movement and available moisture for plant 

growth. The bulk of this region is now used for pasture and range.”

Honey mesquite (Prosopis glandulosa) is the primary tree in the East Central Texas Plains 

ecoregion; however, many other trees and shrubs are found including other species of mesquite, 

acacias (Acacia spp.), and dwarf oak (Quercus margaretta) (McMahan 1984). The East Central 

Texas Plains support a diversity of animal species due to the range of habitat types available. Near 

tropical species that are common in Mexico, grassland species that are found in the north, and even 

desert species can be found in this region (Diamond 2010). 

Both units of SAAN fall within the San Antonio River watershed, which is further divided into 

“upper” and “lower” sections. The Missions Unit is in the Upper San Antonio River Watershed and 

the Rancho Unit is in the Lower San Antonio River Watershed.
10

Figure 3. Ecoregions surrounding SAAN park units (EPA 2011).
11

2.2.2 Resource Descriptions

Cultural Resources

The Missions within SAAN were founded by 

Spanish missionaries during the 18th century (NPS 

2001). These missions were established near water, a 

resource that was invaluable at the time. The San 

Antonio River was diverted for irrigation and other 

mission needs using acequias (hand-dug irrigation 

ditches) (NPS 2001). The acequias create oases of 

unique riparian habitat that are home to an 

assortment of wildlife, including fish, amphibians, 

small mammals, and many species of birds. Today, 

only two acequias remain: the Espada and San Juan 

Acequias (Photo 1a). The Espada Acequia includes a 

historic and still functioning aqueduct. Constructed 

in 1748, the Espada Aqueduct is the only 

continuously operating Spanish colonial aqueduct in the country (NPS 2001).

The churches within SAAN are still active parishes, 

owned and operated by the Archdiocese of San 

Antonio (NPS 2001; Photo 1b). NPS staff oversees 

care for all the buildings not associated with the 

active parishes, as well as managing other historic 

structures within the park. Park staff are responsible 

for preserving and interpreting the landscapes of the 

missions and providing a historical account of the 

lives of missionaries and inhabitants of the original 

mission compounds (NPS 2001).

Biological Resources

The vegetation communities in SAAN contain a high level of diversity, with just over 570 plant 

species documented as present in the park (NPS 2014a). Historically, the San Antonio area was 

primarily grassland with few trees or woodlands and riparian forests along the San Antonio River 

(Van Auken and Bush 1984, Cooper et al. 2005). Brush or shrublands containing acacia species and 

honey mesquite were more common around the Rancho Unit (Cooper et al. 2005, Cogan 2007). No 

native grassland currently remains within park boundaries, although restoration efforts have been 

initiated in both units (Mitchell 2013). Upland shrublands are common at SAAN and support many 

native species such as huisache (Acacia farnesiana), agarito (Berberis trifoliolata; also called 

algerita), Texan hogplum (Colubrina texensis), and hackberries (Celtis spp.) (Carr 2003a, Cogan 

2007). Both units also support riparian areas with tree species such as pecan (Carya illinoinensis), 

black willow (Salix nigra), cedar elm (Ulmus crassifolia), and eastern cottonwood (Populus 

deltoides) (Cogan 2007).

Photo 1a. The San Juan Acequia (above) and 

Espada Aqueduct (below) (Photos by 

Shannon Amberg, SMUMN GSS 2013).

Photo 1b. Espada Aqueduct (below) (Photos 

by Shannon Amberg, SMUMN GSS 2013).
12

The varied habitats in SAAN are home to a 

surprising diversity of wildlife. Mammals observed 

in the park include the coyote (Canis latrans), whitetailed deer (Odocoileus virginianus), raccoon 

(Procyon lotor), collared peccary or javelina 

(Tayassu tajacu), and nine-banded armadillo 

(Dasypus novemcinctus) (NPS 2014a). Also present 

in the park are several species of bats and many 

rodent species (NPS 2014a). 

Of the over 220 bird species observed in SAAN, 

approximately 70 are thought to breed within the 

park (NPS 2014a). The riparian woodland and 

brushland habitats within the park along the San 

Antonio River in the Missions Unit and along the 

river corridor in the Rancho Unit provide important 

habitat for a variety of birds during migration and for nesting and breeding (NPS 2010). SAAN 

supports several unique species whose breeding ranges only extend into the U.S. near the 

U.S./Mexico border, such as the crested caracara (Caracara cheriway; Photo 2), the painted bunting 

(Passerina ciris), and the great kiskadee (Pitangus sulphuratus) (NPS 2014a).

Reptiles are common in SAAN, including snakes, turtles, 

and lizards (NPS 2014a). Amphibians are present but are 

less common (NPS 2014a). The Texas tortoise (Gopherus 

berlandieri), listed as threatened in the state of Texas, was 

historically present in the park; however, the species has 

not been seen at SAAN since 2007 (Dittmer and Fitzgerald 

2011). It is likely extirpated from the Missions Unit and 

may also be absent from the Rancho Unit. Native fish have 

been documented in SAAN, both in the acequias and the 

San Antonio River and its tributaries (SARA 2005). 

Species include largemouth bass (Micropterus salmoides), 

catfish (order Siluriformes), shiners (Notropis and 

Cyprinella spp.), and western mosquito-fish (Gambusia 

affinis) (SARA 2005, NPS 2014a).

Although little is known about the park’s invertebrate 

communities (Cooper et al. 2005), both terrestrial and 

aquatic, they perform important functions for the 

ecosystems. Insects in particular play critical roles in 

pollination, decomposition, and as a food source for other 

animals (Losey and Vaughan 2006).

Photo 2. Crested caracara (USFWS 

photo).

Photo 1c. The church at Mission Espada 

(Photo by Shannon Amberg, SMUMN GSS 

2013).
13

2.2.3 Resource Issues Overview

Urban Development and Land Use

The Missions Unit of SAAN lies within San Antonio, the seventh most populated city in the United 

States with over 1.4 million people (USCB 2015). San Antonio has also been among the top five U.S.

cities for population growth (USCB 2012). As the city of San Antonio continues to grow, so too does 

its need for private development of lands surrounding the Missions. Additional developments would 

further threaten the integrity of the park (NPS 2001).

Over the past few centuries, human development and eventual urbanization have impacted native 

vegetation through overgrazing, fire suppression, exotic plant species introduction, and other 

activities (NPS 2001). These changes contribute to habitat loss and fragmentation that impact native 

wildlife species. The proximity of developed areas to the Missions also impacts visitor experience, as 

many sights and sounds (e.g., aircraft overflights, highway traffic) that would not have been 

historically present are now commonplace (NPS 2001, Lynch 2009). 

Water Threats

The Missions were intentionally established near water, which continues to be an essential element 

within the park today. The park is dependent upon and a stakeholder in water quality and quantity of 

the San Antonio River (Meiman 2012). The NPS staff has little to no control over the San Antonio 

River and its subsequent effects on the park (NPS 2001). Due to drainage into the river by a city with 

a population of over 1.4 million, the Upper San Antonio River has water quality issues. It is on the 

Texas 303(d) list for non-attainment status for bacteria (E. coli) and impaired fish habitat (Meiman 

2012). Other problems in park waters include depressed oxygen levels and elevated nutrient 

concentrations (e.g., phosphorous) (Cooper et al. 2005, Meiman 2012). The San Antonio area has 

experienced much alteration, modification, and development of its waterways and surrounding areas. 

Flood hazard reduction and channel modification projects in the mid-20th century transformed the 

San Antonio River into a straight, largely uniform channel, which degraded aquatic and riparian 

habitat (Meiman 2012). The majority of the threats to the San Antonio River and other surface 

waters, such as urban runoff, originate outside the park boundary and are beyond NPS control. 

Non-native (Exotic) and Invasive Species

Of the 889 organisms considered present in the park, 177 of these are classified as non-native (NPS 

2010). Plants make up the majority of the non-native invasive species found in the park and are a 

threat due to their ability to outcompete native plant species (Cooper et al. 2005). Exotic grasses such 

as Bermudagrass (Cynodon dactylon), yellow (or King’s ranch) bluestem (Bothriochloa ischaemum), 

and Johnson grass (Sorghum halepense) were introduced for agriculture and now dominate some area 

of the park (Carr 2003a, b). NatureServe, in cooperation with The Nature Conservancy and NPS, 

developed a system for ranking non-native invasive species, based on each species’ ecological 

impact and management difficulty (NPS 2010). Table 3 lists species confirmed within SAAN that 

received high or medium invasiveness ranks. A full list of non-native plant species documented in 

SAAN (by unit) by Halvorson and Guertin (2006) in 2004 can be found in Appendix A.
14

Table 3. Non-native invasive plant species within SAAN receiving high or medium invasiveness rankings 

from NatureServe (adapted from NPS 2010).

Scientific Name Common Name Invasiveness Rank

Arundo donax giant reed high

Pennisetum ciliare buffelgrass high

Triadica sebifera Chinese tallow high

Eichhornia crassipes common water hyacinth high

Albizia julibrissin silktree high/low

Nandina domestica sacred bamboo high/low

Pennisetum setaceum crimson fountaingrass high/medium

Sorghum halepense Johnsongrass high/medium

Lonicera japonica Japanese honeysuckle high/medium

Hydrilla verticillata water thyme high/medium

Ligustrum sinense Chinese privet high/medium

Morus alba white mulberry high/medium

Centaurea melitensis Maltese star-thistle medium

Alternanthera philoxeroides alligatorweed medium

Lolium perenne perennial ryegrass medium

Vinca major bigleaf periwinkle medium

Lantana camara lantana medium

Ailanthus altissima tree of heaven medium

Ficus carica edible fig medium

An exotic plant control program has been active in the park since 2000 (Mitchell, written 

communication, February 2015). Early efforts focused on Chinaberry (Melia azedarach), privet 

(Ligustrum spp.), and giant reed (Arundo donax) (NPS 2001). Recent work has expanded to include 

many more species. Areas where exotic plant removal has occurred, along with the number of times 

each area has been treated, are shown in Figure 4.

The main threat from non-native mammalian species is from the feral hog (Sus scrofa). These hogs 

have been present in Texas since at least the 1930s and are now abundant in the state (Taylor 2003). 

The feral hog is highly adaptive and able to thrive in almost any environment, but prefers habitats 

with areas for wallowing; this can be anywhere mud forms, including creek banks, ponds, and 

drainages. Feral hogs reproduce quickly, with reproductive maturity achieved as early as 6 months in 

a healthy female, and litters of up to 12 piglets (Taylor 2003). As opportunistic omnivores, hogs 

compete for food with a variety of wildlife species; their destructive rooting behavior is particularly 
15

damaging to natural resources (Taylor 2003). Feral cats and dogs also occur in the park (NPS 2001); 

these have an unknown impact on native animal populations and are a potential safety concern for 

visitors. Feral cats are known to impact bird populations through predation (Loss et al. 2012).
16

Figure 4. Exotic plant removal areas with the number of times each area has been treated since 2001 

(NPS 2014b).
17

Climate Change

Global climate change is expected to impact the entire U.S. during this century, although the 

expected changes vary across the country. Since 1951, the regional climate around SAAN has shown 

little change. Annual mean temperatures have remained relatively stable, while annual precipitation 

has increased slightly, primarily due to increases in summer precipitation (Figure 5; PRISM 2014). 

Over the next century, mean annual precipitation around SAAN is predicted to decrease slightly 

(Figure 6), due primarily to significant decreases in winter and spring precipitation (Figure 7, Figure ; 

Maurer et al. 2007). In contrast, summer precipitation may increase slightly (Figure 8; Maurer et al. 

2007). Annual mean temperature is expected to increase approximately 1.7-2.2°C (3-4°F) by 2050 

and 3.3-3.9°C (6-7°F) by 2100 (Figure 9; Maurer et al. 2007). These expected temperature increases 

will increase evaporation rates and plant transpiration (i.e., plant moisture use); combined with 

seasonal precipitation declines, this will result in greater aridity, meaning overall drier conditions, 

particularly in the winter and spring (Figure 10; Maurer et al. 2007).

Figure 5. Change in mean annual precipitation (left) and mean summer precipitation (right) in the SAAN 

region between 1951 and 2006 (PRISM 2014).
18

Figure 6. Projected change in mean annual precipitation in the SAAN region by 2050 (left) and by 2100 

(right) (Maurer et al. 2007). Projections based on an ensemble average (E-50) circulation model and the 

A1B (medium) emissions scenario. 

Figure 7. Projected change in mean winter precipitation (left) and mean spring precipitation (right) in the 

SAAN region by 2050 (Maurer et al. 2007). Projections based on an ensemble average (E-50) circulation 

model and the A1B (medium) emissions scenario.
19

Figure 8. Projected change in mean winter precipitation (left) and mean summer precipitation (right) in 

the SAAN region by 2100 (Maurer et al. 2007). Projections based on an ensemble average (E-50) 

circulation model and the A1B (medium) emissions scenario.

Figure 9. Projected change in mean annual temperature in the SAAN region by 2050 (left) and by 2100 

(right) (Maurer et al. 2007). Projections based on an ensemble average (E-50) circulation model and the 

A1B (medium) emissions scenario.
20

Figure 10. Projected change in mean annual aridity (left) and mean spring aridity (right) by 2050, as 

predicted by the change in AET:PET ratio (Maurer et al. 2007). Projections based on an ensemble 

average (E-50) circulation model and the A1B (medium) emissions scenario.

Figure 11. Projected change in mean annual aridity (left) and mean spring aridity (right) by 2100, as 

predicted by the change in AET:PET ratio (Maurer et al. 2007). Projections based on an ensemble 

average (E-50) circulation model and the A1B (medium) emissions scenario.
21

2.3 Resource Stewardship

2.3.1 Management Directives and Planning Guidance

The park’s resource management plan (NPS 2001, p. 7) states, 

“Because the original natural environment of the San Antonio Missions has been 

extensively altered or destroyed by man’s intervention during the past three centuries, 

the goals for natural resource management are limited to protecting and improving the 

condition of the existing resources and, where feasible, returning the condition and 

appearance of the landscape to a state which better reflects the spirit of the mission 

period. The latter must be undertaken only in coordination with management of the 

cultural resources and after sufficient research has been accomplished.”

The plan further outlines natural resources objectives to meet this goal, including (NPS 2001):

 Continue coordination between the natural and cultural resource programs to assure activities 

from each program are compatible with protection and management of both resources. 

 Develop and maintain inventory and monitoring programs to assure that management of the 

park’s natural resources is proactive based on a thorough knowledge and understanding of 

the resources. 

 Cooperate with the State of Texas, other government agencies, and private entities for the 

purpose of protecting natural resources from adverse effects due to non-park uses and 

developments. 

 Promote an understanding of the park’s natural resources to those outside of the park.

2.3.2 Status of Supporting Science

The Gulf Coast Network (GULN) identifies key resources network-wide and for each of its parks 

that can be used to determine the overall health of the parks. These key resources are called Vital 

Signs. In 2007, the GULN completed and released a Vital Signs Monitoring Plan (Segura et al. 

2007); Table 1 shows the GULN Vital Signs selected for monitoring in SAAN.

The San Antonio River Authority (SARA) manages the San Antonio River and its tributaries while 

the NPS retains water rights for the historic Acequias Espada and San Juan (Meiman 2012). In 

October 2007, the GULN contracted with SARA to establish four permanent long-term water quality 

monitoring stations in the park: Piedras Creek, Acequia de Espada, San Antonio River at San Juan 

Capistrano and the Acequia de San Juan. SARA samples these four sites bimonthly as part of its 

Clean Rivers Program monitoring effort (Meiman 2012). SARA has also collected data on fish and 

aquatic macroinvertebrate populations within park waters.
22

Table 1. GULN Vital Signs selected for monitoring in SAAN (Segura et al. 2007). 

Category GULN Vital Sign

Category 

1

a

Category 

2

b

Category 

3

c

No Monitoring 

Planned

Air and 

Climate

Ozone X

Air Contaminants X

Weather/Climate X

Geology and 

Soils

Stream/River Channel 

Dynamics and Geomorphology X

Erosion and Deposition X

Soil Biota X

Soil Chemistry X

Soil Structure and Stability X

Water

Groundwater Hydrology X

Water Chemistry X

Water Nutrients X

Water Toxics X

Biological 

Integrity

Non-native Vegetation X

Non-native Animals X

Riparian Communities X

Forest Health X

Freshwater Invertebrates X

Terrestrial Invertebrates X

Amphibians X

Non T&E Reptiles X

Migratory Birds X

Resident Birds X

Non T&E Small Mammals X

Terrestrial Vegetation X

T&E/Rare Birds X

a Category 1 represents Vital Signs for which the network will develop protocols and implement 

monitoring. 

b Category 2 represents Vital Signs that are monitored by SAAN, another NPS program, or by 

another federal or state agency using other funding. 

c Category 3 represents high-priority Vital Signs for which monitoring will likely be done in the future.
23

Table 4 (continued). GULN Vital Signs selected for monitoring in SAAN (Segura et al. 2007). 

Category GULN Vital Sign

Category 

1

a

Category 

2

b

Category 

3

c

No Monitoring 

Planned

Biological 

Integrity

(continued)

T&E/Rare Freshwater Fish X

T&E/Rare Plants X

T&E/Rare Reptiles X

Human Use Visitor Usage X

Landscapes 

(Ecosystem 

Pattern and 

Processes)

Fire and Fuel Dynamics X

Land Cover/Land Use X

Soundscape X

a Category 1 represents Vital Signs for which the network will develop protocols and implement 

monitoring. 

b Category 2 represents Vital Signs that are monitored by SAAN, another NPS program, or by 

another federal or state agency using other funding. 

c Category 3 represents high-priority Vital Signs for which monitoring will likely be done in the future.

2.4 Literature Cited

Amdor, R. C., M. A. Brooks, and J. Trujillo. 1994. San Antonio Missions National Historical Park: 

Land protection amendment. National Park Service, San Antonio, Texas.

Carr, W. R. 2003a. A botanical inventory of San Antonio Missions National Historical Park. Part II: 

For the portion in Wilson County, Texas. National Park Service, San Antonio, Texas.

Carr, W. R. 2003b. A botanical inventory of San Antonio Missions National Historical Park. Part I: 

For the portion in Bexar County, Texas. National Park Service, San Antonio, Texas.

Cogan, D. 2007. Vegetation classification and mapping project report, San Antonio Missions 

National Historical Park. Natural Resource Technical Report NPS/GULN/NRTR—2007/074. 

National Park Service, Fort Collins, Colorado.

Cooper, R. J., S. B. Cederbaum, and J. Gannon. 2005. Natural resource summary for San Antonio 

Missions National Historical Park. National Park Service, Gulf Coast Network, Lafayette, 

Louisiana.

Diamond, D. D. 2010. Handbook of Texas: Grasslands. Texas State Historical Association. 

http://www.tshaonline.org/handbook/online/articles/gqg01 (accessed 17 February 2015).

Dittmer, D. E., and L. A. Fitzgerald. 2010. Assessment of the sustainability of rare reptiles in the San 

Antonio Mission National Historic Park. Interim Report. National Park Service, San Antonio, 

Texas.
24

Environmental Protection Agency (EPA). 2010. Primary distinguishing characteristics of Level III 

and IV Ecoregions of the continental United States. 

http://www.epa.gov/wed/pages/ecoregions/level_iii_iv.htm (accessed 17 February 2015).

Environmental Protection Agency (EPA). 2011. Level III ecoregions of the conterminous United 

States. ArcGIS shapefile.

Griffith, G. E., S. A. Bryce, J. M. Omernik, J. A. Comstock, A. C. Rodgers, B. Harrison, S. L. Hatch, 

and D. Bezanson. 2007. Ecoregions of Texas. U.S. Geological Survey, United States Department 

of Interior, Washington, D.C. 

Halvorson, W. L., and P. Guertin. 2006. Intermountain Region non-native plant inventory and 

mapping program: Final report for San Antonio Missions National Historical Park. USGS 

Southwest Biological Science Center, Tucson, Arizona, and National Park Service, San 

Antonio, Texas.

Losey, J. E., and M. Vaughan. 2006. The economic value of ecological services provided by insects. 

Bioscience 56(4):311-323.

Loss, S. R., T. Will, and P. P. Marra. 2012. The impact of free-ranging domestic cats on wildlife of 

the United States. Nature Communications 4:1396.

Lynch, E. 2009. San Antonio Missions National Historical Park acoustical monitoring report 2009. 

Natural Resource Report NPS/NRPC/NRTR—2009/001. U.S. Department of the Interior, 

National Park Service, Fort Collins, Colorado.

Maurer, E. P., L. Brekke, T. Pruitt, and P. B. Duffy. 2007. Base climate projections (downscaled): 

2050 mid century (2040-2069), 2100 end century (2070-2099) (12km resolution). 

http://www.climatewizard.org/ (accessed 28 July 2014).

McMahan, C. A., R. G. Frye, and K. L. Brown. 1984. The vegetation types of Texas, including 

cropland. Texas Parks and Wildlife Department, Austin, Texas.

Meiman, J. 2012. Gulf Coast Network water quality report: Status of water quality of San Antonio 

Missions National Historical Park. National Park Service, Fort Collins, Colorado.

Mitchell, G. A. 2013. Prairie restoration management plan. San Antonio National Historical Park, 

San Antonio, Texas.

National Climatic Data Center (NCDC). 2015. 1981-2010 normals for San Antonio Stinson 

Municipal Airport and Floresville, TX. http://www.ncdc.noaa.gov/cdo-web/datatools/normals

(accessed 17 February 2015).

National Park Service (NPS). 2000. Strategic plan for San Antonio Missions National Historical 

Park, 1 October 2000 - 30 September 2005. San Antonio Missions National Historical Park, San 

Antonio, Texas.
25

National Park Service (NPS). 2001. Resource management plan. San Antonio Missions National 

Historical Park, San Antonio, Texas. 

National Park Service (NPS). 2010. A summary of biological inventory vertebrate and vascular plant 

inventories data collected at San Antonio Missions National Historical Park. National Park 

Service, Gulf Coast Network, Lafayette, Louisiana.

National Park Service (NPS). 2013. Plan Your Visit. San Antonio Missions National Historical Park.

http://www.nps.gov/saan/planyourvisit/index.htm (accessed 7 January 2014).

National Park Service (NPS). 2014a. NPSpecies online database. 

https://irma.nps.gov/App/Species/Search (accessed 16 September 2014).

National Park Service (NPS). 2014b. SAAN_Park_PlantRemovalAreas_2014.lpk. GIS data received 

from Greg Mitchell, SAAN Natural Resources Program Manager, January 2015.

National Park Service (NPS). 2015a. San Antonio Missions: Environmental factors. 

http://www.nps.gov/saan/naturescience/environmentalfactors.htm (accessed 20 February 2015).

National Park Service (NPS). 2015b. Visitor use statistics. https://irma.nps.gov/Stats/Reports/Park 

(accessed 17 February 2015).

OCULUS. 1998. Rancho de las Cabras cultural landscape report. San Antonio National Historical 

Park, San Antonio, Texas.

PRISM Climate Group. 2014. Climate data: United States (Lower 48 and Conterminous) past 50 

years (1951-2006) (4km resolution). http://www.prism.oregonstate.edu/historical/ (accessed 28 

July 2014).

San Antonio River Authority (SARA). 2005. An inventory of fish species within the San Antonio 

Missions National Historical Park. Final Report. San Antonio River Authority, Environmental 

Services Department, San Antonio, Texas.

Segura, M., R. Woodman, J. Meiman, W. Granger, and J. Bracewell. 2007. Gulf Coast Network Vital 

Signs monitoring plan. Natural Resource Report NPS/GULN/NRR–2007/015. National Park 

Service, Fort Collins, Colorado.

Taylor, R. 2003. The feral hog in Texas. Texas Parks and Wildlife, Austin, Texas.

U.S. Census Bureau (USCB). 2012. Texas dominates list of fastest-growing large cities since 2010 

census, Census Bureau reports. http://www.census.gov/newsroom/releases/archives/

population/cb12-117.html (accessed 20 February 2015). 

U.S. Census Bureau (USCB). 2015. State and county quickfacts: San Antonio, Texas. 

http://quickfacts.census.gov/qfd/states/48/4865000.html (accessed 20 February 2015).
26

Van Auken, O. W., and J. K. Bush. 1984. Changes in plant communities of the San Antonio Missions 

National Historical Park. Pages 28-33 in Proceedings of the Second Annual Missions Research 

Conference. National Park Service, San Antonio, Texas.
27

Chapter 3 Study Scoping and Design

This NRCA is a collaborative project between the NPS and Saint Mary’s University of Minnesota 

Geospatial Services (SMUMN GSS). Project stakeholders include the SAAN resource management 

team and GULN Inventory and Monitoring Program staff. Before embarking on the project, it was 

necessary to identify the specific roles of the NPS and SMUMN GSS. Preliminary scoping meetings 

were held, and a task agreement and a scope of work document were created cooperatively between 

the NPS and SMUMN GSS.

3.1 Preliminary Scoping

A preliminary scoping meeting was held on 19-21 November 2013. At this meeting, SMUMN GSS 

and NPS staff confirmed that the purpose of the NRCA was to evaluate and report on current 

conditions, critical data and knowledge gaps, and selected existing and emerging resource condition 

influences of concern to SAAN managers. Certain constraints were placed on this NRCA, including 

the following:

 Condition assessments are conducted using existing data and information;

 Identification of data needs and gaps is driven by the project framework categories;

 The analysis of natural resource conditions includes a strong geospatial component;

 Resource focus and priorities are primarily driven by SAAN resource management.

This condition assessment provides a “snapshot-in-time” evaluation of the condition of a select set of 

park natural resources that were identified and agreed upon by the project team. Project findings will 

aid SAAN resource managers in the following objectives:

 Develop near-term management priorities (how to allocate limited staff and funding

resources);

 Engage in watershed or landscape scale partnership and education efforts;

 Consider new park planning goals and take steps to further these;

 Report program performance (e.g., Department of Interior Strategic Plan “land health” goals, 

Government Performance and Results Act [GPRA]).

Specific project expectations and outcomes included the following:

 For key natural resource components, consolidate available data, reports, and spatial 

information from appropriate sources including: SAAN resource staff, the NPS Integrated 

Resource Management Application (IRMA) website, Inventory and Monitoring Vital Signs

program, and available third-party sources. The NRCA report will provide a resource 

assessment and summary of pertinent data evaluated through this project.

 When appropriate, define a reference condition so that statements of current condition may 

be developed. The statements will describe the current state of a particular resource with 

respect to an agreed upon reference point.

 Clearly identify “management critical” data (i.e., those data relevant to the key resources).

This will drive the data mining and gap definition process.
28

 Where applicable, develop GIS products that provide spatial representation of resource data, 

ecological processes, resource stressors, trends, or other valuable information that can be 

better interpreted visually.

 Utilize “gray literature” and reports from third party research to the extent practicable.

3.2 Study Design

3.2.1 Indicator Framework, Focal Study Resources and Indicators

Selection of Resources and Measures

As defined by SMUMN GSS in the NRCA process, a “framework” is developed for a park or 

preserve. This framework is a way of organizing, in a hierarchical fashion, bio-geophysical resource 

topics considered important in park management efforts. The primary features in the framework are 

key resource components, measures, stressors, and reference conditions. 

“Components” in this process are defined as natural resources (e.g., birds, plant communities), 

ecological processes or patterns (e.g., natural fire regime), or specific natural features or values (e.g., 

geological formations) that are considered important to current park management. Each key resource 

component has one or more “measures” that best define the current condition of a component being 

assessed in the NRCA. Measures are defined as those values or characterizations that evaluate and 

quantify the state of ecological health or integrity of a component. In addition to measures, current 

condition of components may be influenced by certain “stressors,” which are also considered during 

assessment. A “stressor” is defined as any agent that imposes adverse changes upon a component. 

These typically refer to anthropogenic factors that adversely affect natural ecosystems, but may also 

include natural processes or disturbances such as floods, fires, or predation (adapted from GLEI 

2010). 

During the NRCA scoping process, key resource components were identified by NPS staff and are 

represented as “components” in the NRCA framework. While this list of components is not a 

comprehensive list of all the resources in the park, it includes resources and processes that are unique 

to the park in some way, or are of greatest concern or highest management priority in SAAN. Several 

measures for each component, as well as known or potential stressors, were also identified in 

collaboration with NPS resource staff.

Selection of Reference Conditions

A “reference condition” is a benchmark to which current values of a given component’s measures 

can be compared to determine the condition of that component. A reference condition may be a 

historical condition (e.g., flood frequency prior to dam construction on a river), an established 

ecological threshold (e.g., EPA standards for air quality), or a targeted management goal/objective 

(e.g., a bison herd of at least 200 individuals) (adapted from Stoddard et al. 2006).

Reference conditions in this project were identified during the scoping process using input from NPS 

resource staff. In some cases, reference conditions represent a historical reference before human 

activity and disturbance was a major driver of ecological populations and processes, such as “pre-fire 

suppression.” In other cases, peer-reviewed literature and ecological thresholds helped to define 

appropriate reference conditions. 
29

Finalizing the Framework

An initial framework was adapted from the organizational framework outlined by the H. John Heinz 

III Center for Science’s “State of Our Nation’s Ecosystems 2008” (Heinz Center 2008). Key 

resources for the park were adapted from the GULN Vital Signs Monitoring Plan (Segura et al. 

2007). This initial framework was presented to park resource staff to stimulate meaningful dialogue 

about key resources that should be assessed. Significant collaboration between SMUMN GSS 

analysts and NPS staff was needed to focus the scope of the NRCA project and finalize the 

framework of key resources to be assessed. 

The NRCA framework was finalized in March 2014 following acceptance from NPS resource staff. 

It contains a total of 15 components (Figure 12a-b) and was used to drive analysis in this NRCA. 

This framework outlines the components (resources), most appropriate measures, known or 

perceived stressors and threats to the resources, and the reference conditions for each component for 

comparison to current conditions.
30

Figure 12a. San Antonio Missions National Historical Park natural resource condition assessment framework.

Component Measures Stressors Reference Condition

Ecological Communities

Forested Riparian Corridors 

(including acequias)

Community extent, community composition (e.g., species richness), 

percent coverage of native species, age class structure

Nonnative species (feral hogs, nutria, plants); adjacent land use practices 

(including increased paving carrying more water into acequias and ornamental 

introduction); disease; drought and hydrological changes

Ideally, condition during Missions period, but 

data from this time are not available

Native Grassland/Prairie Community extent, community composition, percent coverage of native 

species

Nonnative species (feral hogs, plants); fire suppression; atmospheric 

deposition of pollutants; drought

Management goal 5 years after seeding: 

coverage of 60-70% native grasses and 30-40% 

forbs and wildflowers; <15% cover by woody 

vegation; minimum of 80% cover by native 

species

Upland Shrublands/Woodlands Community extent, community composition, percent coverage of native 

species

Nonnative species (feral hogs, plants); adjacent land use practices (including 

ornamental introduction); drought; climate change

Ideally, condition during Missions period, but 

data from this time are not available

Reptiles Species richness, relative abundance, reproductive success Nonnative species (feral hogs, cats); habitat loss and fragmentation; drought; 

climate change

Undefined; Strecker (1915) provides some 

information on species richness in San Antonio 

area

Amphibians Species richness, relative abundance, reproductive success Nonnative species (feral hogs, cats); habitat loss; displacement by 

nonnatives (Rio Grande chirping frog); disease; drought; climate change

Undefined; Strecker (1915) provides some 

information on species richness in San Antonio 

area

Breeding Birds Species richness, relative abundance, distribution Habitat loss; brood parasitic species (cowbird); nonnative species (cats, feral 

hogs); adjacent land use; fire ants

Coonan (1987) for species richness; undefined 

for abundance and distribution

Resident/Year-round Birds Species richness, relative abundance, distribution Habitat loss; brood parasitic species (cowbird); nonnative species (cats, feral 

hogs); adjacent land use; fire ants

Coonan (1987) for species richness; undefined 

for abundance and distribution

Aquatic Macroinvertebrates IBI rating

Habitat loss and degradation; water quality impairments; impervious cover 

carrying more water and chemicals into waterways; drought; decreased 

flows; hydrological changes ; past contamination in soils;

TCEQ standards (2007)

Fish Species richness, IBI rating

Habitat loss and degradation; water quality impairments; impervious cover 

carrying more water and chemicals into waterways; drought; decreased 

flows; hydrological changes; climate change 

Standards used by SARA, based on the EPA 

Rapid Bioassessment Protocol V (RBP, EPA 

1989)

Water Quality 

Water temperature, pH, specific conductance (TDS), dissolved oxygen, 

total suspended solids (turbidity), coliform bacteria, nutrients 

(phosphorus, nitrogen), chloride, sulfate

Impervious surface runoff; drought (introduction of reuse water); flooding; 

adjacent land uses; point and non-point source pollution TCEQ standards (2014)

Air quality Ozone, deposition of nitrogen, deposition of sulfur, visibility, particulate 

matter

Urban development and land use; vehicle traffic; coal-burning powerplant; 

nearby oil refinery and fracking; meat packing facility NPS ARD guidelines, based on NAAQS

Biotic Composition

Environmental Quality

Herptiles

Birds

Freshwater Biota

San Antonio Missions National Historic Park

Natural Resource Condition Assessment Framework
31

Figure 12b. San Antonio Missions National Historical Park natural resource condition assessment framework. 

Component Measures Stressors Reference Condition

Soundscape Loudness, frequency, and percent of time audible of non-contributing 

human-caused sound

Urban development and land use; Stinson airport operations (overflights); vehicle 

traffic; railroad noise

Loudness: 52 dBA (level of speech interference for 

interpretive programs (EPA 1974); Percent of time 

audible: no increase above levels documented by Lynch 

(2009); Frequency: undetermined

Dark Night Skies NPS Night Sky Team's suite of measures Urban lights/development; lights along Hwy 410; refinery flaring; blinking lights on 

cell towers Conditions at the time the Missions were active

Viewscape

Number of non-contributing features visible within the park, number of 

non-contributing features visible outside of park, appearance of San 

Juan labores

Urban development expanding south; powerline corridors, cell towers, encroaching 

vegetation, in-park development

Non-contributing features visible within the park: no 

increase from current; management goal of zero woody 

vegetation in the labores and intact shrub/tree rows 

between fields. 

Hydrology (surface and ground 

water)

Stream flow rates (amount and timing), width:depth ratio, depth to 

groundwater (Rancho only)

Drought; extreme flooding events; climate change (changes in precipitation 

patterns); repurposing of the reuse water

Undefined; Ideally, condition during Missions period but 

this is no longer feasible given the significant alterations 

to the San Antonio River 

Environmental Quality

Physical Characteristics

San Antonio Missions National Historic Park

Natural Resource Condition Assessment Framework
32

3.2.2 General Approach and Methods

This study involved gathering and reviewing existing literature and data relevant to each of the key 

resource components included in the framework. No new data were collected for this study; however, 

where appropriate, existing data were further analyzed to provide summaries of resource condition or 

to create new spatial representations. After all data and literature relevant to the measures of each 

component were reviewed and considered, a qualitative statement of overall current condition was 

created and compared to the reference condition when possible.

Data Mining

The data mining process (acquiring as much relevant data about key resources as possible) began at 

the initial scoping meeting, at which time SAAN staff provided data and literature in multiple forms, 

including: NPS reports and monitoring plans, reports from various state and federal agencies, 

published and unpublished research documents, databases, tabular data, and charts. GIS data were 

also provided by NPS staff. Additional data and literature were acquired through online bibliographic 

literature searches and inquiries on various state and federal government websites. Data and literature 

acquired throughout the data mining process were inventoried and analyzed for thoroughness, 

relevancy, and quality regarding the resource components identified at the scoping meeting.

Data Development and Analysis

Data development and analysis was highly specific to each component in the framework and 

depended largely on the amount of information and data available for the component, as well as 

recommendations from NPS reviewers and sources of expertise including NPS staff from SAAN and 

the GULN. Specific approaches to data development and analysis can be found within the respective 

component assessment sections located in Chapter 4 of this report.

Scoring Methods and Assigning Condition

Significance Level

A set of measures are useful in describing the condition of a particular component, but all measures 

may not be equally important. A “Significance Level” represents a numeric categorization (integer 

scale from 1-3) of the importance of each measure in assessing the component’s condition; each 

Significance Level is defined in Table 2. This categorization allows measures that are more important 

for determining condition of a component (higher Significance Level) to be more heavily weighted in 

calculating an overall condition. Significance Levels were determined for each component measure 

in this assessment through discussions with park staff and/or outside resource experts.
33

Table 2. Scale for a measure’s Significance Level in determining a components overall condition.

Significance 

Level (SL) Description

1 Measure is of low importance in defining the condition of this component.

2 Measure is of moderate importance in defining the condition of this component.

3 Measure is of high importance in defining the condition of this component.

Condition Level

After each component assessment is completed (including any possible data analysis), SMUMN GSS 

analysts assign a Condition Level for each measure on a 0-3 integer scale (Table 3). This is based on 

all the available literature and data reviewed for the component, as well as communications with park 

and outside experts.

Table 3. Scale for Condition Level of individual measures.

Condition 

Level (CL) Description

0 Of NO concern. No net loss, degradation, negative change, or alteration.

1 Of LOW concern. Signs of limited and isolated degradation of the component.

2 Of MODERATE concern. Pronounced signs of widespread and uncontrolled degradation.

3

Of HIGH concern. Nearing catastrophic, complete, and irreparable degradation of the 

component.

Weighted Condition Score

After the Significance Levels (SL) and Condition Levels (CL) are assigned, a Weighted Condition 

Score (WCS) is calculated via the following equation:

WCS =

∑ SLi ∗ CLi

# of measures

i=1

3 ∗ ∑ SLi

# of measures

i=1

The resulting WCS value is placed into one of three possible categories: good condition (WCS = 0.0 

– 0.33); condition of moderate concern (WCS = 0.34 - 0.66); and condition of significant concern 

(WCS = 0.67 to 1.0). Figure 13 displays the potential graphics used to represent a component’s 

condition in this assessment. The colored circles represent the categorized WCS; red circles signify a 

significant concern, yellow circles a moderate concern and green circles that a resource is in good 

condition. White circles are used to represent situations in which SMUMN GSS analysts and park 

staff felt there were currently insufficient data to make a statement about the condition of a 

component. For example, condition is not assessed when no recent data or information are available, 
34

as the purpose of an NRCA is to provide a “snapshot-in-time” of current resource conditions. The 

arrows inside the circles indicate the trend of the condition of a resource component, based on data 

and literature from the past 5-10 years, as well as expert opinion. An upward pointing arrow indicates 

the condition of the component has been improving in recent times. A horizontal arrow indicates an 

unchanging condition or trend, and an arrow pointing down indicates deterioration in the condition of 

a component in recent times. These are only used when it is appropriate to comment on the trend of 

condition of a component. In situations where the trend of the component’s condition is currently

unknown, no arrow is given.

Figure 13. Description of symbology used for individual component assessments.
35

Examples of how the symbols should be interpreted:

Resource is in good condition, its condition is improving, high confidence in the 

assessment.

Condition of resource warrants moderate concern; condition is unchanging; 

medium confidence in the assessment.

Condition of resource warrants significant concern; trend in condition is unknown 

or not applicable; low confidence in the assessment.

Current condition is unknown or indeterminate due to inadequate data, lack of 

reference value(s) for comparative purposes, and/or insufficient expert knowledge 

to reach a more specific condition determination; trend in condition is unknown or 

not applicable; low confidence in the assessment. 

Preparation and Review of Component Draft Assessments

The preparation of draft assessments for each component was a highly cooperative process among 

SMUMN GSS analysts and SAAN and GULN staff. Though SMUMN GSS analysts rely heavily on 

peer-reviewed literature and existing data in conducting the assessment, the expertise of NPS 

resource staff also plays a significant and invaluable role in providing insights into the appropriate 

direction for analysis and assessment of each component. This step is especially important when data 

or literature are limited for a resource component.

The process of developing draft documents for each component began with a detailed phone or email conversation with an individual or multiple individuals considered local experts on the resource 

components under examination. These conversations were a way for analysts to verify the most 

relevant data and literature sources that should be used and also to formulate ideas about current 

condition with respect to the NPS staff opinions. Upon completion, draft assessments were forwarded 

to component experts for initial review and comments.

Development and Review of Final Component Assessments

Following review of the component draft assessments, analysts used the review feedback from 

resource experts to compile the final component assessments. As a result of this process, and based 

on the recommendations and insights provided by SAAN resource staff and other experts, the final 

component assessments represent the most relevant and current data available for each component 

and the sentiments of park resource staff and outside resource experts. 

Format of Component Assessment Documents

All resource component assessments are presented in a standard format. The format and structure of 

these assessments is described below.
36

Description

This section describes the relevance of the resource component to the park and the context within 

which it occurs in the park setting. For example, a component may represent a unique feature of the 

park, it may be a key process or resource in park ecology, or it may be a resource that is of high 

management priority. Also emphasized are interrelationships that occur among the featured 

component and other resource components included in the NRCA.

Measures

Resource component measures were defined in the scoping process and refined through dialogue 

with resource experts. Those measures deemed most appropriate for assessing the current condition 

of a component are listed in this section, typically as bulleted items.

Reference Conditions/Values

This section explains the reference condition determined for each resource component as it is defined 

in the framework. Explanation is provided as to why specific reference conditions are appropriate or 

logical to use. Also included in this section is a discussion of any available data and literature that 

explain and elaborate on the designated reference conditions. If these conditions or values originated 

with the NPS experts or SMUMN GSS analysts, an explanation of how they were developed is 

provided.

Data and Methods

This section includes a discussion of the data sets used to evaluate the component and if or how these 

data sets were adjusted or processed as a lead-up to analysis. If adjustment or processing of data 

involved an extensive or highly technical process, these descriptions are included in an appendix for 

the reader or a GIS metadata file. Also discussed is how the data were evaluated and analyzed to 

determine current condition (and trend when appropriate). 

Current Condition and Trend

This section presents and discusses in-depth key findings regarding the current condition of the 

resource component and trends (when available). The information is presented primarily with text 

but is often accompanied by detailed maps or plates that display different analyses, as well as graphs, 

charts, and/or tables that summarize relevant data or show interesting relationships. All relevant data 

and information for a component are presented and interpreted in this section.

Threats and Stressor Factors

This section provides a summary of the threats and stressors that may impact the resource and 

influence to varying degrees the current condition of a resource component. Relevant stressors were 

described in the scoping process and are outlined in the NRCA framework. However, these are 

elaborated on in this section to create a summary of threats and stressors based on a combination of 

available data and literature, and discussions with resource experts and NPS natural resources staff. 

Data Needs/Gaps

This section outlines critical data needs or gaps for the resource component. Specifically, what is 

discussed is how these data needs/gaps, if addressed, would provide further insight in determining 
37

the current condition or trend of a given component in future assessments. In some cases, the data 

needs/gaps are significant enough to make it inappropriate or impossible to determine condition of 

the resource component. In these cases, stating the data needs/gaps is useful to natural resources staff 

seeking to prioritize monitoring or data gathering efforts.

Overall Condition 

This section provides a qualitative summary statement of the current condition that was determined 

for the resource component using the WCS method. Condition is determined after thoughtful review 

of available literature, data, and any insights from NPS staff and experts, which are presented in the 

Current Condition and Trend section. The Overall Condition section summarizes the key findings 

and highlights the key elements used in determining and justifying the level of concern, if any, that 

analysts attribute to the condition of the resource component. Also included in this section are the 

graphics used to represent the component condition.

Sources of Expertise

This is a listing of the individuals (including their title and affiliation with offices or programs) who 

had a primary role in providing expertise, insight, and interpretation to determine current condition 

(and trend when appropriate) for each resource component.

Literature Cited

This is a list of formal citations for literature or datasets used in the analysis and assessment of 

condition for the resource component. Note, citations used in appendices referenced in each section 

(component) of Chapter 4 are listed in that component’s “Literature Cited” section. 

3.3 Literature Cited

Great Lakes Environmental Indicators Project (GLEI). 2010. Glossary, Stressor. 

http://glei.nrri.umn.edu/default/glossary.htm (accessed 19 January 2015).

The H. John Heinz III Center for Science, Economics, and the Environment. 2008. The state of the 

nation’s ecosystems 2008: Measuring the land, waters, and living resources of the United States. 

Island Press, Washington, D.C.

Segura, M., R. Woodman, J. Meiman, W. Granger, and J. Bracewell. 2007. Gulf Coast Network Vital 

Signs monitoring plan. Natural Resource Report NPS/GULN/NRR–2007/015. National Park 

Service, Fort Collins, Colorado.

Stoddard, J. L., D. P. Larsen, C. P. Hawkins, R. K. Johnson, and R. J. Norris. 2006. Setting 

expectations for the ecological condition of streams: the concept of reference condition. 

Ecological Applications 16(4):1267-1276.

39

Chapter 4 Natural Resource Conditions

This chapter presents the background, analysis, and condition summaries for the 15 key resource 

components in the project framework. The following sections discuss the key resources and their 

measures, stressors, and reference conditions. The summary for each component is arranged around 

the following sections:

 Description

 Measures

 Reference Condition

 Data and Methods

 Current Condition and Trend (including threats and stressor factors, data needs/gaps, and 

overall condition)

 Sources of Expertise

 Literature Cited

The order of components follows the project framework (Figure 12a-b):

4.1 Forested Riparian Corridors

4.2 Native Grasslands 

4.3 Upland Shrublands/Woodlands

4.4 Reptiles

4.5 Amphibians

4.6 Breeding Birds

4.7 Resident Birds

4.8 Aquatic Macroinvertebrates

4.9 Fish

4.10 Water Quality

4.11 Air Quality

4.12 Soundscape

4.13 Dark Night Skies

4.14 Viewscape

4.15 Hydrology
40

4.1 Forested Riparian Corridors

4.1.1 Description

Along the San Antonio River, Piedras Creek, 

Picosa Creek, other tributaries, and the historic 

acequias, there are forested riparian areas with 

diverse plant communities in mid to late stages 

of succession (Photo 3). These are often 

considered critical habitat for both flora and 

fauna (Wagner 2003, Cogan 2007). Riparian 

corridors serve important ecological functions, 

partly by maintaining water quality. The 

vegetation provides shade which regulates the 

water temperature, the plants physically bind 

streambanks together which provides channel 

stability, and perhaps most importantly, 

captures excess nutrients and sediment that are 

transported by runoff (Wagner 2003). These 

structural features all improve water quality and 

promote diversity, supporting a wide variety of 

both aquatic and terrestrial species (Wagner 

2003).

In SAAN, elements of Chihuahuan Desert, 

coastal grassland, subtropical woodland, and 

Tamaulipan thornscrub are intermingled within 

the riparian zones (Cogan 2007). Typically, 

riparian forest communities are layered with tall 

trees, shrubs, and wetland herbaceous plants. There are mixes of native and introduced species in 

various combinations comprising the forested riparian corridors of SAAN (Cogan 2007). The 

composition of plant species in these communities is influenced by the climate, soil composition, and 

topography (Cogan 2007). Introduced exotic species and past land management practices (e.g., fire 

suppression) have also had a strong effect on plant community composition in SAAN (Cogan 2007).

Tree species that are common in the riparian areas of the Missions Unit include pecan (Carya 

illinoinensis), black willow (Salix nigra), sugarberry (Celtis laevigata), cedar elm (Ulmus 

crassifolia), and box elder (Acer negundo). These trees occur in large, mixed stands along the main 

channel and tributaries in the unit (Cogan 2007). The Rancho de las Cabras Unit has a similar 

riparian community structure, with some additional tree species, including eastern cottonwood 

(Populus deltoides) (Cogan 2007). These trees create the upper layer of SAAN’s forested riparian 

communities, and at Rancho de las Cabras there are also underlying shrub communities associated 

with both the riparian and upland scrublands (Cogan 2007). Common species are blackbrush acacia 

(Acacia rigidula), Texas hogplum (Colubrina texensis), rough leaf dogwood (Cornus drummondii), 

and Brazilian bluewood (Condalia hookeri) (Cogan 2007). These communities are referred to as 

Photo 3. An example of a forested riparian corridor 

located along the Acequia de Espada (photo by 

Kathy Allen, SMUMN GSS 2013).
41

palustrine, where roots are wetted regularly in the summer, but lack flowing water and undergo short 

dry periods (Cogan 2007).

4.1.2 Measures

 Community extent

 Community composition

 Percent coverage of native species

 Age class structure

4.1.3 Reference Conditions/Values

Ideally, a reference condition from the Missions period would serve as a baseline for the measures in 

this assessment. Unfortunately, there are not sufficient descriptions available from that reference 

period. There are very limited data and descriptions of the forested riparian corridors in SAAN to use 

in comparison with the current conditions or trends in these communities. The information presented 

in this report may be considered the baseline for studies of the park’s forested riparian corridors in 

the future.

4.1.4 Data and Methods

Carr (2003a, b) conducted a botanical inventory of both the Missions and Rancho de las Cabras Units 

of SAAN over a two-year period. The purpose of the study was to obtain baseline inventories of flora 

as part of the NPS Inventory and Monitoring (I&M) Program (Carr 2003a, b). Field work was 

completed concurrently in the Missions and Rancho de las Cabras from July through October in 

2001, and March through October in 2002 (Carr 2003a). Fieldwork consisted of transect sampling in 

each macrohabitat of the Missions and Rancho de las Cabras Units, including riparian woodlands 

(Carr 2003a, b). 

Cogan (2007) completed vegetation classification and mapping in and around SAAN (Figure 14), 

based on field work conducted in 2005-2006. The results provide mapped vegetation communities, 

extent of acreage for each type, and lists of species typically found in each community. Classification 

methods and categories followed the National Vegetation Classification Standard (NVCS) accepted 

by the Federal Geographic Data Committee (FGDC 2008). 
42

Figure 14. Cogan’s (2007) study boundary (yellow) relative to the park boundaries.
43

4.1.5 Current Condition and Trend

Community Extent

Vegetation communities were mapped throughout both units of the park by Cogan (2007). The extent 

of forested riparian communities is provided in Table 7 and shown by location in Figure 15, Figure 

16, and Figure 17.

Table 4. Extent of forested riparian communities (in hectares) within park boundaries and within Cogan’s 

(2007) study area.

Forested Riparian Corridors

Extent (ha)

Missions

(303)

Rancho

(41)

Cogan (2007) 

Study Area

Eastern cottonwood temporarily 

flooded forest alliance

0.0 3.3 26.0

Live oak temporarily flooded forest 

alliance

0.9 0.9 37.1

Black willow temporarily flooded 

shrubland alliance stand

0.0 0.2 0.4

Pecan-Sugarberry Forest 71.2 0.0 198.6

Cedar Elm-Sugarberry/Possumhaw/Virginia wild rye forest17.9 8.8 215.3

Totals 89.8 13.2 477.4

The eastern cottonwood and live oak (Quercus virginiana) temporarily flooded alliances occur in 

both the Missions and the Rancho de las Cabras Units of SAAN. The live oak alliance is primarily 

found in small patches in the northwestern Missions Unit (Figure 15) and Rancho de las Cabras..

The most abundant forested riparian community type is the pecan-sugarberry forest, which is found 

primarily in the southeastern Missions (Figure 16). The second most extensive community type is the 

cedar elm-sugarberry/possum-haw/Virginia wild rye forest, which is also the predominant riparian 

type in the Rancho de las Cabras Unit. The black willow temporarily flooded forest alliance is very 

small, with just one stand located in the Rancho de las Cabras Unit; the size of this alliance in the 

park is below the minimum mapping unit and is not included in the spatial file that shows the layout 

of other riparian vegetation types at SAAN (Figure 16). 

In comparison to the entire Cogan (2007) study area, some of these forested riparian corridors are 

found outside of the park in larger acreages; for example, the pecan-sugarberry forest within the park 

comprises 71 ha (175.4 ac) while the total for the study is 198.6 ha (485.8 ac). The cedar elmsugarberry/possum-haw/Virginia wild rye forest total is 215.3 ha (532ac), the largest of the four 

types, but only 26.7 ha (66ac) is inside of SAAN. In summary, out of the total hectares of riparian 

areas that were mapped for the project, only about 22% of them are protected by the NPS within the 

boundaries of SAAN. Approximately 36% of the total pecan-sugarberry forest, 13% of eastern 
44

cottonwood temporarily flooded forest alliance, 13% of cedar elm-sugarberry/possum-haw/Virginia 

wild rye forest, and 5% of live oak temporarily flooded forest alliance were documented inside of 

SAAN (Cogan 2007). Half of the black willow temporarily flooded shrubland alliance stand is within 

SAAN, covering slightly less than half a hectare (Cogan 2007).

Figure 15. Forested riparian communities within the northwestern area of the Missions Unit (data from 

Cogan 2007).
45

Figure 16. Forested riparian communities within the southeastern Missions Unit at SAAN (Cogan 2007).
46

Figure 17. Forested riparian communities within the Rancho de las Cabras Unit at SAAN (Cogan 2007).

Community Composition

The inventory conducted by Carr (2003a, b) documented 188 plant species associated with riparian 

woodland and forest communities in SAAN. Riparian species that occur in each of the park’s units 

are listed in Appendix B. There were 128 species documented within the Missions Unit and 117 

species in the Rancho de las Cabras, including 42 total non-native species (Carr 2003a, b). Cogan 

(2007) listed species that were associated with the forested riparian corridors and included them with 

the descriptions of each type (excluding black willow).

Pecan-Sugarberry Forest

Pecan-sugarberry riparian forest canopy (15-25 m [49-82 ft] height) in the late successional phase in 

SAAN is dominated by pecan and boxelder (Acer negundo) trees, with a thick layer of sugarberry 

sub-canopy (Cogan 2007). The sub-canopy is mostly underlain with a sparse shrub layer of shrubs 

and saplings, mostly roughleaf dogwood and American black elderberry (Sambucus nigra) (Cogan 

2007). Beneath the sub-canopy are several species of low shrubs and vines, as well as shade-tolerant 

forbs that make up the often sparse (<50%), ground layer (Table 5; Cogan 2007). Amongst the 

typical ground layer species are also seedlings of the various species in this riparian forest. 

Chinaberry trees (Melia azedarch) are common in the pecan-sugarberry forests and are an invasive 

exotic species (Cogan 2007). 
47

Table 5. Species occurring in the pecan-sugarberry forest (recreated from Cogan 2007).

Type Scientific Name Common Name

Tree Carya illinoinensis pecan

Celtis laevigata sugarberry

Acer negundo boxelder

Melia azedarach* Chinaberrytree

Shrub Cornus drummondii roughleaf dogwood

Herb Rubus riograndis Rio Grande dewberry

Toxicodendron radicans poison ivy

Ambrosia trifida great ragweed

Calyptocarpus vialis straggler daisy

Galium aparine cleavers, stickwilly

Malvaviscus arboreus wax mallow

Torilis arvensis* spreading hedgeparsely

Elymus virginicus Virginia wild rye

Invasive Ligustrum japonicum* Japanese privet

* Non-native

In the mid-successional phase the sugarberry dominated canopy seldom exceeds 15 m (49 ft) and 

usually has 75% cover (Cogan 2007). There are some sites where Chinaberry trees got an early 

foothold and are the dominant canopy species; the invasive exotic Japanese privet (Ligustrum 

japonicum) is often found in this forest type as well. The ground layer is thicker in the midsuccessional phase (up to 70% thicker) and is dominated by cleavers (Galium aparine) and spreading 

hedgeparsley (Torilis arvensis) (Cogan 2007). 

Eastern Cottonwood Temporarily Flooded Forest Alliance

This riparian forest type is considered the dominant association for both height and density amongst 

the riparian forests of SAAN; this is likely due to the tendency of cottonwood trees, which are the 

dominant canopy species, to reach such towering heights (Cogan 2007). On average, the canopy 

reaches up to 30 m (98 ft) and has a wide range of coverage (40% to 70%), with a sub-canopy 

coverage that is equal and at times greater than the upper canopy (Cogan 2007). Both the subdominant canopy and the sub-canopy species consist of boxelder, pecan, sugarberry, American elm 

(Ulmus americana), and cedar elm (Cogan 2007). This forest type tends to have a sparse shrub layer 

with a fairly thick ground layer with up to 40% cover (Table 6; Cogan 2007). Many of the ground 

layer species are vines, such as Rio Grande dewberry (Rubus riograndis), saw greenbriar (Smilax 

bona-nox), and poison ivy (Toxicodendron radicans), and shade-tolerant grasses such as Indian 

woodoats (Chasmanthium latifolium) and Virginia wild rye (Elymus virginicus).
48

Table 6. Species occurring in the eastern cottonwood temporarily flooded forest alliance (recreated from 

Cogan 2007).

Type Scientific Name Common Name

Tree Populus deltoides eastern cottonwood

Acer negundo boxelder

Carya illinoinensis pecan

Celtis laevigata sugarberry

Ulmus americana American elm

Ulmus crassifolia cedar elm

Herb Rubus riograndis Rio Grande dewberry

Toxicodendron radicans poison ivy

Smilax bona-nox saw greenbrier

Ambrosia trifida great ragweed

Chasmanthium latifolium Indian woodoats

Elymus virginicus Virginia wild rye

Cedar Elm-Sugarberry/Possum-haw/Virginia Wild Rye Forest

This riparian forest type has canopies that range from 15 to 20 m (49 –66 ft) in height and cover is 

generally around 70-90% in the main areas (Cogan 2007). There are areas upslope of the main body 

that tend to have less than 15 m (49 ft) canopy height and around 50% cover where the vegetation is 

growing in narrow ravines (Cogan 2007). The dominant species in this riparian forest type is cedar 

elm, but may include various ratios of live oak, sugarberry, white mulberry (Morus alba), and honey 

mesquite (Prosopis glandulosa) (Table 7; Cogan 2007). The sub-canopy cover in main areas is 

around 30%, but in the upslope ravines is much thicker with about 70% cover (Cogan 2007). 

Important species include Brazilian bluewood, Texas persimmon (Diospyros texana), and common 

hoptree (Ptelea trifoliata); these species are found sporadically, but are not widely associated with 

the cedar elm-sugarberry riparian forest alliances (Cogan 2007). 
49

Table 7. Species occurring in the cedar elm-sugarberry/possum-haw/Virginia wild rye forest (recreated 

from Cogan 2007).

Type Scientific Name Common Name

Tree Ulmus crassifolia cedar elm

Quercus virginiana live oak

Celtis laevigata sugarberry

Prosopis glandulosa honey mesquite

Herb Elymus virginicus Virginia wild rye

Invasive Ligustrum japonicum* Japanese privet

Melia azedarach* Chinaberrytree

Torilis arvensis* spreading hedge parsely

Morus alba* white mulberry

* Non-native

Live Oak Temporarily Flooded Forest Alliance

The canopy height of this riparian forest type ranges from 15 to 20 m (49 –66 ft) with high closure 

(80%) and has a far lighter understory of around 30% cover (Cogan 2007). Live oak dominates over 

cedar elm, with few other species occuring in these areas (Cogan 2007). This riparian forest alliance 

has very little in terms of understory and ground cover, though there are some shade-tolerant grasses 

sparsely scattered on the forest floors (Table 8) where flooding likely prevents any substantial 

vegetation from establishing itself (Cogan 2007). 

Table 8. Species occurring in the live oak forest alliance (recreated from Cogan 2007).

Type Scientific Name Common Name

Shrub Quercus virginiana live oak

Tree Ulmus crassifolia cedar elm

Herb Chasmanthium latifolium Indian woodoats

Elymus virginicus Virginia wild rye

Percent Coverage of Native Species

The percent cover of native species, especially in comparison to cover of exotic species, can provide 

an indication of how similar current riparian forests are to the historic forests present during the 

Missions period, prior to most exotic species invasions. However, no information is available with 

regard to the percent coverage of native species in the forested riparian corridors of SAAN. The 

park’s exotic plant control program has been working to clear non-native plants from the park since 
50

2000 (Greg Mitchell, SAAN Natural Resources Program Manager, written communication, February 

2015), which has likely increased the percent coverage of native species. 

Age Class Structure

Age class structure can be helpful in determining both the history and current successional status of 

forested areas. The age class structure of forested riparian corridors at SAAN has not been studied at 

this time. Currently this measure is considered a data gap.

Threats and Stressor Factors

Threats to SAAN’s forested riparian corridors include non-native species, disease, hydrological 

changes, adjacent land use practices, and drought. Many of these threats are exacerbated by the 

fragmented and isolated nature of the park units (Robert Woodman, GULN Ecologist, written 

communication, February 2015).

The feral hog (Sus scrofa) is a highly destructive non-native species in most of Texas and is prolific 

throughout the San Antonio area despite the densely populated areas around the Missions and 

Rancho de las Cabras. The omnivorous nature of feral hogs and their destructive wallowing behavior 

cause particularly high levels of damage to riparian areas, which is a preferred habitat (Taylor 2003).

The nutria (Myocastor coypus) is a large, exotic invasive rodent species that originated in South 

America, where they are native (Carter 2014). Nutrias are large (8.2-9.1kg) semiaquatic creatures 

that were introduced to North America in the late 1800s for their furs (Texas Invasives 2011). In the 

late 1940s, a hurricane dispersed nutria along the Gulf of Mexico coastlines of Texas and Louisiana, 

which is likely how they became established in Texas (Texas Invasives 2011). Nutria have been 

confirmed in SAAN, and are a threat to the forested riparian corridors since their feeding habits cause 

damage to vegetation (NPS 2014, Carter 2014).

Introduction of exotic ornamental plant species can be problematic in native plant communities as 

they can become established and out-compete the native flora. There are several invasive 

ornamentals already present in SAAN that are among the 42 listed exotics confirmed within the 

forested riparian corridors (Carr 2003a, b). These include Chinese tallow (Triadica sebifera), Chinese 

privet (Ligustrum sinense), Japanese honeysuckle (Lonicera japonica), golden bamboo 

(Phyllostachys aurea), Chinaberrytree, and giant reed (Arundo donax; Photo 4).

There are disease risks that threaten a few of the tree species in forested riparian corridors. These 

include the live oaks and the two elm species (cedar and American) that occur in the riparian forests. 

Live oaks are susceptible to a fungal disease called oak wilt that causes defoliation and eventual 

death of the affected tree (TOW 2012). The other disease is a vascular pathogen called Dutch elm 

disease (Ophiostoma novo-ulmi) that affects the cedar elm and the American elm tree species (Appel 

2009). The American elm is highly susceptible and the cedar elms are considered intermediately 

susceptible to the disease, which is contagious to neighboring trees, and some appear to have varying 

degrees of resistance to infection (Appel 2009).
51

Photo 4. The front-most vegetation is the invasive giant reed growing in the San Juan Woods (Photo by 

Shannon Amberg, SMUMN GSS 2013).

Over the last 100 years, the San Antonio River, which flows through both units of SAAN, has 

undergone drastic hydrological changes (Cawthon 2008). The basin has become heavily urbanized 

and as a result, impervious surface cover has increased dramatically (Cawthon 2008). This, combined 

with channelization of the river, has compounded the effects of runoff during and after storm events 

(Cawthon 2008). Runoff water from urban areas is often highly toxic, full of contaminants and high 

levels of nutrients that can degrade water quality and destabilize channels (Cawthon 2008). Forested 

riparian corridors serve as both a catchment mechanism, stabilization, and as a filtration system and 

therefore are very important to both human communities as well as the natural ecology of the San 

Antonio River basin (Wagner 2003, Cawthon 2008). Focusing conservation efforts and remediation 

activities on the preservation and restoration of existing and future riparian communities will not 

only alleviate damaging flood pulse affects, but also preserve the integrity of the SAAN aesthetic 

setting (Wagner 2003, Cawthon 2008). This is especially important during periods of drought, which 

have been major in Texas during the past 5 to 10 years (USDM 2014). The storm events following a 

period of drought will often carry more contaminant-loaded material into waterways because it has 

been allowed time to build up on the terrestrial surface. These drought periods can result in the 

desiccation of vegetation, which is important to soil stability. Without adequate vegetation cover, soil 

is washed directly into waterways, especially where there lacks a riparian corridor to filter and soak 

up solids and excess water. Recently, SARA and the U.S. Army Corps of Engineers have been 

working to improve the Missions Reach of the San Antonio River by restoring more natural flow 

conditions and native vegetation (SARIP 2013). This will likely benefit riparian corridors in and 

around the park.
52

Data Needs/Gaps

The lack of data to use for reference condition renders the current condition useful only as a baseline 

to compare with future studies and surveys. There are no studies available addressing the percent 

coverage of native species or age class structure so these measures are data gaps in both reference 

condition and current condition. However, surveys that are currently taking place or are starting soon 

will provide some insight in these areas.

The GULN is currently developing a vegetation monitoring protocol that will begin gathering data at 

both the Missions and Rancho Units by 2016 (Woodman, written communication, December 2014). 

This sampling will provide information on plant community composition and coverage, and will 

identify trends in those parameters and species richness, as well as monitoring for new non-native 

species (Woodman, written communication, December 2014).

In 2016, Ladybird Johnson Wildflower Center staff will be surveying and mapping exotic plant 

species in the park (Mitchell, written communication, 7 May 2015). This information will be useful 

for evaluation condition in future assessments.

Overall Condition

Community Extent

The measure for community extent was assigned a Significance Level of 2. While there are limited 

historical data for comparison, given the development and hydrological changes that have occurred 

in the San Antonio area, it is almost certain that forested riparian areas currently cover much less area 

than they did during the Missions period. As a result, this measure is assigned a Condition Level of 2, 

indicating moderate concern.

Community Composition

The measure for community composition was assigned a Significance Level of 3. Currently, the 

baseline is Carr (2003a, b), a botanical inventory report that was conducted in 2001 and 2002. 

Assessing a Condition Level for this measure is not possible at this time, as the Carr (2003a, b) 

survey is outdated and there are also no data for a reference condition regarding this measure.

Percent Coverage of Native Species

The Significance Level of percent coverage of native species was assigned a 3. Since there are no 

data for reference condition or current condition, a Condition Level cannot be assigned at this time. 

Age Class Structure

Age class structure was assigned a Significance Level of 3. There are no data for this measure and a 

Condition Level cannot be assigned. There are, however, plans in place to begin collecting age class 

structure data in SAAN in the near future.

Weighted Condition Score

A Weighted Condition Score was not calculated for SAAN’s forested riparian corridors, largely due 

to data gaps. Three of the four measures could not be assigned Condition Levels. Further monitoring 

and data collection will allow trends in these measures to be assessed in the future. The community 
53

extent and composition information presented here can serve as baselines for comparison in future 

studies.

Forested Riparian Corridors

Measures

Significance 

Level

Condition 

Level WCS = N/A

Community Extent 2 2

Community 

Composition 3 n/a

Percent Coverage of 

Native Species 3 n/a

Age Class Structure 3 n/a

4.1.6 Sources of Expertise

Greg Mitchell, SAAN Natural Resources Program Manager

Robert Woodman, GULN Ecologist

4.1.7 Literature Cited

Appel, D. N. 2009. Dutch elm disease in Texas. Texas A&M University, The Newsletter of the 

International Society of Arboriculture Texas Chapter. 32:5.

Carr, W. R. 2003a. A botanical inventory of San Antonio Missions National Historical Park. Part I : 

for the portion in Bexar County. National Park Service, San Antonio, Texas.

Carr, W. R. 2003b. A botanical inventory of San Antonio Missions National Historical Park. Part II: 

for the portion in Wilson County. National Park Service, San Antonio, Texas.

Carter, J. 2014. Worldwide distribution, spread and efforts to eradicate the nutria (Myocastor 

coypus). United States Geological Survey (USGS). 

http://www.nwrc.usgs.gov/special/nutria/index.htm (accessed 9 December 2014).

Cawthon, T. 2008. Channel change on the San Antonio River. Texas Water Development Board, San 

Marcos, Texas.
54

Cogan, D. 2007. Vegetation classification and mapping project report, San Antonio Missions 

National Historical Park. Natural Resource Technical Report NPS/GULN/NRTR—2007/074. 

National Park Service, Fort Collins, Colorado

Federal Geographic Data Committee (FGDC). 2008. National vegetation classification standard, 

version 2. Federal Geographic Data Committee, Vegetation Subcommittee, Reston, Virginia.

National Park Service (NPS). 2014. NPSpecies, San Antonio Missions National Historical Park 

(SAAN) species list. https://irma.nps.gov/NPSpecies/Species/Profile/168762 (accessed 9 

December 2014). 

San Antonio River Improvements Project (SARIP). 2013. San Antonio River improvements project 

fact sheet. San Antonio River Authority, San Antonio, Texas.

Taylor, R. 2003. The Feral Hog in Texas. Texas Parks and Wildlife Department Federal Aid Report,

Austin, Texas.

Texas Invasives. 2011. Invasives database: Myocastor coypus, nutria. 

http://www.texasinvasives.org/animal_database/detail.php?symbol=7 (accessed 9 December 

2014).

Texas Oak Wilt (TOW). 2012. Oak wilt identification. http://texasoakwilt.org/oakwilt/oak-wiltidentification/ (accessed 16 December 2014).

U.S. Drought Monitor (USDM). 2014. Tabular data archive, Texas. 

http://droughtmonitor.unl.edu/MapsAndData/DataTables.aspx?TX (accessed 9 December 2014).

Wagner, M. 2003. Managing riparian habitats for wildlife. Texas Parks & Wildlife, Austin, Texas.
55

4.2 Native Grasslands

4.2.1 Description

Prior to European settlement, much of the upland in the San Antonio area supported native 

grasslands, with just small patches of brush (Cooper et al. 2005). In the area just south and east of the 

city, travelers would have seen, “...a prairie which during the fall was covered largely with perennial 

grasses about 2 ft. tall. During the spring, between the sere grasses was a carpet of flowers” 

(Johnston 1963, p. 457, citing Santleben 1910, Sanchez 1926, Bollaert 1956). The Missions likely 

relied on these grasses as forage for their livestock (Fearing 1981). Native grasslands are the only 

Spanish colonial period landscape currently missing from SAAN (Mitchell 2013).

After the Mission period, ranching continued and intensified. Many areas were overgrazed, which 

resulted in vegetation trampling, soil compaction, and overall degradation of grassland communities 

(OCULUS 1998). The effects of overgrazing, combined with a reduction in fire occurrence, allowed 

honey mesquite and other shrubs to invade, and much of the region’s native prairie was lost 

(OCULUS 1998, Cooper et al. 2005). Additional areas, particularly near the city of San Antonio, 

were cleared for farming and construction (Cogan 2007).

Human settlement and farming lead to the 

introduction of many exotic species, especially 

grasses planted to feed livestock (Carr 2003a, 

Cogan 2007). Any grasslands remaining within 

SAAN today are dominated by these exotic 

grasses, such as Bermudagrass (Cynodon 

dactylon), Kleberg’s bluestem (Dichanthium 

annulatum), yellow bluestem (Bothriochloa 

ischaemum), and Johnsongrass (Sorghum 

halepense) (Cooper et al. 2005, Cogan 2007).

Some native grasses remain, including Texas 

wintergrass (Nassella leucotricha), little bluestem

(Schizachyrium scoparium), and plains lovegrass 

(Eragrostis intermedia), occasionally codominating with the exotics. Additional native 

grass species found around the Missions are 

Virginia wildrye, Ozarkgrass (Limnodea 

arkansana), and purple threeawn (Aristida 

purpurea) (Cogan 2007). Common native 

grassland species at the Rancho de las Cabras 

Unit include sand dropseed (Sporobolus 

cryptandrus), browntop signalgrass (Urochloa 

fusca), Texas signalgrass (Urochloa texana), and 

sideoats grama (Bouteloua curtipendula) (Carr

2003a, Cogan 2007).

Photo 4. Indian blanket (Gaillardia pulchella), a 

native wildflower, in a prairie planting at Mission 

San Juan (Photo by Kathy Allen, SMUMN GSS 

2013).
56

4.2.2 Measures

 Community extent

 Community composition

 Percent coverage of native species

4.2.3 Reference Conditions/Values

The ideal reference condition for this component would be the condition of native grasslands during 

the Mission period. However, given the significant changes in land cover and land use since that time 

(e.g., shrub invasion, city expansion), this is no longer considered feasible. NPS staff have selected 

the following management goals for SAAN prairie restoration areas 5 years after their establishment 

(Mitchell 2013), which will be used as reference conditions for this assessment:

 Minimum of 80% cover by native species

 Coverage of 60-70% native grasses and 30-40% forbs and wildflowers

 <15% cover by woody vegetation

4.2.4 Data and Methods

Since no intact native grasslands currently exist within SAAN, little information is available 

regarding the community. Vegetation studies by Carr (2003a, b) and Cogan (2007) documented some 

native grassland plant species occurring in the park’s old fields. The park has been interested in 

restoring native prairie to the SAAN landscape since 2003. The idea was first proposed in the 1998 

Rancho de las Cabras Cultural Landscape Report (OCULUS 1998). In 2011, funding was obtained 

for prairie restorations in two areas of the park, totaling approximately 8.9 ha (22 ac) (Mitchell 

2013). The park has prepared a restoration management plan (Mitchell 2013) that describes the 

project sites and methods, as well as outlining proposed maintenance and monitoring.

4.2.5 Current Condition and Trend

Community Extent

No intact native grassland communities currently exist at SAAN. Prairie restorations are underway at 

two sites, one at Rancho de las Cabras (4 ha [10 ac]) and one near San Juan Dam (4.9 ha [12 ac]) in 

the Missions Unit. Site preparation (i.e., removal of current woody and non-native vegetation) 

occurred from April 2013 through 2014. Seeding is expected to occur in late 2015 and 2016 

(Mitchell, written communication, December 2014).
57

Figure 18. Native grassland restoration sites at the Rancho Unit (left) and near San Juan Dam in the Missions Unit (right) (close-up aerial photos 

from Mitchell 2013).
58

Community Composition

While native grassland communities are not currently present in SAAN, native plant species that 

would occur in these grasslands are still found at both the Missions and Rancho Units. Carr (2003a, 

b) conducted plant inventories at SAAN and documented 187 native herbaceous species in the park’s 

old field grasslands (Appendix C). One hundred and ten species were found in the Rancho Unit (Carr 

2003a) and 130 at the Missions Unit (Carr 2003b). The species proposed for inclusion in the seed 

mix for the park’s two prairie restoration areas (and, therefore the expected composition of these 

restored grasslands) are listed in Table 9.

Table 9. Native species in the seed mix for SAAN’s prairie restorations (Mitchell 2013).

Grasses Wildflowers

Scientific name Common name Scientific name Common name

Schizachyrium scoparium little bluestem Rudbeckia hirta black-eyed susan 

Sorghastrum nutans Indiangrass Lupinus spp. bluebonnets 

Bouteloua curtipendula sideoats grama Dracopis amplexicaulis clasping coneflower

Setaria sp. Catarina bristlegrass Phlox drummondii Drummond phlox 

Leptochloa dubia green sprangletop Gaillardia pulchella Indian blanket 

Bouteloua repens slender grama Monarda citriodora lemon mint (beebalm)

Pappophorum vaginatum whiplash pappusgrass Ratibida columnifera Mexican hat 

Panicum virgatum switchgrass Coreopsis spp. coreopsis 

Chloris cucullata hooded windmillgrass Oenothera spp. evening primrose

Bothriochloa laguroides 

ssp. torreyana

silver beardgrass Castilleja spp. Indian paintbrush

Percent Coverage of Native Species

In prairie restorations, it often takes several years for native plant species to become established. The 

goals selected by park staff regarding coverage of native species are for five years after seeding at the 

project sites. It will still be a few years before the coverage of native species can be assessed in these 

restoration areas. No information is available regarding the coverage of native species in the park’s 

current old field (non-native dominated) grasslands. 

Threats and Stressor Factors

Once established at SAAN, native grasslands will face many threats, such as non-native invasive 

species, fire suppression, atmospheric deposition of pollutants, and drought. Non-native invasive 

plants will likely be difficult to control in the prairie restoration areas. Over 150 non-native species 

have been documented in SAAN (NPS 2010), although not all of these are invasive and not all would 

threaten grasslands. Some non-native grasses were actually planted historically for hay to feed 

livestock (Carr 2003a, Cooper et al. 2005). Non-natives likely to be of high concern due to their 
59

potential to outcompete native grassland species include buffelgrass (Pennisetum ciliare), 

Johnsongrass, Bermudagrass, and yellow bluestem (also known as King Ranch bluestem) (Cooper et 

al. 2005, NPS 2010). All of these species were documented by Halvorson and Guertin (2006) in 2004 

at both the Missions and Rancho Units (Appendix A).

Historic fire suppression likely led to the conversion of much of the area’s original grasslands to 

shrublands (Van Auken and Bush 1984, Van Auken 2000). Fire eliminates or inhibits woody species 

in favor of native grassland species; in the absence of fire, shrubs such as mesquite and acacias

invade and outcompete grassland species (Van Auken and Bush 1984, Van Auken 2000). It may be a 

challenge to maintain any prairie restorations in the Missions Unit with burning, given that 

opportunities for burning could be limited by concerns over smoke management within the San 

Antonio city limits. 

The deposition of pollutants such as nitrogen and sulfur dioxides can cause acidification and nutrient 

enrichment of soils (Sullivan et al. 2011a, b). Native grasslands in semi-arid regions, like that around 

SAAN, are considered sensitive to excess nitrogen and acidic deposition (Sullivan et al. 2011c, 

2011d). Nutrient enrichment may create favorable conditions for non-native grass invasion (Fenn et 

al. 2003). Air pollution in the region around SAAN is discussed in further detail in section 4.11 of 

this report.

Research has shown that drought can impact grassland species richness and above-ground biomass 

(Tilman and El Haddi 1992). Annual plants and rare species are especially at risk, as one dry year 

could cause them to be lost from a local plant community (Tilman and El Haddi 1992). Droughts 

may increase in frequency and duration as a result of global climate change (Twilley et al. 2001, 

Davey et al. 2007), which could pose a challenge for the park’s grassland restoration efforts. In some 

grasslands, soil water availability (from precipitation) appears to limit grass seedling establishment 

(i.e., recruitment) (Lauenroth et al. 1994). Therefore, it may be difficult to establish native grasslands 

from seed if a drought occurs. 

Data Needs/Gaps

Since the original native grasslands are no longer present at SAAN, very little is known about what 

their exact composition and extent would have been. The current restoration efforts provide an 

excellent opportunity to study the process and the restored grasslands. For example, park staff and 

researchers could learn which species thrive and which struggle at the selected sites, and which nonnative species or other stressors (e.g., drought) are the greatest threat to the restoration. Insight could 

also be gained regarding how the restoration impacts other park resources, such as neighboring 

vegetation communities and wildlife. Any lessons learned could be applied to future restoration 

efforts at the park or in the region.

As mentioned in the previous chapter, the GULN is developing a vegetation monitoring protocol that 

will begin gathering data by 2016 (Woodman, written communication, December 2014). This 

sampling will provide information on plant community composition and coverage.
60

Overall Condition

Community Extent

The project team assigned this measure a Significance Level of 2. At this time, no intact native 

grassland communities exist at SAAN. Native grasslands are the only Spanish colonial period 

landscape currently missing from the park, although staff are in the process of restoring 8.9 ha (22 

ac) at two separate sites (Mitchell 2013). Since native grasslands are not present at SAAN, the 

Condition Level for this measure is a 3, indicating high concern.

Community Composition

The community composition measure was assigned a Significance Level of 3. Since native grasslands 

do not occur at SAAN, their composition cannot be studied. Therefore, this measure is not applicable 

at this time and no Condition Level is assigned. However, a plant inventory by Carr (2003a, b) 

confirmed that many native grassland species still occur, intermixed with non-native species in the 

park’s old fields.

Percent Coverage of Native Species

This measure was assigned a Significance Level of 3. Given that the park’s prairie restoration areas 

are not yet established and no information is available on the coverage of native species in existing 

old fields, a Condition Level could not be assigned for this measure.

Weighted Condition Score

A Weighted Condition Score was not calculated for native grasslands, since two of the three 

measures could not be assessed at this time. This is due to the fact that no intact native grassland 

communities currently exist at SAAN.

Native Grasslands

Measures

Significance 

Level

Condition 

Level WCS = N/A

Community Extent 2 3

Community 

Composition 3 n/a

Percent Coverage of 

Native Species 3 n/a

4.2.6 Sources of Expertise

Greg Mitchell, SAAN Natural Resources Program Manager

Robert Woodman, GULN Ecologist
61

4.2.7 Literature Cited

Bollaert, W. 1956. William Bollaert’s Texas. Hollon, W. E., and R. L. Butler (eds.). University of 

Oklahoma Press, Norman, Oklahoma.

Carr, W. R. 2003a. A botanical inventory of San Antonio Missions National Historical Park. Part II: 

For the portion in Wilson County, Texas. National Park Service, San Antonio, Texas.

Carr, W. R. 2003b. A botanical inventory of San Antonio Missions National Historical Park. Part I: 

For the portion in Bexar County, Texas. National Park Service, San Antonio, Texas.

Cogan, D. 2007. Vegetation classification and mapping project report, San Antonio Missions 

National Historical Park. National Park Service, Gulf Coast Network, Lafayette, Louisiana.

Cooper, R. J., S. B. Cederbaum, and J. Gannon. 2005. Natural resource summary for San Antonio 

Missions National Historical Park. National Park Service, Gulf Coast Network, Lafayette, 

Louisiana.

Davey, C. A., K. T. Redmond, and D. B. Simeral. 2007. Weather and climate inventory, National 

Park Service, Gulf Coast Network. Natural Resource Technical Report NPS/GULN/NRTR. 

2007/011. National Park Service, Fort Collins, Colorado.

Fearing, O. 1981. Ethnobotanical study of plants of the San Antonio Missions National Historical 

Park. San Antonio National Historical Park, San Antonio, Texas.

Fenn, M. E., J. S. Baron, E. B. Allen, H. M. Rueth, K. R. Nydick, L. Geiser, W. D. Bowman, J. O. 

Sickman, T. Meixner, D. W. Johnson, and P. Neitlich. 2003. Ecological effects of nitrogen 

deposition in the western United States. Bioscience 53(4):404-420.

Halvorson, W. L., and P. Guertin. 2006. Intermountain Region non-native plant inventory and 

mapping program: Final report for San Antonio Missions National Historical Park. USGS 

Southwest Biological Science Center, Tucson, Arizona, and National Park Service, San Antonio, 

Texas.

Johnston, M. C. 1963. Past and present grasslands of southern Texas and northeastern Mexico. 

Ecology 44(3):456-466.

Lauenroth, W. K., O. E. Sala, D. P. Coffin, and T. B. Kirchner. 1994. The importance of soil water in 

the recruitment of Bouteloua gracilis in the shortgrass steppe. Ecological Applications 4(4):741-

749.

Mitchell, G. A. 2013. Prairie restoration management plan. San Antonio National Historical Park, 

San Antonio, Texas.

National Park Service (NPS). 2010. A summary of biological inventory data collected at San Antonio 

Missions National Historical Park: Vertebrate and vascular plant inventories. National Park 

Service, Gulf Coast Network, Lafayette, Louisiana.
62

OCULUS. 1998. Rancho de las Cabras cultural landscape report. San Antonio National Historical 

Park, San Antonio, Texas.

Sanchez, J. M. 1926. A trip to Texas in 1828. Diary translated by C. E. Castaneda. Southwestern 

Historical Quarterly 29:249-288.

Santleben, A. 1910. A Texas pioneer. Dafflick, I. (ed.). Neales Publishing Company, New York, 

New York, and Washington, D.C.

Sullivan, T. J., G. T. McPherson, T. C. McDonnell, S. D. Mackey, and D. Moore. 2011a. Evaluation 

of the sensitivity of inventory and monitoring national parks to acidification effects from 

atmospheric sulfur and nitrogen deposition: main report. Natural Resource Report 

NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado.

Sullivan, T. J., T. C. McDonnell, G. T. McPherson, S. D. Mackey, and D. Moore. 2011b. Evaluation 

of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from 

atmospheric nitrogen deposition: main report. Natural Resource Report 

NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado.

Sullivan, T. J., G. T. McPherson, T. C. McDonnell, S. D. Mackey, and D. Moore. 2011c. Evaluation 

of the sensitivity of inventory and monitoring national parks to acidification effects from 

atmospheric sulfur and nitrogen deposition: Gulf Coast Network (GULN). Natural Resource 

Report NPS/NRPC/ARD/NRR—2011/358. National Park Service, Denver, Colorado.

Sullivan, T. J., G. T. McPherson, T. C. McDonnell, S. D. Mackey, and D. Moore. 2011d. Evaluation 

of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from 

atmospheric nitrogen deposition: Gulf Coast Network (GULN). Natural Resource Report 

NPS/NRPC/ARD/NRR—2011/310. National Park Service, Denver, Colorado.

Tilman, D., and A. El Haddi. 1992. Drought and biodiversity in grasslands. Oecologia 89:257-264.

Twilley, R. R., E. J. Barron, H. L. Gholz, M. A. Harwell, R. L. Miller, D. J. Reed, J. B. Rose, E. H. 

Siemann, R. G. Wetzel, and R. J. Zimmerman. 2001. Confronting climate change in the Gulf 

Coast region: Prospects for sustaining our ecological heritage. Union of Concerned Scientists, 

Cambridge, Massachusetts, and Ecological Society of America, Washington, D.C.

Van Auken, O. W., and J. K. Bush. 1984. Changes in plant communities of the San Antonio Missions 

National Historical Park. Pages 28-33 in Proceedings of the Second Annual Missions Research 

Conference. National Park Service, San Antonio, Texas.

Van Auken, O. W. 2000. Shrub invasions of North American semiarid grasslands. Annual Review of 

Ecology and Systematics 31:197-215.
63

4.3 Upland Shrublands/Woodlands

4.3.1 Description

The upland shrublands and woodlands at SAAN are mid-successional communities, occurring 

primarily on former grasslands that will eventually transition to forests in the absence of disturbance 

(Carr 2003a, b, Cogan 2007). The conversion of grasslands to shrublands was aided by ranching 

during and after the Missions period; overgrazing and fire suppression allowed woody species to 

invade native grasslands throughout Texas (Van Auken and Bush 1984, OCULUS 1998). Shrublands 

and woodlands are now common in the abandoned labores (old fields) and on uplands bordering the 

San Antonio River valley (Cogan 2007). Typical species in these communities include huisache 

(Acacia farnesiana), honey mesquite, Texan hogplum, Brazilian bluewood, and hackberries (Celtis 

spp.) (Photo 6; Carr 2003a, Cogan 2007). While the ground layer can be sparse in dense stands, more 

open areas support herbaceous ground cover. Some stands retain the native grasses and forbs that 

occurred previously in the original grasslands, but others are dominated by invasive non- native 

species (Carr 2003a).

Photo 6. Upland woodland at SAAN’s Rancho de las Cabras Unit (photo by Shannon Amberg, SMUMN 

GSS 2013).

4.3.2 Measures

 Community extent

 Community composition

 Percent coverage of native species

4.3.3 Reference Conditions/Values

The ideal reference condition for this component would be the condition of upland shrublands and 

woodlands during the Mission period. However, given the significant changes in land cover and land 
64

use since that time (e.g., city expansion and development), this may no longer be attainable. In 

addition, very little historical information is available regarding shrublands and woodlands in the 

SAAN area. The information presented in this NRCA could be used as a baseline for future 

assessments.

4.3.4 Data and Methods

Carr (2003a, b) conducted botanical inventories at both the Missions and Rancho Units from 2001-

2002. Nine transects were sampled in upland woodland habitats within the Missions Unit, and one 

transect was sampled in each of the two upland habitats (upland woodland and upper-slope 

shrubland) at the Rancho Unit. Cogan (2007) produced a vegetation classification system and map 

for SAAN based on field work conducted from 2005-2006. Classification methods and categories 

followed the National Vegetation Classification Standard (NVCS). 

4.3.5 Current Condition and Trend

Community Extent

As of 2005-06, upland shrubland and woodland communities covered 89.1 ha (220.2 ac) within park 

boundaries (Table 13; Cogan 2007). The majority of these communities (71.6 ha) are in the Missions 

Unit. The most common shrubland/woodland type is the Huisache - (Honey Mesquite) Woodland, 

comprising a total of 55.7 ha (137.6 ac), almost entirely within the Missions Unit (Cogan 2007). The 

most common woodland type at the Rancho Unit is dominated by honey mesquite (Table 13). Privet 

shrubland stands, characterized by the exotic species Japanese privet, were present only in the 

Missions Unit (Cogan 2007). The locations of shrublands and woodlands within the park are shown 

in Figure 19 and Figure 20 (Missions Unit), and Figure 21 (Rancho Unit). In recent years, some of 

these shrublands have been cleared as part of grassland and labores restoration efforts (Woodman, 

written communication, February 2015).

Table 13. Extent of upland shrubland and woodland communities (in hectares) within park boundaries 

and within Cogan’s (2007) study area.

Woodland/Shrubland Type

Extent (ha)

Missions Rancho

Cogan (2007) 

Study Area

Chaparro-Prieto Shrubland 1.4 5.3 144.2

Honey Mesquite - Granjeno/Prickly-pear 

Species - South Texas Ericameria Woodland

10.0 11.7 153.8

Huisache - (Honey Mesquite) Woodland 55.2 0.5 342.1

Privet Shrubland Stand 5.0 0 23.6

Totals 71.6 17.5 663.7
65

Figure 19. Extent of upland shrublands and woodlands in the northwest portion of the Missions Unit (data 

from Cogan 2007).
66

Figure 20. Extent of upland shrublands and woodlands in the southeast portion of the Missions Unit (data 

from Cogan 2007).
67

Figure 21. Extent of upland shrublands and woodlands in the Rancho Unit (data from Cogan 2007).

Community Composition

Carr (2003a, b) conducted botanical inventories at both SAAN units and tracked species occurrence 

by macrohabitat (i.e., vegetation community). Within the Missions Unit, there was just one upland 

woodland macrohabitat, while at Rancho there were two - upland woodlands and upper-slope 

shrubland. The full species list for these communities can be found in Appendix D. A total of 282 

plant species were documented within the park’s upland shrublands and woodlands, including 30 

non-native species. The upland woodlands within the Missions Unit supported 151 plant species, 26 

of which were non-native (Carr 2003b). The Rancho’s upland woodlands and upper-slope shrublands 

contained 133 and 156 species, respectively. Twelve of the plant species in the Rancho’s upper 

woodlands were non-native, while only six non-native species were observed in the upper-slope 

shrublands (Carr 2003a). Native species documented in all three macrohabitats are presented in Table 

14.
68

Table 10. Native plant species found in all three of Carr’s (2003a, b) upland woodland and shrubland 

macrohabitats.

Shrubs and Vines Grasses and Forbs

Scientific name Common name Scientific name Common name

Gutierrezia texana Texas snakeweed Amblyolepis setigera huisache daisy

Berberis trifoliolata algerita; agarito Ambrosia psilostachya western ragweed

Opuntia engelmannii var.

lindheimeri

Texas pricklypear Aphanostephus 

ramosissimus

plains dozedaisy or lazy 

daisy

Diospyros texana Texas persimmon Symphyotrichum ericoides heath aster

Eysenhardtia texana Texas kidneywood Calyptocarpus vialis straggler daisy

Passiflora tenuiloba birdwing passionflower Cirsium texanum Texas thistle

Clematis drummondii Drummond’s clematis Fleischmannia incarnata pink thoroughwort

Colubrina texensis Texan hogplum Helianthus annuus common sunflower

Condalia hookeri var.

hookeri

Brazilian bluewood Croton monanthogynus prairie tea, oneseeded 

croton

Celtis ehrenbergiana spiny hackberry Desmanthus virgatus wild tantan

Celtis laevigata var.

reticulata

netleaf hackberry Oxalis dillenii slender yellow woodsorrel

Phoradendron tomentosum Christmas mistletoe Bothriochloa laguroides 

ssp. torreyana

silver beardgrass

Limnodea arkansana Ozarkgrass

Nassella leucotricha Texas wintergrass

Setaria leucopila streambed or plains 

bristlegrass

Sporobolus cryptandrus sand dropseed

Tridens texanus Texas tridens or fluffgrass

Castilleja indivisa entireleaf Indian 

paintbrush

Plantago rhodosperma redseed plantain

Cogan (2007) included lists of species that were associated with each upland shrubland and 

woodland community type.

Honey Mesquite - Granjeno / Prickly-pear species - South Texas Ericameria Woodland

The canopy in these woodlands is dominated by honey mesquite (10-15 m [32.8-49.2 ft] high), with 

cover ranging from 30-50% (Cogan 2007, Table 11). A sparse shrub layer includes hackberry (Celtis 
69

pallida), Texan hog plum, and sugarberry saplings. The ground layer, dominated by Texas 

wintergrass and weedy or shade tolerant forbs, typically provides 50-70% cover (Cogan 2007). 

Table 11. Species occurring in the Honey Mesquite - Granjeno / Prickly-pear species - South Texas 

Ericameria Woodland (Cogan 2007).

Type Scientific Name Common Name

Tree Prosopis glandulosa honey mesquite

Shrub Celtis laevigata sugarberry

Celtis pallida desert hackberry

Colubrina texensis Texan hog plum

Condalia hookeri Brazilian bluewood

Diospyros texana Texas persimmon

Opuntia leptocaulis Christmas cactus

Herb Croton monanthogynus prairie tea

Gutierrezia texana Texas snakeweed

Justicia pilosella

(Siphonoglossa pilosella) Gregg’s tubetongue

Verbesina virginica white crownbeard

Nassella leucotricha Texas wintergrass

Invasive Cynodon dactylon bermudagrass

Chapparo-Prieto Shrubland

The canopy in this shrubland is only 2-3 m (6.6-9.8 ft) high, with 30-60% cover (Cogan 2007). The 

dominant vegetation is a mix of blackbrush acacia, Texas persimmon, Brazilian bluewood, and 

honey mesquite (Table 12). The ground layer, with 60-70% cover, consists primarily of the native 

grasses purple three-awn and Texas wintergrass (Cogan 2007).

Table 12. Species occurring in the Chapparo-Prieto Shrubland (Cogan 2007).

Type Scientific Name Common Name

Shrub Acacia rigidula blackbrush acacia

Celtis laevigata sugarberry

Celtis pallida desert hackberry

Colubrina texensis Texan hog plum

Condalia hookeri Brazilian bluewood

Diospyros texana Texas persimmon
70

Table (continued). Species occurring in the Chapparo-Prieto Shrubland (Cogan 2007).

Type Scientific Name Common Name

Shrub 

(cont.)

Eysenhardtia texana Texas kidneywood

Guaiacum angustifolium Texas lignum-vitae

Berberis trifoliolata algerita, agarito

Opuntia leptocaulis Christmas cactus

Prosopis glandulosa honey mesquite

Ptelea trifoliata common hoptree

Sideroxylon lanuginosum gum bully

Yucca constricta Buckley’s yucca

Herb Wedelia acapulcensis var. 

hispida

hairy wedelia

Aristida purpurea purple three-awn

Carex planostachys cedar sedge

Nassella leucotricha Texas wintergrass

Huisache-(Honey Mesquite) Woodland

The canopy in these woodlands ranges from 10-60% cover and 5-15 m (16.4-49.2 ft) in height 

(Cogan 2007). The dominant vegetation is typically dominated by huisache, honey mesquite, or a 

mix of the two (Table 13). Shrub layer density is highly variable, but common species include 

hackberry, Brazilian bluewood, Texas persimmon, agarito (Berberis trifoliolata), and sugarberry 

saplings. Ground cover is also highly variable, ranging from 10-80%, depending on shading from the 

canopy. Native grasses such as purple three-awn and Texas wintergrass may dominate, but the nonnative spreading hedgeparsley is common where grasses are absent (Cogan 2007).

Table 13. Species occurring in the Huisache-(Honey Mesquite) Woodland (Cogan 2007).

Type Scientific Name Common Name

Tree Acacia farnesiana huisache; sweet acacia

Prosopis glandulosa honey mesquite

Celtis laevigata Sugarberry

Shrub Celtis pallida desert hackberry

Condalia hookeri Brazilian bluewood

Diospyros texana Texas persimmon

Berberis trifoliolata agarito, algerita
71

Table 17 (continued). Species occurring in the Huisache-(Honey Mesquite) Woodland (Cogan 2007).

Type Scientific Name Common Name

Herb Ambrosia trifida great ragweed

Calyptocarpus vialis straggler daisy

Clematis drummondii Drummond's clematis

Viguiera dentata toothleaf goldeneye

Aristida purpurea purple three-awn

Nassella leucotricha Texas wintergrass

Invasive Ligustrum japonicum Japanese privet

Melia azedarach Chinaberrytree

Torilis arvensis spreading hedgeparsley

Percent Coverage of Native Species

The percent cover of native species, especially in comparison to cover of exotic species, can provide 

an indication of how similar current shrublands and woodlands are to the historic communities that 

were present during the Missions period, prior to most exotic species invasions. No information is 

available regarding the percent coverage of native species in SAAN’s upland shrublands and 

woodlands. However, the park’s exotic plant control program has been working to clear non-native 

plants from the park since 2000 (Mitchell, written communication, February 2015), which has likely 

increased the percent coverage of native species.

Threats and Stressor Factors

Threats to the upland woodlands and shrublands include non-native species, adjacent land use 

practices (particularly introduction of ornamental species), drought, and climate change. Many of 

these threats are exacerbated by the fragmented and isolated nature of the park units (Woodman, 

written communication, February 2015). More than 150 non-native plant species have been 

confirmed within the park (NPS 2010; Appendix A), 30 of which were documented in upland 

woodlands and shrublands by Carr (2003a, b). The highly invasive Japanese privet had become 

dominant in some of the park’s shrublands, but management efforts over the past decade have 

reduced its extent within the park (Mitchell, written communication, 3 February 2015). Growing 

development on adjacent lands can increase the risk of non-native plant introduction through the 

escape of ornamental species (Cogan 2007). Feral hogs, which are a non-native faunal species, are 

also a threat to the park’s shrublands.

Over the past several years, much of Texas has been experiencing moderate to severe drought 

conditions (USDM 2015). Climate change models predict warmer temperatures and likely drier 

conditions for Texas in the future (TWDB 2008, Foster 2011), which could increase the frequency 

and duration of droughts. Extreme drought can cause plant mortality and reduced seedling survival in 
72

shrublands and woodlands (Swetnam and Betancourt 1998). Less severe droughts could still 

influence plant community composition, favoring species that are more tolerant of dry conditions.

Data Needs/Gaps

Due partly to the fact that shrublands and woodlands are often mid-successional communities, 

information on these habitats in the park is limited. The most recent survey of vegetation community 

extent at SAAN was in 2005-2006 (Cogan 2007). An update would help determine if shrublands 

have expanded since this time. Community composition has also not been thoroughly studied since 

Carr (2003a, b), which focused only on species occurrence and did not document percent 

composition of the various plant species. In addition, the percent coverage of native species (as 

opposed to introduced species) has not been studied. The GULN is developing a vegetation 

monitoring protocol that will begin gathering data on plant community composition and coverage by 

2016 (Woodman, written communication, December 2014). 

In 2016, Ladybird Johnson Wildflower Center staff will be surveying and mapping exotic plant 

species in the park (Mitchell, email communication, 7 May 2015). This information will be useful in 

future assessments, particularly in updating the extent of privet shrubland stands within SAAN.

Overall Condition

Community Extent

The project team assigned this measure a Significance Level of 2. Shrublands and woodlands are 

almost certainly more widespread today than they were during the Missions period (Van Auken and 

Bush 1984). This is partly natural succession from grasslands, but the process has been aided by 

overgrazing and fire suppression. Since this community is currently more extensive within SAAN 

than it was historically, this measure is of no concern (Condition Level = 0).

Community Composition

The community composition measure was assigned a Significance Level of 3. Carr (2003a, b) 

documented over 280 plant species in SAAN’s upland woodlands and shrublands, with nearly 90% 

of these species being native. The composition of these communities is currently of low concern 

(Condition Level = 1).

Percent Coverage of Native Species

This measure was assigned a Significance Level of 3. No information is available regarding the 

percent coverage of native species within SAAN’s upland shrublands and woodlands. Therefore, a 

Condition Level could not be assigned for this measure.

Weighted Condition Score

The Weighted Condition Score for upland shrublands and woodlands in SAAN is 0.13, indicating 

good condition. Since vegetation community extent has not been updated since 2006 and community 

composition was last studied in depth over a decade ago, a trend could not be determined. 
73

Upland Shrublands/Woodlands

Measures

Significance 

Level

Condition 

Level WCS = 0.13

Community Extent 3 0

Community 

Composition 2 1

Percent Coverage of 

Native Species 3 n/a

4.3.6 Sources of Expertise

Greg Mitchell, SAAN Natural Resources Program Manager

Robert Woodman, GULN Ecologist

4.3.7 Literature Cited

Carr, W. R. 2003a. A botanical inventory of San Antonio Missions National Historical Park. Part II: 

For the portion in Wilson County, Texas. National Park Service, San Antonio, Texas.

Carr, W. R. 2003b. A botanical inventory of San Antonio Missions National Historical Park. Part I: 

For the portion in Bexar County, Texas. National Park Service, San Antonio, Texas.

Cogan, D. 2007. Vegetation classification and mapping project report, San Antonio Missions 

National Historical Park. National Park Service, Gulf Coast Network, Lafayette, Louisiana.

Foster, H. C. 2011. Climate change and Texas water regulation. Chapter 16 in The changing face of 

water rights 2011. http://www.gdhm.com/images/pdf/hcf_climatechange_and_texas_water_regulation.pdf (accessed 19 December 2014).

National Park Service (NPS). 2010. A summary of biological inventory data collected at San Antonio 

Missions National Historical Park: Vertebrate and vascular plant inventories. National Park 

Service, Gulf Coast Network, Lafayette, Louisiana.

OCULUS. 1998. Rancho de las Cabras cultural landscape report. San Antonio National Historical 

Park, San Antonio, Texas.

Swetnam, T. W., and J. L. Betancourt. 1998. Mesoscale disturbance and ecological response to 

decadal climatic variability in the American southwest. Journal of Climate 11:3128-3147.

Texas Water Development Board (TWDB). 2008. Far West Texas Climate Change Conference: 

Study findings and conference proceedings. Austin, Texas. 
74

http://www.twdb.state.tx.us/publications/reports/special_legislative_reports/doc/climatechange.p

df (accessed 19 December 2014).

U.S. Drought Monitor (USDM). 2015. Tabular data archive - Texas. 

http://droughtmonitor.unl.edu/MapsAndData/DataTables.aspx (accessed 12 January 2015).

Van Auken, O. W., and J. K. Bush. 1984. Changes in plant communities of the San Antonio Missions 

National Historical Park. Pages 28-33 in Proceedings of the Second Annual Missions Research 

Conference. National Park Service, San Antonio, Texas.
75

4.4 Reptiles

4.4.1 Description

Reptiles are sensitive to changes in their 

habitats such as pollution and warmer, drier 

climates (EPA 2012), and are considered 

biological indicators of ecosystem health; 

because of this, reptiles have been selected as a 

Vital Sign by the GULN (Segura et al. 2007). 

Reptiles are an important part of the 

ecosystem’s food chain because some species 

serve as both predators and prey. Reptiles can 

also help control pest populations by 

consuming rodents and insects (ESI 2011).

SAAN provides habitat for a number of reptiles, including snakes, lizards, turtles, and tortoises. 

Snakes are the most diverse reptile group in SAAN, with 21 species documented in the park (Photo 

7; NPS 2014). Twelve turtle species and 10 lizard species have also been documented in SAAN

(Appendix E). Two threatened and endangered (T&E) species have been documented in SAAN: the 

Texas tortoise (Gopherus berlandieri) and the Texas horned lizard (Phrynosoma cornutum) are listed 

as threatened in the state of Texas (Appendix E). These two species are thought to be present in the 

park; however, the Texas tortoise has not been seen at SAAN since 2007, and there are no confirmed 

observations of Texas horned lizard within the park (Duran 2004, Dittmer and Fitzgerald 2011).The 

Cagle’s map turtle (Graptemys caglei) is another T&E species native to SAAN, but it has likely been 

extirpated from the park (Duran 2004). The Cagle map turtle is also listed as threatened in the state of 

Texas.

4.4.2 Measures

 Species richness

 Relative abundance

 Reproductive success

4.4.3 Reference Conditions/Values

A specific reference condition for reptiles was not identified for SAAN; however, Strecker (1915) 

may provide a reference for the San Antonio area. Strecker catalogues herptiles in Texas during the 

early 20th century. Strecker (1915) documented 19 reptile species in or near San Antonio, and

included nine snakes, five turtles, and five lizards. It should also be noted that this study covered a 

larger area than SAAN, and not all species may have occurred in the park. Appendix E displays the 

reptile species that were documented in the general San Antonio area.

4.4.4 Data and Methods

Duran (2004) conducted an inventory of the reptiles and amphibians in SAAN from 2002 to 2003. 

Duran (2004) sampled six sites in SAAN, with major sampling efforts focusing on the upland 

Photo 7. Texas brown snake (Storeria dekayi 

texana) in SAAN in 2003 (photo from Duran 2004).
76

woodlands, grassland/old fields, riparian woodlands, and grassland/riparian areas, which are 

displayed in Figure 22. Trapping methods used in Duran (2004) included drift-fence arrays and 

coverboards, while observation methods included visual and auditory surveys. All observations were 

spatially documented using GPS units. Sampling efforts occurred over a short period of time and 

cannot be considered as comprehensive distributional surveys.

Dittmer and Fitzgerald (2011) surveyed the Missions and Rancho de las Cabras Units for Texas 

tortoise and Texas horned lizard. Surveys were conducted on the weekends (Friday – Saturday) in 

May, June, and October of 2010 as well as May and June of 2011. Survey methods included tortoise 

blitz (an area-defined visual search), coverboard arrays, and PVC pipe traps. Visual encounter 

surveys were also conducted.

Figure 22. Major herptile sampling sites in SAAN at the Missions Unit (left) and Rancho de las Cabras 

Unit (right) (Duran 2004).

Woodman (2013) summarized reptile observation data collected in the two units (Missions, Rancho 

de las Cabras) of SAAN for the 2012 monitoring year. Sampling occurred at monthly intervals for 

the study period. The two sampling methods used were terrestrial cover board and arboreal PVCpipes. There were six coverboard arrays (10 panels each) placed in the Missions Unit; all of the 

arrays were placed in wooded areas along the banks of the San Antonio River. Four cover board 

arrays were placed in the Rancho de las Cabras Unit (Photo 8). Those arrays were placed in the 

upland old fields and upper wooded bank habitat.
77

Photo 8. Cover board used in the Rancho de las Cabras Unit of SAAN (Photo by Shannon Amberg, 

SMUMN GSS 2013).

4.4.5 Current Condition and Trend

Species Richness

Duran (2004) observed 24 reptile species (13 snakes, six lizards, and five turtles) during the 2003 

inventory in SAAN; however, 34 total species were documented with the aid of vouchers and 

literature sources. The species richness was above the assigned reference condition. Appendix E 

displays the list of reptiles that were directly observed during the inventory as well as having 

historically occurred in the park according to Duran (2004).

Dittmer and Fitzgerald (2011) documented five reptile species in SAAN (Missions and Rancho 

Units) between May and June of 2010 and 2011. No reptiles were found using the PVC pipe traps; 

the reptiles found under cover boards included three lizard species and two snake species; the 

Mediterranean gecko (Hemidactylus turcicus) was the only non-native species found. The snake 

species observed were the mountain patch-nose snake (Salvadora grahamiae) and a garter snake 

species (Thamnophis sp.). It should be noted that the species richness in this survey was very low 

compared to the reference condition.

Woodman (2013) documented 15 reptile species in SAAN during the 2012 monitoring year. Eight 

and 10 species were represented at the Missions sites and the Rancho de las Cabras Unit, respectively

(Appendix E). The species richness in this survey was low compared to the reference condition.

The NPS Certified Species List (NPS 2014) documented 34 reptiles in SAAN. Twenty-eight species 

are listed as present in the park, five species recorded as probably present, and one with historic 
78

presence but currently not in the park (Cagle’s map turtle). The Mediterranean gecko was the only 

nonnative species recorded. Appendix E displays all reptile species recorded in SAAN as of 2014. 

Figure 23 displays the species richness from each study addressed in this analysis.

Figure 23. Species richness of reptiles in SAAN (data from Strecker 1915, Gallyoun et al. 2002, Gallyoun

et al. 2003, Duran 2004, Dittmer and Fitzgerald 2010, Woodman 2013, NPS 2014). The reference 

condition (Strecker 1915) is the red bar on the far left. 

Relative Abundance

Duran (2004) observed 24 reptile species during a 2003 inventory in SAAN. The total number of 

observations was recorded for each species documented, showing that some reptiles were more 

commonly observed than others. During Duran’s (2004) inventory, the most commonly observed

species in SAAN were the Texas spiny lizard (Sceloporus olivaceus), ground skink (Scincella 

lateralis), Guadalupe spiny softshell turtle (Apalone spinifera guadalupensis), western diamondback 

rattlesnake (Crotalus atrox), and Mediterranean gecko (Table 18). The Texas tortoise was observed 

four times, while the Texas horned lizard was not observed during the inventory. The Cagle map 

turtle was mentioned in the inventory as being historically present, but it is considered extirpated in 

the area. Some of the species rarely seen during Duran (2004) were the desert king snake 

(Lampropeltis getula splendida), rose-bellied lizard (Sceloporus variabilis marmoratus), Texas 

brown snake (Storeria dekayi texana), and Texas long-nosed snake (Rhinocheilus lecontei 

tessellatus). Table 18 displays the number of observations of all reptile species documented during 

Duran’s (2004) herpetofauna inventory of SAAN. However, it is important to note that reptile survey 

results may be influenced by sampling methods (e.g., drift fences, coverboards, pitfall traps) and 

timing. Certain reptiles may be too large to fit under coverboards or may simply avoid them for 

unknown reasons. Some reptile species are seasonal and can only be found in the park at certain 

times of the year (Woodman, written communication, January 2013) while other species may be

present in the park if adequate rains keep standing water in nearby streams (Duran 2004). 

0

5

10

15

20

25

30

35

40

Strecker (1915) Gallyoun et al.

(2002)

Gallyoun et al.

(2003)

Duran (2004) Dittmer and

Fitzgerald

(2011)

Woodman

(2013)

NPS (2014)

Number of Species Observed

Study
79

Table 18. Reptile species that were observed by Duran (2004) during the 2003 inventory of SAAN.

Scientific Name Common Name

Number of 

Observations

Anolis carolinensis green anole 8

Apalone spinifera guadalupensis Guadalupe spiny softshell 10

Chelydra serpentina common snapping turtle 6

Cnemidophorus gularis gularis Texas spotted whiptail 3

Crotalus atrox western diamondback rattlesnake 10

Elaphe guttata emoryi Great Plains rat snake 6

Elaphe obsoleta Texas rat snake 5

Gopherus berlandieri Texas tortoise 4

Hemidactylus turcicus Mediterranean gecko 10

Lampropeltis getula splendida desert king snake 1

Leptotyphlops dulcis dulcis plains blind snake 8

Masticophis flagellum testaceus western coachwhip 5

Masticophis schotti schotti Schott’s whipsnake 5

Nerodia rhombifer diamondback water snake 4

Pseudemys texana Texas river cooter 4

Rhinocheilus lecontei tessellatus Texas long-nosed snake 1

Salvadora grahamiae lineata Texas patch-nosed snake 3

Sceloporus variabilis marmoratus rose-bellied lizard 1

Sceloporus olivaceus Texas spiny lizard 17

Scincella lateralis ground skink 11

Storeria dekayi texana Texas brown snake 1

Thamnophis marcianus 

marcianus

checkered garter snake 3

Trachemys scripta elegans red-eared slider 7

Virginia striatula rough earth snake 5

Dittmer and Fitzgerald (2011) documented relative abundance of five reptiles in SAAN (Table 19). 

The Texas spotted whiptail and a garter snake species were each only captured once. The mountain 

patch-nose snake and ground skink were captured two and five times, respectively. The 

Mediterranean gecko was the most common species captured during the survey with 14 recorded 

captures. 
80

Table 19. Relative abundance of reptile species captured with coverboard method (Dittmer and Fitzgerald 

2011).

Scientific Name Common Name

Number of 

Coverboard 

Captures

Cnemidopherus gularis Texas spotted whiptail 1

Hemidactylus turcicus Mediterranean gecko 14

Salvadora grahamiae mountain patch-nosed snake 2

Scincella lateralis ground skink 5

Thamnophis sp. garter snake sp. 1

Woodman (2013) recorded relative abundance for 15 reptiles in SAAN between 2011 and 2012. The 

ground skink had the highest relative abundance being observed 16 times in the Missions unit and 12 

times in the Rancho del las Cabras unit. Mediterranean geckos were common (16 observations) in the 

Missions unit, but the geckos were only observed once in the Rancho de las Cabras unit. Reptiles 

with low relative abundance (one observation per species) included plains blind snake (Leptotyphlops 

dulcis dulcis), coachwhip (Masticophis flagellum testaceus), Texas coral snake (Micrurus tener), 

Texas river cooter (Pseudemys texana), blotched water snake (Nerodia erythrogaster transversa), 

Texas spiny lizard, and rough earth snake (Virginia striatula). Table 20 displays the relative 

abundance of reptile species observed at the Missions Unit and Rancho de las Cabras Unit in SAAN 

between 2011 and 2012.

Table 20. Relative abundance of reptile species observed at the Missions Unit and Rancho de las Cabras 

Unit in SAAN between 2011 and 2012 (Woodman 2013).

Scientific Name Common Name

Missions 

Unit

Rancho de las 

Cabras Unit

Anolis carolinensis green anole 4

Cnemidophorus gularis gularis Texas spotted whiptail 2

Elaphe guttata emoryi great plains rat snake 4

Hemidactylus turcicus Mediterranean Gecko 16 1

Leptotyphlops dulcis dulcis plains blind snake 1

Masticophis flagellum coachwhip 1

Masticophis schotti schotti Schott's whipsnake 2 1

Micrurus tener Texas coral snake 1

Nerodia erythrogaster transversa blotched water snake 1

Pseudemys texana Texas river cooter 1

Salvadora grahamiae lineata Texas patch-nose snake 5
81

Table 20 (continued). Relative abundance of reptile species observed at the Missions Unit and Rancho 

de las Cabras Unit in SAAN between 2011 and 2012 (Woodman 2013).

Scientific Name Common Name

Missions 

Unit

Rancho de las 

Cabras Unit

Sceloporus olivaceus Texas spiny lizard 1

Sceloporus variabilis marmoratus rose-bellied lizard 5

Scincella lateralis ground skink 16 12

Virginia striatula rough earth snake 1

NPS (2014) reported relative abundance for 27 reptile species in SAAN. The red-eared slider 

(Trachemys scripta elegans) and Texas river cooter were the two species identified as abundant in 

the park. Fourteen reptile species were documented as common in the park. Nine reptiles were 

classified as uncommon in the park, and the one nonnative species was recorded as being rare. Table 

21 displays the reptile species with reported relative abundance in SAAN.

Table 21. Reptile species with relative abundance in SAAN (NPS 2014).

Scientific Name Common Names Relative Abundance

Anolis carolinensis green anole Common

Apalone spinifera spiny softshell turtle Common

Chelydra serpentina common snapping turtle Common

Cnemidophorus gularis gularis Texas spotted whiptail Uncommon

Crotalus atrox western diamondback rattlesnake Common

Gopherus berlandieri Texas tortoise Uncommon

Hemidactylus turcicus Mediterranean gecko Rare

Kinosternon flavescens yellow mud turtle Unknown

Leptotyphlops dulcis dulcis plains blind snake Common

Masticophis flagellum testaceus western coachwhip Common

Masticophis schotti schotti Schott's whipsnake Common

Micrurus tener Texas coral snake Uncommon

Nerodia erythrogaster transversa blotched water snake Uncommon

Nerodia rhombifer diamondback water snake Common

Opheodrys aestivus rough green snake Uncommon

Pseudemys texana Texas river cooter Abundant
82

Table 21 (continued). Reptile species with relative abundance in SAAN (NPS 2014).

Scientific Name Common Names Relative Abundance

Rhinocheilus lecontei tessellatus Texas long-nosed snake Uncommon

Salvadora grahamiae lineata Texas patch-nosed snake Common

Sceloporus olivaceus Texas spiny lizard Common

Sceloporus variabilis marmoratus rose-bellied lizard Uncommon

Scincella lateralis ground skink Common

Sonora semiannulata ground snake Uncommon

Sternotherus odoratus common musk turtle Common

Storeria dekayi texana Texas brown snake Uncommon

Thamnophis marcianus marcianus checkered garter snake Common

Trachemys scripta elegans red-eared slider Abundant

Virginia striatula rough earth snake Uncommon

Reproductive Success

At the time of publication, there are no data regarding reptile reproductive success in SAAN. 

Continuation of the GULN annual surveys and monitoring programs may allow this measure to be 

assessed in the future.

Threats and Stressor Factors

SAAN staff identified many threats to the reptile population of the park. Some of these threats 

include non-native species, habitat loss and fragmentation, and drought. 

Non-native species

Non-native species are a threat to native reptile species in SAAN. Feral hogs have been known to 

negatively affect native wildlife through habitat loss and depredation. Feral hogs cause habitat loss 

by foraging on native vegetation (Jolley et al. 2010), and have been observed turning over rocks and 

logs and generally disturbing vegetative terrain used by reptiles (Dittmer and Fitzgerald 2011).

According to Dittmer and Fitzgerald (2011), the Missions and Rancho de las Cabras Units showed 

signs of heavy use by feral hogs. 

Red fire ants (Solenopsis invicta) are another non-native species that are a direct and indirect threat to 

reptiles in the park. Fire ants act as predators and competition for reptiles, and have been known to 

prey on eggs and hatchlings, as well as invertebrates that are a key staple of the Texas horned lizard’s 

diet (Allen et al. 1994). According to Dittmer and Fitzgerald (2011), fire ants were found in 

abundance under coverboards set out to trap the Texas horned lizard in the park.
83

Habitat Loss / Fragmentation

Habitat loss can be a major stressor to reptiles. Habitat is lost or fragmented when native vegetation

is cleared for aesthetics, new housing, roadways, and farms. Increased highway traffic has also 

caused mortality to reptiles crossing roads (Thode 1999). Fragmentation and removal of habitat, in 

and around the park, have been caused by landscaping (mowing), land development and conversion. 

Approximately 73 ha (180 ac) of the Missions Unit is actively mowed (Dittmer and Fitzgerald 2011; 

Mitchell, written communication, 16 September 2014), which causes loss of habitat and a direct 

threat to reptiles traveling through mowed areas. During the Duran (2004) inventory, a Texas coral 

snake was struck and killed by a mower. Another factor influencing habitat loss is urbanization. 

According to Duran (2004), urbanization has probably contributed to the elimination of reptile 

species that were historically present in the park.

Drought/Climate Change

Texas has experienced moderate to severe drought conditions that are likely a result of global climate 

change (GCC) (Figure 24). GCC will likely compound the negative effects of habitat fragmentation 

through drought. Drought decreases wetland and other ephemeral inundations, which can further 

increase the distance between aquatic habitats (Walls et al. 2013). Lizards, snakes, and reptiles are all 

affected by climate change; however, each species has varying degrees of vulnerability (Olson and 

Saenz 2013). GCC induced droughts have the greatest negative affect on turtles because of their 

dependency on aquatic environments. Turtle reproductive success may also be of concern because 

they have temperature-sensitive sex determination. If temperatures continue to increase, turtles could 

produce nests of only female offspring (Olson and Saenz 2013). Lizards also rely on temperature for 

reproductive success. Lizard reproduction occurs over a narrow period of time in the spring and 

summer when temperatures are suitable with moist conditions. A warmer, drier climate may cause 

seasons with reproductive failure (Olson and Saenz 2013). Snakes are also affected by warming 

temperatures. As a result of warmer nightly temperatures, GCC has caused changes in snake species 

niches resulting in smaller ranges for some species (rattlesnake spp.) but also increased activity for 

others (rat snake spp.) (Olson and Saenz 2013).
84

Figure 24. Texas is experiencing varying degrees of drought; Bexar county is circled in blue (USDM 

2014).

Data Needs/Gaps

No information is available that characterizes reptile reproductive success in SAAN. Duran (2004) 

documented baseline information such as annotated checklists of reptiles and locations of reptiles 

found during the inventory. However, this inventory occurred over a short period in time and is 

nearly a decade old. Dittmer and Fitzgerald (2011) and Woodman (2013) documented more current 

data on species richness and relative abundance, but the data were also collected over a short period 

of time. Monitoring should continue and will be helpful to park managers in the future.

Overall Condition

Species Richness

The project team defined the Significance Level for species richness as a 3. Species richness is 

relatively high in SAAN, representing several different taxa. Only one nonnative species, the 

Mediterranean gecko, was observed in SAAN during the surveys cited in this assessment. There were 

two studies (Dittmer and Fitzgerald 2011, Woodman 2013) that documented species richness below 

the reference condition. NPS (2014), however, documented species richness above the reference 
85

condition. As a result, the Condition Level of species richness is a 1, representing a low level of 

concern.

Relative Abundance

The project team defined the Significance Level for relative abundance as a 3. Relative abundance is 

moderate in SAAN. Duran (2004) documented that some reptiles were more commonly observed 

than others. The most commonly observed species in SAAN were the Texas spiny lizard, ground 

skink, and Guadalupe spiny softshell turtle, western diamondback rattlesnake, and Mediterranean 

gecko; these species were observed 17, 11, 10, 10, 10 times, respectively. Woodman (2013) recorded

28 ground skinks and 17 Mediterranean geckos during the study. The other species were recorded 

less than or equal to five times each. The Condition Level of relative abundance is a 1, representing a 

low level of concern.

Reproductive Success

The project team defined the Significance Level for reproductive success as a 3. There are no current 

available data characterizing the reproductive success of reptiles in SAAN. Therefore, it is not 

possible to assign a Condition Level for this measure.

Weighted Condition Score (WCS)

The Weighted Condition Score for reptiles in SAAN is 0.22, indicating a low level of concern for this 

resource. After assessing the available data, there appears to be a stable trend in the park.

Reptiles

Measures

Significance 

Level

Condition 

Level WCS = 0.22

Species Richness 3 1

Relative Abundance 3 1

Reproductive 

Success 3 n/a

4.4.6 Sources of Expertise

Robert Woodman, GULN Ecologist

Billy Finney, GULN Field Biologist

4.4.7 Literature Cited

Allen, C. R., S. Demarais, and R. S. Lutz. 1994. Red imported fire ant impact on wildlife: An 

overview. The Texas Journal of Science 46(1):51-59.
86

Dittmer, D. E., and L. A. Fitzgerald. 2011. Assessment of the sustainability of rare reptiles in the San 

Antonio Mission National Historic Park. National Park Service, San Antonio, Texas.

Duran, C. M. 2004. An inventory of reptiles and amphibians of Padre Island National Seashore, San 

Antonio Missions National Historical Park, and Palo Alto Battlefield National Historic Site. 

Texas Conservation Data Center, The Nature Conservancy, San Antonio, Texas.

Endangered Species International (ESI). 2011. Ecological role of reptiles. Endangered Species 

International. http://www.endangeredspeciesinternational.org/reptiles3.html (accessed 11 August 

2014).

Environmental Protection Agency (EPA). 2012. Amphibians and reptiles. 

http://water.epa.gov/type/wetlands/assessment/herps.cfm (accessed 13 March 2014). 

Gallyoun, M., W. R. Carr, C. M. Duran, and Texas Conservation Data Center (TCDC). 2002. 

Inventory of vascular plants and herpetofauna: San Antonio Missions National Historic Park, 

Padre Island National Seashore, Palo Alto Battlefield National Historic Site. Fifth Quarterly 

Report 1 September 2002 to 30 November 2002. The Conservation Data Center, The Nature 

Conservancy, San Antonio, Texas.

Gallyoun, M., W. R. Carr, C. M. Duran, and Texas Conservation Data Center (TCDC). 2003. 

Inventory of vascular plants and herpetofauna: San Antonio Missions National Historic Park, 

Padre Island National Seashore, Palo Alto Battlefield National Historic Site. Fifth Quarterly 

Report 1 June 2003 to 31 August 2003. The Conservation Data Center, The Nature Conservancy, 

San Antonio, Texas.

Jolley, D. B., S. S. Ditchkoff, B. D. Sparklin, L. B. Hanson, M. S. Mitchell, and J. B. Grand. 2010. 

Estimate of herpetofauna depredation by a population of wild pigs. Journal of Mammology 

91(2):519-524. 

National Park Service (NPS). 2014. NPSpecies online database. 

https://irma.nps.gov/App/Species/Search (accessed 17 March 2014).

Olson, D. H., and D. Saenz. 2013. Reptiles and climate change. U.S. Department of Agriculture, 

Forest Service, Climate Change Resource Center. 

http://www.fs.usda.gov/ccrc/topics/wildlife/reptiles (accessed 7 October 2014).

Segura, M., R. Woodman, J. Meiman, W. Granger, and J. Bracewell. 2007. Gulf Coast Network Vital 

Signs monitoring plan. Natural Resource Report NPS/GULN/NRR–2007/015. National Park 

Service, Fort Collins, Colorado.

Strecker, J. K. 1915. Reptiles and amphibians of Texas. Baylor Bulletin, Baylor University Press. 

Waco, Texas. 

Thode, B. R. 1999. The effects of human presence on the Texas tortoise (Gopherus berlandieri) in 

southern Texas and northern Mexico. Cantaurus 7:41-43. 
87

U.S. Drought Monitor (USDM). 2014. Tabular data archive, Texas. 

http://droughtmonitor.unl.edu/MapsAndData/DataTables.aspx?TX (accessed 9 December 2014).

Walls, S. C., W. J. Barichivich, and M. E. Brown. 2013. Drought, deluge and declines: the impact of 

precipitation extremes on amphibians in a changing climate. Biology 2:399-418.

Woodman, R. L. 2013. Reptile & amphibian monitoring at San Antonio Missions National Historical 

Park: Data summary, monitoring year 2012. Natural Resource Data Series NPS/GULN/NRDS—

2013/559. National Park Service, Fort Collins, Colorado.
88

4.5 Amphibians

4.5.1 Description

Amphibians are considered a high priority Vital Sign within all GULN units and are important 

species at SAAN as they are potential indicators of subtle ecological changes (Segura et al. 2007). 

Amphibians are highly sensitive to human impacts such as habitat disturbances, fragmentation, and 

pollutants; they are also of special interest due to their current decline on a global scale (Woodman 

2013). 

The aquatic and riparian habitats that exist in SAAN provide suitable habitat for amphibian species

assemblages that have persevered despite considerable fragmentation due to urban development 

around San Antonio (NPS 2010). Currently, there are nine confirmed amphibian species that occur in 

SAAN; this includes three toads and six frogs (NPS 2014). The Great Plains narrowmouth toad 

(Gastrophryne olivacea), the Blanchard’s cricket frog (Acris crepitans blanchardi), and the nonnative Rio Grande chirping frog (Eleutherodactylus cystignathoides campi) are pictured in Photo 9.

Photo 9. Three amphibian species present in SAAN are shown from left to right; Rio Grande chirping 

frog, Great Plains narrowmouth toad, and the Blanchard’s cricket frog (photo by Duran 2004).

4.5.2 Measures

 Species richness

 Relative abundance

 Reproductive success

4.5.3 Reference Conditions/Values

The ideal reference condition for this component would be the condition of amphibian populations 

during the Mission period; however, there is no information on amphibians from this time. Strecker 

(1915) catalogued herptiles in Texas during the early 20th century, and is likely the oldest available 

data on the amphibian community of the San Antonio area. Species found in the vicinity of where the 

park units are currently located are presented in Table 22. This list, which includes species that 

currently inhabit SAAN as well as some that are no longer present within the park, can be used as a 

reference condition for species richness. Reference conditions have not been determined for relative 

abundance or reproductive success.
89

Table 22. List of amphibian species catalogued by Strecker (1915) in the San Antonio area. Locations are 

shown in Figure 24.

Scientific Name Common Names Observation Location

Rana catesbeiana* (Lithobates 

catesbeianus) 

bull frog Bexar County

Hyla chrysoscelis/versicolor chameleon tree frog *(Cope's grey 

treefrog) 

San Antonio

Hyla cinerea green tree frog San Antonio

Gastrophryne olivacea Great Plains narrow-mouth toad San Antonio

Lithobates berlandieri* (Rana

berlandieri)

Rio Grande leopard frog San Antonio

Scaphiopus couchii Couch's spadefoot From southern Texas to 

north of San Antonio

Bufo punctatus* (Anaxyrus punctatus) spotted toad San Antonio

Chorophilus triseriatus* (Pseudacris 

clarkii)

striped tree frog (spotted chorus frog) Helotes

Acris gryllus1 western cricket frog State wide

Hyla squirella southern tree frog San Antonio

Smilisca baudinii Mexican tree frog Bexar County

Bufo debilis* (Anaxyrus debilis 

debilis)

little green toad Bexar County

Bufo lentiginosus americanus* 

(Anaxyrus americanus)

American toad San Antonio

Ambystoma texanum Texan salamander* (small-mouthed 

salamander)

San Antonio

* indicates a nomenclature or naming update; current, valid names are in parentheses.

1

This was likely Acris crepitans blanchardi, Blanchard’s cricket frog, as the species currently known 

as Acris gryllus does not occur west of the Mississippi.

4.5.4 Data and Methods

Strecker (1915) surveyed the entire state of Texas between 1902 and 1912 for herptiles and listed the 

observations by county and, in some cases, by township (Figure 24).

Duran (2004) inventoried herptiles within GULN; SAAN was surveyed by trapping, visual encounter 

surveys (VES), coverboards, and auditory surveys (Figure 25). Trapping was conducted for two 3-

day periods during the summer of 2003. VES were conducted along transects in the same area as the 

trapping sites and a total of 4 km (2.5 mi) was surveyed on foot (Duran 2004). The coverboards were 

installed and left undisturbed, starting in the summer of 2002, and after 2 months, bi-weekly checks 

were conducted until the spring of 2003. Auditory surveys were conducted later than originally 

planned due to below average rainfall conditions from April-June in 2002. The auditory surveys 

resumed in late June of 2003 when substantial rain occurred and were conducted anytime rain 
90

occurred from July to October of 2003 (Duran 2004). Sampling efforts occurred over a short period 

of time and cannot be considered as comprehensive distributional surveys.

Figure 25. Areas in the vicinity of SAAN where Strecker (1915) observed amphibian species (see Table 

22).

Figure 26. Major sampling sites in SAAN at the Missions Unit (left) and Rancho de las Cabras Unit (right) 

(Duran 2004).
91

Both of the SAAN units were selected for the 

GULN’s recently developed reptile and amphibian 

monitoring protocol (GRAMP), which samples

amphibians and reptiles simultaneously, as well as 

collecting auxiliary data such as temperature and 

relative humidity (Woodman 2013). Terrestrial 

cover-board and arboreal PVC-pipe fixed point 

sampling were conducted during 2012 on a monthly 

schedule (Photo 10). This monitoring is expected to 

continue on an annual basis. Starting in 2015, 

additional reports of this nature will be completed on 

a four to five-year cycle to assess trends in species 

richness, abundance, and assemblage composition 

and structure (Woodman 2013).

4.5.5 Current Condition and Trend

Species Richness

Duran (2004) documented seven species of 

amphibians during the 2002 and 2003 inventory 

(Table 23). Based on previous records, another five 

species were listed as possibly occurring in the park.

Woodman (2013) lists six species that were observed 

during the 2012 GRAMP surveys. Table 23 includes 

observed species in Missions (MS) and Rancho de las Cabras (RS); the difference in amphibian 

community composition between the two units is likely due to the distance between them and 

differences in land uses. The Missions Unit lies within a predominantly urban area, while the lands 

surrounding Rancho de las Cabras have remained largely rural. There are nine amphibian species 

present within SAAN according to the most recent NPS (2014) species list.

Table 23. The amphibian species listed in Duran (2004) and Woodman (2013).

Scientific Name Common Name

Duran*

(2004)

Woodman*

(2013)

NPS*

(2014)

Acris crepitans blanchardi Blanchard's cricket frog x x

Anaxyrus debilis debilis little green toad (eastern green 

toad) P

Incilius nebulifer coastal plain toad x RS x

Anaxyrus speciosus Texas toad P

Eleutherodactylus cystignathoides 

campi Rio Grande chirping frog x MS x

* Symbols key: x=observed in park, P=possibly occurring in park, RS=observed in Rancho de las 

Cabras unit, and MS=observed in Missions unit.

Photo 10. An arboreal PVC-pipe, shown with 

green arrows, mounted on a tree trunk at the 

Rancho Unit; these were used in amphibian 

sampling efforts in 2012 (Photo by Kathy Allen, 

SMUMN GSS 2013).
92

Table 23 (continued). The amphibian species listed in Duran (2004) and Woodman (2013).

Scientific Name Common Name

Duran*

(2004)

Woodman*

(2013)

NPS*

(2014)

Gastrophryne olivacea Great Plains narrowmouth toad x MS/RS x

Hyla chrysoscelis/versicolor Cope's treefrog RS x

Hyla cinerea green tree frog x MS/RS x

Lithobates sphenocephalus southern leopard frog MS/RS

Pseudacris clarkii spotted chorus frog P

Pseudacris streckeri Strecker's chorus frog P

Rana berlandieri Rio Grande leopard frog P x

Rana catesbeiana bull frog x x

Scaphiopus couchii Couch's spadefoot toad x x

* Symbols key: x=observed in park, P=possibly occurring in park, RS=observed in Rancho de las 

Cabras unit, and MS=observed in Missions unit.

Relative Abundance

The abundance of amphibians has not been monitored regularly within the park. Duran (2004) 

categorized species as common, uncommon, or rare. Three species were considered common: the 

Blanchard’s cricket frog, the coastal plain toad (Incilius nebulifer), and the Great Plains narrowmouth 

toad. There were three uncommon species: the green tree frog (Hyla cinerea), the bull frog (Rana 

catesbeiana), and the Rio Grande chirping frog. Only the Couch’s spadefoot toad (Scaphiopus 

couchii) was considered rare (Duran 2004). The most relevant data that relates to the general 

abundance of each species is Woodman (2013), which is shown in Table 24. Future monitoring 

efforts could be compared to this as a baseline to determine if relative abundance is changing within 

the park.

Table 24. The relative abundance (number of individuals) of amphibians during 2012 surveys at the 

Missions Unit and Rancho de las Cabras Unit (Woodman 2013).

Scientific Name Common Name

Missions 

Unit

Rancho 

Unit

Eleutherodactylus cystignathoides Rio Grande chirping frog 68 0

Hyla cinerea green tree frog 3 1

Gastrophryne olivacea Great Plains narrow-mouth toad 70 18

Lithobates sphenocephalus southern leopard frog 1 1

Hyla versicolor/chrysoceles gray tree frog 0 1

Incilius nebulifer coastal plain toad 0 3
93

The NPS (2014) species list provides relative abundances of the species of amphibians that occur in 

SAAN (Table 25). Only three species are considered abundant or common while five are uncommon 

or rare.

Table 25. Amphibian species abundance (NPS 2014).

Scientific Name Common Name Relative Abundance

Incilius nebulifer coastal plain toad Abundant

Eleutherodactylus cystignathoides 

campi Rio Grande chirping frog Uncommon

Acris crepitans blanchardi Blanchard's cricket frog Abundant

Hyla chrysoscelis/versicolor Cope's tree frog Unknown

Hyla cinerea green tree frog Uncommon

Gastrophryne olivacea Great Plains narrowmouth toad Common

Lithobates berlandieri Rio Grande leopard frog Uncommon

Lithobates catesbeianus bull frog Rare

Scaphiopus couchii Couch's spadefoot Uncommon

Reproductive Success

At the time of publication, there are no data regarding amphibian reproductive success in SAAN. 

Continuation of the GULN annual surveys and monitoring programs may allow this measure to be 

assessed in the future.

Threats and Stressor Factors

Habitat Loss

The city of San Antonio has an estimated population of 1.4 million within the 1,194 km2(461 mi2) 

city area. Bexar County, where the largest portion of the park resides, has an estimated population of 

1.8 million; Wilson County, where the smaller Rancho Unit of the park resides, has an estimated 

population of 45,418 (U.S. Census Bureau 2014). The park provides an oasis from the encroachment 

of urban sprawl, but also is connected and susceptible to air and water quality degradation from these 

heavily populated areas where land is converted from vegetation to impermeable surfaces such as 

parking lots and buildings. With urban sprawl comes increased emissions, effluent, and demand on 

water resources, which can leave areas like SAAN depleted of aquatic resources crucial to amphibian 

success (Kreuter et al. 2001).

Displacement by Non-natives (Rio Grande chirping frog)

The Rio Grande chirping frog is an introduced non-native species that currently resides only in the 

Missions unit of SAAN. These frogs do not require standing water for reproduction since their eggs 

hatch as froglets, completely skipping the tadpole phase (Wright and Wright 1949, Hayes-Odum 

1990, as cited by Fuller 2014). This life history trait may allow this species to expand and multiply in 
94

dry periods while other, native species may decline; this may be revealed by monitoring efforts at the 

park.

Non-native Species (Hogs and cats)

Feral hogs are an exotic species, abundant throughout Texas. They compete for food with local 

wildlife as well as livestock since they are opportunistic omnivores and will eat just about anything, 

including amphibian species (Taylor 2003). The hogs are not new to the area, as their introduction 

likely occurred in the 1930s when batches were released for sport hunting and multiplied rapidly in 

the wild (Taylor 2003). Feral hogs reproduce quickly, with reproductive maturity achieved as early 

as 6 months in a healthy female, and litters of up to 12 piglets. The feral hog is highly adaptive and 

able to thrive in almost any environment, but prefers habitats with areas for wallowing; this can be 

anywhere mud forms, including creek banks, ponds, and drainages. Aside from food competition, the 

destructive rooting behavior of the feral hog is what causes the most damage to natural resources 

(Taylor 2003).

Feral cats (Felis catus) are an invasive species found throughout the United States, including the San 

Antonio area. They are considered a threat to the amphibian community at the park since they are 

indiscriminate predators of any small animal, including frogs and toads (Hildreth et al. 2010). Loss et 

al. (2013) estimates that between 95 and 299 million amphibians could be killed by feral cats in the 

United States each year.

Disease

The aquatic Batrachochytrium dendrobatidis (Bd), or chytrid fungus, causes chytridiomycosis, a 

lethal skin disease in amphibians that is linked to population declines in many areas of the world, 

including the GULN region (Weldon et al. 2004, Hossack et al. 2009). The fungus parasitizes the 

host’s keratinized skin and mouthparts, and is afflicting hundreds of species around the world (Kriger 

2006). In a few locations near Austin, Texas, including Bastrop State Park, the headwaters of the San 

Marcos River, Barton Springs, and Brushy Creek, the fungus has been positively identified in 

amphibian sampling (Olson 2014). Sampling for the chytrid fungus has not been conducted within 

SAAN.

Drought/Climate Change

Texas has experienced moderate to severe drought conditions that are likely a result of global climate 

change (GCC) (see Figure 24 in Section 4.4). A limiting factor in amphibian distribution is water 

availability and the local hydrological regime stability. GCC is rapidly changing the hydrologic 

conditions of environments. Walls et al. (2013) states that monitoring efforts should incorporate both 

aquatic and terrestrial components of amphibian life history stages in order to better understand and 

manage the effect that GCC is having on their localized ecology. GCC will likely compound the 

negative effects of habitat fragmentation through drought and deluge. Drought decreases wetland and 

other ephemeral inundations, which can further increase the distance between aquatic habitats. 

Deluges can temporarily connect neighboring sites, causing the introduction of predatory fish and the 

spread of exotic invasive species into otherwise isolated aquatic environments (Walls et al. 2013).
95

Data Needs/Gaps

There are no data on the reproductive success of amphibians in SAAN at this time. There is also no 

information on the impact of the non-native Rio Grande chirping frog and possible competition with 

native amphibians at the park. Future monitoring will focus primarily on species richness, relative 

abundance, and changes in measurable assemblage composition and structure (Woodman 2013). 

Overall Condition

Species Richness

The Significance Level for species richness was assigned a 3. Strecker (1915) documented 14 

amphibian species in the vicinity of San Antonio between 1902 and 1912. More recent studies such 

as Duran (2004) and Woodman (2013) have documented only seven and six amphibians, 

respectively. It is difficult to determine if this represents an actual decline in species richness or just 

differences in inventory methods and taxonomic classifications. However, species richness was 

assigned a Condition Level of 1, or of low concern.

Relative Abundance

The Significance Level for relative abundance was assigned a 3. Woodman (2013) has a count of 

individuals by species and park unit. It should be noted that Woodman (2013) did not document 

relative abundance throughout the entire park. There are no other data to confirm or compare the 

level of relative abundance historically. As a result of the lack of data, relative abundance cannot be 

assigned a Condition Level at this time.

Reproductive Success

The Significance Level for reproductive success was assigned a 3. There are no data for reproductive 

success in the park. Due to this data gap, reproductive success cannot be assigned a Condition Level

at this time.

Weighted Condition Score

The Weighted Condition Score for amphibians in SAAN was not assigned due to the lack of relative 

abundance and reproductive success data. The condition and any trends in this resource are unknown 

at this time.
96

Amphibians

Measures

Significance 

Level

Condition 

Level WCS = N/A

Species Richness 3 1

Relative Abundance 3 n/a

Reproductive 

Success 3 n/a

4.5.6 Sources of Expertise

Billy Finney, GULN Field Biologist

4.5.7 Literature Cited

Duran, M. C. 2004. An inventory of reptiles and amphibians of Padre Island Seashore San Antonio 

Missions National Historic Park and Palo Alto Battlefield National Historic Site. National Park 

Service, San Antonio, Texas.

Fuller, P. 2014. Eleutherodactylus cystignathoides, USGS Nonindigenous aquatic species database. 

Gainesville, Florida. http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=64 (accessed 7 July 

2014).

Hayes-Odum, L. A. 1990. Observations on reproduction and embryonic development in Syrrhophus 

cystignathoides campi (Anura: Leptodactylidae). Southwestern Naturalist 35:358-361.

Hildreth, A. M., S. M. Vantassel, and S. E. Hygnstrom. 2010. Feral cats and their management. 

University of Nebraska-Lincoln Extension, Lincoln, Nebraska.

Hossack, B. R., E. Muths, C. W. Anderson, J. D. Kirshtein, and P. S. Corn. 2009. Distribution limits 

of Batrachochytrium dendrobatidis: a case study in the Rocky Mountains, USA. Journal of 

Wildlife Diseases 45:1198-1202.

Kreuter, U. P., H. G. Harris, M. D. Matlock, and R. E. Lacey. 2001. Change in ecosystem service 

values in the San Antonio area, Texas. Ecological Economics 39:333-346.

Kriger, K. M. 2006. The ecology of chytridiomycosis in eastern Australia. Thesis. Griffith 

University, Gold Coast, Australia.

Loss, S. R., T. Will, and P. P. Marra. 2013. The impact of free-ranging domestic cats on wildlife of 

the United States. Nature Communications 4:1-7.
97

National Park Service (NPS). 2010. A summary of biological inventory vertebrate and vascular plant 

inventories data collected at San Antonio Missions National Historical Park. National Park 

Service, Gulf Coast Network, Lafayette, Louisiana.

National Park Service (NPS). 2014. NPSpecies online database. 

https://irma.nps.gov/App/Species/Search (accessed 7 July 2014).

Olson, D. 2014. Aquatic Ecology and Management Team Batrachochytrium dendrobatidis (Bd) 

global snapshot map. http://www.bd-maps.net/maps/ (accessed 3 July 2014).

Segura, M., R. Woodman, J. Meiman, W. Granger, and J. Bracewell. 2007. Gulf Coast Network Vital 

Signs monitoring plan. Natural Resource Report NPS/GULN/NRR–2007/015. National Park 

Service, Fort Collins, Colorado.

Strecker, J. K. 1915. Reptiles and amphibians of Texas. Baylor University Press, Waco, Texas.

Taylor, R. 2003. The feral hog in Texas. Texas Parks and Wildlife, Austin, Texas.

U.S. Census Bureau. 2014. State and county quick facts data.

http://quickfacts.census.gov/qfd/states/48/48493.html (accessed 3 July 2014).

U.S. Drought Monitor. 2014. Texas drought conditions. 

http://droughtmonitor.unl.edu/data/jpg/20140708/20140708_TX_trd.jpg (accessed 8 July 2014).

Walls, S. C., W. J. Barichivich, and M. E. Brown. 2013. Drought, deluge and declines: the impact of 

precipitation extremes on amphibians in a changing climate. Biology 2:399-418.

Weldon, C., L. H. duPreez, A. D. Hyatt, R. Muller, and R. Speare. 2004. Origin of the amphibian 

chytrid fungus. Emerging Infectious Diseases 10(12):2100-2105.

Woodman, R. L. 2013. Reptile and amphibian monitoring at San Antonio Missions National 

Historical Park: data summary, monitoring year 2012. National Park Service, Fort Collins, 

Colorado.

Wright, A. H., and A. A. Wright. 1949. Handbook of frogs and toads of the United States and 

Canada. Third edition. Comstock Publishing Associates, Ithaca, New York.
98

4.6 Breeding Birds

4.6.1 Description

Bird populations often act as excellent 

indicators of an ecosystem’s health (Morrison 

1986, Hutto 1998, NABCI 2009). Birds are 

often highly visible components of ecosystems, 

and bird communities often reflect the 

abundance and distribution of other organisms 

with which they co-exist (Blakesley et al. 

2010). Despite being a small, urban park, 

SAAN is home to several unique habitat types 

including riparian, grassland, and huisache 

(acacia) woodlands (Van Auken 1981). The 

unique ecosystems and landforms in SAAN 

provide bird species with a variety of habitat 

types and food sources. Monitoring avian 

population health and diversity in SAAN 

habitats will be important for detecting 

population and ecosystem changes. 

The small size and location of the park represents a unique situation, as birds in the park most likely 

indicate ecosystem changes occurring in areas outside of the park. There have been extensive 

restoration efforts along the San Antonio River outside of the park, particularly in regards to the 

riparian corridor. As these restoration efforts continue, it is likely that an increase in abundance and 

diversity in bird species will follow (Woodman, written communication, 19 December 2014). These 

increases will extend into SAAN lands, even though SAAN may harbor only a portion of these 

critical riparian habitats. 

Many of the breeding bird species present in SAAN are common to other areas of the U.S. and 

Mexico (e.g., mourning dove [Zenaida macroura], northern mockingbird [Mimus polyglottos]). 

However, SAAN is also home to several unique species whose breeding ranges only extend into the 

U.S. near the U.S./Mexico border. Examples of these species include the crested caracara (Caracara 

cheriway), the painted bunting (Passerina ciris; Photo 11), and the great kiskadee (Pitangus 

sulphuratus).

4.6.2 Measures

 Species richness 

 Relative abundance

 Distribution

4.6.3 Reference Conditions/Values

Few avian surveys or inventories have taken place in SAAN, and the establishment of a reference 

condition is problematic for this component. Most studies that have taken place in the park have used 

Photo 11. The painted bunting, a South Texas 

specialty species whose breeding range extends 

into SAAN (Photo by Ronnie Maum, USFWS).
99

differing methodologies, timing, and sampling locations, which makes comparisons between studies 

difficult. 

Coonan (1987) represents the earliest inventory in the park, and will serve as the reference condition 

when data sources are comparable. Coonan (1987) reports species richness for the San Juan Woods 

and Espada Labores, but also includes the total number of species observed during the study. For the 

species richness measure in this assessment, only the total number of species observed during 

Coonan (1987) will be used as the reference condition. This will help to eliminate some problems 

and biases that exist when comparing species richness values from different sampling sites. The 

relative abundance and distribution measures are difficult to establish a reference condition for, as the 

data from the three major studies that have taken place in the park are not easily compared. The three 

studies that have taken place in the park have occurred in mostly different locations, and have 

reported relative abundance uniquely. For the purpose of this assessment, a reference condition will 

not be established for these measures. 

4.6.4 Data and Methods

This component focuses exclusively on the breeding bird species of the park, and does not discuss 

any migratory or vagrant bird species. A species was classified as breeding based on the NPS 

Certified Bird Species List (NPS 2014, Appendix F). Species in NPS (2014) that had residency 

designations of “Breeding” were included in this component’s discussion and analysis; the 

designation of “Breeding” solely refers to the fact that SAAN lies within the species’ breeding range, 

and does not signify the species actually breeds annually in the park. Species that were identified as 

“Resident” are discussed in Chapter 4.7 of this document. In instances where NPS (2014) did not 

assign residency, the Cornell University Lab of Ornithology’s All About Birds online database 

(http://www.allaboutbirds.org) was used to approximate a species’ residency as either breeding, 

migratory, resident, or vagrant. Migratory bird species represent a data gap in SAAN, and are not 

discussed separately in this NRCA.

Coonan (1987) inventoried the avian population of SAAN from 1985-1986. Surveys took place four 

times a year in the San Juan Woods and Espada Labores land tracts. One survey transect was set up 

in the San Juan woods, while three transects were set up in the Espada Labores site. Surveyors 

observed and recorded the number of individuals, species, and distance from observer from sunrise 

until about 3 hours post-sunrise. The survey results were grouped based on season: fall (OctoberNovember 1985), winter (December-February 1985-86), spring (March-May 1986), early summer 

(June-July 1986), and late summer (August-September 1986). SMUMN GSS made one modification 

to the data presented in Coonan (1987). Records for the tufted titmouse (Baeolophus bicolor) were 

reclassified as the black-crested titmouse (Baeolophus atricristatus), as was previously done by NPS 

(2014).

From 2003-2005, Scully (2006) attempted to document at least 90% of the bird species believed to 

occur in SAAN. Two major study units were created during these surveys: The City of San Antonio 

Unit (buildings and grounds associated with Missions San Jose, San Juan, Espada, and Concepcion)

(Figure 27), and the Rancho de las Cabras property (40 ha [99 ac] property in Wilson County)

(Figure 28). Within each study unit, a series of 25 survey points were established. Eighteen survey 
100

points were located in the San Antonio unit, and seven points were in the Rancho de las Cabras unit; 

no point was within 250 m (820 ft) of another point (Scully 2006). Surveys began 30 minutes before 

sunrise and continued up until 4 hours post-sunrise. All species observed, whether visually or aurally, 

during 5 minute surveys were recorded. In addition, Scully (2006) documented distance from 

observer, sex, and age class of birds when possible.
101

Figure 27. Scully (2006) sample sites in the City of San Antonio study unit during 2003-2005 surveys of 

SAAN.
102

Figure 28. Scully (2006) sample sites in the Rancho de las Cabras study unit during 2003-2005 surveys 

of SAAN.

As part of a GULN monitoring initiative, Twedt (2013) observed the wintering and breeding bird 

populations of SAAN from 2010-2013. For this assessment, only the data relating to the breeding 

bird surveys were discussed and analyzed. Twedt (2013) monitored the breeding population of 

SAAN from May-June between 2010-2012. In total, 40 point count locations were established in the 

Missions and Rancho units of the park, and each point count was surveyed for 10 minutes. Timing of 

bird observation (i.e., what minute of the point count the bird was observed), species, number of 

individuals, and detection distance were recorded during each survey. Complete, detailed 

methodologies for this study are provided in Twedt (2013).Of note, however, is that Twedt (2013) 

randomly selected the breeding bird sample points. If any of these random sample points fell within 

250 m (820 ft) of a sample point from Scully (2006), the sample point was moved to that legacy 

sample point from Scully (2006). By doing this, some level of continuity was added between the two 

survey efforts.

4.6.5 Current Condition and Trend

Species Richness

The species richness measure allows simultaneous assessment of abundance or presence for the 

entire breeding bird community. This measure can also indicate overall habitat suitability for 

breeding birds, and is vital to understand the effects of changing landscapes on native biodiversity. 
103

NPS Certified Species List (NPS 2014)

The NPS Certified Bird Species List contains 229 species, 71 (31%) of which are potentially 

breeding bird species (Appendix F). This list, however, does not allow for a specific analysis of 

species richness, as no data are collected other than the presence (or historic presence) of the 

identified species.

Coonan (1987)

During an inventory of the avifauna of SAAN from 1985-1986, Coonan (1987) documented 101 bird 

species, 44 of which were breeding species (44%; Appendix F). Coonan (1987) investigated the 

distribution of species in the park as well (discussed in the distribution measure below), and surveyed 

the San Juan Woods and Espada Labores land tracts four times each season (fall, winter, spring, early 

summer, late summer). Table 26 displays the species richness values observed in each season for 

both sampled habitat types. 

Table 26. Species richness values by habitat type and by season observed during Coonan (1987).The 

grand total value represents the reference condition for the species richness measure in this assessment.

San Juan Woods Espada Labores

Fall 12 24

Winter 14 19

Spring 17 24

Early Summer 16 31

Late Summer 17 27

Total Sp. 27 41

Grand Total 44

Scully (2006)

Scully (2006) completed a bird inventory in SAAN from 2004-2006, and sampled park units within 

the City of San Antonio and the Rancho de las Cabras units. Scully (2006) documented 197 species 

total, 68 of which were breeding species (35%; Appendix F); the species richness value obtained by 

Scully (2006) exceeded the Coonan (1987) reference condition value by 24 species (Table 26, Table 

27). The species richness total reported in Scully (2006) includes species detected outside of the 

specified sampling points. Excluding species detected outside of count locations (i.e., incidental 

detections), the species richness for SAAN was 146 species, 65 of which were breeding species 

(45%; Table 27). This value still exceeded the reference condition value of 44 species obtained by 

Coonan (1987) (Table 26).
104

Table 27. Species richness values reported by Scully (2006) for both the units of the park within City of 

San Antonio and the Rancho de las Cabras units of SAAN (2004-2006). Numbers in parentheses indicate 

the number of sample points within each study site.

City of San Antonio (18) Rancho de las Cabras (7)

Species Observed Total 61 52

Species Observed at Points 57 49

Grand Total (sp. observed at 

sample points) 68 (65)

Twedt (2013)

Breeding bird surveys were completed in 2010-2012 between May-June and identified 89 species 

total, 60 of which were breeding species (67%; Appendix F). Species richness values were reported 

yearly by Twedt (2013); richness values for breeding species ranged from 42 species (2010) to 48 

species (2011; Figure 29), and only 2010 had a species richness value that was below the Coonan 

(1987) reference condition. The number of sample points increased from 20 to 30 in 2011, and 

remained at 30 points for the 2012 survey. This difference in sample size may explain why the 2010 

value was lower than subsequent years. The 3-year average for breeding species richness was 45.7, 

which is above the reference condition for this measure. 

Figure 29. Breeding species richness values from 2010-2012 in SAAN. The red line indicates the 3-year 

species richness average value for SAAN (45.7).

Relative Abundance

Coonan (1987)

Coonan (1987) estimated relative abundance (A) for each species using the following formula:

39

40

41

42

43

44

45

46

47

48

49

2010 2011 2012

# of Breeding Species

Year
105

A = (

n

L

) (

1

1,000m of transect

)

n = total number of birds of one species recorded for one season and area

L = total length of transects in that season and area.

Relative abundance was estimated for each sampling transect (i.e., San Juan Woods and Espada 

Labores) during each of the five sampling seasons. Relative abundance estimates for all breeding 

species are presented in Appendix G, and the most abundant species for each season in both sampling 

sites are represented in Table 28 and Table 29.

Table 28. Breeding species with the highest relative abundance values (# of birds/1000 m of transect) 

observed during each season for the San Juan Woods land tract in SAAN, 1985-86. Species are 

arranged alphabetically, and not by overall abundance (Table modified from Coonan 1987).

Species Fall Winter Spring

Early 

Summer

Late 

Summer

Carolina chickadee 4.4 9.6 5.9

Carolina wren 11.8 8.8 14 16.9

chimney swift 7.4

European starling 4.4

golden-fronted woodpecker 6.6 7.4 9.6 8.8

great-tailed grackle 5.2 6.6 4.4 7.4 4.4

lark sparrow 3.7

mourning dove 7.4 10.3

northern mockingbird 3.7 5.2

black-crested titmouse 5.9 10.3 9.6 5.2 5.9

western kingbird 2.9

white-eyed vireo 2.9 2.9 2.9

yellow-billed cuckoo 5.2 3.7

Table 29. Breeding species with the highest relative abundance values (# of birds/1000 m of transect) 

observed during each season for the Espada Labores land tract in SAAN, 1985-86. Species are arranged 

alphabetically, and not by overall abundance (Table modified from Coonan 1987).

Species Fall Winter Spring

Early 

Summer

Late 

Summer

brown-headed cowbird 5.2 10.4 5.2

Carolina chickadee 3

Carolina wren 4 4.2 7.6

chimney swift 5 14.7

European starling 11.7 3
106

Table 29 (continued). Breeding species with the highest relative abundance values (# of birds/1000 m of 

transect) observed during each season for the Espada Labores land tract in SAAN, 1985-86. Species are 

arranged alphabetically, and not by overall abundance (Table modified from Coonan 1987).

Species Fall Winter Spring

Early 

Summer

Late 

Summer

golden-fronted 

woodpecker

3.2 3.4 4.6 4.6

great-tailed grackle 7.2 3.8 5.0 21.1 5.2

house finch 3.4 3.2

lark sparrow 6.0

lesser goldfinch 5.0

loggerhead shrike 2.4

mourning dove 13.5 7.8 11.0 9.0 12.9

northern mockingbird 7.8 6.2 3.6 3.8 2.6

painted bunting 3.0

red-winged blackbird 9.2

scissor-tailed flycatcher 6.0

black-crested titmouse 2.0 5.8

white-winged dove 5.0

Scully (2006)

Scully (2006) recorded relative abundance as the number of times a species was detected (i.e., 

observations) (Appendix H); data were collected during bimonthly surveys from 2004 -2006. In 

addition, Scully (2006) recorded the percentage of a species’ detections that were a result of auditory 

cues only (Table 30). Scully (2006) only reports the number of individuals observed for the 25 most 

commonly observed species (22 of which were breeding species; Table 30).

Table 30. Relative abundance for the 22 most commonly observed breeding bird species during Scully 

(2006). Detections indicate each time a bird was observed at a point count, while # of individuals 

represent the actual number of birds that were counted (table modified from Scully 2006).

Species

# of times 

detected

% detections 

by sound 

alone

# of 

individuals 

detected

Carolina wren 356 96 359

great-tailed grackle 302 31 1476

northern mockingbird 227 71 255

white-eyed vireo 205 97 205

white-winged dove 193 16 737
107

Table 30 (continued). Relative abundance for the 22 most commonly observed breeding bird species 

during Scully (2006). Detections indicate each time a bird was observed at a point count, while # of 

individuals represent the actual number of birds that were counted (table modified from Scully 2006).

Species

# of times 

detected

% detections 

by sound 

alone

# of 

individuals 

detected

American crow 187 76 315

black-crested titmouse 123 91 133

golden-fronted 

woodpecker

122 82 127

mourning dove 100 32 163

red-shouldered hawk 94 74 108

European starling 85 13 407

blue jay 80 83 93

house sparrow 76 70 165

turkey vulture 74 1 335

scissor-tailed flycatcher 67 39 94

ladder-backed 

woodpecker

65 84 66

red-winged blackbird 60 26 1105

black vulture 54 0 192

barn swallow 52 4 90

rock pigeon 51 7 232

yellow-billed cuckoo 49 94 48

black-bellied whistling 

duck

48 21 274

Total 2,670 6,979

March and May were the months with the highest number of breeding bird detections (714 and 954 

detections, respectively; Appendix H), while November had the lowest number of detections (313).

The 2,670 breeding bird detections in Table 30 represent 56% of all bird detections during Scully 

(2006) (i.e., the 22 most common breeding birds were observed at 56% of all bird detections). When 

looking at the total number of all breeding bird detections (3,343; Appendix H), breeding birds were 

observed at 70% of all bird detections.

The great-tailed grackle (Quiscalus mexicanus; Photo 11) and the red-winged blackbird (Agelaius 

phoeniceus) were the most numerous species observed, with 1,476 and 1,105 individuals observed, 

respectively (Table 30). The number of individual breeding birds in Table 30 represents 54% of all 

individuals observed during the Scully (2004) inventory.
108

Twedt (2013)

Twedt (2013) surveyed both the breeding and 

wintering bird populations of SAAN, and 

reported abundance as the number of 

individuals observed per year for each breeding 

species. For this metric, only species counted 

during the breeding season (May-June) are 

summarized. 

In 2010, there were 20 count locations sampled; 

301 individual breeding birds were identified 

(Figure 30, Appendix I), which accounted for 

77% of all individuals observed during the 

survey. In 2011, 30 count locations were 

sampled and 556 individual breeding birds were 

observed (Figure 30). This estimate accounted for 79% of all individuals observed during the survey. 

In 2012, 508 individual breeding birds, accounting for 78% of all individual observations, were 

observed at 30 count locations in SAAN (Figure 30, Appendix I). The 3-year average for breeding 

species abundance was 455 individuals/year (Figure 30). Appendix I displays the relative abundance 

for each species observed from 2010-2012, but does not include observations where detection 

distance of a species could not be recorded (i.e., bird flyovers). 

Figure 30. Number of breeding individuals observed during the Twedt (2013) surveys of SAAN from 

2010-2012. The red line on the figure represents the average number of individuals observed (455), and * 

indicates a survey year where only 20 sample points were used (other years had 30).

0

100

200

300

400

500

600

700

2010* 2011 2012

# of Individuals Observed

Year

Photo 12. Great-tailed grackle, which was among 

the most commonly observed species during Scully 

(2006) (NPS Photo).
109

Distribution

Coonan (1987)

Coonan (1987) compares species richness, density, and diversity between two sampling zones in 

SAAN. The data summarized by Coonan (1987) are not specific to breeding species. Due to this, 

several of the summary statistics discussed in this measure (i.e., diversity, density) will include 

species not classified as breeding species (per the procedure outlined in Section 4.6.4 above). 

Whenever possible, preference was given to sampling periods that took place during the breeding 

season, as this sampling period would be most representative of the breeding species present in the 

park. Regardless, care should be taken when interpreting these data, as they may not be truly 

representative of trends observed only in the breeding species of the park.

The San Juan Woods sampling tract comprised about 10.1 ha (25 ac) and was mainly riparian forest 

and huisache woodlands. The vegetation in this land tract was considered to be fairly representative 

of what the forest stands along the San Antonio River would have been prior to channelization 

(Coonan 1987). Sixty-five species (27 of which were breeding; Table 26) were observed in the San 

Juan Woods during survey efforts, and density estimates were highest in this habitat type during 

every season (Table 31); fall and winter densities were higher compared to other seasons (Table 31). 

Conversely, species diversity values in the San Juan Woods were lower than the Espada Labores in 

all seasons except for the fall (Table 32).

Table 31. Seasonal bird densities (birds/ha) for the San Juan Woods and Espada Labores land tracts at 

SAAN, 1985-86 1, 2(Table reproduced from Coonan 1987).

Season

San Juan Woods

Average ± SD

Espada Labores

Average ± SD

Fall 25.81 ± 5.22 A21.10 ± 1.45 CD

Winter 28.29 ± 2.74 A21.36 ± 4.59 C

Spring 21.38 ± 1.37 AB 15.58 ± 2.45 D

Early Summer 17.40 ± 4.80 B15.59 ± 3.05 D

Late Summer 16.82 ± 0.49 B14.10 ± 2.06 D

1

n = 4 surveys per area/season

2

Two factor ANOVA determined that both season and area affect bird density (F = 13.69, p < 0.0005; 

F = 18.86, p < 0.0005)

A Density means with the same superscript are equivalent, according to Newman-Keuls multiple 

range test

The Espada Labores land tract was about 48.6 ha (120 ac) and contained all of the identified habitat 

types from Van Auken (1981) except for marshlands and parklands (present in the land tract were: 

riparian, grassland, huisache woodlands, and acequia woodlands). However, the majority of the 

habitat in this area was huisache woodlands and grasslands (Coonan 1987). Eighty-seven species (41 

of which were breeding; Table 26) were observed in the Espada Labores during survey efforts, and 

density estimates were consistently lower than what was observed in the San Juan Woods tract 
110

(Table 31). Species diversity values were marginally higher in the Espada Labores tract, with the 

exception of the fall season (Table 32).

Table 32. Seasonal bird species diversities (Shannon-Wiener Diversity Index, H') for the San Juan 

Woods and Espada Labores land tracts at SAAN, 1985-86 1 2 (Table reproduced from Coonan 1987).

Season

San Juan Woods

Average ± SD

Espada Labores

Average ± SD

Fall 0.957 ± 0.132 AB 0.944 ± 0.127 D

Winter 1.089 ± 0.064 A1.197 ± 0.063 C

Spring 0.934 ± 0.1 B1.209 ± 0.02 C

Early Summer 0.868 ± 0.015 B1.19 ± 0.02 C

Late Summer 0.978 ± 0.089 AB 1.177 ± 0.059 C

1

n = 4 surveys per area/season

2

Two factor ANOVA determined that both season and area affect bird species diversity (F = 6.30, p < 

0.001; F = 49.73, p < 0.0005)

A Density means with the same superscript are equivalent, according to Newman-Keuls multiple 

range test

Coonan (1987) offers several hypotheses as to 

why the trends in the observed data may appear 

as they do. The Espada Labores land tract had 

nearly twice as many observed species than the 

San Juan land tract, and Coonan (1987) 

suggests that this may be because of the larger 

area and number of habitats that are found in 

the Espada Labores tract. Additionally, three 

transects were set up in the Espada Labores 

land tract, whereas only one transect was set up 

in the San Juan Woods. These differences and 

sampling biases may have contributed to some 

of the differences in distribution data between 

the two sites.

In terms of the distribution of various foraging guilds, Coonan (1987) observed higher numbers of 

insectivores in the San Juan Woods (28% more in the fall, and 81% more in the spring), and both 

areas had peak numbers of insectivores during the winter months when there is an influx of 

migratory and overwintering species. For each season, there were twice as many (or more) foliage 

insectivores observed in the San Juan Woods compared to the Espada Labores. The stands of mature 

forests and dead snags in the San Juan Woods likely attract and provide more habitat for insects, 

which in turn supports more insectivore species. The only group of insectivores that were more 

abundant in the Espada Labores tract were the ground-dwelling insectivores (e.g., great-tailed 

grackle, northern mockingbird, and European starling [Sturnus vulgaris]).

Photo 13. Northern mockingbird, which was among 

the most abundant ground-dwelling insectivores 

observed in the Espada Labores land tract during 

Coonan (1987) (NPS Photo).
111

Granivores (seed-eating species) were more abundant in the Espada Labores tract, and were nearly 

16 times more abundant in this tract in the late summer when compared to the San Juan Woods 

(Coonan 1987). These species were most commonly observed during the fall and winter when seed 

crops were at peak availability. 

Scully (2006)

Scully (2006) had a primary objective of documenting 90% of the bird species that occurred in 

SAAN. Because of the emphasis on species identification, the number of individuals observed at 

each survey site was not reported. Two major study units (SAAN properties within the City of San 

Antonio, and the Rancho de las Cabras property) were surveyed using point counts from January 

2004-May 2006. The surveys in the City of San Antonio resulted in 61 breeding species being 

observed, 57 of which were observed at a point count location (Appendix H). The Rancho de las 

Cabras property had 52 breeding species observed, 49 of which were observed at a point count 

location. 

Twedt (2013)

Although population estimates, density estimates, and detection probabilities were calculated, Twedt 

(2013) did not document the distribution of breeding bird species in SAAN. 

Threats and Stressor Factors

One of the major threats facing land bird populations across all habitat types is habitat loss due to 

land cover change (Morrison 1986). Land cover change is not restricted to breeding habitat; many 

species depend on specific migratory and wintering habitat types that are also changing. The 

encroachment of non-native plant species may be a contributor to land cover change in all habitats. 

Altered habitats can also compromise the reproductive success or wintering survival rates of species 

adapted to that habitat. They can also allow generalist, non-native avian species, such as the 

European starling or house sparrow (Passer domesticus), to move in and out-compete native bird 

species. Breeding species often require a specific vegetative community (e.g., dense stands of shrubs, 

riparian vegetation) for successful nesting to occur. A loss 

or alteration of these vegetative structures, or competition 

for resources from non-native species could compromise 

the nesting success of these native species in SAAN.

Avian brood parasite species (e.g., brown-headed cowbird

[Molothrus ater]) represent a threat to several avian 

species in SAAN. Brood parasites are species that lay their 

eggs in the nests of other breeding species, which then in 

turn incubate and care for the young (Photo 14; Payne 

1977). Brood parasitism generally reduces the 

reproductive success of the host species, as host species 

typically fledge fewer young compared to other nonparasitized parents of the same species (Payne 1977). 

Photo 14. Brown-headed cowbird egg 

(mottled color), that has been laid in a 

chipping sparrow (Spizella passerina) 

nest (NPS Photo).
112

Brown-headed cowbirds are a native species in SAAN, and can directly contribute to the reduced 

nesting success of host species, as they will often puncture or remove host species eggs (Friedmann 

1963). Brown-headed cowbirds often hatch earlier than host species eggs, and grow larger and faster 

than the host species, which often results in the death of the host chicks due to starvation, neglect, 

overcrowding, or direct mortality by trampling or removal from the nest (Friedmann 1963, Payne 

1977). Many breeding species are targeted by brood parasites, although warblers, blackbirds, and 

vireos are among the most commonly parasitized species. While a natural phenomenon, brood 

parasitism can be actively managed against; instances of cowbird egg removal from host nests has 

resulted in increases in reproductive success in various parts of the species’ home range (Mayfield 

1960, Walkinshaw 1972, Payne 1977).

Non-native animal species also represent a threat to the bird population in the park. Domestic cats are 

one of the largest causes of bird mortality in the United States. According to Loss et al. (2012), 

annual bird mortality caused by outdoor cats is estimated to be between 1.4 and 3.7 billion 

individuals. The median number of birds killed by cats was estimated at 2.4 billion individuals, and 

almost 69% of bird mortality due to cat predation was caused by un-owned cats (i.e., strays, barn 

cats, and completely feral cats) (Loss et al. 2012). The urban setting of SAAN likely increases the 

risk for cat predation, as stray and house cats from nearby San Antonio may enter the park. 

Feral hogs, a non-native species, may be a direct and indirect threat to the bird population in SAAN; 

they have been well documented on the Rancho unit of the park. Feral hogs have been known to 

negatively affect native wildlife through habitat loss and depredation. Feral hogs cause habitat loss 

by foraging on native vegetation (Jolley et al. 2010). Feral hog rooting and wallowing can disturb 

large patches of vegetation, destabilizing wetland areas and potentially exposing them to non-native 

plant invasion (Taylor 2003). Additionally, feral hog disturbance can disrupt the nesting of ground 

nesting species. Feral hogs frequently prey upon northern bobwhite (Colinus virginianus) and wild 

turkey (Meleagris gallopavo) eggs (Timmons et al. 2011), both of which are confirmed species in the 

park (NPS 2014). It appears that the Rancho unit may serve as a refuge area for local feral hogs, and 

there is an increased potential for hog impact on birds in that unit (Woodman, written 

communication, 19 December 2014).

As urban areas continue to develop and grow, modern alterations to the landscape often foster 

competition between native and non-native bird species. Human-made structures may fragment and 

reduce the continuity of a landscape, and often as these changes occur, non-native bird species are 

able to inhabit the areas. Marzluff (2001, pp. 26-28) states that, “The most consistent effects of 

increasing settlement were increases in non-native species of birds, increases in birds that use 

buildings as nest sites (e.g., swallows and swifts), increases in nest predators and nest parasites 

(brown-headed cowbirds), and decreases in interior- and ground-nesting species.” Non-native bird 

species are frequently observed at SAAN, and include species such as rock dove (Columba livia), 

Eurasian collared-dove (Streptopelia decaocto), European starling, and house sparrow.

Another threat to the park’s birds are fire ants (Solenopsis geminata, S. invicta) that were accidentally 

brought to the U.S. on a shipping vessel from South America, and have since spread rapidly across 

the southeastern U.S. (Wetterer and Moore 2005). These ant species are well-known predators of bird 
113

hatchlings, and ground nesting bird species are particularly vulnerable. Fire ants can completely 

eliminate ground nesting birds, such as the northern bobwhite, from an area (Allen et al. 2004). 

Additionally, fire ants can outcompete predatory birds, such as the loggerhead shrike (Lanius

ludovicianus), when foraging for invertebrate species. 

Several studies have documented fire ants having detrimental effects on breeding bird species that 

may be observed in SAAN: Kopachena et al. (2000) documented 25% mortality in barn swallows 

(Hirundo rustica) due to fire ants at a study site in Texas, Dickinson and Arnold (1996) observed fire 

ant predation on crested caracara chicks in south Texas, and Cely and Glover (2000) implicated fire 

ants as a major cause for the decline in common ground doves (Columbina passerina) in South 

Carolina.

Data Needs/Gaps

Continued monitoring of the breeding bird community, particularly the work of Twedt (2013), is 

necessary for park managers to establish baseline values for the identified measures in this 

component. An expansion of current survey methods to document the distribution of various 

breeding species would be helpful to identify priority habitats in the park. Continuation of these 

surveys will also allow for trend analysis after 5-10 years of data collection. 

The migratory bird population of the park represents a significant data gap in SAAN, and monitoring 

efforts geared specifically for this group of birds are needed. Survey efforts concentrated on the peak 

spring and fall migratory periods would help managers better understand what species pass through 

the park, and if any migratory species spend extended periods of time in the park.

While not an identified measure in this assessment, monitoring of the trends in breeding species of 

conservation concern is needed. As climate change, habitat fragmentation, and energy development 

efforts threaten bird communities, it will be important to identify potential trends in these indicator 

species. 

Overall Condition

Species Richness

The species richness measure was assigned a Significance Level of 3 during project scoping. NPS 

(2014) has identified 71 breeding species in the park. The number of species observed during the 

various surveys that have been completed in the park since 1985 has ranged from 44 (Coonan 1987) 

to 68 (Scully 2006). The most recent surveys completed by Twedt (2013) spanned 2010-2012, and 

the average number of species per year was 45.7. The 2010 survey by Twedt (2013) was the only 

survey in the park that had a value below Coonan (1987).

When investigating the biodiversity or health of an ecosystem using species richness, it is important 

to understand that changes in the ratio of native to non-native species may not be well represented 

(Lepczyk et al. 2008). While it does not appear to be an issue at this time (only four of the 72 

breeding species identified in NPS [2014] are non-native), this ratio is important to keep in mind for 

future assessments of condition. 
114

Recent estimates of species richness do not indicate any cause for concern for park managers, 

although continued monitoring is advised to determine any long-term trends or variations in this 

measure. The Condition Level for the species richness measure was assigned as a 0, indicating it is 

currently of no concern to park managers.

Relative Abundance

Relative abundance of breeding bird species was assigned a Significance Level of 3 by NPS staff 

during project scoping. While documented by multiple reports, each report used a different definition 

of relative abundance; Coonan (1987) estimated this measure as the number of birds per 1,000 m 

(3,281 ft) of transect, Scully (2006) reported it as the number of times a species was detected, and 

Twedt (2013) reported it as the number of individuals observed per year. 

There do not appear to be any major concerns related to the relative abundance of breeding species in 

the park, and the measure was assigned a Condition Level of 1. While variations are evident in the 

data, this is not unusual as annual fluctuations in breeding species abundance are to be expected. 

Species arrival dates, survey dates/duration, and variation in breeding initiation may all contribute to 

the annual variation in abundance. Additionally, variation observed in abundance in Twedt (2013) is 

likely due to sample size variations; 2010 surveys were completed at 20 count locations, while 2011 

and 2012 had 30 count locations. 

Distribution

The Significance Level for distribution was determined to be 3 by NPS staff. As an urban park, the 

remaining stands of undisturbed habitat along the San Antonio River and the native shrub and 

grasslands likely serve as breeding sanctuaries for many species in the park. Only two surveys have 

documented the distribution of breeding species (Coonan 1987, and to a lesser extent Scully 2006). 

Limited data have been provided for this measure, and future monitoring of the distribution of 

breeding species in the park is needed. There are likely only a few habitat types in the park that can 

support breeding species, and a more complete understanding of how the breeding bird species of 

SAAN utilize these habitats would be of great importance for managers. Because of the data gaps 

that exist for this measure, and the lack of any recent distribution data, a Condition Level was not 

assigned to this measure.

Weighted Condition Score (WCS)

A Weighted Condition Score of 0.17 was calculated for the breeding bird component. A trend arrow 

was not assigned to this component, as data related to distribution are lacking in recent years, and it 

is difficult to determine if apparent trends in richness and abundance from 2010-2012 are due to 

varying sample size, or actual trends in the breeding population.
115

Breeding Birds

Measures

Significance 

Level

Condition 

Level WCS = 0.17

Species Richness 3 0

Relative Abundance 3 1

Distribution 3 n/a

4.6.6 Sources of Expertise

Dan Twedt, USGS Research Wildlife Biologist, Patuxent Wildlife Research Center

Greg Mitchell, SAAN Natural Resources Program Manager

4.6.7 Literature Cited

Allen, C. R., D. M. Epperson, and A. S. Garmestani. 2004. Red imported fire ant impacts on wildlife: 

a decade of research. American Midland Naturalist 152:88-103

Blakesley, J. A., D. C. Pavlacky Jr., and D. J. Hanni. 2010. Monitoring bird populations in Wind 

Cave National Park. Technical Report M-WICA09-01. Rocky Mountain Bird Observatory, 

Brighton, Colorado. 

Cely, J. E., and L. Glover. 2000. Status and distribution of the common ground-dove in South 

Carolina. The Chat 64:37–46.

Coonan, T. 1987. The avifauna of San Antonio Missions National Historical Park. National Park 

Service Unpublished Report, San Antonio, Texas.

Dickinson, V. M., and K. A. Arnold. 1996. Breeding biology of the crested caracara in south Texas. 

Wilson Bulletin 108:516–523.

Friedmann, H. 1963. Host relations of the parasitic cowbirds. Bulletin of the United States National 

Museum 233. Smithsonian Institution, Washington, D. C.

Hutto, R. L. 1998. Using land birds as an indicator species group. Pages 75-92 in Avian 

Conservation: Research and management. Island Press, Washington, D.C. 

Jolley, D. B., S. S. Ditchkoff, B. D. Sparklin, L. B. Hanson, M. S. Mitchell, and J. B. Grand. 2010. 

Estimate of herpetofauna depredation by a population of wild pigs. Journal of Mammalogy 

91(2):519–524. 
116

Kopachena, J. G., A. J. Buckley, and G. A. Potts. 2000. Effects of the red imported fire ant 

(Solenopsis invicta) on reproductive success of barn swallows (Hirundo rustica) in northeast 

Texas. Southwest Naturalist 45:477–482.

Lepczyk, C. A., C. H. Flather, V. C. Radeloff, A. M. Pidgeon, R. B. Hammer, and J. Liu. 2008. 

Human impacts on regional avian diversity and abundance. Conservation Biology 22(2):405-416.

Loss, S. R., T. Will, and P. P. Marra. 2012. The impact of free-ranging domestic cats on wildlife of 

the United States. Nature Communications 4:1396.

Marzluff, J. M. 2001. Worldwide urbanization and its effects on birds. Pages 19-47 in Avian ecology 

in an urbanizing world. Kluwer Academic Publishers, Norwell, Massachusetts.

Mayfield, H. 1960. The Kirtland’s warbler. Cranbrook Institute of Science Bulletin 40. Cranbrook 

Institute of Science, Bloomfield Hills, Michigan.

Morrison, M. L. 1986. Bird populations as indicators of environmental change. Current Ornithology 

3:429-451.

North American Bird Conservation Initiative, U.S. Committee (NABCI). 2009. The state of the birds, 

United States of America, 2009. U.S. Department of the Interior, Washington, D.C.

National Park Service (NPS). 2014. NPSpecies online database. 

https://irma.nps.gov/App/Species/Search (accessed 16 September 2014).

Payne, R. B. 1977. The ecology of brood parasitism in birds. Annual Review of Ecology, Evolution, 

and Systematics 8:1-28.

Scully, M. J. 2006. An inventory of bird species occurring within the San Antonio Missions National 

Historic Park. National Park Service Unpublished Report, San Antonio, Texas.

Taylor, R. 2003. The feral hog in Texas. Texas Parks and Wildlife, Austin, Texas.

Timmons, J., J. C. Cathey, D. Rollins, N. Dictson, and M. McFarland. 2011. Feral hogs impact 

ground-nesting birds. Texas A&M University: Texas AgriLife Extension Service Unpublished 

Report, College Station, Texas.

Twedt, D. J. 2013. Winter and breeding bird monitoring data analysis 2010-2012: San Antonio 

Missions National Historical Park. Natural Resource Data Series NPS/GULN/NRDS—2013/556. 

National Park Service, Fort Collins, Colorado.

Van Auken, O. W. 1981. Determination of the presence of threatened and endangered plant species 

on the grounds of San Antonio Missions National Historical Park. National Park Service 

Unpublished Report, San Antonio, Texas.

Walkinshaw, L. H. 1972. Kirtland’s warbler-endangered. American Birds 26(1):3-9.
117

Wetterer, J. K., and J. A. Moore. 2005. Red imported fire ants (Hymenoptera: Formicidae) at gopher 

tortoise (Testundines: Testutudinae) burrows. Florida Entomologist 88(4):349-354.
118

4.7 Resident Birds

4.7.1 Description

Resident bird species are birds that remain in 

one area throughout the year and do not migrate 

(Mettke-Hofmann et al. 2009). Unlike 

migratory birds, trends in resident bird species’ 

populations are likely due to changes occurring 

in their immediate habitat or ecosystem, and (in 

theory) it is possible to study all of their 

population processes directly throughout the 

year (Koskimies 1989). This particular 

assemblage of birds serves as a valuable 

ecological indicator for the park, as they are 

year-round residents and their health and 

abundance are dependent upon many 

ecosystems found in and around SAAN 

ecosystems.

The small area of SAAN incorporates many neighboring ecosystems, and the resident bird species of 

the park and their associated ecosystems are likely more extensive than the park’s boundaries. 

Changes in resident bird populations are likely to reflect changes that are occurring outside of 

SAAN, perhaps moreso than changes that are occurring within the park.

Excluding breeding bird species (which are discussed in Chapter 4.6), NPS (2014) identifies 91 

resident bird species in the park; these include waterfowl, raptors, and passerine species. Several of 

the resident species in the park, such as the gadwall (Anas strepera) and the black-necked stilt 

(Himantopus mexicanus), are dependent upon the river/shoreline habitat along the San Antonio 

River, while other species, such as the eastern meadowlark (Sturnella magna; Photo 15) and the 

Swainson’s hawk (Buteo swainsoni), rely on the grassland and shrub habitats in and around SAAN.

Monitoring of the resident bird populations in SAAN may help managers to protect the vital bird 

habitats present in the park.

4.7.2 Measures

 Species richness 

 Relative abundance

 Distribution

4.7.3 Reference Conditions/Values

Few avian surveys or inventories have taken place in SAAN, and the establishment of a reference 

condition is problematic for this component. Most studies that have taken place in the park have used 

differing methodologies, timing, and sampling locations, which makes comparisons between studies 

difficult. 

Photo 15. Eastern meadowlark, a common resident 

species in SAAN (NPS Photo).
119

Coonan (1987) represents the earliest inventory in the park, and will serve as the reference condition 

when data sources are comparable. Coonan (1987) reports species richness for the San Juan Woods 

and Espada Labores, but also includes the total number of species observed during the study. For the 

species richness measure in this assessment, only the total number of species observed during 

Coonan (1987) will be used as the reference condition. This will help to eliminate some problems 

and biases that exist when comparing species richness values from different sampling sites. The 

relative abundance and distribution measures are difficult to establish a reference condition for, as the 

data from the three major studies that have taken place in the park are not easily compared. The three 

studies that have taken place in the park have occurred in mostly different locations, and have 

reported relative abundance uniquely. For the purpose of this assessment, a reference condition will 

not be established for these measures. 

4.7.4 Data and Methods

This component focuses exclusively on the resident bird species of the park, and does not discuss any 

migratory or vagrant bird species. A species was classified as a resident based on the NPS Certified 

Bird Species List (NPS 2014, Appendix J). Species in NPS (2014) that had residency designations of 

“Resident” were included in this component’s discussion and analysis. Species that were identified as 

“Breeding” are discussed in Chapter 4.6 of this document. In instances where NPS (2014) did not 

assign residency, the Cornell University Lab of Ornithology’s All About Birds online database 

(http://www.allaboutbirds.org) was used to approximate a species’ residency as either breeding, 

migratory, resident, or vagrant. Migratory bird species represent a data gap in SAAN, and are not 

discussed separately in this NRCA.

Coonan (1987) inventoried the avian population of SAAN from 1985-1986. Surveys took place four 

times a year in the San Juan Woods and Espada Labores land tracts. One survey transect was set up 

in the San Juan Woods, while three transects were set up at the Espada Labores site. Surveyors 

observed and recorded the number of individuals, species, and distance from observer from sunrise 

until about 3 hours post-sunrise. The survey results were grouped based on season: fall (OctoberNovember 1985), winter (December-February 1985-86), spring (March-May 1986), early summer 

(June-July 1986), and late summer (August-September 1986). SMUMN GSS made one modification 

to the data presented in Coonan (1987). Records for the green-backed heron were changed to green 

heron (Butorides virescens) to reflect the correct taxonomy for that species.

From 2003-2005, Scully (2006) attempted to document at least 90% of the bird species believed to 

occur in SAAN. Two major study units were created during these surveys: The City of San Antonio 

Unit (buildings and grounds associated with Missions San Jose, San Juan, Espada, and Concepcion), 

and the Rancho de las Cabras property (40 ha [99 ac] property in Wilson County). Within each study 

unit, a series of 25 survey points were established. Eighteen survey points were located in the San 

Antonio unit, and seven points were in the Rancho de las Cabras unit; no point was within 250 m 

(820 ft) of another point (Scully 2006). Surveys began 30 minutes before sunrise and continued up 

until 4 hours post-sunrise. All species observed, whether visually or aurally, during 5 minute surveys 

were recorded. In addition, Scully (2006) documented distance from observer, sex, and age class of 

birds when possible.
120

As part of a GULN monitoring initiative, Twedt (2013) monitored the wintering and breeding bird 

populations of SAAN from 2010-2013. Twedt (2013) surveyed during the breeding season in SAAN 

from May-June 2010-2012. Forty point count locations were established in the park (utilizing habitat 

in both the Missions and Rancho de las Cabras Units), and each point was surveyed for 10 minutes. 

Timing of bird observation (i.e., what minute of the point count the bird was observed), species, 

number of individuals, and detection distance were recorded during each survey. Complete, detailed 

methodologies for this study are provided in Twedt (2013).

4.7.5 Current Condition and Trend

Species Richness

The species richness measure allows simultaneous assessment of abundance or presence for the 

entire breeding bird community. This measure can also indicate overall habitat suitability for 

breeding birds, and is vital to understand the effects of changing landscapes on native biodiversity. 

NPS Certified Species List (NPS 2014)

The NPS Certified Bird Species List contains 229 species, 91 (40%) of which are resident bird 

species (Appendix J). This list, however, does not allow for a specific analysis of species richness, as 

no data are collected other than the presence (or historic presence) of the identified species.

Coonan (1987)

From 1985-1986, Coonan (1987) documented 101 bird species, 40 of which were resident species 

(Appendix J). Coonan (1987) also investigated the distribution of species in the park (discussed in 

the distribution measure below), and surveyed the San Juan Woods and Espada Labores land tracts 

four times each season (fall, winter, spring, early summer, and late summer). Table 33 displays the 

species richness values observed in each season for both sampled habitat types.

Table 33. Species richness values for resident species sorted by habitat type and by season observed 

during Coonan (1987).

Season

San Juan 

Woods

Espada 

Labores

Fall 13 20

Winter 21 24

Spring 10 18

Early Summer 3 5

Late Summer 5 9

Total Sp. 26 34

Grand Total 40

Scully (2006)

From 2004-2006, Scully (2006) inventoried the bird population of SAAN and sampled park units 

within the City of San Antonio and the Rancho de las Cabras units. Scully (2006) documented 197 
121

bird species in total, 81 of which were resident species (41%; Appendix J); the species richness value 

obtained by Scully (2006) exceeded the Coonan (1987) reference condition by 41 species (Table 33, 

Table 34). The species richness total reported in Scully (2006) includes species detected outside of 

the specified sampling points. When species detected outside of count locations (i.e., incidental 

observations) were excluded, the species richness for SAAN was 146 species, 61 of which were 

resident species (42%, Table 34). This value still exceeded the reference condition value of 40 

species obtained by Coonan (1987).

Table 34. Species richness values reported by Scully (2006) for both the units of the park within the City 

of San Antonio and the Rancho de las Cabras units of SAAN (2004-2006). Numbers in parentheses in the 

table header indicate the number of sample points within each study site.

City of San Antonio (18) Rancho de las Cabras (7)

Species Observed Total 74 43

Species Observed at Points 56 32

Grand Total (sp. observed at 

sample points) 81 (61)

Twedt (2013)

Twedt surveyed the bird population of SAAN from 2010-2013, and timed surveys to coincide with 

the overwintering period and the breeding season. When the breeding and winter survey results were 

combined, 56 resident bird species were observed in the park (Appendix J), which is above the 

Coonan (1987) reference condition of 40 species (Table 33). Species richness results from the winter 

surveys were pooled across all years, and were not reported yearly (as was done for breeding 

surveys). From 2010-2013, 48 resident bird species were observed during winter surveys (Appendix 

K); 35 of these resident bird species were observed within a 50 m (164 ft) radius from the point count 

location. The winter survey species richness estimate (48) exceeded the reference condition of 40 

species obtained by Coonan (1987).

The Twedt (2013) surveys that took place during the breeding season (May-June) resulted in the 

observation of 18 resident species (Appendix L); eight of the species observed during the breeding 

survey were not observed during winter surveys. Species richness values were reported yearly during 

the breeding surveys and ranged from eight species (2010) to 13 species (2011; Figure 31); the 3-

year average for resident species richness was 10.3 (Figure 31). The number of sample points 

increased from 20 to 30 in 2011, and remained at 30 points for the 2012 survey. All survey years 

were below the Coonan (1987) reference condition for species richness.
122

Figure 31. Resident species richness values from 2010-2012 in SAAN (Twedt 2013). The red line 

indicates the 3-year average for species richness in SAAN (10.3).

Relative Abundance

Coonan (1987)

Coonan (1987) estimated relative abundance (A) for each species using the following formula:

A = (

n

L

) (

1

1,000m of transect

)

n = total number of birds of one species recorded for one season and area

L = total length of transects in that season and area.

Relative abundance was estimated for each sampling transect (i.e., San Juan Woods and Espada 

Labores) during each of the five sampling seasons. Relative abundance estimates for all resident 

species are presented in Appendix M, and the most abundant species for each season in both 

sampling sites are represented in Table 35 and Table 36.

Table 35. The most abundant resident bird species in each season for the San Juan Woods land tract in 

SAAN, 1985-1986 (Coonan 1987). Values are reported as number of birds per 1,000m of transect, and 

are arranged alphabetically.

Species Fall Winter Spring

Early 

Summer

Late 

Summer

American robin 24.3

blue-gray gnatcatcher 4.4 2.9

cedar waxwing 16.2 8.1

eastern phoebe 3.7

0

2

4

6

8

10

12

14

2010* 2011 2012

# of Resident Species

Year
123

Table 35 (continued). The most abundant resident bird species in each season for the San Juan Woods 

land tract in SAAN, 1985-1986 (Coonan 1987). Values are reported as number of birds per 1,000m of 

transect, and are arranged alphabetically.

Species Fall Winter Spring

Early 

Summer

Late 

Summer

golden-crowned kinglet 6.6

Lincoln's sparrow 2.9

northern cardinal 19.9 16.2 44.9 38.2 33.8

ruby-crowned kinglet 5.2 8.8

yellow-rumped warbler 13.2 28.7 2.9

Table 36. The most abundant resident bird species in each season for the Espada Labores land tract in 

SAAN, 1985-1986 (Coonan 1987). Values are reported as number of birds per 1,000 m of transect, and 

are arranged alphabetically.

Species Fall Winter Spring

Early 

Summer

Late 

Summer

American goldfinch 7.2

American robin 7.4 12.5

cedar waxwing 12.9 6.8

eastern bluebird 4.4

eastern meadowlark 4.0

field sparrow 2.4

northern cardinal 10.7 15.7 21.5 21.1 16.9

northern oriole 4.8

ruby-crowned kinglet 3.6

vesper sparrow 17.1

western sandpiper 5.2

yellow-rumped warbler 6.2

Scully (2006)

Scully (2006) recorded relative abundance as the number of times a species was detected during 

surveys (i.e., the number of times a species was observed; Appendix E). Data were collected during 

bimonthly surveys from 2004-2006, and observers recorded the number of detections for each 

species (1,368 total detections; Appendix N), number of individuals detected, and the percentage of a 

species’ detections that were the result of auditory cues only. However, the number of individuals 

observed and the percentage of detections that were due to sound were only summarized for the 25 

most commonly observed species during the study, and most of these species (22 of 25) were 

breeding species; the breeding species data are summarized in Chapter 4.6 of this report.
124

March and January were the months with the highest 

number of resident bird detections, with 321 and 308 

detections, respectively (Appendix N). September had the 

lowest number of resident bird detections, with only 98 

detections recorded. The 1,368 resident bird detections 

represent 29% of all bird detections during Scully (2006). 

The northern cardinal (Cardinalis cardinalis; Photo 16) was 

the most abundant species during each month of the survey, 

and was detected 674 times. Northern cardinal detections 

made up 49% of all resident species detections and 14% of 

all species detections (resident, migratory, and breeding). 

Other commonly detected species included the great egret 

(Ardea alba; 90 detections), ruby-crowned kinglet (Regulus 

calendula; 61 detections), snowy egret (Egretta thula; 48 

detections), and the American goldfinch (Carduelis tristis; 

44 detections) (Appendix N). 

Twedt (2013)

Twedt (2013) surveyed the avifauna of SAAN during both 

the winter and breeding seasons from 2010-2013, and 

reported abundance as the number of individuals observed 

per year for each resident species. Each winter, Twedt (2013) selected 30 count locations at random,

and area searches at each location lasted 20 minutes. From 2010-2013, a total of 90 area searches at 

40 locations in the park were completed. In total, 1,932 resident bird individuals were observed 

during winter surveys in SAAN from 2010-2013 (Appendix K). When the results were adjusted to 

include only resident species that were observed within a 50 m (164 ft) radius of the point count 

location (i.e., excluding flyovers and distant observations), 952 individuals were observed. The most 

abundant resident species observed during the 2010-2013 winter surveys (including all observations) 

were the American goldfinch (283 individuals), northern cardinal (261 individuals), and the yellowrumped warbler (Setophaga coronata; 226 individuals) (Appendix K).

Breeding season surveys occurred in May and June of 2010-2012. The same 40 locations as the 

winter surveys were randomly selected as point count locations for these surveys; 20 point counts 

were used in 2010, while 30 point counts were used in 2011 and 2012. Surveys lasted only 10 

minutes during the breeding season, compared to the 20 minute area searches used during the winter. 

Total abundance values for resident birds during the breeding season varied by year, and ranged from 

88 individuals (2010) to 136 individuals (2011; Figure 32). The 3-year average for resident species 

abundance was 117.7 individuals (Figure 32). The most abundant resident bird species during the 

breeding surveys was the northern cardinal, with several other species being observed in comparably

low numbers throughout the duration of the survey (Table 37).

Photo 16. A northern cardinal, one 

of the most commonly observed 

resident species in SAAN (NPS 

Photo).
125

Figure 32. Number of resident individuals observed during the Twedt (2013) breeding surveys of SAAN 

from 2010-2012. The red line on the figure represents the average number of individuals observed 

(117.7), and * indicates a survey year where only 20 sample points were used (other years had 30 

sample points).

Table 37. Resident bird species and number detected during 10-minute surveys of 40 randomly located 

point locations in SAAN during the breeding season (May-June) from 2010-2012. Birds for which no 

detection distance was recorded (i.e., flyovers) are not reported in this table. * indicated a species not 

observed during winter surveys by Twedt 2013 (Table modified from Twedt 2013).

Common Name 2010 2011 2012

black-crowned night-heron* 1

blue-headed vireo 1

black-necked stilt* 1

cattle egret* 3 2

chipping sparrow 1

eastern bluebird 1 2

eastern phoebe 1 1

field sparrow* 2

great egret 2 8 2

green heron* 1 1

little blue heron 1

monk parakeet* 1

Neotropic cormorant 1 3 2

0

20

40

60

80

100

120

140

160

2010* 2011 2012

# of Individuals Observed

Year
126

Table 37 (continued). Resident bird species and number detected during 10-minute surveys of 40 

randomly located point locations in SAAN during the breeding season (May-June) from 2010-2012. Birds 

for which no detection distance was recorded (i.e., flyovers) are not reported in this table. * indicated a 

species not observed during winter surveys by Twedt 2013 (Table modified from Twedt 2013).

Common Name 2010 2011 2012

northern cardinal 79 109 115

snowy egret 3 2

spotted sandpiper 1

Swainson's hawk* 1

yellow-crowned night-heron* 1 2 2

Individuals detected 88 136 129

Species detected 8 13 10

Distribution

Coonan (1987)

Coonan (1987) compared species richness, density, and diversity between two sampling zones in 

SAAN. However, the data summarized by Coonan (1987) (e.g., diversity, and density) were not 

specific to resident species, and it is not possible to isolate the resident species-specific data from the 

report. For a detailed summary of the distribution data for all bird species and groups please see 

Chapter 4.6 of this NRCA (Breeding Birds). 

Scully (2006)

Scully (2006) had a primary objective of documenting 90% of the bird species that occurred in 

SAAN. Because of the emphasis on species identification, the number of individuals observed at 

each survey site was not reported. Two major study units (SAAN properties within the City of San 

Antonio, and the Rancho de las Cabras property) were surveyed using point counts from January 

2004-May 2006. The surveys in the City of San Antonio resulted in 74 resident species being 

observed, 56 of which were observed at a point count location (Appendix N). The Rancho de las 

Cabras property had 43 breeding species observed, 32 of which were observed at a point count 

location.

Twedt (2013)

Although population estimates, density estimates, and detection probabilities were calculated for 

SAAN as a whole, Twedt (2013) did not document the distribution of resident bird species in SAAN.

Threats and Stressor Factors

Because resident bird species do not migrate, they are entirely dependent upon the SAAN ecosystem 

for their survival. As a result, stressors on the SAAN landscape become stressors to the resident bird 

population; a decline in the resident bird population is likely indicative of a much larger issue 

occurring within the park. The breeding bird chapter of this NRCA (Chapter 4.6) summarizes the 
127

stressors of the avifaunal community. Many, if not all, of the stressors summarized in that component 

are applicable to the resident bird community of SAAN.

Data Needs/Gaps

Continued monitoring of the resident bird community, particularly the work of Twedt (2013) during 

the winter, is necessary for park managers to establish baseline values for the identified measures in 

this component. An expansion of current survey methods to document the distribution of various 

resident species would be helpful to identify priority habitats in the park. Continuation of these 

surveys will also allow for trend analysis after 5-10 years of data collection. 

While not an identified measure in this assessment, monitoring of the trends in resident species of 

conservation concern is needed. As climate change, habitat fragmentation, and energy development 

efforts threaten bird communities, it will be important to identify potential trends in these indicator 

species.

Overall Condition

Species Richness

The species richness measure was assigned a Significance Level of 3 during project scoping. NPS 

(2014) identifies 71 resident bird species as confirmed in the park, and the surveys that have occurred 

in the park have had species richness values ranging from 40 (Coonan 1987) to 68 (Scully 2006). The 

most recent surveys to take place in the park (Twedt 2013) identified 48 resident species during

winter surveys, and 18 species during breeding season surveys. Twedt (2013) was hesitant to draw 

any assumptions about the trends in SAAN’s bird population, as the data were collected over only 3 

years, and patterns may not yet be evident. However, the breeding season surveys in the park were 

the only surveys to fall below the species richness reference condition from Coonan (1987) of 40 

species. Through the various surveys in the park, it does not appear that the species richness in 

SAAN is of major concern, and a Condition Level of 1 was assigned to this measure.

Relative Abundance

Relative abundance of breeding bird species was assigned a Significance Level of 3 by NPS staff 

during project scoping. While documented by multiple reports, each report used a different definition 

of relative abundance; Coonan (1987) estimated this measure as the number of birds per 1,000 m of 

transect, Scully (2006) reported it as the number of times a species was detected, and Twedt (2013) 

reported it as the number of individuals observed per year. 

There do not appear to be any major concerns related to the relative abundance of resident species in 

the park, and the measure was assigned a Condition Level of 1. While resident species abundance 

was lower than breeding species abundance, the annual variations were not extreme. Additionally, 

variation observed in abundance in Twedt (2013) was likely due to sample size variations; 2010 

surveys were completed at 20 count locations, while 2011 and 2012 had 30 count locations. Winter

months produced the highest relative abundance estimates in the park, and the most abundant 

resident species in all studies were consistent (northern cardinal, American goldfinch, and yellowrumped warbler). Twedt (2013) was hesitant to draw any conclusions regarding trends or population 
128

estimates for the park, as the data collected for that study spanned only 3 years. As data collection 

continues, trend analysis and a more accurate estimate of the resident population size of SAAN may 

be possible.

Distribution

The Significance Level for distribution was determined to be 3 by NPS staff. As an urban park, the 

remaining stands of undisturbed habitat along the San Antonio River and the native shrub and 

grasslands likely serve as vital habitat for many species in the park. Only two surveys have 

documented the distribution of resident species in SAAN (Coonan 1987, and to a lesser extent Scully 

2006). Limited data have been provided for this measure, and future monitoring of the distribution of 

resident species in the park is needed. A more complete understanding of how the resident bird 

species of SAAN utilize these habitats would be of great importance for managers. Because of the 

data gaps that exist for this measure, and the lack of any recent distribution data, a Condition Level

was not assigned to this measure.

Weighted Condition Score (WCS)

A Weighted Condition Score of 0.33 was calculated for the resident bird component, indicating good 

condition. A trend was not assigned to this component, as data related to distribution are lacking in 

recent years, and it is difficult to determine if apparent trends in richness and abundance from 2010-

2012 are due to varying sample size, or actual trends in the resident population.

Resident Birds

Measures

Significance 

Level

Condition 

Level WCS = 0.33

Species Richness 3 1

Relative Abundance 3 1

Distribution 3 n/a

4.7.6 Sources of Expertise

Dan Twedt, USGS Research Wildlife Biologist, Patuxent Wildlife Research Center

Greg Mitchell, SAAN Natural Resources Program Manager 

4.7.7 Literature Cited

Coonan, T. 1987. The avifauna of San Antonio Missions National Historical Park. National Park 

Service Unpublished Report, San Antonio, Texas.
129

Koskimies, P. 1989. Birds as a tool in environmental monitoring. Annales Zoologici Fennici 26:153-

166.

Mettke-Hofmann, C., S. Lorentzen, E. Schlicht, J. Schneider, and F. Werner. 2009. Spatial neophilia 

and spatial neophobia in resident and migratory warblers (Sylvia). Ethology 115:482-492.

Morrison, M. L. 1986. Bird populations as indicators of environmental change. Current Ornithology 

3:429-451.

National Park Service (NPS). 2014. NPSpecies online database. 

https://irma.nps.gov/App/Species/Search (accessed 16 September 2014).

Scully, M. J. 2006. An inventory of bird species occurring within the San Antonio Missions National 

Historic Park. National Park Service Unpublished Report, San Antonio, Texas.

Twedt, D. J. 2013. Winter and breeding bird monitoring data analysis 2010-2012: San Antonio 

Missions National Historical Park. Natural Resource Data Series NPS/GULN/NRDS—2013/556. 

National Park Service, Fort Collins, Colorado.
130

4.8 Aquatic Macroinvertebrates

4.8.1 Description

Macroinvertebrates are often used as biological indicators in assessing overall aquatic ecosystem 

health: the absence of macroinvertebrates in an aquatic ecosystem may reflect disturbances, such as 

pollution, that can affect higher trophic levels (EPA 2012). Additionally, macroinvertebrates are an 

important food source for birds, fish, and other wildlife in SAAN (EPA 2012).

The Missions Units are located within the upper segment of the San Antonio River Basin, and the 

Rancho Unit is within the lower segment (Figure 33). The upper reach (segment 1911) of the San 

Antonio River has been heavily impacted by channelization, non-native plants, pollution, and 

drought. This is largely the result of urban sprawl of the city of San Antonio. 

Figure 33. The location of SAAN units in the San Antonio River Basin.

Macroinvertebrate indicator species can range from sensitive species such as caddisflies (order 

Trichoptera) and Unionids (freshwater mussels of the family Unionidae, also known as naiads), to 

the much more tolerant midge (Diptera) and aquatic worm (Oligochaeta) species. Other benthic 

organisms that are categorized as aquatic macroinvertebrates include leeches (phylum Annelida), 

snails (class Gastropoda), flatworms (phylum Platyhelminthes), and various insects in their aquatic 

life stage (e.g. mayflies [order Ephemeroptera], dragon and damsel flies [order Odonata], and 

stoneflies [order Plecoptera]) (TCEQ 2007). In the upper San Antonio River segment, 15 families of 

benthic macroinvertebrates were identified, 11 of which are considered intolerant to degradation of 

the habitat (SARA 2007).
131

Freshwater invertebrates, or aquatic macroinvertebrates, are considered a Vital Sign by the GULN, 

but the network has no foreseeable plans to conduct invertebrate-specific monitoring in SAAN 

waterways (Segura et al. 2007). The monitoring of aquatic macroinvertebrates that has occurred in or 

near SAAN has been conducted by the San Antonio River Authority (SARA), the Texas Commission 

on Environmental Quality (TCEQ), and the Texas Clean Rivers Program (CRP) as part of a 

collaborative, long-term water quality monitoring effort (SARA 2013). 

4.8.2 Measures

 Index of Biotic Integrity (IBI) Rating

4.8.3 Reference Conditions/Values

The reference condition for the park is based on the TCEQ (2007) metrics and scoring criteria for 

benthic macroinvertebrates. The scoring metrics include taxa richness, Ephemeroptera, Plecoptera, 

and Trichoptera (EPT) taxa abundance, biotic index (HBI), percent Chironomidae, percent dominant 

taxon, percent dominant functional feeding group (FFG), percent predators, ratio of intolerant : 

tolerant taxa, percent of total Trichoptera as Hydropsychidae, number of non-insect taxa, percent 

collector-gatherers, and percent of total number as Elmidae. These metrics are used to calculate IBI. 

An IBI is defined by TCEQ (2007, Appendix F, p. 3) as: “A composite index of the overall condition 

of a fish or benthic community based on the cumulative score of separate metrics.” An aquatic life 

use point score (ALU) is determined by the IBI and has four categorical levels (Table 38). The 

TECQ (2007, Appendix F, p. 1) defines the ALU as:

A beneficial use designation (in state water quality standards) in which the water body 

provides suitable habitat for survival and reproduction of desirable fish, benthic 

macroinvertebrates, shellfish, and other aquatic organisms. 

For this assessment, the reference condition will be the high range or above (Table 38). 

Table 38. Aquatic Life Use scores (ALU) are based on the points calculated with the metrics listed above 

to evaluate the benthic invertebrate sample to assess the condition of the aquatic habitat (TCEQ 2007).

ALU Category IBI Ranges

Exceptional >36

High 29-36

Intermediate 22-28

Limited <22

IBIs have also been calculated for aquatic habitats using TCEQ (2007) methods. Characteristics 

considered by this method include instream channel characteristics (e.g., riffles, substrate type), 

stream morphology (e.g., width, depth, flow), and the riparian environment (vegetation, bank slope, 

etc.). These habitat evaluations are helpful in determining the potential for a stream to support 

aquatic life (TCEQ 2007). Habitat IBIs and ALU designations will be included in this assessment to 
132

supplement the limited macroinvertebrate IBI data. The habitat IBI ranges are different from those 

for macroinvertebrates, as shown in Table 39.

Table 39. The ALU and IBI values for aquatic habitat assessments (TCEQ 2007).

ALU Category IBI Ranges

Exceptional 23-31

High 20-25

Intermediate 14-19

Limited ≤13

4.8.4 Data and Methods

SARA (2003) conducted collaborative water quality monitoring for the San Antonio River watershed 

which involved limited sampling of benthic macroinvertebrates and assessing aquatic habitat quality. 

Routine sampling involved collecting data on field and conventional parameters, nutrients, and 

bacteria; metals, nekton, benthic, and habitat assessments were collected annually. The bulk of data 

were collected by SARA, but TCEQ, U.S. Geological Survey (USGS), and the Guadalupe-Blanco

River Authority (GBRA) were also partners in the effort; the CRP facilitated the collaboration of data 

entities (SARA 2003). The areas that pertain to SAAN park units are river segments 1911 and 1901, 

which are the upper and lower San Antonio River watersheds. Stations where sampling occurred 

included Mitchell St., Mission Road, and Loop 410 (Figure 34; SARA 2003). Data collection was 

conducted from January 1998 through December 2002 under the quality assurance project plan 

(QAPP). Trend analysis was derived from data collected, where applicable, from January 1993 

through December 2002; it should be noted that data collected before 1996 had not been conducted 

under the QAPP, which was developed by the CRP (SARA 2003).

SARA (2008) sampled benthic macroinvertebrates in 2003 at Mission Road, and again in 2004 at 

Loop 410. Habitat assessments were also completed for each of these locations, as well as at the 

Mitchell St. location (Figure 34). Samples were also taken for two locations in 2012 (SARA 2012).

4.8.5 Current Condition and Trend

IBI Rating

The IBI is a measure that captures the aquatic biological community structure and is often an 

additional metric to standard water quality monitoring parameters (TCEQ 2007). This measure is 

assessed by sampling the area of interest to see which species of fish, invertebrates, or plants are 

most abundant. This can then indicate the conditions and detect impairment of the aquatic and 

riparian habitat. From the IBI score, an aquatic life use level (ALU) is determined (TCEQ 2007).

SARA (2003) calculated benthic macroinvertebrate and habitat IBIs for several locations within 

SAAN between 2000 and 2002 (Table 40). Benthic macroinvertebrates were sampled at two 

locations during the survey period while habitat was assessed at three sites (see Figure 35). While six 
133

out of seven habitat assessments resulted in high ALU designations, two out of three 

macroinvertebrate ALUs were in the limited range.

SARA (2005) conducted habitat assessments in 2004 at eight monitoring stations that are within or 

adjacent to SAAN (Table 41). Six of the seven locations received IBI scores in the intermediate

range with only one location (Piedras Creek) scoring in the high range.

SARA (2008) presented benthic macroinvertebrates ALU designations for stations on the upper San 

Antonio River in 2003-2004. The only stations sampled within SAAN were Mission Road and Loop 

410. While a high ratio of intolerant to tolerant taxa at the Mission Road location suggested favorable 

conditions for the macroinvertebrate community, low ratings for percent of predator, gatherer, and 

dominant taxa reflected an imbalance in the community structure; this was possibly due to a 

physiochemical imbalance and the overall degradation of the site location (SARA 2008). The Loop 

410 site had an elevated number of tolerant taxa, indicative of disturbances in the physiochemical 

composition. A high percentage of Chironomidae and percent total Trichoptera as Hydropsychidae

suggest a community structure imbalance (SARA 2008). The resulting ALU scores for both Mission 

Road and Loop 410 were limited, indicating a fair amount of degradation (Table 42). While the exact 

cause of degradation is not known, these scores merit the need for further investigation and 

monitoring of the benthic community.

SARA (2012) collected samples and calculated IBIs for two locations in SAAN in 2012: Piedras 

Creek at Espada Aqueduct and Ashley Road. Piedras Creek received an intermediate rating while 

Ashley Road was limited (Table 43).
134

Figure 34. Locations of the water quality monitoring stations that are within, or in close proximity, to the 

SAAN units. SAR=San Antonio River.
135

Table 40. Results of San Antonio River water quality monitoring, 2000-2002 (SARA 2003).

Station Date Macroinvertebrate ALU (IBI) Habitat ALU (IBI)

Mitchell Street 3/28/2000 Limited (<22) High (26-31)

3/20/2001 - High (26-31)

3/18/2002 - High (26-31)

Mission Road 3/26/2001 - High (26-31)

3/25/2002 - Intermediate (14-19)

Loop 410 4/18/2000 Limited (<22) High (26-31)

4/1/2002 Intermediate (22-28) High (26-31)

Table 41. Results of SARA habitat assessments (SARA 2005).

Segment* Station Date Habitat IBI ALU

1911 San Juan Dam 6/24/2004 17.0 Intermediate

Below Espada Dam 5/18/2004 19.0 Intermediate

Acequia de Espada 5/6/2004 17.0 Intermediate

Ashley Road 7/15/2004 19.0 Intermediate

Piedras Creek 5/20/2004 21.0 High

Loop 410 4/13/2004 19.0 Intermediate

1901 Picosa Creek 9/16/2004 17.5 Intermediate

*Segment refers to the Upper San Antonio River (1911) and the Lower San Antonio River (1901).

Table 42. Results of San Antonio River water quality monitoring, 2003-2004 (SARA 2008).

Station Date Macroinvertebrate ALU (IBI)

Mission Road 2003 Limited (<22)

Loop 410 2004 Limited (<22)

Table 43. Results of San Antonio River water quality monitoring, 2012 (SARA 2012).

Station Date Macroinvertebrate ALU (IBI)

Piedras Creek June 2012 Intermediate (28)

Ashley Road June 2012 Limited (21)
136

Threats and Stressor Factors

Habitat loss and degradation; water quality impairments; impervious cover carrying more water and 

chemicals into waterways; drought; decreased flows; hydrological changes (e.g., lower water tables 

and water diversions); and past contamination in soils were identified as the major stressors to 

aquatic macroinvertebrates in SAAN. Additionally, hydraulic fracturing, persistent organic 

pollutants, contaminants in sediment, and potential contaminants in personal care and pharmaceutical 

products are currently a challenge to monitor and assess (SARA 2013a).

Habitat loss and degradation is a threat to the aquatic macroinvertebrate communities in SAAN. 

Habitat degradation has been at least partly caused by the expanding population of San Antonio, 

which continues to grow (SARA 2013a). The upper and middle segments of the upper San Antonio 

River have been engineered for flood control, which has reduced habitat quality for fish and benthic 

macroinvertebrates (SARA 2008). Water quality impairments are also a threat, as they adversely 

affect intolerant invertebrate species. According to SARA (2013a), the upper San Antonio River 

segment had impaired fish communities in 2012, meaning that it did not support the high aquatic life 

use designation for the segment. This impairment could be due to habitat conditions, levels of 

nutrients, and/or the presence of E.coli in the river segment. Given that conditions are impaired for 

fish, it is likely that they are unfavorable for intolerant macroinvertebrate assemblages as well.

Urbanization Impacts

Impervious surfaces (e.g., paved roads, parking lots, roofs) increase with urban development of land 

(urbanization), and divert water directly into streams and rivers as runoff. This runoff can greatly 

increase the river’s flow, causing channel alteration by expansion laterally or by incision (Cawthon 

2008). Urbanization can also cause unnatural flood peak levels, especially after storm events, and 

alter the overall flow regimes of streams and rivers (Cawthon 2008). In response to this phenomenon, 

managers will often alter the river channel via dikes, levees, and terraces to carry the excess runoff 

water away from the urban areas faster and stabilize the river channel so it cannot naturally meander. 

This inevitably increases the erosion of natural streambed materials at the channelized area and 

contributes to increased aggradation (channel filling in with the deposition of sediment) downstream 

(Cawthon 2008). These alterations can degrade aquatic habitat conditions and adversely affect the 

benthic community.

According to Cawthon (2008), increased flow rates in the San Antonio River are partially attributed 

to impervious surface increases in and around San Antonio due to urbanization. This increased runoff 

is accompanied by pollutants and contaminants that are carried directly into rivers and streams 

(SARA 2013a, b). Under natural conditions, rainfall has time to infiltrate soils, recharge underground 

water tables, evaporate, and be absorbed by plants with very little runoff. This process also filters out 

substances that would otherwise impair waterways, such as bacteria, sediment, and other dissolved 

materials (SARA 2013b). The San Antonio River basin is now heavily urbanized and the channel has 

been engineered to carry away runoff pulses after storm events to avoid disastrous flooding. This has 

impacted the water quality, making conditions less than ideal for the benthic community to thrive, 

especially those that are sensitive to changes in the water physiochemical parameters that can be 

severely altered by runoff contamination. Alterations to riparian habitat can be detrimental to the 
137

benthic community by reducing bank stability which increases turbidity, decreased temperature 

regulation of the water, and eliminating refuge from predators (SARA 2013b). 

Drought

In the San Antonio River basin, another compounding factor of the urbanization issue is drought 

(SARA 2013a). Periods of drought can cause the remaining pervious surfaces such as lawns, farm 

fields, and other permeable surfaces to accumulate materials and become extremely dry. The rainfall 

following a prolonged period of drought not only runs off of the impervious surfaces, but will not 

soak in to over-dry surfaces either. The runoff moves fast, carrying accumulated bacteria, nutrients 

(e.g., pet waste), petroleum on parking lots and pavement, dust, topsoil, and other materials that have 

settled on the ground from the air, directly into the water (SARA 2013a). This can impair water 

quality and negatively impact aquatic organisms; excess nutrients from runoff cause algae blooms 

that can severely decrease dissolved oxygen which is crucial to aquatic ecological health (SARA 

2013a). Drought also can drop the rivers and streams below normal flow, reducing the available 

habitat, and can concentrate levels of contaminants since they become less diluted as the volume of

water is reduced. The 2011 drought conditions were exceptional, and the area around the park is still 

experiencing abnormally dry conditions with severe drought conditions to the north (Figure 35; U.S. 

Drought Monitor 2014).

Data Needs/Gaps

Many of the monitoring efforts in the park have not collected aquatic macroinvertebrates, or have 

collected only sporadically, which leaves many gaps in data (both spatially and temporally). For 

example, no macroinvertebrate IBIs have been calculated within the park’s Rancho Unit. The data 

discussed above are outdated and not sufficient for an assessment of any trends in SAAN in regard to 

the aquatic macroinvertebrate community. However, there are plans for ongoing, long-term 

monitoring of the San Antonio River segment that runs through SAAN (SARA 2013a). 
138

Figure 35. The severity of drought in Texas 2011-2014. Drought severity ranges from the darkest red 

areas, which represent “exceptional” droughts, to yellow areas, which are “abnormally dry” (reproduced 

from U.S. Drought Monitor 2014).

Overall Condition

IBI Rating

The project team assigned a Significance Level of 3 for the IBI rating measure. While the IBI scores 

that are available for macroinvertebrates suggest the community is likely degraded, there is not 

enough data to assess the condition of aquatic macroinvertebrates within SAAN at this time. 

Therefore, a Condition Level cannot be assigned. 
139

Weighted Condition Score

A Weighted Condition Score cannot be calculated at this time, due to the lack of data for the only 

measure. The current condition and any trends for the aquatic macroinvertebrate community are 

unknown. 

Aquatic Macroinvertebrates

Measures

Significance 

Level

Condition 

Level WCS = N/A

IBI Score 3 n/a

4.8.6 Sources of Expertise 

San Antonio River Authority (SARA)

4.8.7 Literature Cited

Cawthon, T. 2008. Channel change on the San Antonio River. Texas Water Development Board, San 

Marcos, Texas.

Environmental Protection Agency (EPA). 2012. Macroinvertebrates and habitat. U.S. Environmental 

Protection Agency. http://water.epa.gov/type/rsl/monitoring/vms40.cfm (accessed 3 September 

2014).

San Antonio River Authority (SARA). 2003. Basin summary report for the San Antonio River Basin. 

San Antonio River Authority, San Antonio, Texas.

San Antonio River Authority (SARA). 2005. An inventory of fish species within the San Antonio 

Missions National Historical Park. Final Report. San Antonio River Authority, Environmental 

Services Department, San Antonio, Texas.

San Antonio River Authority (SARA). 2007. San Antonio River basin 2007 basin highlights report. 

San Antonio River Authority, San Antonio, Texas.

San Antonio River Authority (SARA). 2008. San Antonio River basin summary report. San Antonio 

River Authority, San Antonio, Texas.

San Antonio River Authority (SARA). 2012. Unpublished macroinvertebrate monitoring data. 

Received from Chuck Lorea, SARA CRP Project Manager, 23 September 2014.

San Antonio River Authority (SARA). 2013a. San Antonio River basin 2013 summary report. San 

Antonio River Authority, San Antonio, Texas.
140

San Antonio River Authority (SARA). 2013b. San Antonio River Basin creek book: a guide to 

healthy creeks and rivers. San Antonio River Authority, San Antonio, Texas.

Segura, M., R. Woodman, J. Meiman, W. Granger, and J. Bracewell. 2007. Gulf Coast Network Vital 

Signs Monitoring Plan. Natural Resource Report NPS/GULN/NRR–2007/015. National Park 

Service, Fort Collins, Colorado.

Texas Commission on Environmental Quality (TCEQ). 2007. Surface water quality monitoring 

procedures, volume 2: methods for collecting and analyzing biological assemblage and habitat 

data. TCEQ Monitoring Operations Division, Austin, Texas.

U.S. Drought Monitor. 2014. Texas. 

http://droughtmonitor.unl.edu/Home/StateDroughtMonitor.aspx?TX (accessed 10 September 

2014).
141

4.9 Fish

4.9.1 Description

Fish play an important part in aquatic ecosystems, as they act as predators that control 

macroinvertebrate populations, and as a food source for predatory aquatic and terrestrial species 

(SARA 2014). Fish communities are good indicators of water quality because some species are more 

intolerant of changes in nutrient level, turbidity, water temperature and dissolved oxygen levels (DO) 

than other species. For example, the USDA (2001) identifies species of darter, sunfish, and suckers 

that are sensitive/intolerant to stream degradation, siltation, and the presence of chemicals, 

respectively. Although the fish species that occur within SAAN are not known to be sensitive 

species, they are still a valuable and important component in assessing the overall health of the 

aquatic habitats in the park.

The San Antonio River runs through both units of SAAN, and there are over 70 species of fish 

confirmed to exist within the watershed (SARA 2005). According to NPS (2014), the fish species in 

the SAAN reach of the river represent six orders and eight families. Orders represented in the park 

include: Characiformes, Cypriniformes (such as the common carp [Cyprinus carpio]), Clupeiformes, 

Cyprinodontiformes, Perciformes (such as the largemouth bass [Micropterus salmoides]), and 

Siluriformes (such as the channel catfish [Ictalurus punctatus]) (Photo 17). The species pictured 

above are three of several fish species considered common in the park’s aquatic habitats (NPS 2014). 

Two native species that are considered rare in SAAN are the American gizzard shad (Dorosoma 

cepedianum) and the green sunfish (Lepomis cyanellus) (NPS 2014). There are several non-native 

fish in SAAN, with four species considered abundant in the park: the Mexican tetra (Astyanax 

mexicanus), a Rio Grande cichlid (Herichthys cyanoguttatum), Mozambique mouth-breeder 

(Oreochromis mossambicus), and sailfin molly (Poecilia latipinna) (NPS 2014).

Photo 17. From top to bottom, the largemouth bass, and channel catfish (photos by SARA 2014).
142

4.9.2 Measures

 Species richness

 IBI rating

4.9.3 Reference Conditions/Values

The reference condition for fish in SAAN is based on the EPA Rapid Bioassessment Protocol V 

(RBP) (EPA 1989), which is used by SARA to assess fish communities in the watershed. The RBP 

includes an index of biotic integrity (IBI) based on methods developed by Karr (1981). Table 44

displays the range of total IBI scores, integrity classes, and associated attributes. IBI is a multimetric 

index; metrics included in the index calculation are the number of fish species and individuals, 

number of darters, number of species of sunfish, number of species of suckers, number of intolerant 

species, percentage of tolerant species, percent omnivores and piscivores, percentage of diseased 

fish, and percentage of species with multiple age groups (USDA 2001). For the purpose of this 

assessment, the reference condition for IBI will be scores in the good integrity class or above. 

Table 44. Total IBI score, integrity class, and attributes to those respective scores (reproduced from 

SARA 2005).

Total IBI Score Integrity Class Attributes 

58-60 Excellent Comparable to the best situations without human disturbance; all 

regionally expected species for the habitat and stream size, 

including the most intolerant forms, are present with a full array of 

age (size) classes; balanced trophic structure.

53-57

48-52

Very Good

Good

Species richness somewhat below expectations, especially due to 

the loss of the most intolerant forms; some species are present with 

less than optimal abundances or size distributions; trophic structure 

shows some signs of stress.

45-47

39-44

Good to Fair

Fair

Signs of additional deterioration include loss of intolerant forms, 

fewer species, highly skewed trophic structure (e.g., increasing 

frequency of omnivores and cichlids or other tolerant species); older 

age classes of top predators may be rare.

36-38

28-35

Fair to Poor

Poor

Dominated by omnivores, tolerant forms, and habitat generalists; 

few top carnivores; growth rates and condition factors commonly 

depressed; hybrids and diseased fish often present.

24-27

12-23

Poor to Very Poor

Very Poor

Few fish are present, mostly introduced or tolerant forms; hybrids 

common; disease, parasites, fin damage, and other anomalies 

regular.

No Fish Repeated sampling finds no fish.

4.9.4 Data and Methods

SARA (2003) compiled a summary report for monitoring activities in the San Antonio River Basin. 

Data were collected between 1998 and 2002, with eight water quality monitoring stations sampled 

from the Upper (segment 1911) and Lower San Antonio River Basin (segment 1901) (see Figure 29

in the previous section). Generally, stations were monitored for fish once per year; the Mitchell Street 
143

station was sampled twice in 2000. Three of the eight stations that were assessed for fish IBIs were

located within SAAN.

SARA (2005) conducted inventories of fish species in SAAN during 2003 and 2004. Four stations 

were sampled during 2003, and eight during 2004. In 2003, three of the four stations were located in 

the San Antonio River at Mission Road, San Juan Dam, and below Espada Dam, while the fourth 

station was in Piedras Creek (for station locations, see Figure 35 in the previous section). In 2004, 

four of the eight stations sampled were located on the San Antonio River: San Juan Dam, below 

Espada Dam, Ashley Road, and South Loop 410. The other three stations sampled in 2004 were at 

Acequia de Espada, Piedras Creek, and Picosa Creek. In 2003, the stations were each sampled once 

in the month of October (7 October – 28 October). In 2004, the stations were sampled between 

March and September (SARA 2005). The inventory documented the fish species identified, 

distribution, and frequency of occurrence. An IBI score was calculated for each station sampled 

(SARA 2005). The document also contains a list of fish species occurring in the Upper San Antonio 

River taken from SARA (1996).

Sampling was conducted by SARA at three locations in 2011, 2012, and 2013. The Espada Aqueduct 

at Piedras Creek, Aquequia de Espada (Loop 410), and Ashley Road monitoring stations were 

sampled and IBIs for fish were calculated in June of 2011 and 2012, and May and June of 2013 

(SARA 2011, 2012, 2013b).

NPS (2014) represents an annotated list of fish species for SAAN, which documents occurrence (e.g., 

present, probably present), nativeness, and relative abundance.

4.9.5 Current Condition and Trend

Species Richness

SARA (2005) documented 27 fish species in the San 

Antonio River and its tributaries within SAAN. The 

most commonly observed native species were red 

shiners (Cyprinella lutrensis) (Photo 18), central 

stonerollers (Campostoma anomalum), and western 

mosquitofish (Gambusia affinis). Commonly 

observed introduced species included sailfin molly, 

Amazon molly (Poecilia formosa), Rio Grande 

cichlid, and Mexican tetra. The inventory also 

included a fish species list for the Upper San Antonio 

River from 1996 that documented 31 fish. Table 45

displays the fish shiners that are a native species 

inventory in 2005. 

Photo 18. Red shiners are a native species 

species commonly observed at SAAN (photo 

by shiners that (SARA 2014).
144

Table 45. List of fish species by source and documentation in SAAN. Note that SARA (1996) covers the 

Upper San Antonio River and is not exclusive to SAAN.

Scientific Name Common Name

SARA 

(1996)

SARA 

(2005)

NPS

(2014)

Ameiurus melas black bullhead X^

Ameiurus natalis yellow bullhead X X X

Astyanax mexicanus Mexican tetra* X X X

Atractosteus spatula alligator gar X

Campostoma anomalum central stoneroller X X

Chaenobryttus gulosus Warmouth X X X

Cyprinella lutrensis red shiner X X X

Cyprinella venusta blacktail shiner X

Cyprinus carpio common carp* X X

Dionda episcopa roundnose minnow X

Dorosoma cepedianum gizzard shad X X X

Gambusia affinis western mosquitofish X X X

Herichthys cyanoguttatum Rio Grande cichlid* X X X

Hypostomus plecostomus suckermouth catfish* X X

Ictalurus furcatus blue catfish X X^

Ictalurus punctatus channel catfish X X X

Lepisosteus oculatus spotted gar X

Lepisosteus osseus longnose gar X

Lepomis auritus redbreast sunfish X X X

Lepomis cyanellus green sunfish X X X

Lepomis macrochirus bluegill X X X

Lepomis megalotis longear sunfish X X X

Lepomis microlophus redear sunfish X

Lepomis punctatus spotted sunfish X

Liposarcus multiradiatus sailfin catfish X X

Micropterus punctulatus spotted bass X X

Micropterus salmoides largemouth bass X X X

Moxostoma congestum gray redhorse X

*introduced species, ^unconfirmed presence
145

Table 45 (continued). List of fish species by source and documentation in SAAN. Note that SARA (1996) 

covers the Upper San Antonio River and is not exclusive to SAAN.

Scientific Name Common Name

SARA 

(1996)

SARA 

(2005)

NPS

(2014)

Notropis amabilis Texas shiner X X

Notropis buchanani ghost shiner X X

Notropis texanus weed shiner X X

Notropis volucellus mimic shiner X X X

Noturus gyrinus tadpole madtom X

Oreochromis mossambicus Mozambique mouth-breeder* X X

Pimephales promelas fathead minnow X

Pimephales vigilax bullhead minnow X X X

Poecilia formosa Amazon molly* X X X

Poecilia latipinna sailfin molly* X X X

Pylodictis olivaris flathead catfish X

Tilapia aurea blue tilapia* X

Tilapia mossambica Mozambique tilapia* X X

Tilapia zillii redbelly tilapia* X X

*introduced species, ^unconfirmed presence

NPS (2014) documented 29 species of fish as “present” or “probably present” in SAAN (Table 45). 

Most fish species have been confirmed as present in the park; the only two species that were listed as 

“probably present” or “not confirmed” were black bullhead (Ameiurus melas) and blue catfish 

(Ictalurus furcatus). Of the 29 identified species, nine are non-native to SAAN (see Table 45). The 

western mosquitofish is considered abundant in the park, while other common fish species are yellow 

bullhead (Ameiurus natalis), red shiner, and weed shiner (Notropis texanus).

IBI Rating

SARA (2003) documented IBI integrity classes for fish that ranged from poor to good along river 

segment 1911, which comprises the Upper San Antonio River Basin where the Missions Unit is 

located. Only three of the segment 1911 stations are located within the boundaries of SAAN: 

Mitchell Street, Mission Road, and Loop 410 (Figure 30). The Loop 410 station was rated in the 

good integrity class, and the other 1911 stations ranged from fair to poor, though the later samples 

(2001, 2002) were in the poor integrity class (Table 46). According to SARA (2003), insectivores 

were the dominant taxa in comparison to omnivore taxa throughout segment 1911. The Mitchell 

Street and Mission Road stations had the greatest numbers of omnivores, although omnivores were 

still in lower ratios to insectivores at these sites. Table 46 displays the IBI integrity class summary of 

San Antonio River stations within the park sampled between 1998 and 2002.
146

Table 46. IBI and integrity class summary for stations in SAAN, 1998-2002 (SARA 2003).

River Segment Stations Date IBI Integrity Class

1911 Mitchell Street 6/10/1998 <35 Poor

3/28/2000 39-44 Fair

8/1/2000 <35 Poor

3/20/2001 <35 Poor

3/18/2002 <35 Poor

Mission Road 3/26/2001 <35 Poor

3/25/2002 <35 Poor

Loop 410 4/18/2000 48-52 Good

4/1/2002 48-52 Good

SARA (2005) contains IBI scores for fish at seven stations that are within or adjacent to SAAN’s 

Missions Unit and one within the Rancho Unit (Picosa Creek). Sampling occurred in 2003 and 2004, 

with six stations sampled twice and two stations sampled once. In 2003, four stations were sampled 

for fish and integrity classes ranged from poor at the Mission Road station, to fair at the Piedras 

Creek and Espada Dam stations (Table 47). In 2004, seven stations in SAAN were sampled for fish 

(three stations were sampled twice). The majority of these samples showed little change in fish 

integrity classes. The stations sampled twice in the same year showed no change in fish IBI scores,

with the exception of the Acequia de Espada station. The Acequia de Espada station had an IBI of 36 

in the late-spring and increased to 42 in early summer. The San Juan Dam station showed 

improvement between fall of 2003 and mid-summer of 2004; IBI went from a 38 to a 44, changing 

the integrity class from the fair to poor category to fair (Table 47). The single IBI rating from the 

Rancho Unit (Picosa Creek) was in the good class (SARA 2005).

Table 47. IBI ratings for the SAAN fish community in river segments 1911 and 1901, 2003-2004 (SARA 

2005).

River Segment Stations Date IBI Integrity Class

1911 Mission Road 10/7/2003 34 Poor

Piedras Creek 10/7/2003 40 Fair

5/20/2004 42 Fair

San Juan Dam 10/21/2003 38 Fair to Poor

San Juan Dam 6/24/2004 44 Fair

Below Espada 

Dam

10/28/2003 44 Fair

5/18/2004 42 Fair
147

Table 47 (continued). IBI ratings for the SAAN fish community in river segments 1911 and 1901, 2003-

2004 (SARA 2005).

River Segment Stations Date IBI Integrity Class

1911 (cont.) Ashley Road 3/23/2004 42 Fair

7/15/2004 46 Good to Fair

Loop 410 4/13/2004 46 Good to Fair

6/29/2004 48 Good

Acequia de 

Espada

5/6/2004 36 Fair to Poor

6/15/2004 42 Fair

1901 Picosa Creek 9/16/2004 48 Good

In 2010, assessments were performed at three stations on the upper (1911) segment of the San 

Antonio River. The results reflect a decline of 8 IBI points at the Ashley Creek station, 6 at Piedras 

Creek, and only 4 at Acequia de Espada (SARA 2010). The decline changed the integrity classes for 

Ashley Creek and Piedras Creek, but Acequia de Espada remained the same (SARA 2010).

Table 48. IBI scores for fish collected in 2010 in the San Antonio River in August (SARA 2010).

River Segment Station Date IBI Integrity Class

1911 Piedras Creek 8/5/2010 36 Fair to Poor

Ashley Road 8/16/2010 38 Fair to Poor

Acequia de Espada 8/17/2010 38 Fair to Poor

SARA (2011) sampled fish and assessed IBIs at three stations in 2011 (Table 49). The Ashley Road 

station had an IBI of 38 in 2010 and a 46 in 2011, increasing the integrity class to fair (Table 48 and 

Table 49). The Piedras Creek station had an IBI of 36 in 2010 and 40 in 2011, also changing the 

integrity class for the better (Table 49). The Acequia de Espada station did not change in IBI score 

(SARA 2011).

SARA (2012) sampling results show an increase of only two IBI points at Piedras Creek, which did 

not affect the integrity class standing for that station. Ashley road IBI, however, declined four points 

which brought the integrity class down from good to fair to fair (Table 50). Additionally, Acequia de 

Espada couldn’t be sampled in 2012 due to no-flow conditions. This was likely due to acequia 

maintenance or construction activities (Mitchell, written communication, 22 September 2015).
148

Table 49. IBI scores for fish collected at three (segment 1911) stations in June of 2011 (SARA 2011).

River Segment Stations Date IBI Integrity Class

1911 Ashley Road 6/6/2011 46 Good to Fair

Piedras Creek 6/27/2011 40 Fair

Acequia de Espada 6/28/2011 38 Fair

Table 50. IBI scores for fish collected at three (segment 1911) stations in June of 2012 (SARA 2012).

River Segment Stations Date IBI Integrity Class

1911 Ashley Road 6/14/2012 42 Fair

Piedras Creek 6/11/2012 42 Fair

Aceqia de Espada N/A No sampling due to 

no-flow conditions

SARA (2013b) sampled the same three stations in SAAN (Table 49, Table 50, and Table 51). The 

IBI scores overall declined from 2011 to 2013 suggesting some type of degradation was likely to

have occurred in these areas, although what caused the decline is not clear. All of the scores from 

2011, 2012, and 2013 are also below the selected reference condition of the good integrity class or 

higher (≥48). 

Table 51. IBI scores for fish collected at three (segment 1911) stations in May and June of 2013 (SARA 

2013b).

River Segment Stations Date IBI Integrity Class

1911 Ashley Road 6/12/2013 34 Poor

Piedras Creek 5/15/2013 38 Fair

Acequia de Espada 5/20/2013 36 Poor

Threats and Stressor Factors

Habitat loss and degradation are a threat to the fish communities in SAAN. Habitat degradation has 

been partly caused by the continually expanding population in San Antonio (SARA 2013a). The 

upper and middle segments of the upper San Antonio River have been engineered for flood control, 

which has reduced habitat quality for fish (SARA 2008). Water quality impairments are also a threat 

to the fish community in SAAN, as they adversely affect intolerant fish species. According to SARA 

(2013a), the Upper San Antonio River segment had impaired fish communities in 2012. River 

segment 1911, which runs through the park, was placed in the category of not supporting the water 

quality standards for fish community IBI. This assessment of poor fish conditions could be due to the 

concerning habitat condition, level of nutrients, and the presence of E.coli in the river segment. 

These threats and stressors are discussed in more detail in Chapter 4.8 of this document, as the 
149

aquatic macroinvertebrate communities in SAAN face many of the same threats as the fish 

community.

Climate change has implications for the aquatic ecosystem, with increased severity and frequency of 

drought and warming temperatures expected in the SAAN region. Water temperatures are affected by 

the ambient air temperature, and at SAAN water temperatures vary by nearly 25°C (45°F) during a 

typical year due to seasonal air temperature fluctuations (Meiman 2012). From 1999 to 2012, some 

stations had detected periodic water temperatures that exceeded the state standard, a maximum of 

32.2°C (Meiman 2012). The recent water temperature spikes were attributed to the warming climate 

trend, and are expected to become more common in the future, although the restoration of riparian 

zones may offset the impacts of rising air temperatures on the water temperature (Meiman 2012). 

Higher water temperatures reduce capacity to carry dissolved oxygen (DO) which is essential to fish 

health and survival. Low DO can also be the result of nutrient overload, which is often a problem 

after significant rainfall events, when storm runoff washes excess nutrients and contaminants into the 

water (SARA 2013a). Droughts will likely become more frequent and longer in duration as the 

climate changes (Twilley et al. 2001, Davey et al. 2007). In 2011, the drought conditions in Texas 

reduced Picosa Creek in the Rancho Unit to patches of lentic, shallow ponds fit for intense algal 

blooms and unfavorable for fish survival (Meiman 2012; Photo 19). 

Data Needs/Gaps

Limited data exist for both measures used in this assessment. The establishment of annual, routine 

monitoring of fish species richness and IBI would aid in the management of fish communities in the 

San Antonio River and its tributaries within SAAN. Furthermore, the only data for Rancho de las 

Cabras are from one date in 2004 at the Picosa Creek station (SARA 2005). The 2011 drought in

Texas likely negatively affected the fish community.

There is no information regarding the impacts of nonnative fish on native fish species. The fish 

community may be shifting towards nonnative species, given that all the nonnative fish species 

confirmed in SAAN are considered common or abundant (NPS 2014). The number of native fish 

species listed in SARA (1996) was 25 with six nonnative species, which is a 19% nonnative fish 

community for the Upper San Antonio River at that time. SARA (2005) listed 20 native and seven 

nonnative species of fish, or nearly 26% nonnative. The official NPS (2014) list for SAAN shows 21 

native species (two are unconfirmed) and eight nonnative species, which is over 27% nonnative. Fish 

inventories will be important for assessing the trends in the native and nonnative fish communities 

and should continue with future monitoring efforts in SAAN. 
150

Photo 19. Picosa Creek during the 2011 drought (NPS photo by Joe Meiman).

Overall Condition

Species Richness

The project team defined the Significance Level for species richness as a 2. The earliest available 

species list for the Upper San Antonio River contains 31 species, six of which are nonnative (SARA 

1996). Nearly 10 years later, SARA (2005) observed 27 species of fish within SAAN, with seven 

nonnative species. NPS (2014) lists 29 species of fish occurring in SAAN, with eight nonnative 

species that are considered common or abundant. Given that data on species richness is somewhat 

limited and out-of-date, the Condition Level for this measure cannot be assigned at this time.

IBI Rating

The project team defined the Significance Level for the IBI rating as a 3. SARA monitoring (2003, 

2005, 2011, 2012, 2013b) has shown varied IBI ratings ranging from poor to good with at least three 
151

areas showing signs of possible degradation. The Acequia de Espada location has experienced 

degradation between 2004 and 2013, declining from the fair to poor range in 2004 to poor in 2013. 

Ashley Road has also declined, from good to fair in 2011 to poor in 2013. Since all of the most 

recent IBI ratings (2011, 2013) for locations within SAAN are below the selected reference condition 

of a good integrity class or higher, the Condition Level for this measure has been assigned a 2, 

indicating moderate concern.

Weighted Condition Score

Although the Condition Level for the species richness measure cannot be assigned at this time due to 

a temporal gap in data, the IBI ratings are low for SAAN and are in decline for some areas. The 

Weighted Condition Score for the fish community is a 0.67, which indicates moderate concern.

Fish

Measures

Significance 

Level

Condition 

Level WCS = 0.67

Species Richness 2 n/a

IBI 3 2

4.9.6 Sources of Expertise

San Antonio River Authority (SARA)

4.9.7 Literature Cited

Davey, C. A., K. T. Redmond, and D. B. Simeral. 2007. Weather and Climate Inventory, National

Park Service, Gulf Coast Network. Natural Resource Technical Report NPS/GULN/NRTR. 

2007/011. National Park Service, Fort Collins, Colorado.

Environmental Protection Agency (EPA). 1989. Rapid Bioassessment protocols for use in streams 

and rivers, benthic macroinvertebrates and fish. EPA/444/4-89/001. U.S. Environmental 

Protection Agency, Office of Water, Washington, D.C. 

Karr, J. 1981. Assessment of biotic integrity using fish communities. Fisheries 6:21-27.

Meiman, J. 2012. Gulf Coast Network (GULN) water quality report: Status of water quality of San 

Antonio Missions National Historical Park. Natural Resource Technical Report 

NPS/GULN/NRTR 2012/588. National Park Service, Fort Collins, Colorado.

National Park Service (NPS). 2014. NPSpecies online database. 

https://irma.nps.gov/App/Species/Search (accessed 7 July 2014).
152

San Antonio River Authority (SARA). 1996. Evaluation of aquatic ecosystems of streams in the San 

Antonio River Watershed based on rapid bioassessment protocols. San Antonio River Authority. 

San Antonio, Texas.

San Antonio River Authority (SARA). 2003. Basin summary report for the San Antonio River Basin. 

Texas Clean Rivers Program, San Antonio River Authority, San Antonio, Texas.

San Antonio River Authority (SARA). 2005. An inventory of fish species within the San Antonio 

Missions National Historical Park. Final Report. San Antonio River Authority, Environmental 

Services Department, San Antonio, Texas.

San Antonio River Authority (SARA). 2008. San Antonio River basin summary report. San 

Antonio River Authority, San Antonio, Texas.

San Antonio River Authority (SARA). 2010. Unpublished fish monitoring data. Excel spreadsheet 

received from Joe Meiman, GULN hydrologist, 26 June 2014. 

San Antonio River Authority (SARA). 2011. Unpublished fish monitoring data. Excel spreadsheet 

received from Joe Meiman, GULN hydrologist, 26 June 2014. 

San Antonio River Authority (SARA). 2012. Unpublished fish monitoring data. Excel spreadsheet 

received from Joe Meiman, GULN hydrologist, 26 June 2014. 

San Antonio River Authority (SARA). 2013a. San Antonio River Basin: 2013 summary report. San 

Antonio River Authority, San Antonio, Texas.

San Antonio River Authority (SARA). 2013b. Unpublished fish monitoring data. Excel spreadsheet 

received from Joe Meiman, GULN hydrologist, 26 June 2014. 

San Antonio River Authority (SARA). 2014. Fish. https://www.saratx.org/public_resources/field_guide/?cat_id=53 (accessed 1 April 2014).

Twilley, R. R., E. J. Barron, H. L. Gholz, M. A. Harwell, R. L. Miller, D. J. Reed, J. B. Rose, E. H. 

Siemann, R. G. Wetzel, and R. J. Zimmerman. 2001. Confronting climate change in the Gulf 

Coast region: Prospects for sustaining our ecological heritage. Union of Concerned Scientists, 

Cambridge, Massachusetts, and Ecological Society of America, Washington, D.C.

U.S. Department of Agriculture (USDA). 2001. Index of biotic integrity (IBI). 

ftp://ftp.wcc.nrcs.usda.gov/wntsc/strmRest/wshedCondition/IndexOfBioticIntegrity.pdf (accessed 

1 April 2014).
153

4.10 Water Quality

4.10.1 Description

Water quality is a Vital Sign for parks in the 

GULN, including SAAN. The water quality of 

the San Antonio River has long been a focus of 

attention and its quality has been the focus of 

regulation since the late 1700s (Porter 2009, as 

cited by Meiman 2012). Situated in the semiarid region of Texas, the river is a highly valued 

resource and the primary reason the original 

mission locations were chosen by their 

founders. 

The San Antonio River is central to the 

character of both SAAN park units. Extending 

from and running parallel to the main channel 

of the river is a system of Spanish-built 

acequias from the 18th century (Meiman 2012). 

These gravity fed irrigation ditches provided 

water to the surrounding fields and allowed 

agriculture to flourish in support of the 

missionaries and settlers. The two remaining 

acequias within SAAN, Acequia de San Juan 

(constructed in 1731) and Acequia de Espada 

(constructed 1731-1745; Photo 20) (TSHA 

2014), are still flowing today.

In modern times, development around and upstream of San Antonio has increased water demand, 

decreasing the natural water supply that historically maintained flows in the San Antonio River. The 

San Antonio Water System (SAWS) has developed an innovative water re-use system. Presently, 

during the dry months of summer or during drought conditions, 95% or more of the water flowing in 

the urban segment of the San Antonio River is actually highly treated recycled water (Meiman 2012). 

This recycled water is introduced into the river in downtown San Antonio and is indistinguishable 

from the river’s natural flow to the observer. While this water is visually indistinguishable, several 

components of water quality are impacted when compared to the quality of the natural source of the 

river, the Edwards Aquifer. 

Photo 20. Acequia de Espada at the Espada 

Aqueduct (photo by Shannon Amberg, SMUMN 

GSS 2013).
154

Photo 21. Aqueduct along the Espada Acequia (photo by Kathy Allen, SMUMN GSS 2013).

The areas surrounding the missions have become extremely developed and urban in nature. 

According to the NPS (2012), “Few other parks in the country have as much alteration, modification, 

or development of its watershed and surrounding areas as the San Antonio Missions National 

Historical Park”. With the city of San Antonio’s population now in excess of 1.4 million (USCB 

2015) and the diverse array of land uses present in the area, the natural state of the park provides a 

sharp contrast to its urban surroundings.

The Concepción, San José, San Juan, and Espada Missions are each located within the urban 

footprint of San Antonio (Figure 36). SAAN’s southernmost unit, Rancho de las Cabras lies 

southeast of the city and is quite rural. Following the flow of the San Antonio River, the Rancho de 

las Cabras Unit is located approximately 80 km (50 m) downstream from Mission Espada. 
155

Figure 36. The San Antonio Missions Unit with water quality sampling locations (Meiman 2012). Sites 

with four-letter identifications are park of the GULN water quality program. Numeric identifies are part of 

the SARA Clean Rivers Monitoring Program. Both programs use the same protocol and schedule. SARA 

is contracted by the GULN to conduct sampling on the four SAAN sites; PCPC (Piedras Creek), AEAE 

(Acequia Espada), SJSR (San Antonio River at Mission San Juan de Capistrano, and ASJC (Acequia 

San Juan de Capistrano).

Site #12899

Site SJSR

Site PCPC

Site ASJC

Site #12897

Site #12881

Site #20350

Site #17066

Rancho de las Cabras unit 

80 km south (by river)/ 40 

km southeast by road.
156

4.10.2 Measures

 Temperature

 Total dissolved solids (as measured by specific conductance)

 Dissolved oxygen

 pH

 Prevalence of coliform bacteria

 Prevalence of nutrients (phosphates, nitrates)

 Prevalence of sulfate

 Prevalence of chloride

 Total suspended solids (as measured by turbidity)

Temperature

Water temperature greatly influences water chemistry and the organisms that live in aquatic systems. 

Not only can temperature affect the ability of water to hold oxygen, but it also affects biological 

activity and growth within water systems (USGS 2010). All aquatic organisms, from fish to insects to 

zoo- and phytoplankton, have a preferred or ideal temperature range for existence (USGS 2010). As 

temperature increases or decreases too far past this range, the number of species and individuals able 

to survive eventually decreases. In addition, higher temperatures allow some compounds or 

pollutants to dissolve more easily in water, making them more toxic to aquatic life (USGS 2010).

Total Dissolved Solids

Total dissolved solids (TDS) represent the concentration of dissolved inorganic and organic 

compounds in the water. Most TDS are inorganic salts including calcium, magnesium, carbonates, 

nitrates, chlorides, and sulfates (SDWF 2012). These make their way into waterways primarily 

through runoff. Sources of TDS often include erodible landscapes that deposit materials into 

waterways, mineral springs, and agricultural or urban runoff. The concentration of TDS affects the 

water balance in the cells of aquatic organisms (EPA 2012); if the TDS are extremely low, an 

organism’s cells will swell, and if the TDS are too high, an organism’s cells will shrink. The TDS 

influences an organism’s ability to remain in the water column (EPA 2012). One way of measuring 

the presence of dissolved solids is through specific conductance of water, which is the measure of the 

ionic activity and content of water, or water’s ability to conduct electricity. The higher the 

concentration of dissolved solids (calcium, various salts, magnesium, etc.), the higher the 

conductivity of the water. Specific conductance is included here as a measure for understanding 

concentrations of dissolved solids in the San Antonio River that flows through SAAN.

Dissolved Oxygen

Dissolved oxygen (DO) is critical for organisms that live in water. In order to survive, fish and 

zooplankton filter out or “breathe” dissolved oxygen from the water (USGS 2010). Oxygen enters 

water from the air, when atmospheric oxygen mixes with water at turbulent, shallow riffles in a 

waterway, or when released by algae and other plants as a byproduct of photosynthesis. As the 

amount of DO drops, it becomes more difficult for aquatic organisms to survive (USGS 2010). The 

concentration of DO in a water body is closely related to water temperature; cold water holds more 
157

DO than warm water (USGS 2010). Thus, DO concentrations are subject to seasonal fluctuations as 

low temperatures in the winter and spring allow water to hold more oxygen, and warmer 

temperatures in the summer and fall allow water to hold less oxygen (USGS 2010).

pH

pH is a measure of the level of acidity or alkalinity of water and is measured on a scale from 0 to 14, 

with 7 being neutral (USGS 2010). Water with a pH of less than 7.0 indicates acidity, whereas water 

with a pH greater than 7.0 indicates alkalinity. Aquatic organisms have a preferred pH range that is 

ideal for growth and survival (USGS 2010). Chemicals in water can change the pH and harm animals 

and plants living in the water; thus, monitoring pH can be useful for detecting natural and humancaused changes in water chemistry (USGS 2010).

Indicator Bacteria (coliform spp.)

Bacteria are a common natural component of surface waterways and are mostly harmless to humans. 

However, certain bacteria, specifically those found in the intestinal tracts and feces of warm-blooded 

animals, can cause illness in humans (USGS 2011). Fecal coliform bacteria are a subgroup of 

coliform bacteria that, when used in monitoring water quality, can indicate if fecal contamination has 

occurred in a specific waterway. Escherichia coli (E. coli) is a specific species of bacteria that 

belongs to the larger group of coliform bacteria and is characterized by its ability to break down 

urease (an enzyme that breaks down urea into carbon dioxide and ammonia) (USGS 2011). Thus, E. 

coli is a preferred indicator for determining if potential pathogens are present in freshwater resources. 

It is tested by counting colonies that grow on micron filters placed in an incubator for 22-24 hours. 

High concentrations of E. coli can cause serious illness in humans (USGS 2011).

Nutrients

Nutrients, such as nitrogen and phosphorus, are crucial in supporting healthy aquatic environments.

However, elevated concentrations of these nutrients can negatively impact water quality and threaten 

the ability of plants and aquatic organisms to thrive (USGS 2013a). Nitrogen occurs naturally in the 

atmosphere and in soils and is deposited into surface waters through precipitation and runoff; 

nitrogen deposition is increased by human inputs such as sewage, fertilizers, and livestock waste 

(USGS 2013b). Nitrates can cause a host of water quality related problems when present in high 

concentrations including, but not limited to, excessive plant and algae growth, eutrophication, and 

depleted dissolved oxygen available to aquatic organisms (USGS 2013b). Nitrate in drinking water 

can be harmful to humans, particularly young children, and livestock (USGS 2013b). Phosphorus is 

commonly found in agricultural fertilizers, manure, organic wastes in sewage, and sometimes 

industrial effluent (USGS 2013b). In excess, phosphorus in water systems can increase the rate of 

eutrophication, encourage overgrowth of aquatic plants, deplete dissolved oxygen, and threaten fish 

and macroinvertebrate populations (USGS 2013b). Soil erosion is the primary contributor of 

phosphorus input into surface waters, in which enriched soils are deposited into waterways through 

runoff during heavy precipitation events (USGS 2013b).
158

Sulfate and Chloride

Chloride is an inorganic salt found naturally in water, but additional chloride can be washed into 

surface waters from several general sources, including road salting, agricultural runoff, and oil and 

gas wells (McDaniel 2012). In arid landscapes, higher rates of evaporation increase mineral 

accumulation (such as sodium chloride, borates, or gypsum) in soils, lakes, and rivers (USGS 1997). 

Large amounts of chloride in surface water are toxic to aquatic life such as fish and 

macroinvertebrates. Chloride becomes more toxic when combined with potassium or magnesium 

(NHDES 2008). Toxic metals can also be released when chloride is present in water. Dissolved 

oxygen levels, are reduced when these metals are released, causing added stress to the aquatic life in 

the area (NHDES 2008).

Sulfate, like chloride, is an inorganic salt found naturally in surface and ground water. In arid 

landscapes, sulfates can become concentrated in soils due to higher rates of evaporation (USGS 

1997); these can then be carried into waterways by runoff. Elevated levels of sulfate in waterways 

can be toxic to aquatic life (Lenntech 2011). Some aquatic species are more sensitive to sulfate than 

others, such as intolerant macroinvertebrates. Possible sources of excess sulfate include sulfate ores, 

large deposits resulting from evaporation, and industrial wastes (Lenntech 2011).

Total Suspended Sediment (TSS)

Total suspended sediments (TSS) are inorganic and organic particles (e.g., sand, silt, algae) 

suspended within a water body. The suspended sediments are often measured by their dry weight as

collected from the water column and expressed in milligrams per liter (Meiman 2012). Sample water 

is passed through a glass filter of known weight and pore size (Michaud 1994). This filter is then 

dried and re-weighed with the difference between the beginning weight and end weight being the 

TSS (Michaud 1994). 

TSS can also be estimated indirectly from turbidity (Michaud 1994). Using a turbidity meter, 

Nephlelometric turbidity units (NTU), Jackson Turbidity Units (JTU), and Formazin Turbidity Units 

(FTU), the extent to which light penetrates the sample is estimated and used as an approximation of 

TSS (Robertson et al. 2006). Using turbidity as an estimation of TSS, however, has linear regression 

limitations as it is affected by particle size, shape and color, unlike the dry weight method of 

measuring TSS (Joe Meiman, NPS Hydrologist, written communication, 14 October 2014).

4.10.3 Reference Conditions/Values

The reference conditions for water quality in SAAN are the TCEQ 2014 water quality criteria

considered to be protective of aquatic life and human recreation and bathing. Table 52 shows the 

standards for various surface water quality parameters set by the TCEQ. For some measures (e.g., 

nutrients), neither TCEQ nor the EPA have set applicable standards. The TCEQ has published 

“screening levels”, or levels of concern, indicating that if these levels are exceeded a concern for 

water quality is warranted.
159

Table 52. Texas Commission on Environmental Quality surface water quality standards for surface-water 

quality (TCEQ 2014).

Water Quality Measure TCEQ Standard

Temperature Maximum 90°F (32.2°C)

Total Dissolved Solids ≤750 mg/L

Dissolved oxygen (mg/L) ≥5.0 mg/L

pH 6.5 – 9.0

Indicator bacteria (coliform) ≤126 CFU/100 mL

Chloride ≤150 mg/L

Sulfate ≤150 mg/L

Nutrients (nitrates, phosphates) Phosphorous ≤ 0.69 mg/l, Nitrate ≤ 1.95 mg/l * State Screening Levels

Suspended Solids (TSS) No TCEQ standard

4.10.4 Data and Methods

NPS (1999) and Meiman (2012) were primary sources for this assessment. No specific long-term 

water quality monitoring studies have been completed within SAAN boundaries. Meiman (2012) is 

intended as the beginning of such a long-term study.

NPS (1999) contains an extensive baseline of water quality data for the parks and surrounding areas. 

The study area for this document included areas 4.8 km (3 mi) upstream and 1.6 km (1 mi) 

downstream of each of the park units (NPS 1999). The EPA’s database resources used in this study 

included; Storage and Retrieval System (STORET), Industrial Facilities Discharge (IFD), DRINKS 

(Drinking Water Supplies), GAGES (Water Gages), DAMS (Water Impoundments), and RF3 (River 

Reach File, Version 3). The report summarized the number of observations that exceeded EPA and 

NPS water quality criteria for a variety of water quality parameters.

Meiman (2012) provides more recent data and concentrates on only eight sampling locations either 

within or immediately adjacent to the park. The data were collected between 1999 and 2011. The 

metrics focused on by Meiman (2012) coincide well with the measures chosen by the park for this 

NRCA. 

4.10.5 Current Condition and Trend

Temperature

Water temperature in SAAN is greatly influenced by the urban environment surrounding the parks. 

The urban population of approximately 1.4 million people and the concentration of industry and 

infrastructure impact the water temperature of the San Antonio River. The high demand for water 

supply reduces the water flow in the river and development reduces the natural ground and vegetative 
160

cover, thereby reducing infiltration and allowing warmer rain water to run off into the river. Water 

temperature can vary as much as 25°C throughout the year (Meiman 2012).

Water temperature does not have a federal or EPA regulated standard. As such, the NPS (1999) 

document did not analyze the level of compliance for this measure. More than 15,000 observations 

were recorded at 160 sampling locations from 1975 – 1998 (NPS 1999). These data are available for 

review but no summary or compliance analysis was performed on this measure. Only one 

temperature observation was reported from the monitoring station inside the park (SAAN 0070) a 

reading of 19.4°C (67°F) in January 1976.

Meiman (2012) reports that during the summer months, when flow is naturally low and air 

temperatures reach their highest, water temperature readings have exceeded the TCEQ standards. On 

several occasions since 1999, temperature readings have exceeded the TCEQ standard of 32.2°C 

(Figure 37) at three different sampling locations (#12987, #17006, SJSR) (Meiman 2012).

Figure 37. Water temperature readings (Received from Joe Meiman, February 2015).

Total Dissolved Solids

Total dissolved solids, as measured by specific conductance (SpC), is also a highly variable measure 

in the San Antonio River at SAAN (Meiman 2012). SpC has a naturally inverse relationship with 

stream flow. Barring anthropogenic influence, as flow increases the volume of water the in relation to 

the portion of dissolved solids increases thereby decreasing the overall SpC. Lower flow volumes are 

associated with higher SpC measurements.
161

The TCEQ standard for TDS is ≤750 mg/L. While no federal standard exists for SpC, it is being used 

to estimate TDS. As such, NPS (1999) did not analyze the level of compliance for this measure. 

15,835 SpC observations were recorded at 236 sampling locations from 1975 – 1998 in the SAAN 

study area (NPS 1999). These data are available for review but no summary or compliance analysis 

was performed. Only one specific conductance observation of 1050 μS/cm in January 1976 was 

reported from inside the park (NPS 1999).

Meiman (2012) reports several unusually high SpC measurements at site #20350 (Figure 38). This 

site is located on Picosa Creek and routinely experiences low or stagnant flow. This fact, coupled 

with the presence of a large dairy operation nearby, may account for these unusual measurements. 

Picosa Creek is a seasonal tributary to the San Antonio River at the Rancho de las Cabras Unit.

Figure 38. Specific conductance in SAAN (Received from Joe Meiman, February 2015).

Dissolved Oxygen

NPS (1999) reported 11,303 DO observations from 1975-1998 at a total of 108 stations in the SAAN 

study area. DO during this time period did not meet the EPA cold-water (1 day) standard value of 4 

mg/L on 1,092 occasions or 10% of the time. The one DO observation within the park (January 

1976) was 8.5 mg/L (NPS 1999).

As shown in Figure 39, six of the nine sampling locations have recorded readings below the state 

instantaneous DO standard of 5 mg/L with four of the nine sampling locations dropping below the 

standard with some regularity. None of these low DO sampling sites were located on the main stem 

of the San Antonio River. Meiman (2012) notes that two of these locations are acequias and do not 

undergo the aeration process of a normal stream. Another location (Piedras Creek) frequently 

experiences low flow during the summer months which often results in stagnant, warm water 
162

(Meiman 2012). And the final location was on Picosa Creek, which may be unnaturally impacted by 

local dairy farming practices (Meiman 2012).

Figure 39. Dissolved oxygen data for SAAN (Received from Joe Meiman, February 2015).

pH

NPS (1999) documented 8,190 pH (field recordings) observations from 1975-1998 at a total of 141 

stations and 10,844 pH (lab results) during that same time period from 188 stations in the SAAN 

study area. pH as recorded in this document exceeded the EPA standard value of 6.5 – 9 on 284 

occasions for an exceedance probability of 1%. The single pH observation at SAAN 0070 made in 

January 1976 was 6.6 (NPS 1999).

According to Meiman (2012), the San Antonio River is naturally alkaline. The lowest pH values 

recorded were on a tributary close to the Rancho de las Cabras, which is to be expected as no 

limestone bedrock is exposed in that watershed (Meiman 2012). Two sampling locations (SARA 

12897 and SARA 12899) recorded some pH values above 9, which exceeds the state reference 

conditions (Figure 40; Meiman 2012). No reason for this exceedance is known at this time (Meiman 

2012).

Prevalence of Coliform Bacteria

Total coliform bacteria exceeded the state standard in 81% of the samples in the SAAN study area 

between 1973 and 1998 (NPS 1999). The NPS (1999) report indicates 6,785 total observations at 140 

sampling locations. One total coliform measurement of 2,600 CFU/100 ml and a fecal coliform 

measurement of 430 CFU/100 ml were reported from the park in 1976 (NPS 1999). These values 

exceed water quality criteria.
163

Figure 40. pH readings from SAAN, 2000-2012 (Received from Joe Meiman, February 2015).

Meiman (2012) reports that the urban stretch of the San Antonio River (from Mission Concepción to 

Mission Espada) is on the Texas 303(d) list for non-attainment due to bacteria (E. coli). While this 

report does not contain data on bacteria levels, he comments that “A river that is draining a city’s 

population of 1.3 million, and which is nearly 100 percent recharged by reuse water during the 

summer months, obviously has water quality issues...Without reuse water, the San Antonio River 

would not flow during most summer months and during drought” (Meiman 2012, p. 41). 

Prevalence of Nutrients (phosphates, nitrates)

Total phosphorous was measured 3,333 times between 1975 and 1998 from 123 sampling locations 

(NPS 1999). No EPA or state limits have been set for this nutrient, so no summary or compliance 

analysis was reported in the NPS (1999) document. No phosphorous observations were reported from 

the park during this time. 

Meiman (2012) reports that phosphorous measurements in SAAN are typically high and coincide 

with elevated nitrogen measurements. These elevated measures are most likely caused by the urban 

environment surrounding the SAAN locations. While there are no EPA or state reference conditions 

for phosphorous, the state has set a “screening level” of 0.69 for mg/L. While four of nine sampling 

locations exceed the state screening level for phosphorous, only two of the nine sampling locations 

exceed that in multiple sample years (Figure 41).
164

Figure 41. Total phosphorous levels in SAAN (Received from Joe Meiman, February 2015).

Total nitrogen was measured 391 times between 1975 and 1984 from 19 sampling locations (NPS 

1999). No EPA or state limits have been set for this nutrient, so no summary or compliance analysis 

was reported in the NPS (1999) document. No nitrogen observations were reported from the park 

during this time.

Total nitrate nitrogen was measured 10,650 times between 1975 and 1984 from 162 sampling 

locations (NPS 1999). Total nitrate plus nitrite was measured 1,480 times between 1975 and 1984 

from 81 sampling locations. Lastly, Total Kjeldahl nitrogen was measured 1,871 times between 1975 

and 1984 from 102 sampling locations. No EPA or state limits have been set for these nutrients, so 

no summary or compliance analysis was reported in NPS (1999).

Meiman (2012) reports that nitrate levels in the San Antonio River are notoriously high and are 

attributable to the intense urban environment surrounding SAAN (Figure 42). These elevated 

nitrogen loads are most likely the result of the recycled wastewater introduced into the river. While 

there is no EPA or state reference condition for nitrate, the state has set a “screening level” of 1.95 

mg/L. Nitrate levels in the San Antonio River appear to increase when the elevation of the Edwards 

Aquifer water table declines (NPS 2015). When the water table drops, headwater springs that feed 

the river dry up, and the contribution of supplemental recycled wastewater (higher in nitrates) 

increases (NPS 2015). This is shown in Figure 43, which relates nitrate concentrations to the water 

table elevation at the Edwards Aquifer Authority’s monitoring well J17. 
165

Figure 42. Nitrate concentrations (Received from Joe Meiman, February 2015).

Figure 43. Nitrate concentrations and monitoring well elevation (Received from Joe Meiman, February 

2015).
166

EPA or state reference criteria for nitrite do not exist. In Meiman (2012), only two of the nine 

sampling locations exhibited high nitrite levels (Figure 44). One of these sites is in an acequia, and is 

not representative of the main channel of the San Antonio River (Meiman 2012). 

Figure 44. Nitrite levels in SAAN (Received from Joe Meiman, February 2015).

EPA or state reference criteria for total Kjeldahl nitrogen (TKN) do not exist. The only extremely 

high reading for TKN in Meiman (2012) was from the same acequia that was high in nitrite and is 

not representative of the main channel of the San Antonio River (Figure 45) (Meiman 2012).

Prevalence of Sulfate

According to NPS (1999), total sulfate was sampled a total of 13,410 times at 232 different sampling 

locations from 1963 to 1998. Total sulfate was found to exceed the EPA reference criteria in 6% of 

the samples. A single sulfate observation of 22 mg/L was reported from in the park in 1976 (NPS 

1999).

Sulfate levels in the Meiman (2012) report were below the state standard of 150 mg/L in all but three 

of the samples (Figure 46). All three samples were from the same location in a tributary to the main 

channel (Piedras Creek) and were associated with times of very low flow (Meiman 2012). 
167

Figure 45. Total Kjeldahl nitrogen (TKN) (Received from Joe Meiman, February 2015).

Figure 46. Total sulfate in SAAN (Received from Joe Meiman, February 2015).
168

Prevalence of Chloride

Total chloride was sampled 14,367 times between 1955 and 1998 (NPS 1999). Total chloride was 

found to exceed the EPA reference criteria in 1% of the samples. The only measurement of chloride 

from in the park was 28 mg/L in 1976 (NPS 1999).

According to Figure 47, chloride was below the state standard of 150 mg/L in all but eight of the 

samples. Four of the samples were from the same location in a tributary to the main channel (Piedras 

Creek) and were associated with times of very low flow. 

Figure 47. Chloride levels within SAAN (Received from Joe Meiman, February 2015).

Total Suspended Solids

Total suspended solids (TSS), as estimated by turbidity (measured in Jackson Candle Units), was 

recorded in the NPS (1999) report. Turbidity data were collected on 318 occasions from 1985 

through 1998. Forty percent of these observations exceeded the EPA water quality criteria (NPS 

1999). Turbidity (Hach Turbidimeter) was measured 2,291 times and was found to exceed the EPA 

water quality criteria 29% of the time (NPS 1999). Neither TSS nor turbidity were measured inside 

the park during the NPS (1999) study period. 

Meiman (2012) also did not address TSS as a measured parameter. Meiman (2012) did report that as

part of SARA’s monitoring program, five locations in and around SAAN have monitored TSS, along 

with several other parameters, since 1999. Likely due to the lack of state or federal criteria for TSS,

this water quality parameter was not included in the Meiman (2012) report.
169

Threats and Stressor Factors

The densely urban character of the land surrounding SAAN is the primary source of threats to the 

water quality in the parks. With an ever increasing population currently at 1.4 million (USCB 2015) 

and a growing business economy, the threat to water quality will likely only increase. Continued 

urbanization of the surrounding landscape could lead to more impervious surface areas in the 

watersheds, which could in turn lead to increased runoff at increased temperatures. The rapid 

changes in land use are a concern and could contribute to both point and non-point sources of 

contaminants.

Recycled wastewater is also considered a stressor to water quality in SAAN. During the dry months 

of summer nearly 100% of water flowing within the San Antonio River (in the area of the Missions 

Unit) consists of recycled wastewater. The quality of this water is obviously a significant concern to 

SAAN. While the river is in non-attainment status for bacteria (E. coli) and listed as impaired for fish 

habitat due to this recycled water, it must rely on this source of water or go dry (Meiman 2012). The 

quality of the recycled water is known and tested routinely in order to minimize the risk of severely 

degrading the water quality.

At certain times of year and during drought, up to 100% of the water flow in the San Antonio River’s 

urban reach is composed of recycled waste water; it is important to understand the water quality 

characteristics associated with this water. High levels of conductivity, nitrates, ammonia, and 

phosphate are indicative of recycled waste water (Meiman 2012). Table 53 is a comparison of the 

natural source water for the San Antonio River, the Edwards Aquifer, and the recycled wastewater.

Table 53. Typical water quality from the Edwards Aquifer and San Antonio recycled water. Values that 

routinely exceeded state screening levels are in bold (Meiman 2012).

Component Units

Edwards 

Aquifer

Recycled 

Water

pH pH 7.2 7.4

Calcium as CaCO3 mg/l 205 225

Magnesium as CaCO3 mg/l 58 75

M-Alkalinity as CaCO3 mg/l 228 215

Conductivity μS/cm 460 1,000

Silica as SiO2 mg/l 12 14

Chlorides as Cl mg/l 25 117

Sulfates as SO4 mg/l 26 53

Iron as Fe mg/l <0.2 0.05

Nitrate as NO3 mg/l <1.0 31–71

Nitrite as NO2 mg/l 0.0 0.0–1.2

Ammonia as NH3 mg/l 0.0 1.1–4.2

Total Phosphate as PO4 mg/l 0.2 4–11
170

Table 53 (continued). Typical water quality from the Edwards Aquifer and San Antonio recycled water. 

Values that routinely exceeded state screening levels are in bold (Meiman 2012).

Component Units

Edwards 

Aquifer

Recycled 

Water

Organics as BOD mg/l 0.0 2

Total Suspended Solids mg/l <5 0.5–1.0

Total Chlorine as Cl2 mg/l <1.0 1.0–1.5

In the rural area of the Rancho Unit, it is not urbanization that is a potential threat as much as the 

agricultural nature of the area. Common threats in this area include grazing of livestock, conversion 

of riparian areas to pasture or crop land, as well as the application of fertilizers, pesticides, and 

disposal of animal wastes and byproducts.

Flooding is an ongoing concern for SAAN. Flooding can drastically alter the course of the water 

channel as well as bring in potentially harmful quantities of nutrients and pollutants into the stream. 

The arid climate in Texas is often deluged with excessive rainfall at different times of the year. 

Storms are common in the spring and fall as patterns of air movement change with the seasons. The 

city of San Antonio and SAAN are situated directly south of a geologic feature known as the 

Balcones Escarpment (Figure 48). The Balcones Escarpment is a geologic uplift across central Texas 

with an elevation increase varying from 30 m – 150 m (100 ft – 500 ft) (Caran and Baker 1986). As 

the warm, moist air from the Gulf of Mexico moves northward and inland, heavy rainfalls often 

occur along the Balcones Escarpment (Caran and Baker 1986). The increase in elevation at the 

escarpment causes the moisture laden air to rise abruptly and then drop its cargo of moisture on the 

region as precipitation. 

Figure 48. Balcones Escarpment geologic uplift indicated in red letters.
171

Just as rainfall events around SAAN are often unpredictable and intense, the other extreme of 

drought is present as well. Drought has a long history in Texas and at present, the state is in one of its 

worst droughts in history (Figure 49). Threats from drought associated with water quality include 

decreased surface flow; increased concentration of contaminants, sediments and salts; decreased 

water resources available from aquifers; and increased wildfire potential.

Figure 49. Palmer Drought Severity Index for Texas (USDOC 2014).

Data Needs/Gaps

No long term water quality studies have been completed within SAAN. Meiman (2012) 

acknowledges the GULN’s intention to implement long term monitoring and indicates the report 

itself is part of that endeavor. 

Large amounts of data exist and have been assembled in the NPS (1999) report. However, analysis 

including the TCEQ standards is lacking. The data are perhaps too broad, as a 4.8 km (3 mi) up river 

area and a 1.6 km (1 mi) down river area were included in the study. Considering that much of the 

year the primary source of water in the river is recycled waste water, a smaller study area may more 

accurately reflect conditions within SAAN. A recompilation of the data from the NPS (1999) report, 

with a more limited geographic area, as well as any new data, and focusing on EPA as well as TCEQ 

standards might yield a better picture of the water quality in SAAN.

-7

-5

-3

-1

1

3

5

7

Year

196619671968196919711972197319741976197719781979198119821983198419861987198819891991199219931994199619971998199920012002200320042006200720082009201120122013

Texas Statewide Palmer Drought Severity Index (PDSI)

January 1965 - August 2014

PDSI
172

Overall Condition

Water Temperature

The project team defined the Significance Level for water temperature as a 2. Meiman (2012) 

evaluated water temperature over the last 12 years and concluded that, due to the nature of the 

recycled water and the lack of flow from the source aquifer during summer months, temperatures 

were as expected. Only seven measurements exceeded the state standard during the reported time 

period and these were identified as exceptions due to drought conditions (Meiman 2012). Therefore, 

water temperature is of low concern (Condition Level = 1).

Total Dissolved Solids (as estimated by specific conductance)

The Significance Level for specific conductance was also defined as a 2. Total dissolved solids (TDS) 

were not measured directly but were estimated by the measurement of specific conductance (SpC). 

The value of TDS is estimated by multiplying SpC x 0.65 (Joe Meiman, NPS Hydrologist, written 

communication, 14 October 2014). Using this formula to convert the Texas TDS standard to SpC 

measurements, yields approximately ≤1,154 mg/l (SpC) to be the equivalent of the TCEQ standard of 

≤ 750 mg/l for TDS. Based on this estimate, Figure 49 illustrates that while exceptions did occur, the 

vast majority of SpC measurements were below the TCEQ standard. Using this estimation method, 

TDS is currently of low concern (Condition Level = 1).

Dissolved Oxygen

The project team defined the Significance Level for dissolved oxygen as a 3. The TCEQ standard is a 

DO value ≥5.0 mg/l. The only exceedances recorded within SAAN from 2007 to 2011 occurred at 

sampling locations AEAE and PCPC (Meiman 2012). AEAE is the Acequia de Espada, which is not 

a natural stream channel and as such does not experience normal aeration activity. PCPC is a site on 

a tributary where low flow is common. Having satisfactory explanations for these low DO readings 

allows the DO data as a whole to be viewed as meeting the TCEQ standard. As a result, dissolved 

oxygen is currently of no concern (Condition Level = 0).

pH

The Significance Level for pH was defined as a 2. Meiman (2012) reports that the TCEQ pH standard 

has only been exceeded four times in a period of 12 years. Meiman (2012) does caution, however, 

that many of the sites have less than 25 samples and must be interpreted with discretion. pH, 

therefore, is of no concern (Condition Level = 0).

Coliform Bacteria

The project team defined the Significance Level for coliform bacteria as a 3. The NPS (1999) 

baseline inventory reported that bacteria (E. coli) exceeded the state standard in 81% of the 6,735 

measured observations. The presence of E. coli, most likely via the recycled wastewater, is extensive 

but expected. Coliform bacteria are currently of high concern (Condition Level = 3).

Total Suspended Solids (sediment)

The project team defined the Significance Level for total suspended sediment (TSS) as a 3. While 

TSS was not measured directly, turbidity measurements were recorded in the NPS (1999) study. 

Turbidity and TSS do not have a direct correlation but turbidity has been used to approximate TSS. 
173

Cautiously using the NPS (1999) results, turbidity (as measured by Jackson Candle Units) exceeded 

the EPA water quality criteria in 40% of the tests (NPS 1999). Turbidity (as measured by Hach 

Turbidimeter) was found to exceed the EPA water quality criteria in 29% of the tests. However, these 

data are over a decade old and no more recent data are available from NPS or SARA sampling. Since 

total suspended solids do not seem to be recognized as a major issue by park or river managers, this 

measure is considered of low concern (Condition Level = 1).

Nutrients

The project team defined the Significance Level for nutrients as a 3. Nutrient levels are notoriously 

high (Meiman 2012) due to the intense urban environment and the input of recycled wastewater into 

the river. Many of the phosphorous and nitrate observations reported in Meiman (2012) exceeded the 

TCEQ “screening level”. Therefore, nutrients are of high concern (Condition Level = 3).

Sulfate

The project team defined the Significance Level for sulfate as a 2. Sulfate exceeded EPA standards in 

only 6% of the observations in the NPS (1999) document. Meiman (2012) also identified sulfates as 

exceeding standards only rarely. As a result, sulfates are of low concern (Condition Level = 1).

Chloride

The project team defined the Significance Level for chloride as a 2. Chloride exceeded EPA 

standards in only 1% of the observations in the NPS (1999) document. Meiman (2012) also identified 

chloride as exceeding standards only rarely. Therefore, chloride is of low concern (Condition Level = 

1).

Weighted Condition Score

The Weighted Condition Score for water quality in SAAN is 0.44. This score indicates that water 

quality, while stable in recent years, still warrants moderate concern. 
174

Water Quality

Measures

Significance 

Level

Condition 

Level WCS = 0.44

Water Temperature 2 1

TDS (SpC) 2 1

Dissolved Oxygen 3 0

pH 2 0

Coliform Bacteria 3 3

TSS (Turbidity) 3 1

Nutrients 3 3

Sulfate 2 1

Chloride 2 1

4.10.6 Sources of Expertise

Joe Meiman, NPS Hydrologist, Gulf Coast Region

4.10.7 Literature Cited

Caran, C. S., and V. R. Baker. Flooding along the Balcones Escarpment, Central Texas, Geological 

Society of America. http://www.lib.utexas.edu/geo/balcones_escarpment/pages1-14.html

(accessed 14 October 2014).

Environmental Protection Agency (EPA). 2012. Total solids. 

http://water.epa.gov/type/rsl/monitoring/vms58.cfm (accessed 11 July 2014).

Lenntech. 2011. Sulfates. Water treatment solutions. http://www.lenntech.com/sulfates.htm (accessed 

11 July 2014).
175

McDaniel, L. 2012. Understanding Iowa’s water quality standards. Iowa DNR. 

http://www.iowadnr.gov/portals/idnr/uploads/water/standards/ws_fact.pdf (accessed 11 July 

2014).

Meiman, J. 2012. Gulf Coast Network water quality report: Status of water quality of San Antonio 

Missions National Historical Park. Natural Resource Technical Report NPS/GULN/NRTR—

2012/588. National Park Service, Fort Collins, Colorado.

Michaud, J. P. 1994. Measuring total suspended solids and turbidity in lakes and streams. A Citizen's 

Guide to Understanding and Monitoring Lakes and Streams. State of Washington, Department of 

Ecology. http://www.ecy.wa.gov/programs/wq/plants/management/joysmanual/turbidity.html

(accessed 1 January 2015). 

National Park Service (NPS). 1999. Baseline water quality data inventory and analysis; San Antonio 

Missions National Historical Park. Technical Report NPS/NRWRD/NRTR—99/222. National 

Park Service, Fort Collins, Colorado.

National Park Service (NPS). 2012. Gulf Coast Network Resource Brief: San Antonio Missions 

National Historical Park, water quality. National Park Service, Gulf Coast Network, Lafayette, 

Louisiana.

National Park Service (NPS). 2015. Gulf Coast Network Resource Brief: San Antonio Missions 

National Historical Park, water quality summary calendar year 2014. National Park Service, Gulf 

Coast Network, Lafayette, Louisiana.

Robertson, M. J., D. A. Scruton, R. S. Gregory, and K. D. Clarke 2006. Effect of suspended sediment 

on freshwater fish and fish habitat. Canadian Technical Report of Fisheries and Aquatic Sciences 

2644. Fisheries and Oceans Canada, St. John’s, Newfoundland and Labrador.

Safe Drinking Water Foundation (SDWF). 2014. TDS and pH. 

http://www.safewater.org/PDFS/resourcesknowthefacts/TDS_AND%20_pH.pdf (accessed 11 

July 2014).

Texas Commission on Environmental Quality (TCEQ). 2014. Texas surface water quality standards. 

https://www.tceq.texas.gov/waterquality/standards/2014standards.html/#EPA Review (accessed 

11 July 2014).

Texas State Historical Association (TSHA). 2014. Acequias. 

http://www.tshaonline.org/handbook/online/articles/ruasg (accessed 8 October 2014).

United States Census Bureau (USCB). 2015. State and county quick facts. 

http://quickfacts.census.gov/qfd/states/48/4865000.html (accessed 20 February 2015).

U.S. Department of Commerce (USDOC). National Oceanic and Atmospheric Administration Earth 

System Research Laboratory | Physical Sciences Division http://www.esrl.noaa.gov/psd/cgibin/data/timeseries/timeseries1.pl (accessed 9 October 2014).
176

U.S. Geological Survey (USGS). 1997. Mineral resources in deserts.

http://pubs.usgs.gov/gip/deserts/minerals/ (accessed 11 July 2014).

U.S. Geological Survey (USGS). 2010. Common water measurements: USGS water science for 

schools. U.S. Geological Survey. Information from “A Primer on Water Quality” by Swanson, H. 

A., and H. L. Baldwin, U.S. Geological Survey, 1965. 

http://ga.water.usgs.gov/edu/characteristics.html (accessed 11 July 2014).

U.S. Geological Survey (USGS). 2011. Bacteria in water. http://ga.water.usgs.gov/edu/bacteria.html

(accessed 11 July 2014).

U.S. Geological Survey (USGS). 2013a. Effects of nutrient enrichment on stream ecosystems. 

http://wa.water.usgs.gov/neet/index.html (accessed 11 July 2014). 

U.S. Geological Survey (USGS). 2013b. The effects of urbanization on water quality. 

http://ga.water.usgs.gov/edu/urbanmet.html (accessed 11 July 2014). 
177

4.11 Air Quality

4.11.1 Description

Air pollution can significantly affect natural 

resources and their associated ecological 

processes. Consequently, air quality in parks 

and wilderness areas is protected and regulated 

through the 1916 Organic Act, the Clean Air 

Act of 1977 (CAA) and the CAA’s subsequent 

amendments. The CAA defines two distinct 

categories of protection for natural areas, Class 

I and Class II airsheds. Class I airsheds receive 

the highest level of air quality protection as 

offered through the CAA; only a small amount 

of additional air pollution is permitted in the 

airshed above baseline levels (EPA 2013a). For 

Class II airsheds, the increment ceilings for 

additional air pollution above baseline levels are slightly greater than for Class I areas and allow for 

moderate development (EPA 2013a). SAAN is designated as a Class II airshed.

Parks designated as Class I and II airsheds typically use the EPA’s National Ambient Air Quality 

Standards (NAAQS) for criteria air pollutants as the ceiling standards for allowable levels of air 

pollution. The EPA believes these standards, if not exceeded, protect human health and the health of 

natural resources (EPA 2013a). The CAA also establishes that current visibility impairment in these 

areas must be remedied and future impairment prevented (EPA 2013a). However, the EPA 

acknowledges that the current NAAQS are not necessarily protective of ecosystems and is currently 

developing secondary NAAQS for ozone, nitrogen, and sulfur compounds to protect sensitive plants, 

lakes, streams, and soils (EPA 2010, EPA 2011a). To comply with CAA and NPS Organic Act 

mandates, the NPS established a monitoring program that measures air quality trends in many park 

units for key air quality indicators, including atmospheric deposition, ozone, and visibility (NPS 

2008).

4.11.2 Measures

 Nitrogen deposition

 Sulfate deposition

 Ozone concentration

 Particulate matter (PM2.5)

 Visibility

Atmospheric Deposition of Nitrogen and Sulfur

Nitrogen and sulfur oxides are emitted into the atmosphere primarily through the burning of fossil 

fuels, industrial processes, and agricultural activities (EPA 2012a). While in the atmosphere, these 

emissions form compounds that may be transported long distances and settle out of the atmosphere in 

Photo 22. Gas flaring at the Calumet Refinery next 

to Acequia Park, south of Espada Dam (Photo by

Shannon Amberg, SMUMN GSS, 2013)
178

the form of pollutants such as particulate matter (e.g., sulfates, nitrates, ammonium) or gases (e.g., 

nitrogen dioxide, sulfur dioxide, nitric acid, ammonia) (EPA 2012a, NPS 2008). Atmospheric 

deposition can be in wet (i.e., pollutants dissolved in atmospheric moisture and deposited in rain, 

snow, low clouds, or fog) or dry (i.e., particles or gases that settle on dry surfaces as with windblown 

dusts) form (EPA 2012a). Deposition of sulfur and nitrogen can have significant effects on 

ecosystems, including acidification of water and soils, excess fertilization or increased 

eutrophication, changes in the chemical and physical characteristics of water and soils, and 

accumulation of toxins in soils, water, and vegetation (NPS 2008, reviewed in Sullivan et al. 2011a 

and 2011b). The native vegetation in the semi-arid plant communities in SAAN is considered 

sensitive to excess nitrogen and acidic deposition (Sullivan et al. 2011c, 2011d).

Ozone

Ozone occurs naturally in the earth’s atmosphere where, in the upper atmosphere, it protects the 

earth’s surface against ultraviolet radiation (EPA 2012a). However, it also occurs at the ground level 

(i.e., ground-level ozone) where it is created by a chemical reaction between nitrogen oxides and 

volatile organic compounds (VOCs) in the presence of heat and sunlight (NPS 2008). Ozone is also 

one of the most widespread pollutants affecting vegetation and human health in the U.S. (NPS 2008). 

Considered phytotoxic, ozone can cause significant foliar injury and growth effects for sensitive 

plants in natural ecosystems (EPA 2012c, NPS 2008). Specific effects include reduced 

photosynthesis, premature leaf loss, and reduced biomass, and prolonged exposure can increase 

vulnerability to insects and diseases or other environmental stressors (NPS 2008). At high 

concentrations, ozone can aggravate respiratory and cardiovascular diseases in humans, reduce lung 

function, cause acute respiratory problems, and increase susceptibility to respiratory infections (EPA 

2012a, EPA 2012d, EPA 2013b); this could be a concern for visitors and staff engaging in aerobic

activities in the park, such as walking the trails.

Particulate Matter (PM) and Visibility

Particulate matter (PM) is a complex mixture of extremely small particles and liquid droplets 

suspended in the atmosphere. Fine particles (PM2.5) are those smaller than 2.5 micrometers in 

diameter (EPA 2009). Particulate matter largely consists of acids (such as nitrates and sulfates), 

organic chemicals, metals, and soil or dust particles (EPA 2009, EPA 2013c). Fine particles are a 

major cause of reduced visibility (haze) in many national parks and wildernesses (EPA 2012a). PM2.5

can be directly emitted from sources such as forest fires, or they can form when gases emitted from 

power plants, industries, and/or vehicles react with air (EPA 2009, EPA 2012a). Particulate matter 

either absorbs or scatters light. As a result, the clarity, color, and distance that humans can see 

decreases. Water in the atmosphere causes particles like nitrates and sulfates to expand, increasing 

their light-scattering efficiency (EPA 2012a). PM2.5 is also a concern for human health as these 

particles can easily pass through the throat and nose and enter the lungs (EPA 2009, EPA 2012a, 

EPA 2013c). Short-term exposure to these particles can cause shortness of breath, fatigue, and lung 

irritation (EPA 2009, EPA 2012a, EPA 2013c).
179

4.11.3 Reference Conditions/Values

The NPS Air Resources Division (ARD) developed an approach for rating air quality conditions in 

national parks, based on the current NAAQS, ecosystem thresholds, and visibility improvement goals 

(Table 54) (NPS 2011). Assessment of current condition of nitrogen and sulfur atmospheric 

deposition is based on wet (rain and snow) deposition. Ozone condition is based on the NAAQS 

standard of 75 parts per billion (ppb) (an annual fourth-highest daily maximum 8-hr concentration, 

averaged over 3 years). Visibility conditions are assessed in terms of a Haze Index, a measure of 

visibility (termed deciviews) that is derived from calculated light extinction and represents the 

minimal perceptible change in visibility to the human eye (NPS 2011). Finally, NPS ARD 

recommends the following values for determining air quality condition (Table 54). The “good 

condition” metrics may be considered the reference condition for SAAN.

Table 54. National Park Service Air Resources Division air quality index values (NPS 2011).

Condition

Ozone 

concentration

(ppb)

Wet Deposition 

of N or S 

(kg/ha/yr)

Visibility

(dv*)

Significant Concern ≥76 >3 >8

Moderate Condition 61-75 1-3 2-8

Good Condition ≤60 <1 <2

*a unit of visibility proportional to the logarithm of the atmospheric extinction (TCEQ 2012); one 

deciview represents the minimal perceptible change in visibility to the human eye.

4.11.4 Data and Methods

Monitoring in the Park

There is no active on-site monitoring of air quality parameters at SAAN (Segura et al. 2007).

NPS Data Resources

Although data on air quality parameters are not actively collected within park boundaries, data 

collected at several regional monitoring stations for various parameters can be used to estimate air 

quality conditions in SAAN. NPS ARD provides estimates of ozone, wet deposition of nitrogen and 

sulfur, and visibility that are based on data interpolations from all air quality monitoring stations 

operated by the NPS, the EPA, various states and other entities, averaged over the most recent five 

years (e.g., 2008-2012). These estimates are available from the Explore Air website (NPS 2014) and 

are used to evaluate air quality conditions. On-site or nearby data are needed for a statistically valid 

trends analysis, while a 5-year average interpolated estimate is preferred for the condition 

assessment.

Other Air Quality Data Resources

The National Atmospheric Deposition Program–National Trends Network (NADP) database 

provides annual average summary data for nitrogen and sulfur concentration and deposition across 

Texas. The nearest NADP monitoring site (TX16) is located in Edwards County, Texas, 

approximately 130 km (80 mi) northwest of SAAN. The site has actively collected data from 1984 
180

through 2012. However, this distance from SAAN makes it difficult to extrapolate conditions 

accurately; thus, data from this monitoring station were not considered in this assessment.

The EPA Air Trends Database provides annual average summary data for ozone concentrations near 

SAAN. Ozone concentrations are collected at the Pecan Valley monitoring site (ID 48-029-0055), 

approximately 8 km (5 mi) northeast of the northern portion of the park (Figure 50). Data are 

gathered by Dios Dado Environmental Ltd and reported to the TCEQ. Data are available from 1999 

through August 2014 (TCEQ 2014a). Another monitoring location with long-term data is Calaveras 

Lake (ID 48-029-0059), located approximately 16 km (10 mi) east of the SAAN complex of 

properties and 23 km (14 mi) northwest of the town of Floresville (near the Rancho Unit; Figure 50). 

The site is operated by the TCEQ and has collected data from May 1998 through March 2014 (EPA 

2014a). The Pecan Valley and Calaveras Lake monitoring sites also collect data on particulate matter 

concentrations (PM2.5). Data collection began in 2007 at Pecan Valley and in 2008 at Calaveras Lake

(TCEQ 2014b). Results from monitors located within 16 km (10 mi) from parks are generally 

considered to be representative of park conditions (Ellen Porter, NPS Air Resources Division Air 

Quality Specialist, phone communication, 25 October 2012). Data recorded at monitors beyond this 

distance from parks may represent regional conditions, but may not be representative of actual park 

conditions.

The Clean Air Status and Trends Network (CASTNet) provides summaries of the composition of 

nitrogen and sulfur deposition in various regions around the U.S. Similarly, the Interagency 

Monitoring of Protected Visual Environments Program (IMPROVE) actively monitors visibility 

conditions in Class I airsheds across the U.S. However, the nearest IMPROVE monitoring sites are 

located in Big Bend National Park, approximately 482 km (300 mi) west of SAAN, and in Houston, 

Texas, approximately 322 km (200 mi) east of SAAN. This distance and the variations in terrain 

make it difficult to extrapolate data accurately; thus, data from these monitoring stations were not 

considered in this assessment.

Special Air Quality Studies

Sullivan et al. (2011a) assessed the relative sensitivity of national parks to the potential effects of 

acidification caused by acidic atmospheric deposition from nitrogen and sulfur compounds. The 

relative risk for each park was assessed by examining three variables: the level of exposure to 

emissions and deposition of nitrogen and sulfur; inherent sensitivity of park ecosystems to acidifying 

compounds (N and/or S) from deposition; and level of mandated park protection against air pollution 

degradation (i.e., wilderness and Class I). The outcome was an overall risk assessment that estimates 

the relative risk of acidification impacts to park resources from atmospheric deposition of nitrogen 

and sulfur (Sullivan et al. 2011a). Using the same approach, Sullivan et al. (2011b) assessed the 

sensitivity of national parks to the effects of nutrient enrichment by atmospheric deposition of 

nitrogen. The outcome was an overall risk assessment that estimates the relative risk to park 

resources of nutrient enrichment from increased nitrogen deposition.
181

Figure 50. Locations of ozone and PM monitoring stations relative to the two SAAN park units.
182

4.11.5 Current Condition and Trend

Atmospheric Deposition of Nitrogen and Sulfur

Five-year interpolated averages of total nitrogen (from nitrate and ammonium) wet deposition and 

total sulfur (from sulfate) wet deposition are used to estimate condition for deposition; using a 5-year 

average smoothes out annual variations in precipitation, such as heavy precipitation one year versus 

drought conditions in another. The current 5-year average (2008-2012) estimates total wet deposition 

of nitrogen in SAAN at 3.3 kg/ha/yr, while total wet deposition of sulfur is 2.7 kg/ha/yr (NPS 2014). 

Relative to the NPS ratings for air quality conditions (see Table 54 for ratings values), atmospheric 

deposition of nitrogen falls under the Significant Concern category while sulfur is in the Moderate 

Condition category. 

Relative risk of acidification and nutrient enrichment of ecosystems was assessed by examining 

exposure to nitrogen deposition and acidification, inherent sensitivity of park ecosystems, and 

mandates for park protection. Sullivan et al. (2011c) ranked SAAN as having moderate exposure to 

acidifying (nitrogen and sulfur) pollutants, low ecosystem sensitivity to acidification, and moderate 

park protection due to its Class II airshed status. The ranking of overall risk from acidification due to 

acid deposition was moderate relative to other parks (Sullivan et al. 2011c). In a separate 

examination, Sullivan et al. (2011d) used the same approach to assess the sensitivity of national parks 

to nutrient enrichment effects from atmospheric nitrogen deposition relative to other parks. SAAN 

was ranked as having moderate risk for nitrogen pollutant exposure, high ecosystem sensitivity, and 

moderate park protection mandates (Class II airshed). The ranking of overall risk of effects from 

nutrient enrichment from atmospheric nitrogen deposition was high relative to other parks (Sullivan 

et al. 2011d).

Ozone Concentration

The NAAQS standard for ground-level ozone is the benchmark for assessing current ozone 

conditions within park units. In 2008, the standard was strengthened from 80 ppb to 75 ppb, based on 

the annual fourth highest daily maximum 8-hour concentration, averaged over 3 years (EPA 2012b). 

The condition of ozone in NPS units is determined by calculating the 5-year average of the fourthhighest daily maximum of 8-hour average ozone concentrations measured at each monitor within an 

area over each year (NPS 2011). The current 5-year average (from 2008-2012) for SAAN indicates 

an average ground-level ozone concentration of 72.3 ppb (NPS 2014), which falls under the 

Moderate Condition category based on NPS guidelines (NPS 2013). 

Long-term data that characterize ozone concentrations within the park do not exist. However, ozone 

concentrations are monitored daily at the Pecan Valley and Calaveras Lake monitoring sites, 

approximately 8 km (5 mi) northeast and 16 km (10 mi) east of SAAN, respectively. Conditions in 

the northern, more urban sections of the park are likely closer to those at the Pecan Valley site, while 

conditions in the southern, suburban units may be similar to those at Calaveras Lake. The Rancho 

Unit is even further away from the city than the Calaveras Lake station, and therefore, ozone levels 

may be even lower at Rancho. Figure 51 illustrates the trend in annual fourth-highest daily maximum 

8-hour values from 1999 to 2014 at Pecan Valley; these are presented with both the old and revised 

national standards to provide perspective on acceptable versus potentially harmful ozone conditions 
183

in the region. Since 2008, the fourth-highest daily maximum 8-hour value has approached or 

exceeded the new standard of 75 ppb three times.

Figure 51. Annual 4th highest 8-hour maximum ozone (O3) concentrations (ppb) at the Pecan Valley 

monitoring station (site 48-029-0055), 1999-2014 (TCEQ 2014a). Note: this site is located in San Antonio, 

Texas, approximately 8 km (5 mi) northeast of SAAN. Prior to 2008, the NAAQS ozone standard was 0.08 

ppm (80 ppb) (shown in red); in March 2008, the standard was amended to 0.075 ppm (75 ppb) (shown in 

blue).

Figure 52 shows the trend in annual fourth-highest daily maximum 8-hour values from 1998 to 2013 

at Pecan Valley. Measurements within the last 7 years appear to be well within the updated NAAQS 

standard considered to be protective of human health.

40

50

60

70

80

90

100

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014

Ozone Concentration (ppb)

New National Standard

Old National Standard
184

Figure 52. Annual 4th highest 8-hour maximum ozone (O3) concentrations (ppb) at the Calaveras Lake 

monitoring station (site 48-029-0059), 1998-2013 (EPA 2014a). Note: this site is located southeast of San 

Antonio, Texas, approximately 16 km (10 mi) east of SAAN and northwest of Floresville (near the Rancho 

Unit). Prior to 2008, the NAAQS ozone standard was 0.08 ppm (80 ppb) (shown in red); in March 2008, 

the standard was amended to 0.075 ppm (75 ppb) (shown in blue).

Kohut (2004) assessed ozone concentrations in GULN and the risk of injury to plant species that are 

sensitive to sustained ozone exposure. Estimations by interpolation indicate that, from 1995-1999, 

ambient ozone concentrations around SAAN frequently exceeded 60 ppb each year and occasionally 

exceeded 80 ppb. Concentrations exceeded 100 ppb intermittently, although one year catalogued 30 

hours above this threshold; at these levels, it is possible for vegetation to sustain injury. Sensitive 

plant species begin to experience foliar injury when exposed to ozone concentrations of 80-120 

ppb/hour for extended periods of time (8 hours or more); however, the levels of exposure 

experienced in SAAN are not likely to cause foliar damage (Kohut 2004). Overall, the risk of foliar 

injury from ozone is moderate due to frequent exposures to ozone greater than 80 ppb and occasional 

exposure to concentrations of 100 ppb (Kohut 2004). American elder (Sambucus canadensis), 

American sycamore (Platanus occidentalis), and redbud (Cercis canadensis) are identified as plant 

species in SAAN that are sensitive to elevated ozone levels, and which may be used as bioindicators 

for extended periods of elevated ozone concentrations (Kohut 2004).

Particulate Matter (PM2.5)

The NAAQS standard for PM2.5 is a weighted annual mean of 15.0 μg/m3or 35 μg/m3in a 24-hour 

period over an average of 3 years (EPA 2012b). Particulate matter concentrations collected at the

Pecan Valley and Calaveras Lake monitoring sites are presented in Figure 53 and Figure 54, 

40

50

60

70

80

90

100

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Ozone Concentration (ppb)

New National Standard

Old National Standard
185

respectively. Weighted annual average PM2.5 concentrations in the SAAN region have been relatively 

stable since monitoring began at the sites, fluctuating between 7.75 and 9.5 μg/m3at Calaveras Lake, 

and 9.0 and 10.5 μg/m3at Pecan Valley. All measurements are well within the EPA standards for 

levels that are protective of human health; concentrations on the haziest days contribute to occasional 

impaired visibility in the park.

Figure 53. Annual particulate matter (PM2.5) concentrations (weighted annual mean) at Pecan Valley (site 

48-029-0055), 2007 - August 2014 (TCEQ 2014b). Note: this site is located in San Antonio, Texas, 

approximately 8 km (5 mi) northeast of SAAN.

0

5

10

15

20

25

30

2008 2009 2010 2011 2012 2013

Concentration (μg/m3

)

National Standard 
186

Figure 54. Annual particulate matter (PM2.5) concentrations (weighted annual mean) near SAAN, 2008-

2013 (EPA 2014a). Note: Calaveras Lake monitoring site (ID 48-029-0059) is located approximately 16 

km (10 mi) east of SAAN.

Visibility

Visibility impairment occurs when airborne particles and gases scatter and absorb light; the net effect 

is called “light extinction,” which is a reduction in the amount of light from a view that is returned to 

an observer (EPA 2003). In response to the mandates of the CAA of 1977, federal and regional 

organizations established IMPROVE in 1985 to aid in monitoring of visibility conditions in Class I 

airsheds. The goals of the program are to 1) establish current visibility conditions in Class I airsheds; 

2) identify pollutants and emission sources causing the existing visibility problems; and 3) document 

long-term trends in visibility (NPS 2010, NPS 2013). 

The most current 5-year average (2008-2012) estimates average visibility in SAAN to be 8.8 dv 

above average natural visibility conditions (NPS 2013, NPS 2014). This falls into the Significant

Concern category for NPS air quality condition assessment (NPS 2013). 

The clearest and haziest 20% of days each year are also examined for parks (NPS 2014), as these are 

the measures used by states and EPA to assess progress towards meeting the national visibility goal. 

Conditions measured near 0 dv are clear and provide excellent visibility, and as dv measurements 

increase, visibility conditions become hazier. The most current 5-year average (2008-2012) estimates 

visibility at SAAN at 8.6 dv on the 20% clearest days and 19.8 dv on the 20% haziest days (NPS 

2014). Even on the 20% clearest days, visibility still falls into the significant concern category.

Threats and Stressor Factors

Park managers have identified a number of threats and stressors to air quality in SAAN, including 

land use activities within and adjacent to the park (particularly emissions from development and gas 

0

5

10

15

20

25

30

2008 2009 2010 2011 2012 2013

Concentration (μg/m3

)

National Standard 
187

flaring from nearby refineries), vehicle emissions from nearby highway/roads (SAAN is an urban 

park), and smoke from grassland fires in and around the park.

Nitrogen deposition results from nitrogen oxides in vehicle emissions, power plants, and other 

combustion sources, and ammonia from agricultural activities and fires. In ecosystems adapted to 

naturally low amounts of nitrogen (such as semi-arid systems and grasslands), increased nitrogen 

deposition can alter plant communities and reduce diversity (Sullivan 2011b). Higher nitrogen levels 

favor certain plant species, like fast-growing invasive species, at the expense of native forbs and 

shrubs (Sullivan 2011b). Sulfur emissions and particulate matter often originate from such sources as 

coal-fired power plants, petroleum refining, and chemical processing operations, many of which are 

located in central, southern and coastal Texas, as well as northern Mexico. Prevailing seasonal winds 

may carry these emissions into SAAN.

Oil and gas development in the Eagle Ford Shale, which includes the southern portion of Wilson 

County (where the Rancho Unit is located), is a potential threat to the area’s air quality. Production 

and exploration produce nitrogen oxides and VOCs, which are precursors to ozone (AACOG 2013). 

A trend analysis conducted by the Alamo Area Council of Governments (AACOG) predicts that 

VOC emissions from the Eagle Ford Shale will double between 2012 and 2023 (AACOG 2013).

According to the EPA and IPCC, global climate change is expected to negatively affect air quality 

(EPA 2011b). Both ozone and particulate pollution are heavily influenced by weather shifts. The 

EPA projects that climate change could increase summertime average ground-level ozone 

concentrations in many areas by 2-8 ppb. It could also cause particulate pollution to increase in some 

regions and decrease in others (EPA 2011b).

Data Needs/Gaps 

Monitors located at Pecan Valley and Calaveras Lake provide data on particulate matter and ozone 

concentration as both daily and annual average summaries for the region; these monitors are near 

enough to SAAN to be considered representative of the conditions in the Missions Unit of the park. 

However, Calaveras Lake (23 km northwest of Floresville) may not be close enough to the Rancho 

Unit, which is south of Floresville, to accurately represent conditions there (see Figure 52). The 

nearest active NADP monitor that provides annual averages for nitrogen and sulfur deposition is 

located in Edwards County, Texas, approximately 130 km (80 mi) northwest of SAAN. Finally, the 

nearest CASTNet and IMPROVE sites, which monitor acid deposition and visibility respectively, are 

located in Big Bend National Park, approximately 482 km (300 mi) west of SAAN and in Houston, 

Texas, approximately 322 km (200 mi) east of SAAN. Monitoring of nitrogen and sulfur deposition 

and visibility in or near both units of the park would help managers better understand the local air 

quality conditions in and around SAAN.

Overall Condition

Nitrogen Deposition

The Significance Level for atmospheric deposition of nitrogen was defined as a 2. Current NPS 

interpolated averages for nitrogen deposition are considered to be of significant concern (NPS 2014) 

based on NPS criteria for rating air quality when factoring in the sensitivity of the ecosystem.
188

Likewise, Sullivan et al. (2011b, 2011d) rate SAAN as having moderate risk for pollutant exposure 

and high ecosystem sensitivity, with an overall high risk of nutrient enrichment relative to other 

parks. Deposition of nitrogen is of high concern in SAAN (Condition Level = 3).

Sulfate Deposition 

The Significance Level for atmospheric deposition of sulfate was defined as a 2. Current NPS 

interpolated averages for sulfate deposition are considered to be of moderate condition (NPS 2014) 

based on NPS criteria for rating air quality when factoring in the sensitivity of the ecosystem. 

Sullivan et al. (2011a, 2011c) rate SAAN as having moderate exposure to acidifying pollutants, low 

ecosystem sensitivity to acidification, and moderate park protection against pollution. The overall 

risk due to acid deposition was categorized as moderate relative to other parks. Deposition of sulfate 

is of moderate concern in SAAN (Condition Level = 2).

Ozone Concentration

The Significance Level for ozone concentration was defined as a 3. Current average ground-level 

ozone concentrations fall into the moderate condition category based on NPS criteria for rating air 

quality condition. Annual 4th highest 8-hour maximum concentrations (1998 through 2014) suggest a 

declining trend since the mid-2000s, but with fluctuations between 60 and 76 ppb at Pecan Valley 

and 65 and 72 ppb at Calaveras Lake in the last six years. All measurements at Calaveras Lake are 

within EPA standards protective of human health, while this standard has been matched or exceeded 

three times at Pecan Valley since 2008. Kohut (2004) suggests the risk of foliar injury from ozone is 

moderate for the park. However, it should be noted that the EPA is currently reviewing the NAAQS 

ground-level ozone standard and may suggest a stricter standard between 60-70 ppb (EPA 2014b). If 

a stricter standard is enacted, much of the SAAN region would be in “nonattainment” (i.e., not 

meeting the federal air quality standard). Therefore, the Condition Level for ozone concentration is a 

3, of high concern.

Particulate Matter Concentration (PM2.5)

The Significance Level for concentration of fine particulate matter (PM2.5) was defined as a 3. 

Average PM2.5 concentrations near SAAN have been relatively stable over the last 5 years and are 

well within the EPA standards for levels that are protective of human health. The Condition Level for 

PM2.5 is a 1, of low concern. 

Visibility

The Significance Level for visibility was defined as a 2. Current interpolated average visibility 

estimates for SAAN fall into the significant concern category based on NPS criteria. However, no 

data are collected at the park, and the nearest visibility monitor is over 482 km (300 miles) west of 

the park; this makes it difficult to determine average conditions or trends in visibility conditions in 

SAAN. The Condition Level for visibility could not be determined.

Weighted Condition Score

The Weighted Condition Score (WCS) for the air quality component is 0.73, indicating the condition 

warrants high concern; this condition is assigned with a moderate level of confidence. Air quality is 

considered a vital sign for SAAN and, although it is not monitored directly in the park, air quality 
189

information is interpolated from regional air monitors and parameters are estimated for SAAN on a 

yearly basis. No trend was determined based on limited long-term data for air quality in the region 

and at the park specifically. This condition designation is more representative of the Missions Unit of 

the park and may not fully reflect conditions at the Rancho Unit, which is further from air quality 

monitoring stations and from the urban area of San Antonio, where air quality is possibly less 

degraded.

Air Quality

Measures

Significance 

Level

Condition 

Level WCS = 0.73

Nitrogen Deposition 2 3

Sulfate Deposition 2 2

Ozone Concentration 3 3

Particulate Matter 3 1

Visibility 2 n/a

4.11.6 Sources of Expertise

Ellen Porter, Biologist, NPS Air Resources Division

Greg Mitchell, SAAN Natural Resources Program Manager

4.11.7 Literature Cited

Alamo Area Council of Governments (AACOG). 2013. Emissions trend analysis for the SanAntonio-New Braunfels MSA: 1999, 2002, 2006, 2012, 2018, and 2023. Alamo Area Council of 

Governments, San Antonio, Texas.

Environmental Protection Agency (EPA). 2003. Guidance for estimating natural visibility conditions 

under the Regional Haze Rule. EPA-454/B-03-005. Office of Air Quality Planning and 

Standards. Emissions, Monitoring and Analysis Division, Research Triangle Park, North 

Carolina.

Environmental Protection Agency (EPA). 2009. Air quality index: a guide to air quality and your 

health. EPA-456/F-09-002. Office of Air Quality Planning and Standards, Outreach and 

Information Division, Research Triangle Park, North Carolina.
190

Environmental Protection Agency (EPA). 2010. Approval and promulgation of implementation plans 

and designation of areas for air quality planning purposes: Beaumont/Port Arthur ozone 

nonattainment area – redesignation to attainment for the 1997 8-hour ozone standard and 

determination of attainment for the 1-hour ozone standard. EPA-R06-OAR-2008-0932. Federal 

Register doc. 2010-25314. Environmental Protection Agency. 

Environmental Protection Agency (EPA). 2011a. Policy assessment for the review of the secondary 

national ambient air quality standards for oxides of nitrogen and oxides of sulfur. EPA-452/R-11-

005a. Office of Air Quality Planning and Standards Health and Environmental Impacts Division. 

Research Triangle Park, North Carolina.

Environmental Protection Agency (EPA). 2011b. Climate change and air quality. 

http://www.epa.gov/airquality/airtrends/2011/report/climatechange.pdf (accessed 22 July 2014).

Environmental Protection Agency (EPA). 2012a. Our nation’s air: status and trends through 2010. 

EPA-454/R-12-001. Office of Air Quality Planning and Standards, Air Quality Assessment 

Division, Research Triangle Park, North Carolina.

Environmental Protection Agency (EPA). 2012b. Air & radiation: National Ambient Air Quality 

Standards (NAAQS). http://www.epa.gov/air/criteria.html (accessed 31 March 2014).

Environmental Protection Agency (EPA). 2012c. Ground level ozone: ecosystem effects. 

http://www.epa.gov/airquality/ozonepollution/ecosystem.html (accessed 1 April 2014).

Environmental Protection Agency (EPA). 2012d. Ground level ozone: health effects. 

http://www.epa.gov/airquality/ozonepollution/health.html (accessed 1 April 2014).

Environmental Protection Agency (EPA). 2013a. Clean Air Act: Title I Air Pollution Prevention and 

Control. http://epa.gov/oar/caa/title1.html#ic (accessed 26 March 2014).

Environmental Protection Agency (EPA). 2013b. Ground-level ozone standards designations. 

http://www.epa.gov/ozonedesignations/ (accessed 1 April 2014).

Environmental Protection Agency (EPA). 2013c. Particulate matter (PM). 

http://www.epa.gov/airquality/particlepollution/ (accessed 1 April 2014).

Environmental Protection Agency (EPA). 2014a. AirData: access to monitored air quality data. 

http://www.epa.gov/airdata/ad_maps.html (accessed 31 March 2014). 

Environmental Protection Agency (EPA). 2014b. Policy assessment for the review of the ozone 

national ambient air quality standards: Second external review draft. Environmental Protection 

Agency, Office of Air Quality Planning and Standards, Ambient Standards Group, Research 

Triangle Park, North Carolina.

Kohut, R. J. 2004. Ozone risk assessment for Gulf Coast Network. NPS/NRPC/ARD/NRTR—2004. 

National Park Service, Fort Collins, Colorado.
191

http://www.nature.nps.gov/air/Pubs/pdf/03Risk/gulnO3RiskOct04.pdf (accessed 28 March 

2014).

National Park Service (NPS). 2008. Air atlas summary tables for I&M parks. 

http://www.nature.nps.gov/air/permits/aris/networks/docs/SummariesAirAtlasRevised11072003.

pdf (accessed 25 March 2014). 

National Park Service (NPS). 2010. Air quality in national parks: 2009 annual performance and 

progress report. Natural Resource Report NPS/NRPC/ARD/NRR—2010/266. National Park 

Service, Denver, Colorado. 

National Park Service (NPS). 2011. Rating air quality conditions. Air Resources Division, Natural 

Resources Program Center. National Park Service, Denver, Colorado. 

http://www.nature.nps.gov/air/planning/docs/20111122_Rating-AQ-Conditions.pdf (accessed 25 

March 2014).

National Park Service (NPS). 2013. Air quality in national parks: trends (2000-2009) and conditions 

(2005-2009). Natural Resources Report NPS/NRSS/ARD/NRR—2013/683. National Park 

Service, Denver, Colorado.

National Park Service (NPS). 2014. NPS air quality estimates: ozone, wet deposition, and visibility. 

http://www.nature.nps.gov/air/Maps/AirAtlas/IM_materials.cfm (accessed 25 March 2014).

Segura, M., R. Woodman, J. Meiman, W. Granger, and J. Bracewell. 2007. Gulf Coast Network Vital 

Signs monitoring plan. Natural Resource Report NPS/GULN/NRR–2007/015. National Park 

Service, Fort Collins, Colorado.

Sullivan, T. J., G. T. McPherson, T. C. McDonnell, S. D. Mackey, and D. Moore. 2011a. Evaluation 

of the sensitivity of inventory and monitoring national parks to acidification effects from 

atmospheric sulfur and nitrogen deposition: main report. Natural Resource Report 

NPS/NRPC/ARD/NRR—2011/349. National Park Service, Denver, Colorado.

Sullivan, T. J., T. C. McDonnell, G. T. McPherson, S. D. Mackey, and D. Moore. 2011b. Evaluation 

of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from 

atmospheric nitrogen deposition: main report. Natural Resource Report 

NPS/NRPC/ARD/NRR—2011/313. National Park Service, Denver, Colorado.

Sullivan, T. J., G. T. McPherson, T. C. McDonnell, S. D. Mackey, and D. Moore. 2011c. Evaluation 

of the sensitivity of inventory and monitoring national parks to acidification effects from 

atmospheric sulfur and nitrogen deposition: Gulf Coast Network (GULN). Natural Resource 

Report NPS/NRPC/ARD/NRR—2011/358. National Park Service, Denver, Colorado.

Sullivan, T. J., G. T. McPherson, T. C. McDonnell, S. D. Mackey, and D. Moore. 2011d. Evaluation 

of the sensitivity of inventory and monitoring national parks to nutrient enrichment effects from 

atmospheric nitrogen deposition: Gulf Coast Network (GULN). Natural Resource Report 

NPS/NRPC/ARD/NRR—2011/310. National Park Service, Denver, Colorado.
192

Texas Commission on Environmental Quality (TCEQ). 2012. Overview: regional haze. 

http://www.tceq.texas.gov/airquality/sip/bart/haze_overview.html (accessed 4 April 2014).

Texas Commission on Environmental Quality (TCEQ). 2014a. Four highest ozone concentrations in 

2014. http://www.tceq.state.tx.us/cgi-bin/compliance/monops /8hr_4highest.pl (accessed 28 

August 2014).

Texas Commission on Environmental Quality (TCEQ). 2014b. Daily mean values for calendar year 

2014. http://www.tceq.state.tx.us/cgi-bin/compliance/monops/24hr_annual.pl (accessed 28 

August 2014).
193

4.12 Soundscape

4.12.1 Description

The definition of soundscape in a national park 

is the total ambient sound level of the park, 

comprised of both natural ambient sound and 

human-made sounds (NPS 2000). The NPS’s 

mission is to preserve natural resources, 

including natural soundscapes, associated with 

the national park units. Intrusive sounds are of 

concern to park visitors, as they detract from 

their natural and cultural resource experiences 

(NPS 2000). In addition, traffic or other humancaused noise sources can interrupt interpretive 

programs being held within a park. According 

to a survey conducted by the NPS, many 

visitors come to national parks to enjoy, 

equally, the natural soundscape and natural 

scenery (NPS 2000).

Noise not only affects visitor experience, it can 

also alter the behavior of wildlife. Repeated 

noise can cause chronic stress to animals, 

possibly affecting their energy use, reproductive 

success, and long-term survival (Radle 2007). 

Many factors affect how visitors and wildlife 

perceive and respond to noise. Primary 

acoustical factors include the loudness, frequency (i.e., pitch), and duration of the noise. Nonacoustical factors, such as climate, vegetation, topography, and individual hearing sensitivity also 

play a role in how visitors and wildlife respond to noise (NPS 2014). 

SAAN has a very unique soundscape due to the urban location of most of the park and the rapid 

expansion of San Antonio. Because SAAN is a historical park representing the Missions Period, 

some anthropogenic sounds are expected (e.g., conversations, tolling bells, and other noises 

associated with mission life). However, the Missions Unit has become surrounded by sounds from 

the city that would not have occurred during the Missions Period. These are considered “noncontributing” sounds, as they do not contribute to the historical experience at the park. The noncontributing sounds of traffic, airplanes, and trains can be heard almost constantly at the Missions 

Unit and have become a large part of the park’s unique soundscape. These sounds are less prevalent 

but still heard occasionally at the more rural Rancho Unit southeast of San Antonio.

4.12.2 Measures

 Loudness of non-contributing human-caused sound

 Frequency of non-contributing human-caused sound

Photo 23. Church at Mission San Juan (NPS photo).
194

 Percent of time non-contributing human-caused sound is audible

4.12.3 Reference Conditions/Values

The ideal reference condition for soundscape at SAAN would be a sound environment similar to at 

the time of the active Missions period (might be helpful to provide a range of years that this period 

spanned). However, given the urban development that has occurred around SAAN since that time, 

this goal is no longer feasible. For the purpose of this assessment, the reference condition for 

loudness will be that non-contributing human-caused sounds do not exceed 52 dBA, which is the 

level that interferes with speech and would interrupt interpretive programs (EPA 1974; Table 14). 

For the percent of time non-contributing sound is audible, the reference condition will be no further 

increase over baseline levels documented in Lynch (2009) for the Missions Unit; since no baseline 

data has been gathered at the Rancho Unit, baseline levels are currently unknown. No reference 

condition has been established for frequency.

Table 14. Explanation of sound level values, for reference (Lynch 2009).

Sound Levels 

(dBA) Relevance

35 Blood pressure and heart rate increase in sleeping humans (Haralabidis et al. 2008)

Also, ANSI standard for sound level in classrooms without people (ASA 2008)

45 World Health Organization’s recommendation for maximum noise levels inside bedrooms 

(Berglund et al. 1999)

52 Speech interference for interpretive programs (EPA 1974)

60 Speech interruption for normal conversation (EPA 1974)

4.12.4 Data and Methods

Lynch (2009) conducted a noise and vibration study

at the Tufa House at Mission San Juan in SAAN in 

2008 (Photo 24, Figure 55). Lynch (2009) collected 

sound level data for 27 days using a Larson Davis 

831 sound level meter (SLM). The Larson Davis 831 

SLM is a real-time data analyzer that records sound 

pressure levels and exports the data to external 

storage devices; the SLM station at SAAN included a 

microphone with environmental shroud, a 

preamplifier, 10 12-volt lantern cell batteries, an 

anemometer, an MP3 recorder, and a meteorological 

data logger (Lynch 2009). Data collected by the SLM 

included sound pressure level (SPL) data in the form 

of A-weighted decibel readings (dBA), continuous 

digital audio recordings, and one-third octave band 

Photo 24. Sound monitoring equipment at 

Tufa House (NPS photo).
195

data ranging from 12.5 Hz to 20,000 Hz. In addition to the SLM station, researchers also listened to a 

subset of recordings to identify the sources of sounds and their durations (Lynch 2009). 

Kimley-Horn and Associates (2013) updated the Stinson Municipal Airport’s master plan. The 

Stinson Municipal Airport is located to the west of SAAN (Figure 55). The master plan update 

included an inventory of facilities and services, aviation activity forecast, demand/capacity analysis 

and facility requirements, alternatives development, environmental review, financial plan, and a set 

of drawings for the airport layout plan. The activity forecast extends to 2031.

No information is available regarding soundscape at the Rancho Unit. Therefore, the following 

condition sections will apply only to the Missions Unit.
196

Figure 55. The location of Tufa House (Mission San Juan) within SAAN, and the Stinson Municipal 

Airport.
197

4.12.5 Current Condition and Trend

Loudness of Non-contributing Human-caused Sound

Lynch (2009) documented the percent exceedances for four sound levels (35 dBA, 45 dBA, 52 dBA, 

and 60 dBA) at the Tufa House site in SAAN. Sound levels at this site exceeded 35 dBA 100% of the 

time during both the daytime and the nighttime (7:00 PM to 6:59 AM) periods. Sound levels 

exceeded 52 dBA 25.7% of the time during the daytime, and 8.2% during the night time (Table 56).

Table 56. Percent time sound exceeds the given dBA level (Lynch 2009).

Site Name

% Exceedence nighttime (7pm - 6:59 am) % Exceedence daytime (7am - 6:59 pm)

35 dBA 45 dBA 52 dBA 60 dBA 35 dBA 45 dBA 52 dBA 60 dBA

Tufa House 100.0 60.1 8.2 1.0 100.0 93.4 25.7 2.8

Frequency of Non-contributing Human-caused Sound

The frequency of sounds, typically measured in hertz (Hz), can influence the perceived loudness of a 

sound; some frequencies that occur are inaudible to humans. Most unnatural human-caused sounds 

range in frequencies from 100 Hz to 1,000 Hz, as seen in Figure 56. At SAAN, lower frequency 

noises are typically louder (i.e., higher sound levels in dB). Not enough data have been collected to 

establish a mean frequency of non-contributing human-caused sounds.

Figure 56. Day and night dBA measurements by frequency for 27 days at SAAN’s Tufa House sampling 

site. Gray shaded areas represent sound levels typically outside the range of human hearing (Lynch 

2009).
198

Percent of Time Non-contributing Human-caused Sound is Audible

Lynch (2009) documented the number of times a sound source was heard and the percent of time that 

source was audible at SAAN over 27 days. The most frequent sources of sound were aircrafts, 

people, vehicles, and grounds care (Table 57). The sounds from people and aircraft activity occurred 

most often, with 103 counts over the study period. Vehicle noise was counted 75 times and grounds 

care noise counted 55 times. Vehicle noise occurred approximately 86% of the time, aircraft 

propellers were heard 30% of the time, grounds care 18%, and people 10% of the time. Non- natural 

sound sources, as a whole, were audible 99.4% of the time. Table 57 displays the summary of sound 

sources and the frequency count during an audible survey in SAAN.

Table 57. Summary of sound sources identified during on site audible surveys in SAAN (Lynch 2009). SD 

= standard deviation.

Sound Source

Percent 

Time 

Audible

Max Event 

Length 

(seconds)

Mean Event 

Length 

(seconds)

Min Event 

Length 

(seconds)

SD Event 

Length 

(seconds) Count

Aircraft 0 26 26 26 1

Jet 1 45 27 6 14 7

Aircraft, Propeller 30 230 53 4 47 103

Helicopter 3 176 60 2 55 8

Vehicle 86 1,372 207 3 294 75

Alarm, Horn 1 14 3 0 3 45

Brakes 0 4 1 0 1 27

Siren 2 110 72 32 30 5

Motorcycle 2 93 36 3 38 9

Bus (capacity > 9 people) 1 57 23 3 25 5

Truck (6+ tires) 3 64 15 2 13 31

Train 1 102 102 102 1

Train Horn 0 10 9 6 2 3

Grounds Care 18 794 59 2 135 55

People 10 153 18 0 26 103

Interpretive Talk 0 38 38 38 1

Non-natural Other 2 85 11 1 16 36

All Aircraft 33.4

All Road Vehicles 87.9

All Non-natural Sources 99.4
199

Lynch (2009) recorded 17 human-caused sound sources from five on-site audible survey sessions in 

SAAN. The three human sources that had the longest duration were vehicles, grounds care, and 

aircraft propellers. The noise from vehicles had the longest maximum length of 1,372 seconds 

(nearly 23 minutes); however, vehicle sounds could also be as short in duration as 3 seconds. 

Grounds care could last anywhere from 794 seconds (13.2 minutes) to only 2 seconds. Aircraft 

propellers were similar in duration, ranging from 4 seconds to 230 seconds (3.4 minutes). There were 

sources that had a constant duration length throughout the survey. Trains, interpretive talk, and 

aircrafts occurred for 26 seconds, 38 seconds, and 102 seconds, respectively. Table 57 displays the 

minimum, average, and maximum duration lengths of human-caused sound sources.

Kimley-Horn and Associates (2013) documented an activity forecast for Stinson Municipal Airport 

for a 20-year planning period that included peak monthly operations. Aircraft operations are 

estimated to increase in frequency from 14,900 operations per month in 2011 to 28,500 operations a 

month by the end of the 20-year planning period. 

Threats and Stressor Factors

Due to the location of SAAN, there are many threats and stressors to the park’s soundscape. The 

Stinson Municipal Airport (SSF) is a major threat to SAAN soundscape and is a concern to park 

managers seeking to preserve the natural atmosphere of SAAN. Aircraft noise also impacts visitor 

activities, as noise frequently interrupts interpretive programs at the Missions Unit in SAAN. The 

airport is located less than 3.2 km (2 mi) from the western border of SAAN. According to AirNav 

(2014), there was an average of 250 aircraft operations a day in 2013. Local general aviation was the 

most common operation, occurring 54% of the time; approximately 35%, 11%, and 1% were 

transient general aviation, military, and air taxi operations, respectively. The average maximum 

sound levels for all types of aircraft overflights exceed the reference condition of 52 dBA selected for 

this assessment (Table 58). The SSF plans on expanding the number of based aircrafts as well as the 

number of annual operations within the next 20 years. As of 2011, there were a total of 140,700 

operations that occurred, and by 2031 the total annual operations are estimated to be 268,800 

(Kimley-Horn and Associates 2013). This is nearly a doubling in activity over 20 years. In 2007, SSF 

applied to lengthen their runway by 1524 m. (5,000 ft.), a proposal which was later approved by the 

Texas Department of Transportation.

Table 58. Average maximum dB levels for aircraft overflights during Lynch’s (2009) 27 day monitoring 

period.

Aircraft Type Count Average Max dB

Helicopter 18 69.3

Jet 89 59.2

Military Propeller 59 75.1

Propeller 1,294 60.8
200

There are three other airports in the city of San Antonio. The San Antonio International Airport 

(SAT) is the most utilized and could pose a threat, even though it is located approximately 15 km 

(9.32 mi) north of SAAN. Marrow et al. (2009) produced a Noise Compatibility Planning Study for 

SAT in 2009. Operations with sound levels at or higher than 65 dBA have been documented at the 

airport since 1990. According to Marrow et al. (2009), the number of yearly operations peaked in 

1998 with over 270,000 operations. After 1998, the number of operations decreased to 223,501 

operations a year, with an average of 612 operations a day. However, a 3% increase to 229,651

operations was predicted by 2014 (Marrow et al. 2009). 

Due to the park’s proximity to Route 122 and Interstate 410, vehicles are the most common humancaused sound (audible 86% of the time; Lynch 2009). Trains are also heard occasionally. Between 

the highway traffic and the almost non-stop air traffic, the typical noise free interval (NFI) at SAAN 

is very short. The mean NFI was 12 seconds, while the maximum was 46 seconds (Lynch 2009). 

These short NFIs suggest that SAAN is highly affected by human-caused noise; on average a visitor 

can go about 12 seconds without hearing unnatural human-caused sound (Lynch 2009). 

Data Needs/Gaps

The acoustical monitoring study (Lynch 2009) was performed prior to the expansion of SSF; the 

National Sounds Program recommends that another monitoring system be deployed within 2 to 3

years of completion of the construction at SSF. Although the study was thorough, it was only 

conducted for 27 days at one location during April and May. There are no long-term sound data for 

SAAN, making it impossible to determine how much the soundscape has deteriorated over time. In 

addition there are no soundscape data at all for the Rancho Unit of the park. Given its more rural 

setting, soundscape conditions at this location are likely very different from those within the 

Missions Unit. A baseline survey should be conducted at the Rancho Unit as soon as possible to 

document conditions before they are further impacted by surrounding activities.

Overall Condition

Loudness of Non-contributing Human-caused Sound

The project team assigned this measure a Significance Level of 3. Lynch (2009) suggested that the 

loudness of non-contributing human sounds is a concern at SAAN. Since there were no soundscape 

studies at SAAN prior to Lynch (2009), there is no baseline sound level to compare recent data to. 

For this assessment, a reference level of 52 dBA was selected, because noise at that level interferes 

with interpretive programs (EPA 1974). During Lynch’s (2009) monitoring, sound level reached or 

exceeded 52 dBA 25.7% of the time, possibly causing functional effects on visitors. This gives 

reason for moderate concern (Condition Level = 2). 

Frequency of Non-contributing Human-caused Sound

This measure was also assigned a Significance Level of 3. Due to the lack of data on frequency and 

any analysis of its influence on overall sound conditions at SAAN, a Condition Level could not be 

assigned. Further studies regarding frequency in hertz should be performed in order to get a proper 

condition level.
201

Percent of Time Non-contributing Human-caused Sound is Audible

The project team assigned this measure a Significance Level of 3. Lynch (2009) shows that humancaused noises could be heard in SAAN approximately 98.4% of the day. Although some humancaused sounds are culturally acceptable within SAAN’s soundscape, the majority of these sounds are

non-contributing. Noise from vehicles was heard 86% of the time and had a mean duration of 1,372 

seconds. Aircraft were heard 30% of the time with duration ranging from 4 to 230 seconds. With 

non-contributing sounds being heard so often, there is high concern (Condition Level = 3) about their 

impact on the park’s soundscape.

Weighted Condition Score (WCS)

The Weighted Condition Score for SAAN soundscape is 0.83. The overall condition for the Missions 

Unit is of significant concern and is likely deteriorating. This is due to the park’s location within the 

city limits of San Antonio, which severely impacts the soundscape. Unfortunately, park staff have 

little control over the soundscape and its condition due to the park’s geographic locale. The condition 

of soundscape at the Rancho Unit is unknown due to a lack of data.

Soundscape

Measures

Significance 

Level

Condition 

Level WCS = 0.83

Loudness 3 2

Frequency 3 n/a

Percent of Time 3 3

4.12.6 Sources of Expertise

Greg Mitchell, SAAN Natural Resources Program Manager

4.12.7 Literature Cited

Acoustical Society of America, Standards Secretariat (ASA). 2008. Criteria for evaluating room 

noise. ANSI/ASA S12.2-2008.

AirNav LLC. 2014. FAA information effective 24 July 2014. Stinson Municipal Airport. 

http://www.airnav.com/airport/KSSF (accessed 4 August 2014).

Berglund, B., T. Lindvall, and D. H. Schwela (eds.). 1999. Guidelines for community noise. World 

Health Organization, Geneva, Switzerland.
202

Haralabidis, A. S., K. Dimakopoulou, F. Vigna-Taglianti, M. Giampaolo, A. Borgini, M. Dudley, G. 

Pershagen, G. Bluhm, D. Houthuijs, W. Babisch, and more. 2008. Acute effects of night-time 

noise exposure on blood pressure in populations living near airports. European Heart Journal 

29(5):658-664.

Kimley-Horn and Associates, Inc. 2013. Stinson Municipal Airport master plan update. City of San 

Antonio Airport System, San Antonio, Texas.

Lynch, E. 2009. San Antonio Missions National Historical Park acoustical monitoring report 2009. 

Natural Resource Report NPS/NRPC/NRTR—2009/001. U.S. Department of the Interior, 

National Park Service, Fort Collins, Colorado.

Marrow, C., R. Bassarab, B. Manning, and B. Geiger. 2009. Noise exposure map report and noise 

compatibility program update for San Antonio International Airport. WYLE Aviation Services, 

Arlington, Virginia.

National Park Service (NPS). 2000. Directors Order #47: Soundscape preservation and noise 

management. http://www.nps.gov/policy/DOrders/DOrder47.html (accessed 15 October 2014).

National Park Service (NPS). 2014. Science of sound. http://www.nature.nps.gov/sound/science.cfm

(accessed 22 October 2014).

Radle, A. L. 2007. The effect of noise on wildlife: a literature review. World Forum for Acoustic 

Ecology Online Reader. http://wfae.proscenia.net/library/articles/radle_effect_noise_wildlife.pdf

(accessed 22 October 2014).

U.S. Environmental Protection Agency (EPA). 1974. Information on levels of environmental noise 

requisite to protect public health and welfare with an adequate margin of safety. Environmental 

Protection Agency, Washington, D.C.
203

4.13 Dark Night Skies

4.13.1 Description

A “lightscape” is a place or environment characterized by the natural rhythm of the sun and moon 

cycles, clean air, and of dark nights unperturbed by artificial light (NPS 2007). The NPS directs each 

of its units to preserve, to the greatest extent possible, these natural lightscapes (NPS 2006). Natural 

cycles of dark and light periods during the course of a day affect the evolution of species and other 

natural processes such as plant phenology (NPS 2006, 2014a). Several species require darkness to 

hunt, hide their location, navigate, or reproduce (NPS 2014a). In addition to the ecological 

importance of dark night skies, park visitors expect skies to be free of light pollution and allow for 

star observation. 

4.13.2 Measures

During site visits, the NPS Night Sky Team (NST) collects data for a suite of measures in order to 

define the current condition of dark night skies in a park unit. While the NST has not visited SAAN, 

the suite of measures that they would use on a visit includes:

 Sky luminance over the hemisphere in high resolution (thousands of measurements comprise 

a data set), reported in photometric luminance units (V magnitudes per square arc second or 

milli-candela per square meter) or relative to natural conditions, often shown as a sky 

brightness contour map of the entire sky. V magnitude is a broadband photometric term in 

astronomy, meaning the total flux from a source striking a detector after passing through a 

“Johnson-Cousins V” filter. It is similar to the “CIE photopic” broadband function for 

wavelengths of light to which the human eye is sensitive (Bessell 1990);

 Integrated measures of anthropogenic sky glow from selected areas of sky that may be 

attributed to individual cities or towns (known as city light domes), reported in milli-Lux of 

hemispheric illuminance or vertical illuminance;

 Integration of the entire sky illuminance measures, reported either in milli-Lux of total 

hemispheric (or horizontal) illuminance, milli-Lux of anthropogenic hemispheric (or 

horizontal) illuminance, V-magnitudes of the integrated hemisphere, or ratio of 

anthropogenic illuminance to natural illuminance;

 Vertical illuminance from individual (or groups of) outdoor lighting fixtures at a given 

observing location (such as the Wilderness boundary), in milli-Lux;

 Visual observations by a human observer, such as Bortle Class and Zenithal limiting 

magnitude;

 Integrated synthesized measure of the luminance of the sky within 50 degrees of the Zenith, 

as reported by the Unihedron Sky Quality Meter, in V magnitudes per square arc second;

4.13.3 Reference Conditions/Values

The reference condition for dark night skies in SAAN is defined as the night sky visibility as 

observed when the Missions were active. 
204

The NST defines reference condition in terms of sky luminance and illuminance at the observer’s 

location from anthropogenic sources as follows:

No portion of the sky background brightness exceeds natural levels by more than 200 

percent, and the sky brightness at the Zenith does not exceed natural Zenith sky brightness by 

more than 10 percent. The ratio of anthropogenic hemispheric illuminance to natural 

hemispheric illuminance from the entire night sky does not exceed 20 percent. The observed 

light from a single visible anthropogenic source (light trespass) is not observed as brighter 

than the planet Venus (0.1 milli-Lux) when viewed from within any area of the park 

designated the naturally dark zone (Dan Duriscoe, NPS Night Sky Team, pers. comm., 2011).

Achieving this reference condition for preserving natural night skies is well summarized in the NPS 

Management Policies (2006, p. 57) as follows in section 4.10:

The Service will preserve, to the greatest extent possible, the natural lightscapes of 

parks, which are natural resources and values that exist in the absence of humancaused light.

Implementing this directive in SAAN requires that facilities within the park and local communities

around the park meet outdoor lighting standards that provide for the maximum amount of 

environmental protection while meeting human needs for safety, security, and convenience. This 

means that outdoor lights within the park: 

 produce zero light trespass beyond the boundary of their intended use; 

 be of an intensity that meets the minimum requirement for the task but does not excessively 

exceed that requirement; 

 be of a color that is toward the yellow or orange end of the spectrum to minimize sky glow; 

 be controlled intelligently, preventing unnecessary dusk to dawn bright illumination of areas.

4.13.4 Data and Methods

SAAN is a unique NPS unit because it is separated into two units (Missions, Rancho de las Cabras) 

located in two different geographical settings. The Missions Unit is located in the city of San

Antonio. Since the Missions Unit is located within the San Antonio city limits, it is greatly affected 

by light pollution. The Missions closer to downtown (further north, e.g., Concepción) are more 

heavily impacted than those in more of a neighborhood setting (e.g., Espada). The Rancho de las 

Cabras Unit, which is comprised of historic ranch land for the Missions, is approximately 51.5 km

(32 mi) south of the city of San Antonio and is less affected by light pollution than the Missions Unit. 

Unfortunately, no data have been collected by the NPS in SAAN related to dark night skies.

4.13.5 Current Condition and Trend

Background for NPS Night Sky Team’s Suite of Measures

While no data have been collected in SAAN, it is important to recognize that anthropogenic light in 

the night environment can be significant, especially on moonless nights. Unshielded lamps mounted 

on tall poles have the greatest potential to cause light pollution, since light directly emitted by the 
205

lamp has the potential to follow an unobstructed path into the sky or the distant landscape. This type 

of light spill has been called glare, intrusive light, or light trespass (Narisada and Schreuder 2004). 

The dark-adapted human eye will see these individual light sources as extremely bright points in a 

natural environment. These sources also have the potential to illuminate the landscape, especially 

vertical surfaces aligned perpendicular to them, often to a level that approaches or surpasses 

moonlight. The brightness of such objects may be measured as the amount of light per unit area 

striking a “detector” or a measuring device, or entering the observer’s pupil. This type of measure is 

called illuminance (Ryer 1997).

Illuminance is measured in lux (metric) or foot-candles (English). It is usually defined as luminous 

flux per unit area of a flat surface (1 lux = 1 lumen / m2). However, different surface geometries may 

be employed, such as a cylindrical surface or a hemispheric surface. Integrated illuminance of a 

hemisphere (summed flux per unit area from all angles above the horizon) is a useful, unbiased 

metric for determining the brightness of the entire night sky. Horizontal and vertical illuminance are 

also used; horizontal illuminance weights areas near the Zenith are much greater than areas near the 

horizon, while vertical illuminance preferentially weights areas near the horizon, and an azimuth of 

orientation must be specified.

Direct vertical illuminance from a nearby anthropogenic source will vary considerably with the 

location of the observer, since this value varies as the inverse of the square of the distance from light 

source to observer (Ryer 1997). Therefore, measures of light trespass are usually made in sensitive 

areas (such as public campgrounds).

Anthropogenic light which results in an upward component will be visible to an observer as “sky 

glow”. This is because the atmosphere effectively scatters light passing through it. The sky is blue in 

daytime because of Rayleigh scattering by air molecules, which is more effective for light of shorter 

wavelengths. For this reason, bluish light from outdoor fixtures will produce more sky glow than 

reddish light. Larger particles in the atmosphere (aerosols and water vapor droplets) cause Mie 

scattering and absorption of light, which is not as wavelength-dependent and is more directional. 

When the air is full of larger particles, this process gives clouds their white appearance and produces 

a whitish glow around bright objects (e.g., the sun and moon). The pattern of sky glow as seen by a 

distant observer will appear as a dome of light of decreasing intensity from the center of the city on 

the horizon. As the observer moves closer to the source, the dome gets larger until the entire sky 

appears to be luminous (Garstang 1989).

Light propagated at an angle near the horizon will be effectively scattered and the sky glow produced 

will be highly visible to an observer located in the direction of propagation. Predictions of the 

apparent light dome produced by a sky glow model demonstrate this (Luginbuhl et al. 2009). Light 

reflected off surfaces (e.g., a concrete road or parking area) becomes visible light pollution when it is 

scattered by the atmosphere above it, even if the light fixture has a “full cutoff” design and is not 

visible as glare or light trespass to a distant observer. For this reason, the intensity and color of 

outdoor lights must be carefully considered, especially if light-colored surfaces are present near the 

light source.
206

Light domes from many cities, as they appear from a location within Joshua Tree National Park, are 

shown in Figure 57 and Figure 58, as a grayscale and in false color. This graphic demonstrates that 

the core of the light dome may be tens or hundreds of times brighter than the extremities. A 

logarithmic scale for sky luminance and false color are commonly used to display monochromatic 

images or data with a very large dynamic range, and are used extensively in reports of sky brightness 

by the NST.

Figure 57. Grayscale representation of sky luminance from a location in Joshua Tree National Park, 

California (Figure provided by Dan Duriscoe, NPS Night Sky Team).

Figure 58. False color representation of Figure 56 after a logarithmic stretch of pixel values (Figure 

provided by Dan Duriscoe, NPS Night Sky Team).

The brightness (or luminance) of the sky in the region of the light domes may be measured as the 

number of photons per second reaching the observer for a given viewing angle, or area of the sky 

(such as a square degree, square arc minute, or square arc second). The NST utilizes a digital camera 

with a large, dynamic range, monochromatic charge-coupled device (CCD) detector and an extensive 

system of data collection, calibration, and analysis procedures (Duriscoe et al. 2007). This system 

allows for the accurate measurement of both luminance and illuminance, since it is calibrated on 

standard stars that appear in the same images as the data and the image scale in arc seconds per pixel 

is accurately known. Sky luminance is reported in astronomical units of V-magnitudes per square arc 

second, and in engineering units of milli-candela per square meter. High resolution imagery of the 

entire night sky reveals details of individual light domes that may be attributed to anthropogenic light 

from distant cities or nearby individual sources. These data sets may be used for both resource 

condition assessment and long-term monitoring.
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Figure 57 and Figure 58 contain information on natural sources of light in the night sky as well as 

anthropogenic sources. The appearance of the natural night sky may be modeled and predicted in 

terms of sky luminance and illuminance over the hemisphere, given the location, date, time, and the 

relative brightness of the natural airglow (the so-called “permanent aurora” which varies in intensity 

over time) (Roach and Gordon 1973). The NST has constructed such a model, and uses it in analysis 

of data sets to remove the natural components. This results in a more accurate measure of 

anthropogenic sky glow (Figure 59). Figure 58 represents “total sky brightness” while Figure 59

displays “anthropogenic sky glow” or “net light pollution.” This is an important distinction, 

especially in areas where anthropogenic sky glow is of relatively low intensity.

Figure 59. Contour map of anthropogenic sky glow at a location in Joshua Tree National Park, analogous 

to Figure 58 with natural sources of light subtracted (Figure provided by Dan Duriscoe, NPS Night Sky 

Team).

The accurate measurement of both anthropogenic light in the night sky and the accurate prediction of 

the brightness and distribution of natural sources of light allows for the use of a very intuitive metric 

of the resource condition - a ratio of anthropogenic to natural light. Both luminance and illuminance 

for the entire sky or a given area of the sky may be described in this manner (Hollan 2008). This socalled “light pollution ratio” is unitless and is always referenced to the brightness of a natural 

moonless sky under average atmospheric conditions, or, in the case of the NST data, the atmospheric 

conditions determined from each individual data set.

The reference conditions for anthropogenic sky luminance were identified as no more than 200 

percent brighter than natural conditions in any area of the sky and no more than 10 percent brighter at 

the Zenith. These values correspond to light pollution ratios of 2.0 and 0.1, respectively. The NST 

has obtained values of 50-100 for this measure at the core of city light domes seen from several areas 

administered by the NPS, including Lake Mead National Recreation Area, Saguaro National Park, 

and Colorado National Monument (NPS Night Sky Team, unpublished data). This is because these 

NPS areas are very close to the cities of Las Vegas, Nevada; Tucson, Arizona; and Grand Junction, 

Colorado, respectively. 
208

A quick and accurate method of quantifying sky brightness near the Zenith is the use of a Unihedron 

Sky Quality Meter. The Unihedron Sky Quality Meter is a single-channeled hand-held photometric 

device. A single number in magnitudes per square arc second is read from the front of the device 

after its photodiode and associated electronics are pointed at the Zenith and the processor completes 

its integration of photon detection. Because the meter is relatively inexpensive and easy to use, a 

database of measures has grown since its introduction (see 

http://unihedron.com/projects/darksky/database/index.php). The NST produces values from each data 

set as both a synthesized value derived from the high-resolution images and by hand held measures 

with a Unihedron Sky Quality Meter. The performance of the Sky Quality Meter has been tested and 

reviewed by Cinzano (2005). While fairly accurate and easy to use, the value it produces is biased 

toward the Zenith. Therefore, the robustness of data collected in this manner is limited to areas with 

relatively bright sky glow near the Zenith, corresponding to severely light polluted areas. While not 

included in the reference condition, a value of about 21.85 would be considered “pristine”, providing 

the Milky Way is not overhead and/or the natural airglow is not unusually bright when the reading is 

taken. 

Visual observations are important in defining sky quality, especially in defining the aesthetic 

character of night sky features. A published attempt at a semi-quantitative method of visual 

observations is described in the Bortle Dark Sky Scale (Bortle 2001). Observations of several 

features of the night sky and anthropogenic sky glow are synthesized into a 1-9 integer interval scale, 

where class 1 represents a “pristine sky” filled with easily observable features and class 9 represents 

an “inner city sky” where anthropogenic sky glow obliterates all the features except a few bright 

stars. Bortle Class 1 and 2 skies possess virtually no observable anthropogenic sky glow (Bortle 

2001).

Another visual method for assessing sky quality is Zenithal Limiting Magnitude (ZLM), which is the 

apparent brightness or magnitude of the faintest star observable to the unaided human eye, which 

usually occurs near the Zenith. This method involves many factors, the most important of which is 

variability from observer to observer. A ZLM of 7.0-7.2 is usually considered “pristine” or 

representing what should be observed under natural conditions; observation of ZLM is one of the 

factors included in the Bortle Dark Sky Scale. Zenith Limiting Magnitude is often referenced in 

literature on the quality of the night sky, and is the basis for the international “Globe at Night” 

citizen-scientist program (see http://www.globeatnight.org/index.html). The NST has experimented 

with the use of this observation in predicting sky quality, and has found that it is a much coarser 

measure and prone to much greater error than accurate photometric measures over the entire sky. For 

these reasons, it is not included in the reference conditions section. 

Threats and Stressor Factors

Situated in close proximity to a major urban area (San Antonio, Texas), the Missions Unit of SAAN 

is subjected to high levels of anthropogenic light pollution. This light pollution comes from human 

developments on the land surrounding the park, and areas further away from the park (downtown San 

Antonio, Texas) also contribute light pollution. Many businesses have unobstructed lights that are 

orientated upwards, and these lights remain on even when the business’s operating hours have 
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passed. The Rancho de las Cabras Unit is located in a rural area and is subjected to lower levels of 

light pollution. Lorenz (2006) and Danko (2014) recreated a light pollution map that displays the 

level of light pollution occurring in San Antonio and surrounding areas (Figure 60). The Missions 

Unit is located in several levels of light pollution ranging from five to eight on the Bortle Scale, 

which means the dark night sky is moderately to heavily impaired. The Rancho de las Cabras Unit is 

located in an area of moderate light pollution. 

The park’s urban location also results in high levels of traffic passing by the site, and at night the 

lights from passing vehicles contribute to light pollution. Transportation infrastructure (i.e., street 

lights) has increased in size in the past decade, most notably the lights along Texas State Highway 

410, which runs through the southern portion of the Missions Unit. 

Refinery flaring is another source of light pollution and threat to dark night skies in SAAN, 

especially at the Missions Unit as two refineries are located within a mile of park boundaries. Figure 

61 displays the location of the nearest refineries in relation to SAAN. Blinking lights on cell towers 

are also a source of light pollution affecting dark night skies.

Air pollution from the city of San Antonio may adversely affect the dark night skies in SAAN. 

According to NPS (2014b), light pollution is scattered more when air quality is poor, which results in 

brighter skies near sources of light. 

Data Needs/Gaps

There has been no collection of dark night skies baseline data at SAAN. Without these data, an 

assessment of the condition of the night skies cannot be completed. A visit from the NST would 

allow for measurements of the entire sky brightness condition. Measurements should occur on a 

periodic basis, about once every 5 years, with the highest point in the park serving as the preferred 

observing site, in order to track external threats.
210

Figure 60. Levels of light pollution occurring in San Antonio and surrounding areas (Lorenz 2006; Danko 

2014). 
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Figure 61. Location of refineries near the SAAN Missions Unit.

Overall Condition

NPS Night Sky Team’s Suite of Measures

During scoping meetings, the SAAN NRCA team assigned the NPS Night Sky Team’s suite of 

measures a Significance Level of 3. Despite the lack of available data, it is clear that the current 

condition of dark night skies is negatively impacted by the urbanization of the areas surrounding 

SAAN. It should be noted that conditions likely vary between the two park units, considering the 

Missions Unit is in San Antonio and the Rancho de las Cabras Unit is in a rural area. While a 

Condition Level cannot be assigned to this resource due to the lack of recent data, the level of 
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concern for this resource is believed to be high. A visit from the NPS NST would provide baseline 

dark night sky measurements and would allow for a more accurate depiction of current condition and 

trend for SAAN.

Weighted Condition Score

Because SMUMN GSS could not assign a Condition Level for the selected measure, no Weighted 

Condition Score was assigned. The current condition of dark night skies at SAAN is unknown.

Dark Night Skies

Measures

Significance 

Level

Condition 

Level WCS = 0.83

NPS Night Sky 

Team Suite of 

Measures

3 n/a

4.13.6 Sources of Expertise

National Park Service Night Sky Team members Dan Duriscoe, Chad Moore, Teresa Jiles, Jeremy 

White, and Robert Meadows

4.13. 7 Literature Cited

Bessell, M. S. 1990. UBVRI Passbands. Publications of the Astronomical Society of the Pacific 102: 

1181.

Bortle, J. 2001. Introducing the Bortle dark-sky scale. Sky & Telescope 101(2):126-129. 

Cinzano, P. 2005. Night sky photometry with sky quality meter. ISTIL Internal Report n. 9, v. 1.4. 

http://www.unihedron.com/projects/darksky/sqmreport_v1p4.pdf (accessed 22 October 2014).

Danko, A. 2014. San Antonio light pollution map. Clear Dark Sky Online. 

http://cleardarksky.com/lp/SanAnTXlp.html?latlong=&choose_disp=roadmap&newwindow=1

(accessed 20 October 2014).

Duriscoe, D. M., C. B. Luginbuhl, and C. A. Moore. 2007. Measuring night-sky brightness with a 

wide-field CCD camera. Publications of the Astronomical Society of the Pacific 119:192-213.

Garstang, R. H. 1989. Night-sky brightness at observatories and sites. Publications of the 

Astronomical Society of the Pacific 101:306-329.

Hollan, J. 2008. What is light pollution and how do we quantify it? Workshop paper at Darksky 2007 

conference, Brno, Czech Republic. http://amper.ped.muni.cz/hollan/light/lp_what_is.pdf

(accessed 22 October 2014).
213

Lorenz, D. 2006. Light pollution atlas 2006. http://djlorenz.github.io/astronomy/lp2006/ (accessed 21 

October 2014).

Luginbuhl, C. B., D. M. Duriscoe, C. W. Moore, A. Richman, G. W. Lockwood, and D. R. Davis. 

2009. From the ground up II: sky glow and near-ground artificial light propagation in Flagstaff, 

Arizona. Publications of the Astronomical Society of the Pacific 121:204-212. 

Narisada, K., and D. Schreuder. 2004. Light pollution handbook. Astrophysics and Space Sciences 

Library volume 322. Springer Publishing, New York, New York.

National Park Service (NPS). 2006. Management policies 2006. ISBM 0-16-076874-8. National Park 

Service, Washington, D.C.

National Park Service (NPS). 2014a. Night sky. http://nature.nps.gov/night/index.cfm (accessed 9 

April 2015).

National Park Service (NPS). 2014b. Measuring lightscapes. 

http://www.nature.nps.gov/night/measure.cfm (accessed 22 October 2014).

Roach, F. E., and J. L Gordon. 1973. The light of the night sky. D. Reidel Publishing, Dordrecht, 

Holland. 

Ryer, A. 1997. The light measurement handbook. International Light, Inc., Technical Publications 

Division, Newburyport, Massachusetts.
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4.14 Viewscape

4.14.1 Description

For this assessment, viewscape refers to the visible natural and cultural features on the landscape in 

SAAN. A viewshed is the area that is visible from a particular location or set of locations, often 

developed using GIS analysis tools. Two datasets are required to calculate a viewshed using GIS: a 

digital elevation model (DEM) and point or polyline data defining points from which a person would 

be viewing a landscape. With the defined data, GIS software determines visibility to and from a 

particular cell or set of cells in a DEM, resulting in a viewshed layer. This viewshed layer is a raster 

that defines the visible area on the landscape from the point or set of points contained within an 

outline of a polygon. Analyzing layers that identify areas of undesirable impacts on the landscape 

within viewsheds creates a quantitative description of visual stress on a viewshed; repeating this 

process for multiple viewshed layers in a pre-defined landscape, such as a national park, provides a 

quantitative description of stress across the viewscape in the area. 

Photo 25. View of Mission Espada (NPS Photo).

Multiple studies indicate that people prefer natural compared to developed landscapes (Sheppard 

2001, Kearney et al. 2008, Han 2010). The National Park Service Organic Act (16 U.S.C. l) implies 

the need to protect the viewscapes of national parks, monuments, and reservations. At SAAN, 

cultural landscape viewing is a primary visitor activity. SAAN cultural vistas include the four 

Missions (San Jose, Concepcion, San Juan, and Espada), the San Juan labores, and ranch land at the 

Rancho de las Cabras site.

4.14.2 Measures

 Number of non-contributing features visible within the park

 Number of non-contributing features visible outside of park

 Appearance of San Juan labores
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4.14.3 Reference Conditions/Values

The ideal reference condition would be the SAAN viewscape at the time when Missions were active. 

However, given the development of the surrounding city of San Antonio, this is no longer feasible. In 

addition, park management has little to no influence over the number of non-contributing features 

outside the park. The reference condition for number of non-contributing features visible within the 

park, which park management has some control over, would be no more than a 10% increase from 

the current condition. This “allowable” percentage of increase would be for future needed park 

development (e.g., signs, and bollards) (James Oliver, SAAN Landscape Architect, written 

communication, 9 March 2015). The reference condition for the labores, located near the southern 

boundary of the Missions Unit, is to maintain zero woody vegetation in the labores and to preserve 

the shrub and tree rows between fields.

4.14.4 Data and Methods

Park staff identified 24 observation points and one trail of interest within or near the park units for 

analysis in this NRCA: eight points from San Juan, seven points from Espada, four points from San 

Jose, three points from Concepcion, two points from Rancho de las Cabras, and one line feature 

following the panhandle entrance to the Rancho Unit (Figure 62). For each of these points or lines, a 

viewshed was calculated using ESRI’s Spatial Analyst Viewshed Tool in ArcGIS 10.2, which 

requires point or polyline GIS data (representing the viewing location) and a DEM. For each of the 

observation points, a point shapefile was created for use with the Viewshed Tool (Figure 63). For 

line features, a polyline was created; the Viewshed Tool uses each vertex in the line to determine the 

viewshed of the feature as a whole.
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Figure 62. Locations of vistas in the Missions (left) and Rancho de las Cabras Units (right).
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Figure 63. Composite viewshed analysis for the 22 vistas in the Missions Unit (left) and three vistas in the Rancho de las Cabras Unit (right). The 

darker shaded areas are visible from the park vistas.
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The DEM used was the 1/3-arc second National Elevation Dataset (NED) DEM. A 1.7-m (5.5-ft) 

offset was applied to each observation point shapefile to account for average human height. The 

result of the operation is a theoretical viewshed layer that represents the visible area from a point 

without correcting for visibility factors (e.g., vegetation, smoke, humidity, heat shimmer, or 

curvature of the earth). Figure 63 displays the viewshed analysis for the Missions Units (left) and the 

Rancho de las Cabras Unit (right).

Current photos were provided by SAAN, to display the non-contributing features visible from within 

and outside of SAAN. These photos from late 2014 and early 2015 were taken by park staff to aid in 

this assessment. 

The City of San Antonio has been actively involved in viewscape conservation for SAAN since 

2008. SAAN has since been nominated for inclusion on the World Heritage Site list (Bailey 2014). 

Cultural Landscape Inventories (CLIs) were completed for each Mission and the Rancho de las 

Cabras Unit during different years. The NPS conducted a CLI for Mission San Jose (NPS 1998a) and 

for Rancho de las Cabras (NPS 1998c) in 1998. NPS (2002) conducted a cultural landscape inventory 

for Mission Concepcion in 2002. In 2011, NPS conducted CLIs for Mission Espada (NPS 2011a) and 

Mission San Juan (NPS 2011b). The CLIs document the contributing and non-contributing features 

within the units and when they were established or built. The CLI also evaluates the integrity of the 

historic identity (location, setting, design, community organization, material/species, workmanship, 

and management techniques) of the park. 

Cultural Landscape Reports (CLRs) were also completed for Missions Concepcion and San Jose as 

well as the Rancho de las Cabras Unit. NPS (1995, 1998b) conducted the CLRs for San Jose and 

Concepcion in 1995 and 1998, respectively. OCULUS (1998) conducted the CLR for the Rancho de 

las Cabras Unit in 1998. The CLRs are similar to the CLIs; however, the CLRs also offer 

recommendations on preserving, restoring, and rehabilitating historically significant features. CLRs 

also evaluate the integrity of the historic identity (location, setting, design, community organization, 

material/species, workmanship, and management techniques) of the park.

4.14.5 Current Condition and Trend

Number of Non-Contributing Features Visible within the Park

Concepcion

NPS (1998b) documented several non-contributing features within or outside of the unit. Noncontributing features were listed under four areas of the compound: core area, foreground, seminary, 

and visitor service areas. Those features included splash blocks, wells, sidewalks (concrete, wood, 

and brick), benches, fencing, steel stairs, grotto/pond, power poles and light fixtures, trash 

receptacles, bike racks, parking lot, signs and panels, basketball court, urban development, 

admissions/visitor contact buildings, and stone seating. NPS (2002) recorded five non-contributing 

landscape features within or outside of the unit. Those non-contributing features include the visitor 

center, utility features, urban development around the unit, mortared stone and pre-cast concrete

splash blocks, and altered hydrological cycle. The visitor center was not visible in the current NPS 
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photos, as it is located southeast of the selected points. It should be noted that there were no noncontributing features inside the park visible from vista 10. 

There were six non-contributing features inside SAAN that were visible from vista 8. The noncontributing features identified from a northern view were sidewalks and park signs (Photo 26). Light 

fixtures and the paved parking lot could be seen to the south of the vista. The paved roads could be 

seen to the west of the vista, and there was chain-link fencing in the park visible from the eastern 

view.

Photo 26. Views of Vista 8 (State archaeological monument on site sign) from all four cardinal directions 

(NPS Photos by Greg Mitchell).

There were 10 non-contributing features inside SAAN that were visible from vista 9. The noncontributing features identified to the north were a sidewalk, a utility pole, stone benches, and 

imported vegetation (Photo 27). A sidewalk was the only non-contributing feature seen to the east of 

the vista. Sidewalks, a parking lot, park signs, a brick splash wall, and light fixtures were visible to 

the south of this vista. A utility marker, paved road, and associated light fixtures were visible in the 

park to the west of Vista 9.
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Photo 27. Views of Vista 9 (Mission Concepcion Church) from all four cardinal directions (NPS Photos by 

Greg Mitchell).

San Jose

NPS (1998a) recorded one non-contributing landscape feature within the unit: the convent garden. 

Other possible non-contributing features may include utility features, and urban development. NPS 

(1995) documented twelve non-contributing features within the San Jose compound. Those features 

include brick walks, flagstone walks and paving, southwest portico, metal grates, metal and wood 

slat bench, Wilson Harris plaque, portable signage on concrete bases, trash receptacles, wooden 

benches, the wooden cross in the convent garden, metal ash cans, and a water fountain. All of these 

features, with the exception of the convent garden, are considered non-contributing because they 

were added after the 1911 – 1941 period of significance. Vistas 2, 3, and 4 were located in the San 

Jose Missions. Vista 11 was a portal associated with the unit, but it was located less than a kilometer 

northwest of this unit. It should be noted that there were no non-contributing features inside the park 

visible from vista 11.

There were six non-contributing features inside SAAN that were visible from Vista 2. A metal grate, 

sidewalks, trash receptacle, and benches can be seen from the northern view (Photo 28). The noncontributing features from the eastern view were imported vegetation, an ash can, and sidewalks. A
221

sidewalk was the only non-contributing feature from the southern view, and a metal bench under a 

tree and the sidewalk were the only non-contributing features in the western view.

Photo 28. Views of Vista 2 (Mission San Jose Church) from all four cardinal directions (NPS Photos by 

Greg Mitchell).

There were 10 non-contributing features in the park at Vista 3 (Visitor Center). According to the 

CLR, the visitor center building is a non-contributing feature to SAAN. Imported or disturbed 

vegetation and sidewalks were visible from all directions (Photo 29). A park sign was visible to the 

north of this vista. Blue barricades and the parking lot were the non-contributing features to the east. 

Roads, associated signs, and light fixtures are visible from the southern view of this vista. A trash 

receptacle, park signs, and metal benches are visible from the western view of this vista.
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Photo 29. Views of Vista 3 (Visitor Center) from all four cardinal directions (NPS Photos by Greg 

Mitchell).

There were eight non-contributing features in the park at Vista 4. It should be noted that construction 

was occurring at Vista 4 while this assessment was being completed. That being said, some noncontributing features may not have been included due to lack of visibility. Imported or disturbed 

vegetation, sidewalks, a road, guard rails, and a marker were visible to the north (Photo 30). A fence 

and shed were the non-contributing features to the east. A brick wall and fence were visible to the 

south of this vista. A trash receptacle, sidewalk, and fence were visible to the west of this vista.
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Photo 30. Views of Vista 4 (GPS mark washer north of Grist Mill) from all four cardinal directions (NPS 

Photos by Greg Mitchell). Tarps and webbed fencing were part of the construction activities occurring at 

this vista.

San Juan

NPS (2011a) documented seven non-contributing features located within or outside of Mission San 

Juan. Those features include: Slattery Hall; a new pump house north of the old dam; a gazebo 

associated with San Antonio State hospital; private, post-colonial houses built on historic labores; 

privately owned houses and outbuildings near former Graf Road; masonry stone walls along the new 

San Juan dam access road; and a well structure associated with San Antonio State Hospital west of 

the old dam. Other non-contributing features may include power lines, light fixtures, paved roads, 

sidewalks, metal benches, and disturbed or imported vegetation. Vistas 0, 5, 12, 14, 15, 16, 17, and 

18 were all located in the San Juan Missions Unit.

Vista 0 is located on the southwest border of the San Juan labores in the San Juan Missions Unit. 

None of the non-contributing features listed in the CLR for Mission San Juan were visible from this 

vista. The only non-contributing features visible in the park from Vista 0 were power lines (west) and 

disturbed vegetation. Disturbed vegetation was visible from all four cardinal directions (Photo 31).
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Photo 31. Views of Vista 0 (Carsonite marker at acequia mile 3.3) from all four cardinal directions (NPS 

Photos by Greg Mitchell).

There were six non-contributing features in the park at Vista 5. The visible non-contributing features 

included disturbed and imported vegetation, street signs, park signs, paved roads, a utility box, and 

power lines. Disturbed or imported vegetation could be seen from all directions (Photo 32).

Disturbed and imported vegetation, roads and associated signs, a utility box, and power lines were 

visible to the north of this vista. A park sign was the only non-contributing feature that was visible to 

the east. A power line was the only non-contributing feature to the west. None of the noncontributing features mentioned in the CLR were visible from this location.
225

Photo 32. Views of Vista 5 (Mission San Juan) from all four cardinal directions (NPS Photos by Greg 

Mitchell).

There were 11 non-contributing features in the park at Vista 12. The major non-contributing feature 

was Slattery Hall; it was located directly east of the vista (Photo 33). Slattery Hall was the only noncontributing feature mentioned in the CLR for this unit. Sidewalks and disturbed or imported 

vegetation could be seen from all directions. The non-contributing features visible to the north of this 

vista include the parking lot, roads, street lamps, and power lines (Photo 33). To the east, a road, 

street signs, and a parking lot were visible. A metal bench and park sign were visible to the south, 

and a bike rack and another metal bench were visible to the west. 
226

Photo 33. Views of Vista 12 from all four cardinal directions (NPS Photos by Greg Mitchell).

There were three non-contributing features in the park at Vista 14. Disturbed vegetation was a noncontributing feature that could be seen from all directions. To the north, a park sign is visible, along 

with some kind of structure in the distance. A bridged road was seen to the west of this vista (Photo 

34). The only non-contributing feature to the east was disturbed vegetation. The road was also visible 

to the south as well as a brick splash wall. None of the non-contributing features mentioned in the 

CLR were visible from this location.
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Photo 34. Views of Vista 14 (Mill Ruins) from all four cardinal directions (NPS Photos by Greg Mitchell).

Vista 15 was located at the Acequia Park security building. There were seven non-contributing 

features in the park at this vista. Disturbed or imported vegetation was visible in all four directions 

(Photo 35). The rest area, signs, road and guard rail were all non-contributing features to the north. A 

parking lot, associated sign, roads, and building beyond the tree line were visible to the east. The 

road and guard rail were the only non-contributing features to the south of this vista. None of the 

non-contributing features mentioned in the CLR were visible from this location.
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Photo 35. Views of Vista 15 (Acequia Park Security Building) from all four cardinal directions (NPS 

Photos by Greg Mitchell).

Vista 16 is located in the grassy area near the dam. There were only two non-contributing features 

visible in the park at this vista (Photo 36). Disturbed or imported vegetation was visible from all four 

directions. A road could be seen to the north, south, and west of this vista.
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Photo 36. Views of Vista 16 (in prairie near the dam) from all four cardinal directions (NPS Photos by 

Greg Mitchell).

Vista 17 was the dam overlook. There were six non-contributing features inside the park that were 

visible from this vista. Brick block retaining walls, a gravel walk, and disturbed and imported 

vegetation were visible to the north (Photo 37). Concrete stairs, metal railing, a brick block retaining 

wall, and disturbed or imported vegetation are visible to the east. Disturbed vegetation may be the 

only non-contributing feature visible to the south, although a road can be seen through the trees when 

they are not in leaf. The dam, chain link fencing, the dam access road, and disturbed vegetation were 

visible to the west of the overlook. None of the non-contributing features mentioned in the CLR were 

visible from this location.
230

Photo 37. Views of Vista 17 (the dam overlook) from all four cardinal directions (NPS Photos by Greg 

Mitchell).

Vista 18 was located at the end of the Acequia Trail. There was one non-contributing feature inside 

the park that was visible from this vista. A fence surrounding the unit boundary was the only feature 

visible; it was visible to the east of this vista (Photo 38). None of the non-contributing features 

mentioned in the CLR were visible from this location.
231

Photo 38. Views of Vista 18 (End of Acequia Trail) from all four cardinal directions (NPS Photos by Greg 

Mitchell).

Espada

NPS (2011b) documented six major non-contributing features located within or outside of Mission 

San Francisco de la Espada. Those features include: the River Rest Pavilion and auxiliary structures; 

Army Corps of Engineers river channel alterations (weir, concrete-lined channels, new dam); former 

Head Start headquarters and playground; Parish Hall; Espada Convent; and mobile homes in the 

labores. Camino Coahuilteca, hiking and biking trail, Interstate Loop 410, low water crossing 

bridges, sidewalks and paths, driveways, park and street signs are minor non-contributing features 

listed for Mission Espada. Other non-contributing features may include power lines, light fixtures, 

metal benches, and disturbed or imported vegetation. Vistas 1, 6, 7, 13, 19, 20, and 21 were located 

in or near the Espada Mission. 

Vista 1 was located near the River Rest Pavilion. There were 11 non-contributing features visible 

inside the park from this vista. The two major non-contributing features visible were Camino 

Coahuilteca, and the River Rest pavilion and auxiliary structures (Photo 39). Camino Coahuilteca, a 

sidewalk, and park sign were visible to the north; a wood fence and sidewalk were visible to the east; 

the pavilion and associated structures (e.g., metal picnic tables, trash receptacles, flag pole), and a

wooden bench were visible to the south; Camino Coahuilteca, utility building, utility pole, light and a 
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fixture were visible to the west. Disturbed or imported vegetation may also be considered a noncontributing feature visible in every direction at this vista.

Photo 39. Views of Vista 1 (River Rest Pavilion) from all four cardinal directions (NPS Photos by Greg 

Mitchell).

Vista 6 was located near the Mission Espada sign. There were 14 non-contributing features visible 

inside the park from this vista. The three major non-contributing features visible were Camino 

Coahuilteca, Parish Hall, and the former Head Start headquarters building, which were both visible to 

the south and east of this vista (Photo 40). There were no non-contributing features visible to the 

north. An unidentified road and wooden guardrail were also visible to the east. A parking lot, trash 

receptacle, park sign, road sign, and fire hydrant were visible to the south. Espada Road, wooden 

guardrail, light fixtures with banners; short brick walls, and residences were visible to the west.
233

Photo 40. Views of Vista 6 from all four cardinal directions (NPS Photos by Greg Mitchell).

Vista 7 is located near the San Francisco de la Espada Mission. There were 12 non-contributing 

features visible inside the park from this vista. The two major non-contributing features visible were 

the former Head Start headquarters building and playground, which were both visible to the east of 

this vista (Photo 41). A wooden guardrail and gravel parking lot were the only non-contributing 

features to the north. A short brick wall was also visible to the east. A park sign, stop sign, and light 

fixture were visible to the south. A short brick wall, benches, sidewalk, park sign, imported 

vegetation, trash receptacle, and wooden guardrail were visible to the west.
234

Photo 41. Views of Vista 7 (San Francisco de la Espada Mission) from all four cardinal directions (NPS 

Photos by Greg Mitchell).

Vista 13 is located near the Espada Aqueduct. There were 10 non-contributing features visible inside 

the park from this vista. There were no major non-contributing features visible at this vista (Photo 

42). A metal bench, sidewalk, and drainage pipe were the non-contributing features visible to the 

north. A sidewalk, paving stones, and a wooden guardrail were visible to the south. A park sign, 

powerlines, light fixture, and a trash receptacle were visible to the west. 
235

Photo 42. Views of Vista 13 (Espada Aqueduct) from all four cardinal directions (NPS Photos by Greg 

Mitchell).

Vista19 is located in the parking lot near the San Francisco de la Espada Mission. There were 15 

non-contributing features visible inside the park from this vista. The two major non-contributing 

features visible were Parish Hall and Camino Coahuilteca, which were visible to the north and south, 

respectively (Photo 43). Camino Coahuilteca was also visible to the east and west of this vista. Other 

non-contributing features to the north include a parking lot, parking signs, park signs, and light 

fixtures. The parking lot was also visible to the east and west. A utility box, light fixtures with 

banners, power lines, a metal gate, and street signs were also visible to the east. Only a fire hydrant 

was visible to the south. A large shed, guardrail, street signs, and more light fixtures with banners 

were visible to the west.
236

Photo 43. Views of Vista 19 (parking lot near the San Francisco de la Espada Mission) from all four 

cardinal directions (NPS Photos by Greg Mitchell).

Vista 20 is located in a grassy area near the aqueduct. There were four non-contributing features 

visible inside the park from this vista. There were no major non-contributing features visible at this 

vista. There were no non-contributing features to the east, south, or west (Photo 44). The parking lot, 

utility box, power lines, and park signs were visible to the north.
237

Photo 44. Views of Vista 20 (grassy area near the aqueduct) from all four cardinal directions (NPS 

Photos by Greg Mitchell).

Vista 21 is located east of the original Espada Dam. There were nine non-contributing features 

visible inside the park from this vista. River-channel alterations of the dam were the major noncontributing features visible at this vista (Photo 45). There were no non-contributing features to the 

south. A wooden guardrail, metal fence, brick marker, sidewalk, and brick retaining were the noncontributing features to the north. A park road, a wooden guardrail, sidewalk, road signs, and a bike 

rack were visible to the east. A retaining wall, park sign, and concrete marker were visible to the 

west.
238

Photo 45. Views of Vista 21 (east of the original dam) from all four cardinal directions (NPS Photos by 

Greg Mitchell).

Rancho de las Cabras

NPS (1998b) and OCULUS (1998) documented several non-contributing features within or outside 

of the Rancho Unit. Features were considered non-contributing if creation or presence in the unit 

occurred after the period of significance. The period of significance for the Rancho Unit is described 

as Spanish colonial. Non-contributing features in the Rancho Unit include the quarry (caliche 

excavation), an earthen dam, electric transmission lines, buried gas line easements, archeological 

investigations, the entrance road and gate, vehicle tracks (along northern and western property, 

upland margin, and surrounding ruins and quarry), early succession from improved pasture 

vegetation community, improved pasture vegetation community, recently disturbed imported and 

quarry vegetation community, gate at the end of the panhandle, fencing (along panhandle, along 

northern southern and western property boundary, along the upland margin, along eastern field 

margin), historical markers and signs at the compound, and views of neighboring residences and 

discarded waste.

Vista 22 is located in the center of the ruins in the Rancho Unit. The non-contributing features visible 

from this vista included the quarry, disturbed and imported vegetation, archeological investigations,
239

the historical marker, gravel road, and fencing. Other non-contributing features (vehicle tracks) may 

be present but are not visible from the photos. Disturbed and imported vegetation could be seen in

every direction in the ruins area. Some archaeological investigations and the quarry are located in the 

northern section of the ruins. More archeological investigation activity was visible south of the vista 

point. A small section of fencing was visible at the eastern edge of the ruins. Photo 46 displays the 

vista 22 which is located at the center of the ruins in the Rancho Unit.

Photo 46. Views of Vista 22, located at the center of the ruins, from all four cardinal directions (NPS 

Photos by Greg Mitchell).

Vista 23 is located at the high point overlook in the Rancho Unit. The non-contributing features 

inside the park and visible from this vista included disturbed and imported vegetation. A road can 

also be seen to the west of this point. Other non-contributing features (vehicle tracks) may be present 

but are not visible from the photos (Photo 47).
240

Photo 47. Views of Vista 23, located at the high point overlook, from all four cardinal directions (NPS 

Photos by Greg Mitchell).

Vista 24 is the entrance road to the Rancho Unit. Three photo points (24, 25, and 26) were used to 

determine the non-contributing features visible inside and outside the park along the entrance road. 

The photos points were located along the entrance road from the eastern most culvert along the 

entrance road to the entrance gate (Photo 48– 50, Figure 64). There were a few non-contributing 

features visible from photo point 24. A water tower can be seen in the distance from the north. 

Grazed (disturbed) vegetation can be seen just past the northern park boundary. Electric transmission 

and power towers could be seen to the south and west of this point. A neighboring residence can also 

be seen to the west. 
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Figure 64. Locations of photo points used to display non-contributing features along the entrance road

(Vista 24).

Photo point 24 was located at the eastern most culvert along the entrance road in the Rancho Unit.

The non-contributing features inside the park and visible from this vista included disturbed and 

imported vegetation and fencing. Fencing and disturbed vegetation could be seen in every direction 

at this vista. Photo 48 displays the views from the eastern point on the entrance road in the Rancho 

Unit.
242

Photo 48. Views of photo point 24, located at the eastern most culvert along the entrance road, from all 

four cardinal directions (NPS Photos by Greg Mitchell).

Photo point 25 is located at the middle of the entrance road in the Rancho Unit. The non-contributing 

features inside the park and visible from this vista included disturbed and imported vegetation, 

fencing, signs, and the entrance road. Fencing and disturbed vegetation could be seen in every 

direction at this vista. A power line corridor can be seen to the north and south. A warning sign is 

seen to the north of the road (Photo 49). 
243

Photo 49. Views of photo point 25, located near the middle point on the entrance road, from all four 

cardinal directions (NPS Photos by Greg Mitchell).

Photo point 26 is located at the entrance gate along the entrance road in the Rancho Unit. The noncontributing features inside the park and visible from this vista included disturbed and imported 

vegetation, fencing, and the entrance road. Fencing and disturbed vegetation could be seen in every 

location at this vista (Photo 50).
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Photo 50. Views of photo point 26, located at the entrance gate of the Rancho Unit, looking northeast 

and east into the park (NPS Photos by Greg Mitchell).

Number of Non-Contributing Features Visible Outside of the Park

Concepcion

Non-contributing features located outside of the park were visible from all three vistas associated 

with Mission Concepcion (8, 9, 10). Urban development (residential/commercial buildings) was the 

main type of non-contributing feature located outside of the park visible from Mission Concepcion 

Vistas. Saint Peter – Saint Joseph Children’s Home is visible to the south and west of Vista 8; more 

residential buildings and a convenience store were north and west of this vista. Saint Peter – Saint 

Joseph Children’s Home is just visible from Vista 9 (see Photo 25 and Photo 26).

Vista 10, a portal location, was located outside SAAN west of Concepcion. The top of the Mission 

can just be seen over the trees to the east. Vista 10 is located at a park pavilion (sidewalks, brick 

mosaic walls, fencing, light fixtures, utility box) which is a non-contributing feature. Imported 

vegetation could have also been placed at this location to add to its aesthetics. To the west of Vista 

10, urban development (residential housing, light fixtures, sidewalks) and a human-altered river 

corridor are the non-contributing features that are visible (Photo 51).
245

Photo 51. Views of Vista 10, portal located to the west of the Mission Concepcion Unit, from all four 

cardinal directions (NPS Photos by Greg Mitchell).

San Jose

Non-contributing features located outside of the park were visible from two vistas (3, 11). Vistas 2 

and 4 were surrounded by the mission walls or vegetation tall enough to limit the viewshed to within 

the park. Vista 3 was located at the visitor center. Urban development (buildings) and power lines 

were non-contributing features visible outside the park at this vista; they were visible to the south 

above the tree line (Photo 28). 

Vista 11 is another portal located in Mission County Park, which is outside of SAAN. Although not 

seen in the selected photos below, Mission San Jose is visible to the southwest from this location. 

Imported or disturbed vegetation, sidewalks, and power lines could be seen in all directions. 

Residential buildings, roads, a light fixture, and trash receptacles are visible to the north. The altered 

river channel, commercial buildings, a bridge, and a playground were visible to the east. The park 

facility building, parking lot, and more residential buildings are visible to the south, and roads and 

residential buildings were visible to the west (Photo 52).
246

Photo 52. Views of Vista 11, portal located to the northeast of the Mission San Jose Unit, from all four 

cardinal directions (NPS Photos by Greg Mitchell).

San Juan

Non-contributing features located outside of the park were visible from five vistas associated with 

Mission San Juan (0, 14, 15, 16, and 18). Vistas 5, 12, and 17 were surrounded by vegetation tall 

enough to limit the viewshed to within the park. Power lines were visible to the east and south, and a 

dumpster was visible past the tree line to the east of Vista 0 (Photo 31). Mission Road, its associated 

road signs, and power lines could be seen to the west of Vista 14 (Photo 34). The refinery smoke 

stacks were the only non-contributing features visible to the north of Vista 15 (Photo 35). North of 

Vista 16, a billboard was visible through a tree line (Photo 36). Vista 18 was located just outside the 

SAAN boundary in Mission San Juan (Photo 38). A sidewalk, bench, and trash receptacle were 

visible to the north of Vista 18. The San Antonio River runs just southeast of Vista 18; human 

influence on San Antonio River corridor may be considered a non-contributing feature occurring to 

the west and south of this vista.

Espada

Non-contributing features located outside of the park were visible from three vistas (1, 20, and 21). 

Vistas 6, 7, 13, and 19 were surrounded by vegetation tall enough to limit the viewshed to within the 

park. At Vista 1, paved sidewalks could be seen to the north and east; an overpass and paved road 
247

were also visible to the north of this vista (Photo 39). Ashley Road, associated road signs, and urban 

development could be seen to the west of Vista 20 (Photo 44). Vista 21 seemed most effected by

non-contributing features outside of the park. The Mission Park Cemetery plots are visible to the 

west, and the tall refinery smoke stacks were visible to the east (Photo 45). 

Rancho de las Cabras

The Rancho Unit may be in a more rural location than the Missions Unit, but tall non-contributing 

features can be seen from all five vistas and photo points in the park. Vistas 22 and 23 were located 

in the main portion of the ranch, surrounded by vegetation. Vista 22 was located in the center of the 

ruins in the Rancho Unit (Photo 46). Tall vegetation prevented visibility of most features outside the 

park from this location. As a result, only one non-contributing feature was visible at this vista. A 

water tower could be seen to the north of the ruins. Vista 23 was located at the high point overlook in 

the Rancho Unit (Photo 47). Tall vegetation prevented visibility of features outside the park to the 

south and west of this location. The non-contributing features visible from this vista included a water 

tower and electric transmission towers and lines. The water tower can be seen to the north and the 

transmission lines comprise the eastern view.

Photo points 24 through 26 (entrance road vista) occur along the entrance road from the eastern most 

culvert along the entrance road to the entrance gate (Figure 65). 

Photo point 24 was near the panhandle of the Rancho Unit (Photo 48, Figure 65). The noncontributing features outside the park and visible from this point included disturbed and imported 

vegetation, neighboring residences, and electric transmission towers and lines. Disturbed and 

imported vegetation can be seen in all directions. Power lines, a water tower, and a neighboring 

residential building were visible to the north of this point. Electric transmission lines and towers as 

well as a neighboring residence can be seen to the west of this point, and an indiscernible feature can 

be seen to the left of the tree line to the south of this point.

Photo point 25 was near the middle of the entrance road vista (near the electric transmission towers) 

in the Rancho Unit (Photo 49, Figure 65). The non-contributing features outside the park and visible 

from this point included disturbed and imported vegetation, neighboring residences, electric 

transmission towers and lines, and fencing. Disturbed and imported vegetation can be seen in all 

directions. Power lines, a water tower, and a neighboring residential building were visible to the 

north of this point. Fencing can be seen in the distance to the east. Electric transmission lines and 

towers, fencing and neighboring residence can be seen to the south of this point. A transmission 

tower is located very close (several meters) to the park and west of this point.

Photo point 26 was located at the entrance gate to the Rancho Unit (Photo 50, Figure 65). This photo

point only displays non-contributing features to the east and northeast. The non-contributing features 

outside the park and visible from this point include disturbed and imported vegetation, neighboring 

residences, electric transmission towers and lines, a water tower, and fencing. Disturbed and 

imported vegetation and transmission lines, and fencing can be seen in both directions. An electric

transmission tower and a water tower can be seen to the northeast, and neighboring residential 

property was visible to the east of this point. 
248

Appearance of San Juan Labores

The San Juan labores, or historic Mission farmland, are a cultural resource in the park. These labores 

were used to grow several crops, including corn, beans, chilies, melons, cotton, sugar cane, and 

squash (NPS 2007). They are located near the southern border of the Missions Unit near the San 

Antonio River, and were historically irrigated by irrigation ditches called acequias (NPS 2007, Figure 

62). Park staff provided current photos of the San Juan labores from several vantage points. 

The reference condition for the San Juan labores is to maintain zero woody vegetation in the labores 

and to preserve the shrub and tree rows between fields. From the aerial view alone, it can be said that 

there is some woody vegetation (shrubs and trees) in the labores north of gate 9155, but most of the 

labores have remained clear of woody vegetation. Photo 53 displays the views of the San Juan 

labores from gates 9155 (left) and 9107 (right).

Photo 53. Views of the San Juan labores from gates 9155 (left) and 9107 (right) (NPS Photos by Greg 

Mitchell).

Threats and Stressor Factors

SAAN park staff have identified several threats that impact the park’s cultural and natural viewscape.

Those threats include urban development expanding south, power line corridors, cell towers, 

encroaching vegetation, and in-park development.

Urban development that is expanding south of the park poses a threat to the SAAN viewscape. 

According to Cooper et al. (2005), adjacent land use and outside development are high priority 

management issues because they may significantly impact several natural resources in the park, 

including viewscape. Figure 66 and Figure 67 display the landcover changes in SAAN and 

surrounding areas from 2001 to 2011. 
249

Figure 65. Extent of the San Juan labores in SAAN. 
250

Figure 66. Landcover change from 2001 to 2011 in SAAN and surrounding areas (MRLC 2014). Areas 

shaded in darker gray are the areas visible from the park vistas.

The electric transmission towers and cell towers are also a threat to the viewscape of SAAN. Due to 

the location of the Missions Unit in San Antonio, the power lines and cell towers can be seen from

most of the unit. The Rancho Unit may be in a more rural location, but a transmission tower is 

located in close proximity to its northern boundary. Power lines or transmission towers can be seen at 

all vistas in the Rancho Unit (Photo 46-Photo 50).

Encroaching vegetation is a potential threat to the SAAN viewscape. The Espada and San Juan 

labores may be at risk of encroachment of exotic species due to the open landscape of native plant 

communities if not consistently managed; however, the labores are mowed annually and therefore are 

currently not at risk (Mitchell, written communication, 9 March 2015). There were two exotics, in 

particular, that may negatively impact unmanaged labores. Those species are Chinaberry and glossy 

privet (Ligustrum lucidum) (Saperstein 2002). According to Saperstein (2002) these exotics occur 

throughout the park, but seem to thrive more in areas of human disturbance. Control actions have 

been put in place to remove these two exotic species, so they do not spread further within the park.
251

Figure 67. Landcover change from 2001 to 2011 in SAAN’s Rancho Unit and surrounding areas (MRLC 

2014). Areas shaded in darker gray are the areas visible from the park vistas.

In-park development is another threat to viewscape in SAAN. A new parking facility and the 

development of the Spanish Colonial demonstration farm are examples of the most current 

developments (Oliver, written communication, 9 March 2015). The demonstration farm will display 

another side to the Missions’ culture. According to Los Compadres de San Antonio Missions (2015), 

Mission San Juan was known for its rich farmlands and pastures. The objectives of the farm will be

to utilize historic farmlands and create an emphasis on SAAN’s living history. While the farm itself 

will be a contributing feature to the cultural landscape, the parking area and any interpretive signage 

or modern structures to support farm operations will be non-contributing features. 

Data Needs/Gaps

Continued development of spatial data that explain landscape change will enable accurate and up-todate viewshed assessments of the metrics examined in this analysis. These data could help park staff 

work with city planners to minimize the impact of surrounding development on the park’s viewshed.
252

Overall Condition

Number of Non-Contributing Features Visible Within the Park

The Significance Level for number of non-contributing features visible within the park boundary was 

defined as a 3. There were several non-contributing features visible inside the park at all of the vistas 

in Missions Concepcion, San Jose, and Espada. A few vistas in San Juan were in less developed 

areas; those vistas had fewer than three non-contributing features each. The number of noncontributing features at both Mission Concepcion and Mission San Jose vistas ranged from six to 10 

features. At Mission Espada vistas, the number of non-contributing features ranged from 4 to 15. The 

number of non-contributing features at Mission San Juan vistas ranged from one to 11 features, while 

the number of non-contributing features at the Rancho de las Cabras Unit vistas ranged from two to 

six features. As a result, the Condition Level for this measure is a 3, indicating high concern.

Number of Non-Contributing Features Visible Outside of the Park

The Significance Level for number of non-contributing features visible outside the park boundaries 

was defined as a 2. There were several non-contributing features visible outside the park at all of the 

vistas. The number of non-contributing features at both Mission Concepcion and Mission San Juan 

vistas was 10 features each. The number of non-contributing features at Mission Espada and Rancho 

Unit vistas totaled five and seven features, respectively. The number of non-contributing features at 

Mission San Jose vistas totaled 12 features. Missions Concepcion and San Jose may be at a higher 

risk of non-contributing features outside of the park than Missions San Juan and Espada because the 

first two units are small and lack tall vegetation bordering the unit boundary. San Juan and Espada 

are also further from the city center, where urban development has not been as intense. The 

Condition Level for this measure is also a 3, or high concern.

Appearance of San Juan Labores

The Significance Level for appearance of the San Juan labores was defined as a 3. The aerial photo 

and NPS photos were helpful in showcasing the appearance of the labores as of 2014. From the aerial 

view alone, it can be said that there are some shrubs and trees in the labores north of gate 9155, but 

most of the labores have remained clear of woody vegetation. The reference condition for the San 

Juan labores is to maintain zero woody vegetation in the labores and to preserve the shrub and tree 

rows between fields. As a result, the Condition Level for this measure is currently a 1, or low 

concern.

Weighted Condition Score

The Weighted Condition Score (WCS) for the component is 0.75, indicating viewscape is of 

significant concern overall. The change in landcover from 2001 to 2011 illustrates a growing city of 

San Antonio. This increase in development surrounding SAAN suggests a declining trend for 

viewscape.
253

Viewscape

Measures

Significance 

Level

Condition 

Level WCS = 0.75

Number of NonContributing Features 

Visible inside of the 

Park

3 3

Number of NonContributing Features 

Visible outside of the 

Park

2 3

Appearance of San 

Juan Labores 3 1

4.14.6 Sources of Expertise

Greg Mitchell, SAAN Natural Resource Specialist

James Oliver, SAAN Landscape Architect

4.14.7 Literature Cited

Bailey, W. S. 2014. San Antonio inches closer to securing World Heritage Site designation for 

historic missions. San Antonio Business Journal. 

http://www.bizjournals.com/sanantonio/blog/2014/01/san-antonio-inches-closer-tosecuring.html?ana=e_du_pub&s=article_du&ed=2014-01-20 (accessed 10 April 2015).

Cooper, R. J., S. B. Cederbaum, and J. Gannon. 2005. Natural resource summary for San Antonio 

Missions National Historical Park (SAAN). Final Report. Warnell School of Forest Resources, 

University of Georgia, Athens, Georgia.

Han, K-T. 2010. An exploration of relationships among responses to natural scenes. Scenic beauty, 

preference and restoration. Environment and Behavior 42(2):243–270.

Kearney, A. R., G. A. Bradley, C. H. Petrich, R. Kaplan, S. Kaplan, and D. Simpson-Colebank. 2008. 

Public perception as support for scenic quality regulation in a nationally treasured landscape. 

Landscape and Urban Planning 87:117–128. 

Los Compadres de San Antonio Missions (2015). San Juan Spanish colonial farm. 

http://loscompadres.org/about-us/san-juan-spanish-colonial-farm (accessed 23 March 2015).

Multi-Resolution Land Characteristics Consortium (MRLC). 2014. National Land Cover Database 

2006 product legend. http://www.mrlc.gov/nlcd06_leg.php (accessed 21 August 2014).
254

National Park Service (NPS). 1995. Mission San Jose: cultural landscape report. San Antonio 

Missions National Historical Park, San Antonio, Texas.

National Park Service (NPS). 1998a. Cultural landscape inventory: Mission San Jose. San Antonio 

Missions National Historical Park, San Antonio, Texas.

National Park Service (NPS). 1998b. Mission Concepcion cultural landscape report, volume 3. 

Contract Number 1443CX700092007. San Antonio Missions National Historical Park, San 

Antonio, Texas.

National Park Service (NPS). 1998c. Rancho de las Cabras: cultural landscape inventory. San 

Antonio Missions National Historical Park, San Antonio, Texas.

National Park Service (NPS). 2002. Cultural landscapes inventory: Mission Concepcion. San 

Antonio Missions National Historical Park, San Antonio, Texas.

National Park Service (NPS). 2007. Mission San Juan Capistrano. NPS brochure. San Antonio 

Missions National Historical Park, San Antonio, Texas.

National Park Service (NPS). 2011a. Cultural landscape inventory: Mission San Fransisco de la 

Espada. San Antonio Missions National Historical Park, San Antonio, Texas.

National Park Service (NPS). 2011b. Cultural landscape inventory: Mission San Juan. San Antonio 

Missions National Historical Park, San Antonio, Texas.

OCULUS. 1998. Rancho de las Cabras: Cultural landscape report. Contract Number 

1443RP760097002. San Antonio Missions National Historical Park, San Antonio, Texas.

Saperstein, A. 2002. Controlling exotic Chinaberry and glossy privet. Implementation Plan for FY 

02. Unpublished Report 2170487. San Antonio Missions National Historical Park, San Antonio, 

Texas.

Sheppard, S. R. J. 2001. Beyond visual resource management: emerging theories of an ecological 

aesthetic and visible stewardship. Pages 149-172 in Forests and landscapes: Linking ecology, 

sustainability and aesthetics. Sheppard, S. R. J., and H. W. Harshaw (eds.). CABI Publishing, 

New York, New York.
255

4.15 Hydrology (Surface and Groundwater)

4.15.1 Description

Availability of a reliable water source is of great importance in semi-arid regions such as southcentral Texas (Meiman 2012). This importance can be seen throughout the park. The Missions that 

make up SAAN would not have been built if not for the San Antonio River, as it was the reliable 

source the native peoples and missionaries used to irrigate their fields and grazing areas (Meiman 

2012). Irrigation was accomplished through a series of acequias (gravity-fed ditches) that carried 

water to the fields and grazing areas (Meiman 2012).

As shown in Figure 68, the San Antonio River has its headwaters at the San Antonio Springs within 

the San Antonio city limits (USACE 1965). The river flows in a southeasterly direction for 

approximately 386 km (240 mi) (USACE 1965, Phillips 2011). The river drains an area of 

approximately 10,859 km2 (4,193 mi2) before it joins the Guadalupe River (Phillips 2011, USDANRCS 2014). This confluence is in a tidally-influenced delta area, just upstream of Tivoli, Texas, 

approximately 11 km (6.5 mi) upstream of Guadalupe/San Antonio Bay (Phillips 2011).

Figure 68. General location of SAAN and the San Antonio River in southeast Texas.

Historically, the main source of base flow in the San Antonio River was from the headwater springs 

and other area springs (TIFP 2009, TIFP 2012). Over the past several decades, the river has evolved 

from a system driven by spring flow to a system that is highly influenced by year-round wastewater 

treatment plant discharges, intermittent diversions, and a mix of various urban and rural land uses 

(TIFP 2009, TIFP 2012). While this is especially the case for the upper reaches of the San Antonio 

River, the hydrology of the lower portion (below USGS gauge 08181800 near Elmendorf [Figure 

67]) continues to be variable with the seasons (TIFP 2009, TIFP 2012). Flow in this reach is

dependent on precipitation patterns and is supported by spring flow (TIFP 2009, 2012). However,
256

recently the flow in the river has been augmented by treated municipal effluent, primarily through 

return flows from groundwater pumped from the Edwards Aquifer (TIFP 2009, 2012).

SAAN is comprised of a series of small disconnected parcels located along the San Antonio River 

within the greater San Antonio River basin. Mission Concepción, Mission San José, Mission San 

Juan and Mission Espada (Missions Unit) are within the San Antonio urban boundary and the 

Rancho de las Cabras (Rancho) is located to the southeast of San Antonio, near Floresville, Texas 

(Figure 68). The San Antonio River basin is comprised of four sub-basins, the Medina, Cibola, Upper 

San Antonio and Lower San Antonio (USDA-NRCS 2014). The Missions Unit is located in the 

Upper San Antonio sub-basin and the Rancho is located within the Lower San Antonio sub-basin 

(Figure 68). The Upper San Antonio and Lower San Antonio sub-basins differ in land use, channel 

characteristics and flow regime (TIFP 2009, 2012, Meiman 2012, NPS 2014).

The Upper San Antonio sub-basin drains approximately 131,274 ha (324,384 ac) of mostly the 

metropolitan San Antonio area. This sub-basin has undergone a great deal of alteration and 

modification over the past several decades due to urban development (TIFP 2009, 2012, NPS 2014). 

The land-use within this sub-basin is primarily developed urban, with a relatively level topography, 

except in the vicinity of the old river channels (Carr 2003a). The channel remnants have become 

riparian habitat for many wildlife species (Cooper et al. 2005). The current active channel of the San 

Antonio River has been highly modified for flood control purposes and is administered and 

maintained by the San Antonio River Authority (SARA) (Carr 2003a). Elevation within the subbasin ranges from about 152 m (500 ft) above mean sea level near Mission Espada to 183 m (600 ft) 

at Mission Concepción (Carr 2003a).

The Lower San Antonio sub-basin drains approximately 384,216 ha (949,418 ac) of primarily rural 

sparsely populated land (SARA 2003). In this basin the San Antonio River becomes a free-flowing 

undeveloped stream (Meiman 2012). The river also becomes more entrenched with steep, muddy 

banks, and is generally deeper than the upper sub-basins (SARA 2003). Elevation within the Rancho 

ranges from about 122 m (420 ft) above mean sea level at the gate along the county road to about 101 

m (330 ft) along the San Antonio River (Carr 2003b).

While SAAN does not own any portion of the San Antonio River, it does have ownership of some 

areas that are within the high-water mark (Meiman 2012). The park also retains water rights to 

supply the two remaining acequias which are owned and maintained by the park (Meiman 2012). The 

Acequia de Espada is located along the west side of the river and the Acequia de San Juan on the east 

side (Meiman 2012). In addition, the park also manages a segment of Piedras Creek, running from 

approximately 60-90 m (200-300 ft) upstream of where it is crossed by the Acequia de Espada 

aqueduct to its confluence with the San Antonio River (Greg Mitchell, SAAN Natural Resources 

Program Manager, written communication, 9 March 2015, Meiman 2012). Surface water resources 

within SAAN are shown in Figure 69. In the Missions Unit area, these resources consist of three 

segments of the San Antonio along with the acequias and Piedras Creek (Cooper et al. 2005). The 

inset of Figure 69 shows the surface water resources at Rancho de las Cabras. They are comprised of 

features including the San Antonio River and Picosa Creek, among others (Cooper et al. 2005).
257

4.15.2 Measures

 Stream flow rates

 Width:depth ratio

 Depth to groundwater (Rancho only)

4.15.3 Reference Conditions/Values

The ideal reference condition for this 

component would be the hydrological 

conditions during the Mission period. However, 

given the significant alterations to the San 

Antonio River basin since that time, this is no 

longer feasible. A specific reference condition 

for hydrology at SAAN was not defined. Given 

the long period of record, historic flows could 

be used as a reference condition.

4.15.4 Data and Methods

The information for this assessment was 

gathered primarily from hydrologic information 

included in several existing studies on the water 

quality, hydrology and geomorphology of the 

San Antonio River (e.g., USACE [1965], 

SARA [2003, 2009, 2012], TIFP [2009 and 

2012], Meiman [2012]). Stream discharge and 

groundwater flow rates were obtained from the 

United States Geological Survey (USGS) Water Information System website. Data for the stream 

gauges located along the San Antonio River, from upstream of Mission Concepción to downstream 

of Rancho (gauges 08178000, 08178050, 08178565, 08181800, 08183200 and 08183500], were 

downloaded for use in the discharge analysis (http://waterdata.usgs.gov/nwis/inventory/). Two 

groundwater wells are located to the west of Rancho de las Cabras near the Ray Farm Airport 

(TWDB 2014c). One well is administrated by the Texas Water Development Board (TWDB) and the 

other is administered by the USGS. Data for USGS groundwater monitoring well 

(290802098232901) were downloaded from the USGS Water Information website 

(http://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=290802098232901) and 

data for the TWDB well (6862104) were downloaded from the TWDB website 

(http://www.waterdatafortexas.org/groundwater/well/6862104). Additional groundwater data for well 

J-17 were also obtained from the Edwards Aquifer Authority (EAA) website. The J-17 index well is 

located near the national cemetery at Fort Sam Houston (Eckhardt 2015). It has a lengthy period of 

record and can be used to identify the effects of groundwater use within San Antonio on the depth to 

groundwater in the Rancho. Data for J-17 were downloaded from the EAA website 

(http://www.edwardsaquifer.org/aquifer-data-and-maps/historical-data/historic-data-downloads). 

Figure 69 Surface hydrology features at SAAN.
258

4.15.5 Current Condition and Trend

Stream Flow Rates

The USGS has monitored streamflow in the San 

Antonio River through a network of gauges 

since the 1920s (TIFP 2009, 2012). Six of these 

stations, with varying periods of record, are 

located in proximity to SAAN property and can 

be used to analyze stream discharge for the park 

(Figure 70). A summary of the data from the 

period of record for these gauges is listed in 

Table 59 and Figure 71 is a hydrograph of daily 

mean discharge for USGS Station 081178565. 

Analysis of streamflow in the San Antonio 

River basin shows that beginning with the 

earliest flow records, an increase in base flow is 

evident at all gauges in the basin (TIFP 2011). 

Several factors have contributed to this 

increase. Since the flow in the river is so 

dependent on reuse water, urban growth, 

groundwater pumping and return flows from 

the San Antonio metropolitan area have 

contributed to the increase in flow (TIFP 2009, 

2011, 2012). Also changes in precipitation have 

also contributed to increase in flow (TIFP 2009, 

2011, 2012). Average annual precipitation has increased from 70.6 cm (27.8 in) per year for the 

period 1940 through 1969 to 83.4 cm (33 in) per year during the period from 1970 to 2007 (TIFP

2009, 2012). The city of San Antonio and surrounding areas receive most of their municipal water 

supply from groundwater pumped from the Edwards Aquifer (TIFP 2009, 2012). According to U.S. 

Census Bureau (2014) data, the population of the city has increased from about 250,000 in 1940 to 

more than 650,000 in 1970 to more than 1.4 million in 2013. The San Antonio metropolitan area is 

projected to grow an additional 8.65% through 2018 (SAEDF 2014). This growth and expansion has, 

and will continue to result in changes in water withdrawals and return flows and to the patterns of 

surface runoff (TIFP 2009, 2012). Discharge from wells in the Edwards Aquifer in 2012 was 

estimated at 47,450 hectare-meters (384,685 acre-feet), which was above the 40,434 hectare-meter 

(327,800 acre-feet) median for the period of record (1934-2012) (EEA 2013). The maximum annual 

well discharge rate over the period of record was 64,684 hectare-meter (524,400 acre-feet), occurring 

in 1989 (EEA 2013). The minimum annual discharge rate over the period of record was 12,569 

hectare-meter (101,900 acre-feet), which occurred in 1934 (EEA 2013). Table 60 summarizes the 

median and mean estimated annual discharge from the Edwards Aquifer for both wells and springs 

for the period or record and the last 10 years.

Figure 70. USGS stream gauges in the vicinity of 

SAAN.
259

Table 59. Discharge observations based on mean daily discharge for USGS streamflow gauges near 

SAAN (TIFP 2012, USGS 2014). The top row for each gauge shows observations for the entire period of 

record, while the second row shows these measurements just over the past decade (2004-2014).

Gauge

Earliest 

Record

Latest 

Record

Minimum Flow 

cms (cfs)

Maximum Flow 

cms (cfs)

Median Flow 

cms (cfs)

Drainage Area 

km2(mi2)

08178000 1915 Present 0.002 (0.1) 90.3 (3190) 0.74 (26) 108.3 (41.8)

2004 - 2014 0.04 (1.4) 4.4 (154) 0.71 (25)

08178050 1992 Present 0.004 (0.1) 77.9 (2750) 0.8 (30) 109.3 (42.2)

2004 - 2014 0.004 (0.1) 76.747 (2710) 0.68 (24)

08178565 1986 Present 0.01 (0.5) 478.6 (16,900) 1.3 (47) 323.7 (125)

2004 - 2014 0.01 (0.5) 396.48 (14000) 1.25 (44)

08181800 1962 Present 0.7 (25) 1,767.2 (62,400) 8.8 (312) 4,514.3 (1,743)

2004 - 2014 1.05 (37) 945.888 (33400) 7.62 (269)

08183200 2006 Present 0.9 (33) 736.3 (26,000) 6.5 (229) 5,086.7 (1,964)

08183500 1925 Present 0.5 (19) 1,523.6 (53,800) 7.3 (258) 5,472.6 (2,113)

2004 - 2014 1.1 (39) 722.2 (25,500) 7.7 (273)

Figure 71. Period of record hydrography for daily mean discharge for USGS 08178565 (USGS 2014).

0

50

100

150

200

250

300

350

400

450

500

550

Daily Discharge (cms)
260

Table 60. Annual estimated groundwater discharge data for Edwards Aquifer, 1934–2012 (measured in 

thousands hectare-meters) (EAA 2013).

For period of record 1934–2012 For period of record 2003–2012

Total for wells

ha-m (ac-ft)

Total for springs

ha-m (ac-ft)

Total for wells

ha-m (ac-ft)

Total for springs

ha-m (ac-ft)

Median discharge 40.4 (327.8) 47.4 (383.9) 47.7 (386.6) 55.9 (453.6)

Mean discharge 38.8 (314.6 ) 47.3 (383.2) 47.5 (385.2) 56.6 (458.7)

During the last 50 years, water use in the San Antonio River basin has undergone a rapid 

transformation (TIFP 2009). This use has had an impact on streamflow in the San Antonio River. 

River flow has been increasingly augmented by return flows from municipal use within the San 

Antonio metropolitan area (TIFP 2009). In fact, the river has changed from a groundwater driven 

system to one highly influenced by year-round treated wastewater discharges, intermittent discharges 

and withdrawals, and a variety of urban and rural land uses (TIFP 2009, Lizarraga and Wehmeyer 

2012). It is so dependent on these augmented flows that without the reuse water, the San Antonio 

River would not flow during most summer months and during periods of drought (Meiman 2012). 

For example, flow at USGS Streamflow Gauge 08178565 (which drains the area from the headwaters 

to Interstate Highway 410 [I-410, or Loop 410] crossing) consists of 70 to 95% reuse water (Meiman 

2012). Other studies have shown that, on average, the annual streamflow in the Lower San Antonio 

sub-basin at USGS Streamflow Gauge 08181800 consisted of 33% stormwater runoff, 22% inflow 

from the Medina River, 20% wastewater discharge, and 18% groundwater inflow (Ockerman and 

McNamara 2002).

Some data are also available for flow rates in Piedras Creek (PCPC) and the Acequia de Espada 

(AEAE) within SAAN for a period between October 2007 and December 2011 (Meiman 2012).

Flows for PCPC ranged from >0.001 to 1 cms (0.01 to 37 cfs), while flows in AEAE ranged from no 

flow to 0.02 cms (0.7 cfs) (Meiman 2012).

Width:Depth Ratio

Stream channel hydraulic geometry analysis was first developed by Leopold and Maddock (1953). 

They related a number of dependent variables including steam width, depth, velocity and total 

sediment load as a function of discharge. These relationships provide a method of quantitatively 

describing channel form and the way in which the underlying variables vary with discharge (Gordon 

et al. 2004). Olson-Rutz and Marlow (1992) described four metrics derived from these variables that 

could be useful for quantifying change in channel form over time through the use of cross-sectional 

data from permanent transects. These matrices were: net percent change in area, absolute percent 

change in area, width/depth ratio, and the Gini coefficient. Net percent change quantifies the net 

change in cross-sectional area of a transect, the absolute percent change in area quantifies cumulative 

channel change, the width/depth ratio is an index of the shape of the stream, and the Gini coefficient 

is calculated as the arithmetic average of the differences between all pairs of depths along the 

transect (Olson-Rutz and Marlow 1992, Gordon et al. 2004). 
261

The width/depth ratio (W/D) is calculated by dividing the bankfull width by the bankfull depth 

(Gordon et al. 2004). It is a very sensitive metric, in that it can reflect even small changes in

streamflow or channel-forming processes (Rosgen 2001). Because of this sensitivity it can be 

diagnostic of channel instability, making it a key variable in determining whether a stream is 

departing from a stable reference condition (Rosgen 2001, EPA 2012). In general, W/D increases in 

the downstream direction, however it is strongly dependent on the composition (soil type, slope and 

vegetative cover) of the stream bank (Gordon et al. 2004).

As W/D changes over time, it is important to distinguish the differences between increases versus 

decreases in the ratio (EPA 2012). Increases in W/D are often associated with accelerated stream 

bank erosion, excessive sediment deposition, streamflow changes, channel widening and direct 

alteration of stream shape from channelization projects (Rosgen 2001). A decrease in W/D is only 

rated as a high risk when accompanied by a low bank height ratio (lowest bank height/maximum 

bankfull depth), which indicates along with the decrease in W/D, there is an associated increase in 

shear stress and unit stream power (EPA 2012).

The W/D can also be used as an indicator of aquatic habitat (Foster et al. 2001). Shade from the 

riparian vegetation, cover from undercut banks, and thermoregulation are all affected by W/D (Foster 

et al. 2001). A high W/D could increase the stream’s exposure to solar radiation, potentially resulting 

in higher temperatures and undercut banks are often reduced (Foster et al. 2001). In general, 

relatively deep and narrow streams (low W/D value) tend to provide better fish habitat than shallow 

wide streams (high W/D value), especially for salmonids (Foster et al. 2001). 

During the 1900s, flood hazard reduction and channel modification projects were implemented on 

the San Antonio River (USACE 2004). Prior to these changes, the San Antonio River was an 

equilibric, less altered system with a natural sediment supply (USACE 2004). The river had a much 

wider flood plain, a higher W/D, along with a low gradient and greater sinuosity (USACE 2004). The 

construction efforts straightened the river, increased the gradient, and narrowed its flood plain 

(USACE 2004). While these efforts did convey flood flows more rapidly, they also resulted in 

increased channel instability and an overall degraded aquatic and riparian habitat (USACE 2004). 

Improved engineering techniques emerged in the 1990s, allowing the river to be converted from 

essentially a drainage ditch to a more natural setting, all the while maintaining its flood water control 

and capacity functions (USACE 2004). The San Antonio River Improvement Project (SARIP) was 

initiated to restore the river to a more natural state (SARA 2001). SAAN is located within the 

“Mission Reach” portion of SARIP. The approach SARIP designed for the Mission Reach was to 

apply fluvial geomorphology metrics to restore the river to a more natural and stable condition 

(SARA 2001). Historic photographs, field surveys of natural channel reaches upstream and 

downstream of the flood control channel, and existing gradient measurements of the San Antonio 

River were used to classify the natural condition (SARA 2001). It was determined that the river 

should be restored to a “C” type stream according to the Rosgen Stream Classification System 

(SARA 2001). In terms of W/D, type “C” streams have a moderate to high W/D (USACE 2004). The

construction of the Mission Reach restoration project was completed in October 2013 (SARIP 2014).
262

Depth to Groundwater (Rancho Only)

The growth in the population and urban boundary of San Antonia has impacted the availability of 

river flow and groundwater in the areas to the south, such as where the Rancho is located (TFIP 

2009, 2012). The growth has led to an increased water demand, much of which has been met through 

increased pumping of groundwater (TFIP 2009). Pumping of groundwater increased from about

15,000 ha-m/year (120,000 ac-ft/year) in 1940 to a maximum of nearly 67,000 ha-m/year (542,000 

ac-ft/year) in 1989 (TFIP 2009). Since that high point, pumping averaged approximately 49,500 ham/year (401,300 ac-ft/year) over the period 199-2007, with a median well production rate of 46,900 

ha-m/year (379,900 ac-ft/year) over the same period (TFIP 2009). This pumping has led to a decline 

in depth to groundwater in the Edwards Aquifer which can be shown using data from the J-17 index 

well located near the national cemetery at Fort Sam Houston (EAA 2013, Eckhardt 2015). Depth to 

groundwater in the Edwards Aquifer has decreased from 16.8 m (55.2 ft) in 1932 to 26.4 m (86.5 ft) 

in April 2015 (EAA 2015). Depth to groundwater for the period of record for J-17 is shown in Figure 

72.

Figure 72. Depth to groundwater for J-17 index well for period November 1932 to April 2015 (EAA 2015).

The Rancho is located within the Carrizo-Wilcox Aquifer (TWDB 2014b). The rest of the SAAN 

properties are located within the Edwards Aquifer (Cooper et al. 2005). The Carrizo-Wilcox is a 

confined aquifer and is primarily composed of sand, interbedded with gravel, silt, clay and lignite 

(TWDB 2014a, 2014c). Two wells with depth to groundwater data are located in the vicinity of the 

Rancho, as shown in Figure 73. Groundwater levels for the period of record for each well are shown 

in Figure 74 and Figure 75. Depth to groundwater has been increasing over the period of record for 

0

5

10

15

20

25

30

35

40

Depth to Groundwater (m)
263

both of these wells. This is consistent with conditions found in the Carrizo-Wilcox aquifer (George et 

al. 2011).

Figure 73. Location of groundwater monitoring wells in relation to the Rancho Unit.

Figure 74. Depth to groundwater levels for groundwater monitoring well USGS 290802098232901 

(USGS 2014).

0

50

100

Depth to Groundwater (m)
264

Figure 75. Depth to groundwater levels for groundwater monitoring well TWDB 6862104 (TWDB 2014c).

Threats and Stressor Factors

SAAN staff identified several potential threats and stressors to the surface water and groundwater 

resources in the park. These are both anthropogenic threats (repurposing of the reuse water) and 

naturally occurring threats that have been exacerbated by human activity (drought, extreme flooding 

events and climate change).

The climate for the San Antonio River Basin is dry to sub-humid with milder winters and hotter

summers (Twidwell and Davis 1987). During the winter, minimum temperatures are rarely below 

freezing, but summertime maximum temperatures usually exceed 32.2° C (90° F) and sometimes

exceed 37.7° C (100° F) (Twidwell and Davis 1987). Average annual rainfall varies over the basin, 

but average monthly rainfall is fairly consistent. Precipitation generally occurs as thunderstorms, so 

the total monthly accumulation may occur in only a handful of days (Twidwell and Davis 1987).

Precipitation peaks in late spring and again in mid fall, with May being the wettest month (Twidwell 

and Davis 1987, Cawthon and Curran 2008). Since the 1970s, there has been a slight increase in the 

average annual precipitation for each decade (Cawthon and Curran 2008). Climate change models do 

not agree on the long term precipitation projections for Texas (TWDB 2008). Of the 23 models 

widely used for climate change projections, the results are split roughly in half between predicting 

drier or wetter conditions for East Texas (TWDB 2008). However, the majority of them do predict 

drier conditions for West Texas (TWDB 2008). Climate change models predict an increase in 

temperature for Texas, with average temperature increasing by 2-5° C (3.6-9° F) by the end of the

21st century (Foster 2011). Depending on the emission scenario used, daily maximum temperature

0

50

100

Depth to Groundwater (m)
265

could shift from the current range of 10-20 days above 37.7° C (100° F) to more than 100 days per 

year exceeding that mark (Foster 2011).

Climate change is a growing concern and threat to surface hydrology at SAAN, as well as across 

Texas (Foster 2011). A conference on climate change in Far West Texas concluded that all surface 

waters in Texas are subject to some level of risk from the potential impacts of climate change 

(TWDB 2008). In a study for the San Antonio Water System, hydraulic modeling was conducted 

using two climate change models under two emission scenarios (CH2M Hill 2008). Results from the 

study projected that streamflow would decrease under all climate change scenarios by 2050, despite a 

projected increase in precipitation. Groundwater at SAAN is also at risk from the impacts of climate 

change (Mace and Wade 2008). Karst aquifers, like the Edwards aquifer, have the potential to be 

more affected than others by climate change. The Edwards aquifer is probably the most vulnerable 

aquifer to climate change impacts in Texas (Mace and Wade 2008). The Carrizo-Wilcox aquifer may 

be less impacted by climate change. Due to its geology and the location of most pumping wells in the 

confined part of the aquifer, the Carrizo-Wilcox aquifer is unlikely to be directly impacted by climate 

change (Mace and Wade 2008). Any impact would likely be an indirect effect, as the Carrizo-Wilcox 

could become an alternative water source for San Antonio and other surrounding communities (Mace 

and Wade 2008).

Periods of drought have had a significant impact on surface water and groundwater supplies in the 

San Antonio area (Meiman 2012). Over time, extended periods of drought have led to the point 

where natural recharge of the San Antonio River is becoming uncommon (Meiman 2012). In fact,

during the latter portion of the 20th century, the San Antonio River would not have had flow without 

augmentation from water pumped from wells in the Edwards aquifer (Meiman 2012).

The Palmer Hydrological Drought Index (PHDI) can be used to show hydrological (long-term 

cumulative) drought and wet conditions, as it more accurately reflects groundwater conditions and 

surface water conditions (NCDC 2013). The PHDI uses 0 as normal condition, and drought 

conditions are shown as negative numbers (Palmer 1965). An index of -4 indicates extreme drought 

conditions, -3 indicates severe drought conditions, -2 indicates moderate drought conditions, and -1 

indicates mild drought conditions (Palmer 1965). Wet conditions are the positive counterpart of these 

designations (Palmer 1965). Figure 76 shows the PHDI for the state of Texas since 1900. Over the 

last 10 years, the extended drought has compounded the existing water quality impairments and 

concerns in the San Antonio River basin (SARA 2013). Climatologists have indicated that the 

drought of 2011 was the worst single-year drought in the period of record. Estimates are that 

approximately 97% of the state experienced either extreme (PDHI = -4) or severe (PDHI = -3) 

drought conditions, including Bexar County where SAAN is located (SARA 2013). In general,

drought conditions have an adverse effect on many water quality parameters, including concentrating 

pollutants, and low dissolved oxygen (DO) levels in waterbodies (SARA 2013). These are mainly 

due to reduced flow levels. Reduced flow also has an adverse impact on the aesthetics of a waterbody 

and the biological communities they support (SARA 2013).
266

Figure 76. Palmer Hydrologic Drought Index (PHDI) for Texas. Graph was created and downloaded from 

time series data from the National Climatic Data Center (NCDC 2014).

SAAN is located in a region commonly referred to as “flash flood alley” (SARA 2008). The natural 

geography of the area tends to allow the collision of tropical storms from the Gulf of Mexico and 

large air masses from the north, resulting in very heavy rain events in Central Texas and the Hill 

Country (SARA 2008). The steep slopes, sparse vegetation, thin soils and increasing development of 

central Texas and the Hill Country create a condition where stormwater runoff is both rapid and 

destructive (SARA 2008). The rapid runoff causes scouring of river channels, disruption or 

destruction of aquatic and riparian habitats, mass wasting and bank failure (USACE 2004, SARA 

2008). The resultant flooding also endangers lives and property (SARA 2008).

As discussed previously, flood hazard reduction and channel modification projects were 

implemented on the San Antonio River during the 1900s (USACE 2004). These projects were 

designed to effectively and efficiently control flood events (SARA 2001). The SARIP restored the 

river to a more natural state while maintaining its flood control capacity (SARA 2001).

Over the last 50 years, the San Antonio River basin has undergone a transformation due to the rapid 

development in the basin, especially in Bexar County (TIFP 2009, Lizarraga and Wehmeyer 2012). 

Flow in the river has been increasingly augmented by return flows from municipal uses within the 

City of San Antonio and the surrounding areas (TIFP 2009, Lizarraga and Wehmeyer 2012). Over 

this period the river has gone from a system driven primarily by groundwater discharge to a system 

that is highly influenced by year-round treated wastewater discharges, intermittent discharges and 

withdrawals, and a variety of urban and rural land uses (TIFP 2009, Lizarraga and Wehmeyer 2012).
267

In more recent years, the increased use of groundwater to sustain this rapid development has resulted 

in increasing base flows in the San Antonio River as the groundwater is returned to the river at reuse 

water discharge points (TIFP 2009). This trend may continue if population growth in the basin is 

supported by additional groundwater usage or surface water transfers from outside the basin (TIFP 

2009). Lower river base flows may also result from employing management strategies such as water 

reuse (TIFP 2009). Without the reuse water, the river would not flow during most summer months 

and especially during drought periods (Meiman 2012). Augmenting the river flow with reuse water 

fulfills an essential economic need and plays a vital ecologic role (Meiman 2012). SAAN is 

dependent upon, and a stakeholder in, water quality and quantity of the San Antonio River (Meiman 

2012). The park lies downstream of reuse water recharge points and the Rancho is downstream of 

even larger reuse discharge points (Meiman 2012). Additionally the two acequia headgates, located 

at the Espada Dam (Acequia de Espada) and the Archimedes Screw (Acequia de San Juan), directly 

draw water from the San Antonio River (Meiman 2012).

Data Needs/Gaps

In reviewing the background literature and data, no major data gaps were found that would have 

affected this assessment. However, establishment of stream transects in the San Antonio River to 

collect stream geomorphology data would allow the assessment of the width:depth ratio over time. 

Since the streambed is managed by SARA, this research could be a collaborative effort. The 

restoration project on the Missions Reach of the San Antonio River was recently completed and a 

period of time is needed for the new channel to establish its equilibrium state in this new design. 

Over time, stream flow in this equilibrium state may cause changes to the as-built conditions.

Overall Condition

Stream Flow Rates

The measure of stream discharge was assigned a Significance Level of 3. Stream flow is only being 

assessed in terms of flow in the San Antonio River. Flows in the acequias are regulated through the 

headgates. The increased use of groundwater as a water supply for the growing population and 

returning it to the river to augment flow has resulted in increased base flows (TIFP 2009, 2012). This 

trend may continue if population growth in the basin is supported by additional groundwater usage or 

surface water transfers from outside the basin (TIFP 2009). The San Antonio River is dependent on 

the input of reuse water to augment its flow (Meiman 2012). However, lower river base flows may 

also result, depending on how reuse management strategies are employed (TIFP 2009). Due to these 

factors and SAAN’s location downstream from water reuse discharge points the Condition Level for 

this measure is 1, indicating low concern.

Width:Depth Ratio

The Significance Level for width:depth ratio was a 3. The width:depth ratio is only assessed for the 

San Antonio River channel. The SARIP recently completed stream restoration projects in the San 

Antonio River basin to return the river to a more natural geomorphological condition, yet still 

maintaining its effectiveness for flood control and flood protection (SARA 2001, SARIP 2014). This 

included altering the width:depth ratio to match the historic conditions. While the restoration efforts 

have restored the San Antonio River to reflect a more natural condition, it is still an engineered 
268

channel. How well the channel maintains its more natural condition will need to be monitored. Since 

the restoration was just recently completed and though more natural in nature, the width:depth ratio 

currently is not the result of a natural flow regime. Due to this, the Condition Level for this measure 

is given a 1, indicating low concern.

Depth to Groundwater (Rancho Only)

The Significance Level for depth to groundwater was a 1. Limited data are available on the depth to 

groundwater at SAAN’s Rancho Unit. Groundwater levels in the area have been declining, but not as 

rapidly as other areas of the Carrizo-Wilcox aquifer (George et al. 2011). Increased dependence on 

groundwater as a water supply could increase this rate of decline (George et al. 2011). Due to this 

potential impact, a Condition Level of 1 is assigned, indicating low concern.

Weighted Condition Score

The Weighted Condition Score for hydrology at SAAN is 0.33, meaning the component is at the 

upper limit of good condition, bordering on moderate concern. Since the concern levels given for the 

measures are based on uncertainty of how the river will respond to the restoration efforts, the level of 

concern may be reduced in future assessments. A trend arrow was not assigned to this component at 

this time. Restoration projects on the San Antonio River were recently completed and, coupled with a 

lack of data on width and depth measurements, it is difficult to make a trend assessment for this 

component. In addition, the flow rates could either increase or decrease in the future dependent on 

factors such as population growth and water repurposing management strategies. 

Hydrology

Measures

Significance 

Level

Condition 

Level WCS = 0.33

Stream flow rates 3 1

Width:depth ratio 3 1

Depth to groundwater 1 1

4.15.6 Sources of Expertise

Greg Mitchell, SAAN Natural Resources Program Manager

Joe Meiman, NPS Hydrologist, Gulf Coast Region

4.15.7 Literature Cited

Carr, W. R. 2003a. A botanical inventory of San Antonio Missions National Historical Park Part I. 

Texas Conservation Data Center, The Nature Conservancy, San Antonio, Texas.
269

Carr, W. R. 2003b. A botanical inventory of San Antonio Missions National Historical Park Part II. 

Texas Conservation Data Center, The Nature Conservancy, San Antonio, Texas.

Cawthon, T. M. and J .C. Curran. 2008. Channel change on the San Antonio River. Texas Water 

Development Board, Project #0604830638. Texas State University, San Marcos, Texas.

CH2M Hill. 2008. Climate change study: Report on evaluation methods and climate scenarios. 

Prepared for Lower Colorado River Authority and San Antonio Water System, San Antonio, 

Texas.

Cooper, R. J., S. B. Cederbaum and J. Gannon. 2005. Natural resources summary for San Antonio 

Missions National Historical Park (SAAN) Final Report. Warnell School of Forest Resources, 

University of Georgia, Athens, Georgia.

Eckhardt, G. 2015. The J-17 index well. http://www.edwardsaquifer.net/j17.html. (accessed 9 April 

2015).

Edwards Aquifer Authority (EAA). 2013. Edwards Aquifer Authority hydrologic data report for 

2012. http://www.edwardsaquifer.org/files/hydrologic/2013_Tremalloetal_HydrologicDataReport2012.pdf (accessed 14 December 2014).

Foster, S. C., S. H. Stein, and K. K. Jones. 2001. A guide to interpreting stream survey reports. 

Oregon Department of Fish and Wildlife, Portland, Oregon. 

https://nrimp.dfw.state.or.us/CRL/Reports/Info/2001-06.pdf (accessed 15 December 2014).

Foster, H. C. 2011. Climate change and Texas water regulation. Chapter 16 in The changing face of 

water rights 2011. State Bar of Texas, San Antonio, Texas. 

http://www.gdhm.com/images/pdf/hcf_climate-change_and_texas_water_regulation.pdf 

(accessed 19 December 2014).

George, P. G., R. E, Mace, and R. Petrossian. 2011. Aquifers of Texas. Texas Water Development 

Board, Austin, Texas. 

http://www.twdb.state.tx.us/publications/reports/numbered_reports/doc/R380_AquifersofTexas.p

df (accessed 23 December 2014).

Gordon, N. D., T. A. McMahon, B. L. Finlayson, C. J. Gippel, and R. J. Nathan. 2004. Stream 

hydrology: An introduction for Ecologists 2nd Edition. John Wiley and Sons, West Sussex, 

England.

Leopold, L. B., and T. Maddock. 1953. The hydraulic geometry of stream channels and some 

physiographic implications. Geological Survey Professional Paper 252. 

http://eps.berkeley.edu/people/lunaleopold/%28040%29%20The%20Hydraulic%20Geometry%2

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273

Chapter 5 Discussion

Chapter 5 provides an opportunity to summarize assessment findings and discuss the overarching 

themes or common threads that have emerged for the featured components. The data gaps and needs 

identified for each component are summarized and the role these play in the designation of current 

condition is discussed. Also addressed is how condition analysis relates to the overall natural 

resource management issues of the park.

5.1 Component Data Gaps

The identification of key data and information gaps is an important objective of NRCAs. Data gaps 

or needs are those pieces of information that are currently unavailable, but are needed to help inform 

the status or overall condition of a key resource component in the park. Data gaps exist for most key 

resource components assessed in this NRCA. Table 61 provides a detailed list of the key data gaps by 

component. Each data gap or need is discussed in further detail in the individual component 

assessments (Chapter 4).

Table 61. Identified data gaps or needs for the featured components.

Component Data Gaps/Needs

Forested Riparian Corridors 

(including acequias)

 No data regarding coverage of native species or age class structure.

Native Grassland/Prairie  Little is known about exact composition and extent of historic native 

grasslands.

 Current restoration efforts provide an opportunity to study the process and 

the restored grasslands.

Upland Shrublands/Woodlands  Update vegetation mapping to determine if shrublands/woodlands have 

expanded.

 Percent coverage of native species has not been studied.

Reptiles  No information on reproductive success.

 Continue monitoring of species richness and abundance to identify any 

changes over time.

Amphibians  No information on reproductive success.

 Continue monitoring of species richness and abundance to identify any 

changes over time.

 Identify any impacts from non-native species (e.g., competition, predation).

Breeding Birds  Continued monitoring to establish baseline values for the identified 

measures.
274

Table 61 (continued). Identified data gaps or needs for the featured components.

Component Data Gaps/Needs

Breeding Birds 

(continued)

 Monitoring/studies of the migratory bird population are needed.

 Monitoring of the trends in breeding species of conservation concern is 

also needed.

Resident Birds  Continued monitoring, especially during winter, to establish baseline 

values for the identified measures.

 Monitoring of the trends in resident species of conservation concern is 

needed.

Aquatic Macroinvertebrates  Sampling has been sporadic, leaving many gaps in data, both spatially and 

temporally. No IBIs have been calculated for the Rancho Unit.

Fish  Establishment of annual, routine monitoring of fish species richness and 

IBI would aid in management.

 No information regarding the impacts of nonnative fish on native fish 

species.

Water Quality  Continuation of GULN monitoring efforts

 A recompilation of data from the NPS (1999) report within a more limited 

geographic area, as well as any new data, and focusing on EPA as well as 

TCEQ standards might yield a better picture of long-term trends in the 

park’s water quality.

Air Quality  Current monitoring stations may not be close enough to the Rancho Unit, 

which is south of Floresville, to accurately represent conditions there.

 Monitoring of nitrogen and sulfur deposition and visibility in or near both 

units would help managers better understand the local air quality 

conditions.

Soundscape  Current available data are for a short period during one season and from 

one location in the park. Additional monitoring should be conducted as 

soon as possible to help document any changes due to surrounding 

development.

 No data for the Rancho Unit; conditions at this rural location are likely very 

different from the more urban Missions Unit. A baseline survey should be 

conducted as soon as possible to document conditions before they are 

further impacted by surrounding activities.

Dark Night Skies  No baseline data has been collected from either park unit.

Viewscape  Continued development of spatial data to explain landscape change, 

enabling accurate and up-to-date viewshed assessments. These data 

could help minimize the impact of surrounding development on the park’s 

viewshed.
275

Table 61 (continued). Identified data gaps or needs for the featured components.

Component Data Gaps/Needs

Hydrology (Surface and 

Groundwater)

 Establishment of stream transects to collect stream geomorphology data 

would allow the assessment of the width:depth ratio over time 

(collaborative effort with SARA).

Some of the park’s data needs involve continuing recently established monitoring programs, to 

accumulate enough data for identifying any trends over time (e.g., reptiles, amphibians, birds). Many 

of the vegetation community data gaps will be addressed through soon-to-be implemented GULN 

monitoring efforts. 

5.2 Component Condition Designations

Table 62 displays the conditions assigned to each resource component presented in Chapter 4 

(definitions of condition graphics are located in Figure 77 following Table 62). It is important to

remember that the graphics represented are simple symbols for the overall condition and trend 

assigned to each component. Because the assigned condition of a component (as represented by the 

symbols in Table 62) is based on a number of factors and an assessment of multiple literature and 

data sources, it is strongly recommended that the reader refer back to each specific component 

assessment in Chapter 4 for a detailed explanation and justification of the assigned condition. 

Condition designations for some components are supported by existing datasets and monitoring 

information and/or the expertise of NPS staff, while other components lack historical data, a clear 

understanding of reference conditions (i.e., what is considered desirable or natural), or even current 

information. Condition could not be determined for five of the 15 selected components: forested 

riparian corridors, native grasslands, amphibians, aquatic macroinvertebrates, and dark night skies.

For featured components with available data and fewer data gaps, assigned conditions varied. Five 

components are considered to be of low concern: upland shrublands/woodlands, reptiles, breeding 

and resident birds, and hydrology. Two components (fish and water quality) were of moderate 

concern. Three components were of high concern: air quality, soundscape, and viewscape. The high 

concern levels are primarily due to the urban land uses surrounding the park and are largely beyond 

NPS control.
276

Figure 77. Description of symbology used for individual component assessments.

Examples of how the symbols should be interpreted:

Resource is in good condition, its condition is improving, high confidence in the 

assessment.

Condition of resource warrants moderate concern; condition is unchanging; medium 

confidence in the assessment.

Condition of resource warrants significant concern; trend in condition is unknown or 

not applicable; low confidence in the assessment.

Current condition is unknown or indeterminate due to inadequate data, lack of 

reference value(s) for comparative purposes, and/or insufficient expert knowledge to 

reach a more specific condition determination; trend in condition is unknown or not 

applicable; low confidence in the assessment.
277

Table 62. Summary of current condition and condition trend for featured NRCA components.

Component WCS Condition

Biological Composition

Ecological communities

Forested Riparian Corridors N/A

Native Grasslands N/A

Upland Shrublands/Woodlands 0.13

Herptiles

Reptiles 0.22

Amphibians N/A

Birds

Breeding Birds 0.17

Resident Birds 0.33

Freshwater Biota

Aquatic Macroinvertebrates N/A

Fish 0.67
278

Table 62 (continued). Summary of current condition and condition trend for featured NRCA components.

Component WCS Condition

Environmental Quality

Air quality 0.79

Water quality 0.53

Soundscape 0.83

Dark Night Skies N/A

Viewscape 0.75

Physical Characteristics

Geologic & Hydrologic

Hydrology (Surface and Groundwater 

Dynamics) 0.33

5.3 Park-wide Condition Observations 

Despite the disjunct nature of SAAN’s units, many of the resources discussed in this report are 

interrelated and share similar management concerns (e.g., data gaps, threats from outside the park).

Vegetation Communities

The vegetation communities of SAAN have been influenced by centuries of human impacts, from 

agricultural use during the Missions period to more recent urban development. However, the plant 

communities still provide habitat for wildlife and perform critical ecological functions. Given a lack

of data for several key measures, a condition could not be determined for forested riparian corridors. 

Many of these information gaps will be addressed by a GULN vegetation monitoring program 

starting soon and by an exotic plant survey and mapping effort scheduled for 2016. A condition was 

not determined for native grasslands because this community is currently absent from the park, 

although some plant species historically found in grasslands can still be found. Efforts are underway 

to restore this habitat to the park at two sites: one in the Missions Unit and one at Rancho de las 

Cabras. Upland shrublands and woodlands are in good condition, as this community is thought to 

have a wider distribution now than it did historically (Van Auken and Bush 1984). 
279

Other Biotics

Animals featured as NRCA components were reptiles, amphibians, breeding and resident birds, fish, 

and aquatic macroinvertebrates. Because of limited data sources, overall condition could not be 

determined for amphibians and aquatic macroinvertebrates. With the continuation of sampling and 

surveys currently underway (by the GULN for amphibians and SARA for macroinvertebrates), 

enough information should be available within a few years to better assess the condition of these 

resources. Reptiles, breeding birds, and resident birds are currently in good condition. Fish are 

considered of moderate concern due to low and/or decreasing IBI ratings over the past decade 

(SARA 2005, 2013a). Habitat loss and degradation, water quality impairments, and droughts (which 

may be exacerbated by climate change) have all likely contributed to degradation of the fish 

community in the SAAN region (SARA 2013b).

Environmental Quality

Environmental quality is important in maintaining healthy functioning ecosystems. The health of 

terrestrial and aquatic organisms in parks can be affected substantially by the condition of air and 

water quality. Air quality is of high concern at SAAN, particularly due to high ozone concentrations 

and nitrogen deposition levels around the city of San Antonio (TCEQ 2014, NPS 2014). Although 

ozone concentrations have only occasionally exceeded standards at monitoring stations near the park 

in recent years, the EPA is currently reviewing the NAAQS ground-level ozone standard and may 

suggest a stricter standard between 60-70 ppb (EPA 2014). If a stricter standard is enacted, much of 

the SAAN region would be in “nonattainment” (i.e., not meeting the federal air quality standard). It 

is also likely that increased oil and gas development southeast of the park and climate change will 

negatively influence air quality in the coming decades (EPA 2011, AACOG 2013)

Water quality is of moderate concern, with nutrients and coliform bacteria as the individual 

parameters of highest concern. Many of the area’s water quality impairments are related to its 

location near an urban environment and the use of recycled wastewater (“reuse water”) to maintain 

flows in the San Antonio River (Meiman 2012). Water quality could also be threatened by climate 

change, as extreme weather events (e.g., droughts, heavy rains, heat waves) are predicted to increase 

(Davey et al. 2007). 

The park’s viewscape and soundscape are of high concern, due to continued urban development 

around the Missions Unit of the park. Anthropogenic sounds such as road and air traffic are audible 

almost constantly around the Missions (Lynch 2009). While view- and soundscape are in better 

condition at the Rancho Unit due to its more rural location, conditions are likely deteriorating here as 

well due to human activities. As mentioned previously, the majority of negative impacts on these 

resources come from outside park boundaries and are largely beyond the control of park managers. A 

condition could not be determined for dark night skies because no data have been gathered at either 

park unit. Given that most of the Missions Unit lies within the city of San Antonio, dark night skies 

are almost certainly impaired there.

Physical Characteristics

The San Antonio River has been greatly manipulated in the San Antonio area, largely due to flood 

control activities. These alterations have influenced hydrology and aquatic habitats. In recent years, 
280

efforts have been made to restore the river to more natural conditions (SARA 2001). However, the 

increasing use of recycled wastewater (“reuse water”) to maintain San Antonio River flows is a 

concern. Without reuse water, portions of the river could dry up in the summer months, especially 

during droughts (Meiman 2012). 

Park-wide Threats and Stressors

Several threats and stressors influence the condition of multiple resources throughout SAAN. These 

include the presence of non-native invasive species and effects of urban development (e.g., habitat 

loss and fragmentation, pollution, hydrologic alterations). Drought is also a looming threat which 

may be exacerbated by climate change. Invasive plant species such as Chinaberry and exotic grasses 

are a threat to all of the park’s vegetation communities, due to their ability to out-compete native 

plants (Cooper et al. 2005, NPS 2010). Among non-native animals, feral hogs are perhaps the 

greatest threat. Their destructive rooting and wallowing behavior could impact all of the park 

vegetation communities as well as native wildlife (herptiles, birds, invertebrates, etc.) (Taylor 2003).

Development and human activity prior to park establishment drastically altered the historic Missions 

landscape, causing widespread habitat loss and fragmentation. Continued development in more 

recent decades, particularly around the Missions Unit, has impacted the environmental quality 

(particularly viewscape and soundscape) of the park. Many of the park’s air and water quality 

concerns are due to the Missions Unit’s urban location. As mentioned previously, these threats and 

stressors are largely beyond the control of park management. 

Much of Texas has been experiencing drought conditions for several years now (U.S. Drought 

Monitor 2014). Droughts negatively impact many park resources, from riparian vegetation, 

amphibians, and fish, to water quality and hydrology. Unfortunately, droughts are likely to increase 

in the future as a result of climate change (Twilley et al. 2001, Davey et al. 2007). Winter and spring 

precipitation are projected to decrease in the San Antonio region over the next century; combined 

with warmer temperatures, this will lead to overall drier conditions in the region (Maurer et al. 2007; 

see Chapter 2).

Overall Conclusions

Despite its largely urban location, SAAN supports a variety of valuable natural resources. These 

resources are key components of the park’s cultural landscape. Although SAAN is impacted by 

adjacent human activities, the natural setting still provides an oasis from the surrounding developed 

areas for both wildlife and human visitors. Maintaining and/or improving these resources will 

contribute to the environmental health of the surrounding area and provide important opportunities 

for urban residents to connect with the natural world. 

5.4 Literature Cited

Alamo Area Council of Governments (AACOG). 2013. Emissions trend analysis for the SanAntonio-New Braunfels MSA: 1999, 2002, 2006, 2012, 2018, and 2023. Alamo Area Council of 

Governments, San Antonio, Texas.
281

Cooper, R. J., S. B. Cederbaum, and J. Gannon. 2005. Natural resource summary for San Antonio 

Missions National Historical Park. National Park Service, Gulf Coast Network, Lafayette, 

Louisiana.

Davey, C. A., K. T. Redmond, and D. B. Simeral. 2007. Weather and Climate Inventory, National 

Park Service, Gulf Coast Network. Natural Resource Technical Report NPS/GULN/NRTR—

2007/011. National Park Service, Fort Collins, Colorado.

Environmental Protection Agency (EPA). 2011. Climate change and air quality. 

http://www.epa.gov/airquality/airtrends/2011/report/climatechange.pdf (accessed 22 July 2014).

Environmental Protection Agency (EPA). 2014. Policy assessment for the review of the ozone 

national ambient air quality standards: Second external review draft. Environmental Protection 

Agency, Office of Air Quality Planning and Standards, Ambient Standards Group, Research 

Triangle Park, North Carolina.

Lynch, E. 2009. San Antonio Missions National Historical Park acoustical monitoring report 2009. 

Natural Resource Report NPS/NRPC/NRTR—2009/001. U.S. Department of the Interior, 

National Park Service, Fort Collins, Colorado.

Maurer, E. P., L. Brekke, T. Pruitt, and P. B. Duffy. 2007. Base climate projections (downscaled): 

2050 mid century (2040-2069), 2100 end century (2070-2099) (12km resolution). 

http://www.climatewizard.org/ (accessed 28 July 2014).

Meiman, J. 2012. Gulf Coast Network water quality report: Status of water quality of San Antonio 

Missions National Historical Park. National Park Service, Fort Collins, Colorado. 

National Park Service (NPS). 1999. Baseline water quality data inventory and analysis; San Antonio 

Missions National Historical Park. Technical Report NPS/NRWRD/NRTR—99/222. National 

Park Service, Fort Collins, Colorado.

National Park Service (NPS). 2010. A summary of biological inventory vertebrate and vascular plant 

inventories data collected at San Antonio Missions National Historical Park. National Park 

Service, Gulf Coast Network, Lafayette, Louisiana.

National Park Service (NPS). 2014. NPS air quality estimates: ozone, wet deposition, and visibility. 

http://www.nature.nps.gov/air/Maps/AirAtlas/IM_materials.cfm (accessed 25 March 2014).

San Antonio River Authority (SARA). 2001. San Antonio River improvements project concept 

design - design guidelines. San Antonio River Authority, San Antonio, Texas.

San Antonio River Authority (SARA). 2005. An inventory of fish species within the San Antonio 

Missions National Historical Park. Final Report. San Antonio River Authority, Environmental 

Services Department, San Antonio, Texas.
282

San Antonio River Authority (SARA). 2013a. Unpublished fish monitoring data. Excel spreadsheet 

received from Joe Meiman, GULN hydrologist, 26 June 2014.

San Antonio River Authority (SARA). 2013b. San Antonio River basin 2013 summary report. San 

Antonio River Authority, San Antonio, Texas. 

Taylor, R. 2003. The feral hog in Texas. Texas Parks and Wildlife, Austin, Texas.

Texas Commission on Environmental Quality (TCEQ). 2014. Four highest ozone concentrations in 

2014. http://www.tceq.state.tx.us/cgi-bin/compliance/monops /8hr_4highest.pl (accessed 28 

August 2014).

Twilley, R. R., E. J. Barron, H. L. Gholz, M. A. Harwell, R. L. Miller, D. J. Reed, J. B. Rose, E. H. 

Siemann, R. G. Wetzel, and R. J. Zimmerman. 2001. Confronting climate change in the Gulf 

Coast region: Prospects for sustaining our ecological heritage. Union of Concerned Scientists, 

Cambridge, Massachusetts, and Ecological Society of America, Washington, D.C.

U.S. Drought Monitor. 2014. Texas. 

http://droughtmonitor.unl.edu/Home/StateDroughtMonitor.aspx?TX (accessed 10 September 

2014).

Van Auken, O. W., and J. K. Bush. 1984. Changes in plant communities of the San Antonio Missions 

National Historical Park. Pages 28-33 in Proceedings of the Second Annual Missions Research 

Conference. National Park Service, San Antonio, Texas.
283

Appendices

Appendix A. Non-native plant species documented in SAAN (ornamentals excluded) (Halvorson and 

Guertin 2006).

Scientific name Common Name Missions Rancho

>20 ha 

infested?

TX noxious 

weed

Ailanthus altissima tree of heaven x x

Albizia julibrissin silktree x

Alternanthera

 Philoxeroides

alligatorweed x x

Ammi majus large bullwort x x

Anagallis arvensis scarlet pimpernel x x x

Antigonon leptopus coral vine x x

Arundo donax giant reed x x x

Asparagus officinalis garden asparagus x

Avena sativa common oat x x x

Bignonia capreolata crossvine x

Bothriochloa ischaemum

 var. songarica

yellow bluestem 

(formerly 

 King’s Ranch blustem)

x x x

Bromus catharticus rescuegrass x x x

Bromus arvensis (formerly

 japonicus)

field brome x x x

Broussonetia papyrifera paper mulberry x x

Buglossoides arvensis corn gromwell x x

Capsella bursa-pastoris shepherd’s purse x x

Centaurea melitensis Maltese star-thistle x x

Chenopodium sp. goosefoot x x x

Clematis terniflora sweet autumn 

 virginsbower

x

Colocasia esculenta coco yam x x

Convolvulus arvensis field bindweed x x x x

Cynodon dactylon Bermudagrass x x x

Cyperus rotundus nutgrass x x

Dichanthium annulatum

 var. annulatum

Diaz bluestem x x
284

Appendix A (continued). Non-native plant species documented in SAAN (ornamentals excluded) 

(Halvorson and Guertin 2006).

Scientific name Common Name Missions Rancho

>20 ha 

infested?

TX noxious 

weed

Dichanthium aristatum Angleton bluestem x

Echinochloa colona jungle rice x x

Eichhornia crassipes common water hyacinth x x

Eleusine indica Indian goosegrass x

Eragrostis barrelieri Mediterranean lovegrass x x

Eragrostis cilianensis stinkgrass x

Eriobotrya sp. loquat x

Erodium cicutarium redstem stork’s bill x

Ficus carica edible fig x

Fumaria officinalis drug fumitory x

Hedera sp. ivy x

Hedypnois cretica Cretanweed x

Heliotropium indicum Indian heliotrope x

Hordeum murinum ssp.

 leporinum

hare barley x

Hydrilla verticillata water thyme x X

Lactuca serriola prickly lettuce x x x

Lagerstroemia indica crapemyrtle x

Lamium amplexicaule henbit deadnettle x

Leucaena leucocephala white leadtree x

Ligustrum japonicum Japanese privet x x

Lolium perenne perennial ryegrass x x

Lonicera japonica Japanese honeysuckle x

Malva parviflora cheeseweed mallow x

Medicago lupulina black medick x x

Medicago polymorpha burclover x x x

Medicago sativa alfalfa x

Melia azedarach Chinaberrytree x x x

Melilotus officinalis sweetclover x
285

Appendix A (continued). Non-native plant species documented in SAAN (ornamentals excluded) 

(Halvorson and Guertin 2006).

Scientific name Common Name Missions Rancho

>20 ha 

infested?

TX noxious 

weed

Melilotus indicus annual yellow 

 sweetclover

x x

Mirabilis jalapa marvel of Peru x

Morus alba white mulberry x x

Nandina domestica sacred bamboo x

Paspalum dilatatum dallisgrass x x

Pennisetum ciliare buffelgrass x x

Phyllostachys aurea golden bamboo x

Pilea microphylla rockweed x

Plantago major common plantain x

Poa annua annual bluegrass x x

Polycarpon tetraphyllum fourleaf manyseed x

Polypogon monspeliensis annual rabbitsfoot grass x

Punica granatum pomegranate x

Ranunculus muricatus spinyfruit buttercup x

Rapistrum rugosum annual bastardcabbage x

Rhynchosia minima least snoutbean x x

Ricinus communis castorbean x

Nasturtium officinale watercress x

Rumex crispus curly dock x x

Rumex pulcher fiddle dock x x

Scandix pecten-veneris shepherdsneedle x

Sisymbrium irio London rocket x x

Sonchus asper spiny sowthistle x x x

Sonchus oleraceus common sowthistle x x

Sorghum halepense Johnsongrass x x x

Stellaria media common chickweed x x

Stenotaphrum

 secundatum

St. Augustine grass x
286

Appendix A (continued). Non-native plant species documented in SAAN (ornamentals excluded) 

(Halvorson and Guertin 2006).

Scientific name Common Name Missions Rancho

>20 ha 

infested?

TX noxious 

weed

Taraxacum officinale common dandelion x

Torilis arvensis spreading hedgeparsley x x x

Torilis nodosa knotted hedgeparsley x x

Triadica sebifera small Chinese tallow x

Tribulus terrestris puncturevine x

Urochloa maxima guineagrass x x

Verbena brasiliensis Brazilian vervain x

Veronica agrestis green field speedwell x

Veronica anagallis- 

 aquatica

water speedwell x

Veronica arvensis corn speedwell x

Veronica persica birdeye speedwell x

Vitex agnus-castus lilac chastetree x

Totals 89 35 24 5
287

Appendix B. Plant species documented in SAAN’s riparian woodlands/forests (Carr 2003a, b). Asterisks 

(*) indicate non-native species.

Scientific Name Common Name Missions Rancho

Acacia farnesiana (formerly minuta) sweet acacia; huisache x x

Acer negundo boxelder x

Acer negundo var. texanum boxelder x

Adiantum capillus-veneris common maidenhair x

Allium canadense var. canadense meadow garlic x x

Alternanthera philoxeroides* alligatorweed x

Ambrosia trifida giant ragweed x x

Ampelopsis arborea peppervine x x

Anemone berlandieri tenpetal thimbleweed x

Antigonon leptopus* coral vine x

Apocynum cannabinum Indianhemp x

Arundo donax* giant reed x

Bignonia capreolata crossvine x

Bowlesia incana hoary bowlesia x x

Bromus catharticus* rescuegrass x

Broussonetia papyrifera* paper mulberry x

Calyptocarpus vialis straggler daisy x x

Campsis radicans trumpet creeper x x

Capsella bursa-pastoris* shepherd’s purse x

Cardiospermum halicacabum* balloon vine x

Carex bulbostylis false hair sedge x x

Carex tetrastachya Britton’s sedge x x

Carya illinoinensis pecan x

Celosia nitida West Indian cock’s comb x x

Celtis ehrenbergiana spiny hackberry x x

Celtis laevigata var. laevigata sugarberry x x

Cephalanthus occidentalis common buttonbush x

Cephalanthus occidentalis var. californicus common buttonbush x

Chaerophyllum tainturieri var. dasycarpum hairyfruit chervil x
288

Appendix B (continued). Plant species documented in SAAN’s riparian woodlands/forests (Carr 2003a, 

b). Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions Rancho

Chaerophyllum tainturieri var. tainturieri hairyfruit chervil x x

Chamaesyce nutans eyebane x

Chamaesyce prostrata prostrate sandmat x

Chasmanthium latifolium Indian woodoats x x

Cheilanthes alabamensis Alabama lipfern x

Chloracantha spinosa spiny chloracantha x

Cirsium texanum Texas thistle x

Cissus trifoliata sorrelvine x x

Clematis drummondii Drummond’s clematis x x

Clematis pitcheri bluebill x x

Clematis terniflora* sweet autumn virginsbower x

Cocculus carolinus Carolina coralbead x

Colubrina texensis Texan hogplum x

Commelina erecta var. erecta whitemouth dayflower x x

Condalia hookeri var. hookeri Brazilian bluewood x

Cooperia pedunculata prairie lily x

Cornus drummondii roughleaf dogwood x x

Corydalis sp. fumewort; scrambled eggs x

Crataegus sp. hawthorn x

Cynodon dactylon* Bermudagrass x x

Cyperus erythrorhizos redroot flatsedge x

Cyperus ochraceus pond flatsedge x x

Dichanthelium oligosanthes var. oligosanthes Heller’s rosette grass x

Dichondra carolinensis Carolina ponysfoot x

Dicliptera brachiata branched foldwing x x

Diospyros texana Texas persimmon x

Echinochloa colona* jungle rice x

Ehretia anacua knockaway; anacua x

Elaeagnus macrophylla* silverberry x
289

Appendix B (continued). Plant species documented in SAAN’s riparian woodlands/forests (Carr 2003a, 

b). Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions Rancho

Chaerophyllum tainturieri var. tainturieri hairyfruit chervil x x

Elymus virginicus var. virginicus Virginia wildrye x

Erigeron philadelphicus Philadelphia fleabane x x

Eupatorium serotinum lateflowering thoroughwort x

Euphorbia spathulata warty spurge x

Ficus carica* edible fig x

Fleischmannia incarnata pink thoroughwort x

Fraxinus berlandieriana Mexican ash x x

Galium aparine cleavers, stickwilly x x

Gamochaeta pensylvanica Pennsylvania everlasting x

Geranium texanum Texas geranium x

Guaiacum angustifolium Texas lignum-vitae x

Helenium microcephalum smallhead sneezeweed x

Heliotropium indicum Indian heliotrope x

Hordeum pusillum little barley x

Hydrocotyle verticillata whorled marshpennywort x

Ilex decidua possumhaw x

Iva annua annual marsh elder x

Juglans nigra black walnut x

Lactuca sp. wild lettuce x

Lactuca floridana woodland lettuce x

Lactuca ludoviciana biannual lettuce x

Lactuca serriola* prickly lettuce x

Lamium amplexicaule* henbit deadnettle x x

Lemna aequinoctialis lesser duckweed x

Ligustrum japonicum* Japanese privet x

Ligustrum sinense* Chinese privet x

Limnodea arkansana Ozarkgrass x

Lolium perenne* perennial ryegrass x
290

Appendix B (continued). Plant species documented in SAAN’s riparian woodlands/forests (Carr 2003a, 

b). Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions Rancho

Chaerophyllum tainturieri var. tainturieri hairyfruit chervil x x

Lonicera japonica* Japanese honeysuckle x

Lycium berlandieri Berlandier’s wolfberry x

Malvaviscus arboreus var. drummondii wax mallow x x

Marsilea macropoda bigfoot waterclover x

Matelea reticulata netted milkvine x x

Medicago lupulina* black medick x

Medicago polymorpha* Burclover x

Melia azedarach* Chinaberrytree x x

Melothria pendula Guadeloupe cucumber x x

Mikania scandens climbing hempvine x

Mirabilis jalapa* marvel of Peru x

Morus alba* white mulberry x

Morus rubra red mulberry x

Nama jamaicense Jamaicanweed x

Nandina domestica* sacred bamboo x

Nassella leucotricha Texas wintergrass x x

Nemophila phacelioides largeflower baby blue eyes x

Nothoscordum bivalve crowpoison x

Oenothera rosea rose evening primrose x

Onosmodium bejariense var. bejariense soft-hair marbleseed x

Oxalis dillenii slender yellow woodsorrel x

Panicum capillare witchgrass x

Panicum dichotomiflorum fall panicgrass x

Parietaria pensylvanica Pennsylvania pellitory x

Parthenocissus quinquefolia Virginia creeper x x

Paspalum denticulatum longtom x

Paspalum dilatatum* dallisgrass x

Paspalum langei rustyseed paspalum x x
291

Appendix B (continued). Plant species documented in SAAN’s riparian woodlands/forests (Carr 2003a, 

b). Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions Rancho

Chaerophyllum tainturieri var. tainturieri hairyfruit chervil x x

Paspalum pubiflorum hairyseed paspalum x

Paspalum urvillei* Vasey’s grass x

Phalaris caroliniana Carolina canarygrass x

Phoradendron tomentosum Christmas mistletoe x

Phyla nodiflora turkey tangle fogfruit x x

Phyllostachys aurea* golden bamboo x

Physalis angulata cutleaf groundcherry x

Plantago major* common plantain x

Plantago rhodosperma redseed plantain x

Poa annua* annual bluegrass x

Polygonum punctatum dotted smartweed x

Polygonum ramosissimum bushy knotweed x

Populus deltoides eastern cottonwood x x

Prosopis glandulosa var. glandulosa honey mesquite x

Ptelea trifoliata common hoptree x

Quercus virginiana live oak x x

Ranunculus muricatus spinyfruit buttercup x

Rapistrum rugosum* annual bastardcabbage x

Rivina humilis rougeplant x x

Rubus riograndis Rio Grande dewberry x x

Rudbeckia hirta var. angustifolia Perdue blackeyed susan x

Ruellia drummondiana Drummond’s wild petunia x

Ruellia nudiflora var. nudiflora violet wild petunia x

Rumex chrysocarpus amamastla x

Rumex pulcher fiddle dock x x

Sabal mexicana Rio Grande palmetto x

Salix nigra black willow x x

Salvia coccinea blood sage x x
292

Appendix B (continued). Plant species documented in SAAN’s riparian woodlands/forests (Carr 2003a, 

b). Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions Rancho

Chaerophyllum tainturieri var. tainturieri hairyfruit chervil x x

Sambucus nigra ssp. canadensis American black elderberry x x

Samolus valerandi ssp. parviflorus seaside brookweed x

Sanicula canadensis Canadian blacksnakeroot x

Sapindus saponaria var. drummondii western soapberry x x

Scandix pecten-veneris* shepherdsneedle x

Scutellaria ovata heartleaf skullcap x

Sesbania sp. riverhemp x

Sideroxylon lanuginosum gum bully x x

Smilax bona-nox saw greenbriar x x

Solidago canadensis Canada goldenrod x

Sonchus asper* spiny sowthistle x x

Sonchus oleraceus* common sowthistle x

Sorghum halepense* Johnsongrass x

Stachys crenata mousesear x

Stellaria media* common chickweed x x

Stellaria prostrata prostrate starwort x

Stenotaphrum secundatum* St. Augustine grass x

Strophostyles helvula amberique-bean; wild bean x

Symphyotrichum ericoides heath aster x

Symphyotrichum lanceolatum ssp. lanceolatum white panicle aster x x

Taxodium distichum bald cypress x

Teucrium canadense Canada germander x

Thelypteris ovata var. lindheimeri Lindheimer’s marsh fern x

Tillandsia recurvata small ballmoss x x

Tinantia anomala widowstears x x

Torilis arvensis* spreading hedgeparsley x x

Toxicodendron radicans poison ivy x x

Tradescantia sp. spiderwort x
293

Appendix B (continued). Plant species documented in SAAN’s riparian woodlands/forests (Carr 2003a, 

b). Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions Rancho

Chaerophyllum tainturieri var. tainturieri hairyfruit chervil x x

Triadica sebifera* Chinese tallow x

Triodanis biflora small Venus' looking-glass x

Ulmus americana American elm x x

Ulmus crassifolia cedar elm x x

Urochloa maxima* guineagrass x

Urtica chamaedryoides heartleaf nettle x

Valerianella radiata beaked cornsalad x

Verbena brasiliensis* Brazilian vervain x

Verbesina virginica white crownbeard x x

Veronica peregrina neckweed x x

Vicia ludoviciana ssp. ludoviciana Lousiana vetch x

Viguiera dentata toothleaf goldeneye x

Vinca major* bigleaf periwinkle x

Viola sp. violet x

Vitex agnus-castus* lilac chastetree x

Vitis cinerea var. helleri Heller’s grape x

Vitis mustangensis mustang grape x x

Xanthium strumarium rough cocklebur x

Totals 128 117
294

Appendix C. Native herbaceous species documented in SAAN’s old fields (Carr 2003a, b).

Scientific Name Common Name Missions Rancho

Carlowrightia texana Texas wrightwort x

Justicia pilosella Gregg’s tube tongue x

Ruellia metziae Metz’s wild petunia x

Ruellia nudiflora var. runyonii Runyon’s wild petunia x

Yucca constricta narrowleaf or Buckley’s yucca x

Amaranthus palmeri carelessweed x

Amaranthus polygonoides Berlandier or tropical amaranth x

Spermolepis inermis Red River scaleseed x

Daucus pusillus American wild carrot x

Aristolochia erecta swanflower x

Asclepias oenotheroides zizotes milkweed x x

Ambrosia confertiflora weakleaf bur ragweed x

Ambrosia psilostachya western ragweed x x

Ambrosia trifida giant ragweed x x

Aphanostephus ramosissimus plains dozedaisy or lazy daisy x x

Aphanostephus skirrhobasis Arkansas dozedaisy x

Symphyotrichum divaricatum southern annual saltmarsh aster x

Symphyotrichum ericoides heath aster x

Astranthium integrifolium entireleaf western daisy x

Baccharis neglecta Rooseveltweed x x

Baccharis texana prairie false willow x

Calyptocarpus vialis straggler daisy x x

Cirsium texanum Texas thistle x

Conyza canadensis horseweed x x

Coreopsis nuecensis crown tickseed x

Coreopsis tinctoria golden tickseed or plains coreopsis x

Thymophylla tenuiloba var.

 tenuiloba

bristleleaf pricklyleaf x

Engelmannia peristenia Engelmann’s daisy x

Gaillardia pulchella Indian blanket X
295

Appendix C (continued). Native herbaceous species documented in SAAN’s old fields (Carr 2003a, b).

Scientific Name Common Name Missions Rancho

Evax verna spring pygmycudweed x

Florestina tripteris sticky florestina x

Gaillardia pulchella Indian blanket x

Grindelia squarrosa curlycup gumweed x

Gutierrezia texana Texas snakeweed x

Helianthus annuus common sunflower x X

Helianthus debilis ssp.

 cucumerifolius

cucumberleaf sunflower x

Helianthus maximiliani Maximilian sunflower x

Heterotheca subaxillaris camphorweed x X

Hymenopappus scabiosaeus var.

 corymbosus

Carolina woolywhite x

Krigia caespitosa weedy dwarfdandelion X

Lindheimera texana Texas yellowstar x

Lygodesmia texana Texas skeletonplant x

Pyrrhopappus pauciflorus smallflower desert chicory X

Ratibida columnifera upright prairie coneflower; Mexican

 hat

x

Rudbeckia hirta var. angustifolia Perdue blackeyed susan X

Solidago canadensis Canada goldenrod x

Thelesperma filifolium stiff greenthread x

Verbesina encelioides golden crownbeard x

Viguiera dentata toothleaf goldeneye x

Xanthisma texanum Texas sleepydaisy x

Arabis petiolaris Brazos rockcress x

Descurainia pinnata western tansymustard x

Draba platycarpa broadpod draba x

Lepidium austrinum southern pepperweed or pepperwort x x

Polypremum procumbens juniper leaf x

Opuntia engelmannii var.

 lindheimeri

Texas pricklypear x x
296

Appendix C (continued). Native herbaceous species documented in SAAN’s old fields (Carr 2003a, b).

Scientific Name Common Name Missions Rancho

Opuntia macrorhiza twistspine pricklypear x

Cylindropuntia leptocaulis Christmas cactus; tasajillo x

Triodanis biflora small Venus' looking-glass x x

Triodanis perfoliata clasping Venus' looking-glass x

Polanisia dodecandra ssp.

 trachysperma

sandyseed clammyweed x

Chenopodium berlandieri pitseed goosefoot x

Commelina erecta var. angustifolia whitemouth dayflower x

Commelina erecta var. erecta whitemouth dayflower x x

Tinantia anomala widowstears x

Tradescantia sp. spiderwort x x

Convolvulus equitans Texas bindweed x

Dichondra recurvate oakwoods ponysfoot x

Ipomoea cordatotriloba tievine x x

Ipomaea hederacea ivyleaf morning-glory x

Merremia dissecta noyau vine x

Cucurbita foetidissima Missouri gourd x

Ibervillea lindheimeri Lindheimer’s globeberry x

Carex tetrastachya Britton’s sedge x

Cyperus retroflexus oneflower flatsedge x

Acalypha lindheimeri shrubby copperleaf x

Acalypha ostryifolia pineland threeseed mercury x

Argythamnia humilis var. humilis low silverbush x

Croton capitatus hogwort x

Croton glandulosus tooth-leaved croton; vente conmigo x

Croton monanthogynus prairie tea, oneseeded croton x x

Euphorbia dentata toothed spurge x x

Euphorbia nutans small eyebane x

Euphorbia peplidion low spurge x

Euphorbia prostrata prostrate sandmat x
297

Appendix C (continued). Native herbaceous species documented in SAAN’s old fields (Carr 2003a, b).

Scientific Name Common Name Missions Rancho

Euphorbia serpens matted sandmat x x

Chamaesyce glyptosperma small ribseed sandmat x

Phyllanthus polygonoides smartweed leaf-flower x

Tragia brevispica shortspike noseburn x x

Tragia ramosa branched noseburn x

Astragalus nuttallianus var.

 trichocarpus

turkeypeas x x

Dalea emarginata wedgeleaf prairie clover x

Desmanthus virgatus wild tantan x X

Mimosa latidens Kairn’s sensitive-briar x

Rhynchosia minima least snoutbean x

Rhynchosia senna var. texana Texas snoutbean x

Vicia ludoviciana ssp. leavenworthii Leavenworth’s vetch x

Vicia ludoviciana ssp. ludoviciana Louisiana vetch x

Sabatia campestris Texas star; prairie rose gentian x

Geranium texanum Texas geranium x

Nama hispidum bristly nama x

Nama jamaicense Jamaicanweed x

Sisyrinchium langloisii roadside blue-eyed grass x x

Hedeoma drummondii Drummond's false pennyroyal x

Hedeoma hispida rough false pennyroyal x

Monarda citriodora ssp. citriodora lemon beebalm x

Monarda punctata spotted beebalm x

Scutellaria drummondii Drummond’s skullcap x

Cooperia drummondii evening rainlily x x

Nothoscordum bivalve crowpoison x x

Linum imbricatum tufted flax x

Rhynchosida physocalyx buffpetal x x

Sida abutifolia spreading fanpetals x x

Sida spinosa prickly fanpetals x x
298

Appendix C (continued). Native herbaceous species documented in SAAN’s old fields (Carr 2003a, b).

Scientific Name Common Name Missions Rancho

Cocculus carolinus Carolina coralbead or snailseed x

Boerhavia diffusa red spiderling x

Boerhavia erecta erect spiderling x

Mollugo verticillata green carpetweed x

Mirabilis linearis narrowleaf four o’clock x x

Nyctaginia capitata devil’s bouquet; scarlet muskflower x

Menodora heterophylla low menodora x

Gaura brachycarpa plains beeblossom x

Gaura coccinea scarlet gaura or beeblossom x

Gaura parviflora velvetweed x x

Gaura sinuata wavyleaf beeblossom x

Oenothera laciniata cutleaf evening primrose x

Oenothera speciosa pinkladies x x

Oxalis dillenii slender yellow woodsorrel x x

Argemone aurantiaca Texas pricklypoppy x

Passiflora foetida var. gossypiifolia cottonleaf passionflower x

Plantago hookeriana California or Hooker plantain x

Plantago rhodosperma redseed plantain x x

Plantago wrightiana Wright’s plantain x

Aristida purpurea var. purpurea purple threeawn x x

Aristida purpurea var. longiseta Fendler threeawn x x

Bothriochloa laguroides ssp.

 torreyana

silver beardgrass x x

Bouteloua dactyloides buffalograss x

Cenchrus spinifex coastal sandbur x x

Chloris ciliata fringed windmill grass x x

Chloris cucullata hooded windmill grass x x

Chloris verticillata tumble windmill grass x

Digitaria ciliaris southern crabgrass X

Digitaria cognata fall witchgrass x x
299

Appendix C (continued). Native herbaceous species documented in SAAN’s old fields (Carr 2003a, b).

Scientific Name Common Name Missions Rancho

Eragrostis curtipedicellata gummy lovegrass x x

Eragrostis intermedia plains lovegrass x x

Eragrostis secundiflora ssp.

 oxylepis

red lovegrass x

Hordeum pusillum little barley x

Leptochloa panicea ssp. mucronata mucronate sprangletop x

Limnodea arkansana Ozarkgrass x x

Nassella leucotricha Texas wintergrass x x

Panicum hallii Hall’s panicgrass x x

Phalaris caroliniana Carolina canarygrass x

Setaria leucopila streambed or plains bristlegrass x

Sporobolus cryptandrus sand dropseed x

Tridens albescens white tridens x

Tridens muticus var. elongatus slim tridens x

Tridens texanus Texas tridens or fluffgrass x

Urochloa ciliatissima fringed signalgrass x

Urochloa fusca browntop signalgrass x x

Urochloa texana Texas signallgrass x

Vulpia octoflora sixweeks fescue x

Phlox drummondii annual phlox x

Portulaca pilosa kiss me quick x

Portulaca umbraticola wingpod purslane x

Anemone berlandieri tenpetal thimbleweed x x

Clematis drummondii Drummond’s clematis x

Galium virgatum southwestern bedstraw x

Houstonia parviflora Greenman’s bluet x

Richardia tricocca prairie Mexican clover x

Cardiospermum halicacabum balloon vine x

Agalinis strictifolia stiffleaf false foxglove x x

Nuttallanthus texanus Texas toadflax x
300

Appendix C (continued). Native herbaceous species documented in SAAN’s old fields (Carr 2003a, b).

Scientific Name Common Name Missions Rancho

Physalis cinerascens var.

 cinerascens

smallflower groundcherry x x

Solanum dimidiatum western horsenettle x

Solanum elaeagnifolium silverleaf nightshade x x

Solanum rostratum buffalobur nightshade x

Melochia pyramidata pyramidflower x

Corchorus hirtus Orinoco jute x

Glandularia bipinnatifida Dakota mock vervain x x

Glandularia pumila pink mock vervain x x

Glandularia quandrangulata beaked mock vervain x

Phyla nodiflora turkey tangle fogfruit x

Verbena canescens gray vervain x

Verbena halei Texas vervain x x

Verbena plicata fanleaf vervain x

Hybanthus verticillatus babyslippers x x

Vitis mustangensis mustang grape x

Number of species 130 110
301

Appendix D. Plant species documented in SAAN’s upland shrublands/woodlands (Carr 2003a, b). UW = 

upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Carlowrightia texana Texas wrightwort x

Dyschoriste linearis polkadots x

Justicia pilosella Gregg’s tube tongue x x

Ruellia nudiflora var. nudiflora violet wild petunia x x

Agave sp.* agave x

Manfreda maculosa spice lily x

Yucca constricta narrowleaf or Buckley’s yucca x x

Yucca treculeana Don Quixote’s lace x x

Amaranthus palmeri carelessweed x

Amaranthus polygonoides Berlandier or tropical amaranth x

Froelichia gracilis slender snakecotton x

Toxicodendron radicans poison ivy x x

Daucus pusillus American wild carrot x x

Torilis arvensis* spreading hedgeparsley x x x

Aristolochia erecta swanflower x

Cynanchum barbigerum bearded swallow-wort x x

Matelea reticulata netted milkvine x

Asclepias oenotheroides zizotes milkweed x

Funastrum cynanchoides ssp.

cynanchoides

fringed twinevine x

Amblyolepis setigera huisache daisy x x x

Ambrosia confertiflora weakleaf bur ragweed x x

Ambrosia psilostachya western ragweed x x x

Ambrosia trifida great ragweed x

Aphanostephus ramosissimus plains dozedaisy or lazy daisy x x x

Aphanostephus riddellii Riddell’s dozedaisy x

Symphyotrichum ericoides heath aster x x x

Astranthium integrifolium entireleaf western daisy x x
302

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Baccharis neglecta Rooseveltweed x

Baccharis texana prairie false willow x

Calyptocarpus vialis straggler daisy x x x

Centaurea melitensis* Maltese star-thistle x x

Chaptalia texana silverpuff x x

Cirsium texanum Texas thistle x x x

Conyza canadensis horseweed x

Coreopsis tinctoria golden tickseed or plains 

coreopsis

x

Coreopsis wrightii rock tickseed x x

Thymophylla pentachaeta var.

pentachaeta

fiveneedle pricklyleaf x

Engelmannia peristenia Engelmann’s daisy x

Evax verna spring pygmycudweed x

Fleischmannia incarnata pink thoroughwort x x x

Florestina tripteris sticky florestina x

Gaillardia pulchella Indian blanket x x

Grindelia squarrosa curlycup gumweed x

Gutierrezia texana Texas snakeweed x x x

Helianthus annuus common sunflower x x x

Helianthus debilis ssp.

cucumerifolius

cucumberleaf sunflower x

Heterotheca subaxillaris camphorweed x x

Lactuca ludoviciana biannual lettuce x

Lactuca serriola* prickly lettuce x

Liatris punctata var. mucronata blazing star X

Lygodesmia texana Texas skeletonplant X

Lindheimera texana Texas yellowstar x

Parthenium confertum Gray’s feverfew X
303

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Parthenium hysterophorus* Santa Maria feverfew x X

Pinaropappus roseus white rocklettuce X

Pyrrhopappus pauciflorus smallflower desert chicory x

Ratibida columnifera upright prairie coneflower; 

Mexican hat

x x

Rudbeckia hirta var. angustifolia Perdue blackeyed susan x

Senecio ampullaceus Texas ragwort x

Simsia calva awnless bushsunflower x X

Solidago canadensis Canada goldenrod x

Solidago gigantea giant goldenrod x

Sonchus asper* spiny sowthistle x x

Sonchus oleraceus* common sowthistle x

Tetraneuris scaposa stemmy four-nerve daisy X

Thelesperma ambiguum Colorado greenthread X

Viguiera dentata toothleaf goldeneye x

Wedelia acapulcensis var. hispida orange zexmenia x X

Berberis trifoliolata algerita; agarito x x X

Ehretia anacua knockaway; anacua x

Cryptantha texana pick me nots x

Lithospermum mirabile San Antonio stoneseed x X

Arabis petiolaris Brazos rockcress X

Lepidium austrinum southern pepperweed or 

pepperwort

x X

Lesquerella argyraea silver bladderpod X

Rapistrum rugosum* annual bastardcabbage x

Tillandsia recurvata small ballmoss x X

Thelocactus setispinus miniature barrel cactus x X

Opuntia engelmannii var. lindheimeri Texas pricklypear x x X

Cylindropuntia leptocaulis Christmas cactus; tasajillo x X
304

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Triodanis biflora small Venus' looking-glass x X

Lonicera japonica* Japanese honeysuckle x

Silene antirrhina sleepy sirene; sticky catchfly x

Stellaria media* common chickweed x

Schaefferia cuneifolia desert yaupon x X

Chenopodium berlandieri pitseed goosefoot x

Commelina erecta var. angustifolia whitemouth dayflower x

Commelina erecta var. erecta whitemouth dayflower x X

Tradescantia sp. spiderwort x x

Convolvulus equitans Texas bindweed x x

Evolvulus sericeus var. sericeus silver dwarf morning-glory x X

Ipomoea cordatotriloba tievine x x

Merremia dissecta noyau vine x

Ibervillea lindheimeri Lindheimer’s globeberry x

Cuscuta sp. dodder x

Carex sp. sedge x x

Carex planostachys cedar sedge x

Diospyros texana Texas persimmon x x x

Acalypha ostryifolia pineland threeseed mercury x

Argythamnia humilis var. humilis low silverbush x

Cnidoscolus texanus Texas bullnettle x

Croton monanthogynus prairie tea, oneseeded croton x x x

Euphorbia spathulata warty spurge x

Jatropha dioica leatherstem x

Phyllanthus polygonoides smartweed leaf-flower x

Tragia brevispica shortspike noseburn x

Tragia ramosa branched noseburn x

Acacia farnesiana (formerly minuta) sweet acacia; huisache x
305

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Acacia greggii var. greggii catclaw acacia x

Acacia rigidula blackbrush acacia x

Astragalus nuttallianus smallflowered milkvetch x

Dalea pogonathera bearded prairie clover x x

Desmanthus velutinus velvet bundleflower x

Desmanthus virgatus wild tantan x x x

Eysenhardtia texana Texas kidneywood x x x

Melilotus indicus* annual yellow sweetclover x

Melilotus officinalis* sweetclover x

Mimosa borealis fragrant mimosa x

Mimosa latidens Kairn’s sensitive-briar x

Neptunia lutea yellow puff x

Parkinsonia aculeata Jerusalem thorn x

Prosopis glandulosa var. glandulosa honey mesquite x x

Rhynchosia minima least snoutbean x

Rhynchosia senna var. texana Texas snoutbean x x

Senna pumilio dwarf senna x

Styphnolobium affine Eve’s necklacepod x

Vicia ludoviciana ssp. leavenworthii Leavenworth’s vetch x x

Corydalis sp. fumewort; scrambled eggs x

Geranium texanum Texas geranium x x

Nama hispidum bristly nama x

Nama jamaicense Jamaicanweed x x

Phacelia congesta caterpillars; blue curls x

Krameria lanceolata trailing krameria x

Hedeoma drummondii Drummond's false pennyroyal x x

Hedeoma hispida rough false pennyroyal x x

Lamium amplexicaule* henbit deadnettle x
306

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Monarda citriodora ssp. citriodora lemon beebalm x

Monarda punctata spotted beebalm x x

Salvia ballotiflora shrubby blue sage X

Scutellaria drummondii Drummond’s skullcap x x

Stachys crenata mousesear x

Teucrium cubense small coastal germander x

Allium canadense var. canadense meadow garlic x

Allium drummondii Drummond’s onion x x

Cooperia drummondii evening rainlily x x

Cooperia pedunculata prairie lily x x

Habranthus tubispathus Rio Grande copperlily x

Schoenocaulon drummondii green feathershank x

Linum imbricatum tufted flax x x

Abutilon fruticosum Texas Indian mallow x

Abutilon wrightii Wright’s Indian mallow

Callirhoe leiocarpa tall poppymallow x x

Malvastrum coromandelianum* threelobe false mallow x x

Malvaviscus arboreus var.

drummondii

wax mallow x

Rhynchosida physocalyx buffpetal x

Melia azedarach* Chinaberrytree x

Cocculus carolinus Carolina coralbead x

Broussonetia papyrifera* paper mulberry x

Boerhavia diffusa red spiderling x

Acleisanthes obtusa Berlandier’s trumpets x x

Acleisanthes longiflora angel’s trumpets x x

Mirabilis albida white four o’clock x

Mirabilis jalapa* marvel of Peru x
307

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Nyctaginia capitata devil’s bouquet; scarlet 

muskflower

x

Menodora heterophylla low menodora x

Forestiera angustifolia Texas swampprivet x x

Ligustrum japonicum* Japanese privet x

Gaura brachycarpa plains beeblossom x x

Gaura coccinea scarlet gaura or beeblossom x

Gaura parviflora velvetweed x x x

Gaura sinuata wavyleaf beeblossom x

Oenothera speciosa pinkladies x

Oxalis dichondrifolia peonyleaf woodsorrel x

Oxalis dillenii slender yellow woodsorrel x x x

Oxalis drummondii Drummond’s woodsorrel x x

Argemone aurantiaca Texas pricklypoppy x

Argemone sanguinea red pricklypoppy x

Passiflora tenuiloba birdwing passionflower x x x

Rivina humilis rougeplant x

Plantago hookeriana California or Hooker plantain x

Plantago rhodosperma redseed plantain x x x

Aristida purpurea var. purpurea purple threeawn x x

Arundo donax* giant reed x

Bothriochloa ischaemum var.

songarica*

yellow bluestem x x X

Bothriochloa laguroides ssp.

torreyana

silver beardgrass x x x

Bouteloua curtipendula sideoats grama x

Bouteloua dactyloides buffalograss x

Bouteloua rigidiseta Texas grama x x

Bouteloua trifida red grama x
308

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Bromus arvensis* (formerly

japonicus)

field brome x

Bromus catharticus* rescuegrass x x

Cenchrus spinifex coastal sandbur x

Chloris ciliata fringed windmill grass x

Chloris cucullata hooded windmill grass x x

Chloris verticillata tumble windmill grass x

Cynodon dactylon* Bermudagrass x x x

Dichanthium annulatum* Kleberg’s bluestem x x x

Digitaria ciliaris southern crabgrass x

Digitaria cognata fall witchgrass x

Eragrostis intermedia plains lovegrass x x

Eragrostis sessilispica tumble lovegrass x

Eriochloa sericea Texas cupgrass x

Hilaria belangeri curly-mesquite x x

Hordeum pusillum little barley x x

Leptochloa dubia green sprangletop x x

Limnodea arkansana Ozarkgrass x x x

Nassella leucotricha Texas wintergrass x x x

Panicum capillarioides slender panicgrass x

Panicum hallii Hall’s panicgrass x

Urochloa maxima* Guineagrass x

Paspalum dilatatum* Dallisgrass x

Paspalum pubiflorum hairyseed paspalum x

Poa annua* annual bluegrass x

Schizachyrium scoparium little bluestem x

Setaria leucopila streambed or plains bristlegrass x x x

Setaria reverchonii ssp. ramiseta Rio Grande bristlegrass x x

Setaria scheelei southwestern bristlegrass x x
309

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Sorghum halepense* Johnsongrass x x

Sporobolus compositus var.

compositus

composite dropseed x

Sporobolus cryptandrus sand dropseed x x x

Trichloris pluriflora multiflower false Rhodes grass x

Tridens albescens white tridens x

Tridens eragrostoides lovegrass tridens x x

Tridens muticus var. muticus slim tridens x

Tridens texanus Texas tridens or fluffgrass x x x

Urochloa fusca browntop signalgrass x

Giliastrum incisum splitleaf gilia x x

Polygala alba white milkwort X

Polygala lindheimeri shrubby milkwort X

Phemeranthus aurantiacus orange fameflower x x

Talinum paniculatum jewels of Opar x

Cheilanthes alabamensis Alabama lipfern x X

Pellaea atropurpurea purple cliffbrake X

Anemone berlandieri tenpetal thimbleweed x x X

Clematis drummondii Drummond’s clematis x x X

Delphinium carolinianum Carolina larkspur X

Colubrina texensis Texan hogplum x x X

Condalia hookeri var. hookeri Brazilian bluewood x x X

Ziziphus obtusifolia lotebush x X

Rubus riograndis Rio Grande dewberry x

Galium aparine cleavers, stickwilly x

Galium virgatum southwestern bedstraw x X

Stenaria nigricans var. nigricans diamondflowers X

Houstonia parviflora Greenman’s bluet X

Ptelea trifoliata common hoptree X
310

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Thamnosma texana rue of the mountains x X

Sapindus saponaria var. drummondii western soapberry x

Sideroxylon lanuginosum gum bully x X

Agalinis strictifolia stiffleaf false foxglove x X

Castilleja indivisa entireleaf Indian paintbrush x x X

Maurandella antirrhiniflora roving sailor x X

Ailanthus altissima* tree of heaven x

Smilax bona-nox saw greenbriar x X

Bouchetia erecta paintedtongue X

Capsicum annuum cayenne pepper x X

Chamaesaracha coronopus greenleaf five eyes x

Lycium berlandieri Berlandier’s wolfberry x X

Physalis cinerascens var.

cinerascens

smallflower groundcherry x X

Solanum elaeagnifolium silverleaf nightshade x X

Solanum triquetrum Texas nightshade x

Hermannia texana Texas burstwort x X

Celtis laevigata var. laevigata sugarberry x

Celtis laevigata var. reticulata netleaf hackberry x x X

Celtis ehrenbergiana spiny hackberry x x X

Ulmus crassifolia cedar elm x X

Parietaria pensylvanica Pennsylvania pellitory X

Aloysia gratissima whitebrush x X

Glandularia bipinnatifida Dakota mock vervain x

Glandularia pumila pink mock vervain x

Glandularia quandrangulata beaked mock vervain x

Lantana urticoides West Indian shrubverbena x X

Tetraclea coulteri Coulter’s wrinklefruit x

Verbena canescens gray vervain x
311

Appendix D (continued). Plant species documented in SAAN’s upland shrublands/woodlands (Carr 

2003a, b). UW = upland woodland, US = upper-slope shrubland. Asterisks (*) indicate non-native species.

Scientific Name Common Name Missions

Rancho

UW US

Verbena halei Texas vervain x

Verbena plicata fanleaf vervain x x

Phoradendron tomentosum Christmas mistletoe x x x

Cissus trifoliata sorrelvine x

Vitis cinerea var. helleri Heller’s grape x

Vitis mustangensis mustang grape x x

Guaiacum angustifolium Texas lignum-vitae x

Kallstroemia parviflora warty caltrop x

Tribulus terrestris* puncturevine x

Totals 151 133 156
312

Appendix E. Reptiles identified in or near SAAN (data compiled from museum vouchers, Strecker 1915, Gallyoun et al. 2002, Gallyoun et al. 

2003, Duran 2004, Woodman 2013, and NPS 2014). Strecker (1915) is highlighted in gray because it serves as the reference condition for this 

NRCA. It should also be noted that Strecker’s (1915) study covered a larger area than SAAN, and not all species occurred in the park.

Scientific Name Common Name

Strecker 

(1915)

Literature/

Museum 

Vouchers

Duran 

(2004)

Woodman 

(2013) NPS (2014)

Agkistrodon contortrix copperhead X X

Agkistrodon piscivorus cottonmouth X R X

Anolis carolinensis green anole X X X X

Apalone spinifera guadalupensis Guadalupe spiny softshell X X X X

Arizona elegans glossy snake X

Chelydra serpentine common snapping turtle X X X X

Cnemidophorus grahamii bold checkered whiptail X

Cnemidophorus gularis gularis Texas spotted whiptail X X X

Coleonyx brevis Texas banded gecko X

Crotalus atrox western diamondback rattlesnake X X X

Crotalus molossus black-tailed rattlesnake X

Crotalus viridis prairie rattlesnake X

Elaphe guttata emoryi Great Plains rat snake X X X

Elaphe obsolete Texas rat snake X X X

Eumeces tetragrammus brevilineatus short-lined skink X PP

X - Direct observation

R - Rare 

PP - Probably Present

* - Historically present in park, extirpated from area
313

Appendix E (continued). Reptiles identified in or near SAAN (data compiled from museum vouchers, Strecker 1915, Gallyoun et al. 2002, 

Gallyoun et al. 2003, Duran 2004, Woodman 2013, and NPS 2014). Strecker (1915) is highlighted in gray because it serves as the reference 

condition for this NRCA. It should also be noted that Strecker’s (1915) study covered a larger area than SAAN, and not all species occurred in the 

park.

Scientific Name Common Name

Strecker 

(1915)

Literature/

Museum 

Vouchers

Duran 

(2004)

Woodman

(2013) NPS (2014)

Gopherus berlandieri Texas tortoise X X X X

Graptemys caglei Cagle's map turtle X X*

Hemidactylus turcicus Mediterranean gecko X X X X

Heterodon platirhinos eastern hognose snake X

Holbrookia maculata lesser earless lizard X

Holbrookia propinqua keeled earless lizard X

Kinosternon flavescens yellow mud turtle X X

Lampropeltis getula splendida desert kingsnake X X X

Lampropeltis Triangulum milk snake X

Leptotyphlops dulcis dulcis plains blind snake X X X X

Macrochelys temminckii alligator snapping turtle X

Masticophis flagellum testaceus western coachwhip X X X X

Masticophis schotti Schott's whipsnake X X X X

Micrurus tener Texas coral snake x X R X X

Nerodia erythrogaster transversa blotched water snake X X X

X - Direct observation

R - Rare 

PP - Probably Present

* - Historically present in park, extirpated from area
314

Appendix E (continued). Reptiles identified in or near SAAN (data compiled from museum vouchers, Strecker 1915, Gallyoun et al. 2002, 

Gallyoun et al. 2003, Duran 2004, Woodman 2013, and NPS 2014). Strecker (1915) is highlighted in gray because it serves as the reference 

condition for this NRCA. It should also be noted that Strecker’s (1915) study covered a larger area than SAAN, and not all species occurred in the 

park.

Scientific Name Common Name

Strecker 

(1915)

Literature/

Museum 

Vouchers

Duran 

(2004)

Woodman 

(2013) NPS (2014)

Nerodia rhombifer diamondback water snake X X X

Opheodrys aestivus rough green snake X R X

Phrynosoma cornutum Texas horned lizard X R PP

Pseudemys texana Texas river cooter X X X X

Regina grahamii Graham's crayfish snake X X PP

Rhinocheilus lecontei tessellatus Texas long-nosed snake X X X

Salvadora grahamiae lineata Texas patch-nosed snake X X X X

Sceloporus consobrinus prairie lizard X X PP

Sceloporus olivaceus Texas spiny lizard X X X X

Sceloporus variabilis marmoratus rose-bellied lizard X X X X X

Scincella lateralis ground skink X X X X

Sonora semiannulata ground snake X

Sternotherus odoratus common musk turtle X X

Storeria dekayi texana Texas brown snake X X X

Tantilla gracilis flat-headed snake X

X - Direct observation

R - Rare 

PP - Probably Present

* - Historically present in park, extirpated from area
315

Appendix E (continued). Reptiles identified in or near SAAN (data compiled from museum vouchers, Strecker 1915, Gallyoun et al. 2002, 

Gallyoun et al. 2003, Duran 2004, Woodman 2013, and NPS 2014). Strecker (1915) is highlighted in gray because it serves as the reference 

condition for this NRCA. It should also be noted that Strecker’s (1915) study covered a larger area than SAAN, and not all species occurred in the 

park.

Scientific Name Common Name

Strecker 

(1915)

Literature/

Museum 

Vouchers

Duran 

(2004)

Woodman 

(2013) NPS (2014)

Tantilla nigriceps plains black-headed snake X

Terrapene carolina common box turtle X

Terrapene ornata ornate box turtle X

Thamnophis marcianus marcianus checkered garter snake X X X

Thamnophis proximus rubrilineatus redstripe ribbon snake X R PP

Trachemys scripta elegans red-eared slider X X X

Tropidoclonion lineatum lined snake X

Virginia striatula rough earth snake X X X X

X - Direct observation

R - Rare 

PP - Probably Present

* - Historically present in park, extirpated from area
316

Appendix F. Breeding bird species observed in SAAN from 1985-2012.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

red-tailed hawk Buteo jamaicensis X X X X

red-shouldered hawk Buteo lineatus X X X X

turkey vulture Cathartes aura X X X X

black vulture Coragyps atratus X X X X

Egyptian goose Alopochen aegyptiaca X

mallard Anas platyrhynchos X X X

black-bellied whistling duck, black-bellied whistling-duck Dendrocygna autumnalis X X X X

chimney swift Chaetura pelagica X X X X

black-chinned hummingbird Archilochus alexandri X X X X

lesser nighthawk Chordeiles acutipennis X X X

common nighthawk Chordeiles minor X X X X

killdeer Charadrius vociferus X X X X

common pigeon, rock dove, rock pigeon Columba livia X X X

Inca dove Columbina inca X X X X

common ground dove, common ground-dove Columbina passerina X X

white-tipped dove Leptotila verreauxi X X

Eurasian collared dove, Eurasian collared-dove Streptopelia decaocto X X X

white-winged dove Zenaida asiatica X X X X

mourning dove Zenaida macroura X X X X

yellow-billed cuckoo Coccyzus americanus X X X X

greater roadrunner Geococcyx californianus X X X

crested caracara, northern crested caracara Caracara cheriway X X X
317

Appendix F (continued). Breeding bird species observed in SAAN from 1985-2012.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

northern bobwhite Colinus virginianus X X X

wild turkey Meleagris gallopavo X X X

pyrrhuloxia Cardinalis sinuatus X X X X

blue grosbeak Passerina caerulea X X X

painted bunting Passerina ciris X X X

indigo bunting Passerina cyanea X X X X

dickcissel Spiza americana X X X

American crow Corvus brachyrhynchos X X X

blue jay Cyanocitta cristata X X X

olive sparrow Arremonops rufivirgatus X X X

lark sparrow Chondestes grammacus X X X

lesser goldfinch Carduelis psaltria X X X X

house finch Carpodacus mexicanus X X X X

barn swallow Hirundo rustica X X X X

cave swallow Petrochelidon fulva X X X

American cliff swallow, cliff swallow Petrochelidon pyrrhonota X X X

purple martin Progne subis X X X X

red-winged blackbird Agelaius phoeniceus X X X X

Bullock's oriole Icterus bullockii X X X

orchard oriole Icterus spurius X X X X

bronzed cowbird Molothrus aeneus X X

brown-headed cowbird Molothrus ater X X X X
318

Appendix F (continued). Breeding bird species observed in SAAN from 1985-2012.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

great-tailed grackle Quiscalus mexicanus X X X X

cedar waxwing Bombycilla cedrorum X

loggerhead shrike Lanius ludovicianus X X X X

northern mockingbird Mimus polyglottos X X X X

curve-billed thrasher Toxostoma curvirostre X X X

long-billed thrasher Toxostoma longirostre X X X

black-crested titmouse Baeolophus atricristatus X X X X

Carolina chickadee Poecile carolinensis X X X X

yellow-breasted chat Icteria virens X X X

house sparrow Passer domesticus X X X X

verdin Auriparus flaviceps X X X

European starling Sturnus vulgaris X X X X

Bewick's wren Thryomanes bewickii X X X X

Carolina wren Thryothorus ludovicianus X X X X

ash-throated flycatcher Myiarchus cinerascens X X X

great crested flycatcher Myiarchus crinitus X X X X

brown-crested flycatcher Myiarchus tyrannulus X X X

great kiskadee Pitangus sulphuratus X X

scissor-tailed flycatcher Tyrannus forficatus X X X X

western kingbird Tyrannus verticalis X X X X

Bell's vireo Vireo bellii X X X

yellow-throated vireo Vireo flavifrons X
319

Appendix F (continued). Breeding bird species observed in SAAN from 1985-2012.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

white-eyed vireo Vireo griseus X X X X

golden-fronted woodpecker Melanerpes aurifrons X X X X

downy woodpecker Picoides pubescens X X X

ladder-backed woodpecker Picoides scalaris X X X X

great horned owl Bubo virginianus X X X

barred owl Strix varia X X X

Total Number of Breeding Species Observed 71 44 68 60
320

Appendix G. Breeding bird species abundance by season for the San Juan Woods (SAJU) and Espada 

Labores (ESPA) land tracts, SAAN, 1985-86 (Appendix reproduced from Coonan 1987).

Species Area Fall Winter Spring

Early 

Summer

Late 

Summer

black-bellied whistling duck SAJU

ESPA 1.2

black vulture SAJU 2.9

ESPA 0.2

turkey vulture SAJU 0.7

ESPA 1 0.2 1.4 1 1

red-shouldered hawk SAJU 0.7

ESPA 0.2 0.4 0.4 1

red-tailed hawk SAJU 1.5 0.7

ESPA 0.4 1.2 1 0.8 0.8

northern bobwhite SAJU

ESPA 0.2 0.2

killdeer SAJU 1.5 2.2

ESPA 1 1.2 1.6 0.2 1.8

white-winged dove SAJU

ESPA 0.2 5

mourning dove SAJU 7.4 10.3 2.2 1.5 0.7

ESPA 13.5 7.8 11 9 12.9

Inca dove SAJU 1.5 1.5 1

ESPA 0.4 0.8 1.6

yellow-billed cuckoo SAJU 0.7 5.2 3.7

ESPA 0.6 1.8 0.2

great horned owl SAJU 0.7 1.5 0.7 1.5

ESPA

common nighthawk SAJU

ESPA 0.2

chimney swift SAJU 7.4 1.5 2.2 1.5

ESPA 1.2 5 14.7

black-chinned hummingbird SAJU 1.5 2.2

ESPA

golden-fronted woodpecker SAJU 2.2 6.6 7.4 9.6 8.8

ESPA 2.4 3.2 3.4 4.6 4.6
321

Appendix G (continued). Breeding bird species abundance by season for the San Juan Woods (SAJU) 

and Espada Labores (ESPA) land tracts, SAAN, 1985-86 (Appendix reproduced from Coonan 1987).

Species Area Fall Winter Spring

Early 

Summer

Late 

Summer

ladder-backed woodpecker SAJU

ESPA 1 0.4

downy woodpecker SAJU

ESPA 0.4

great crested flycatcher SAJU

ESPA 0.8 0.6

western kingbird SAJU 2.9

ESPA 1.6 0.2

scissor-tailed flycatcher SAJU

ESPA 6 0.4 0.8 1.2

purple martin SAJU 0.7

ESPA 0.2

barn swallow SAJU 0.7 2.2

ESPA 0.6 1.8 2.8

Carolina chickadee SAJU 2.2 1.5 4.4 9.6 5.9

ESPA 0.8 2 2 3 2

black-crested titmouse SAJU 5.9 10.3 9.6 5.2 5.9

ESPA 1.8 3 2.8 5.8 2

Carolina wren SAJU 11.8 2.2 8.8 14 16.9

ESPA 4 2.4 2.4 4.2 7.6

Bewick's wren SAJU

ESPA 0.4

northern mockingbird SAJU 3.7 2.9 5.2 1.5

ESPA 7.8 6.2 3.6 3.8 2.6

curve-billed thrasher SAJU 1.5

ESPA 0.2

cedar waxwing SAJU 0.7 16.2 8.1

ESPA 12.9 6.9

loggerhead shrike SAJU

ESPA 2.6 2 0.2 0.2 2.4

European starling SAJU 2.9 0.7 2.2 4.4

ESPA 11.7 6 3 0.2 0.2
322

Appendix G (continued). Breeding bird species abundance by season for the San Juan Woods (SAJU) 

and Espada Labores (ESPA) land tracts, SAAN, 1985-86 (Appendix reproduced from Coonan 1987).

Species Area Fall Winter Spring

Early 

Summer

Late 

Summer

white-eyed vireo SAJU 2.9 2.9 2.9

ESPA 0.2 1.6 1.8

Bell's vireo SAJU

ESPA 0.6

pyrrhuloxia SAJU

ESPA 0.2 0.2 0.2

indigo bunting SAJU

ESPA 0.2

lark sparrow SAJU 3.7

ESPA 6 1.4 2.6 0.2

red-winged blackbird SAJU

ESPA 9.2 1.4 0.4 1

great-tailed grackle SAJU 5.2 6.6 4.4 7.4 4.4

ESPA 7.2 3.8 5 21.1 5.2

brown-headed cowbird SAJU 2.9 ??

ESPA 5.2 10.4 5.2

orchard oriole SAJU 0.7

ESPA

house finch SAJU

ESPA 4 1 3.4 3.2 1

lesser goldfinch SAJU

ESPA 5

house sparrow SAJU

ESPA 0.2

Number of Breeding Species SAJU 31 31 32 33 35

ESPA 39 35 36 41 38
323

Appendix H. Relative abundance and distribution of breeding bird species observed during Scully (2006). Bold species indicate a species that 

was observed at one of the point count locations.

Species Observed Number of Times Detected

Species

City of San 

Antonio (18)

Rancho de las 

Cabras (7) Jan Mar May Jul Sep Nov Total

black-bellied whistling duck X X 2 20 12 6 1 7 48

mallard X 5 8 1 1 2 17

wild turkey X 1 7 5 2 2 17

northern bobwhite X 0

turkey vulture X X 11 19 10 11 18 5 74

black vulture X X 15 15 3 9 9 3 54

red-shouldered hawk X X 20 23 15 5 9 22 94

red-tailed hawk X X 2 1 7 4 1 15

crested caracara X X 8 6 1 2 2 2 21

killdeer X X 7 5 4 2 6 5 29

rock pigeon X 7 12 10 9 3 10 51

Eurasian collared-dove X 1 1

white-winged dove X 18 39 53 43 16 24 193

mourning dove X X 13 24 27 16 14 6 100

Inca dove X X 1 8 3 3 1 16

common ground dove X X 1 8 5 6 20

yellow-billed cuckoo X X 36 13 49

greater roadrunner X 2 1 2 1 6

great horned owl X X 1 1

barred owl X X 1 1 2 4
324

Appendix H (continued). Relative abundance and distribution of breeding bird species observed during Scully (2006). Bold species indicate a 

species that was observed at one of the point count locations.

Species Observed Number of Times Detected

Species

City of San 

Antonio (18)

Rancho de las 

Cabras (7) Jan Mar May Jul Sep Nov Total

lesser nighthawk X 1 1

common nighthawk X X 1 1

chimney swift X X 10 11 14 35

black-chinned hummingbird X X 6 1 7

golden-fronted woodpecker X X 25 42 21 9 9 16 122

ladder-backed woodpecker X X 12 6 15 8 15 9 65

downy woodpecker X 0

ash-throated flycatcher X X 2 1 3

great-crested flycatcher X X 2 12 1 15

brown-crested flycatcher X 1 1

great kiskadee X 1 1

western kingbird X X 8 7 15

scissor-tailed flycatcher X X 8 24 12 23 67

loggerhead shrike X X 6 5 6 5 4 1 27

white-eyed vireo X X 6 63 65 37 33 1 205

Bell's vireo X 1 1

blue jay X 24 12 5 9 13 17 80

American crow X X 47 39 32 13 29 27 187

purple martin X X 7 15 24 46

cliff swallow X X 3 25 14 42
325

Appendix H (continued). Relative abundance and distribution of breeding bird species observed during Scully (2006). Bold species indicate a 

species that was observed at one of the point count locations.

Species Observed Number of Times Detected

Species

City of San 

Antonio (18)

Rancho de las 

Cabras (7) Jan Mar May Jul Sep Nov Total

cave swallow X X 4 17 14 11 1 47

barn swallow X X 12 22 13 5 52

Carolina chickadee X X 8 8 12 2 3 2 35

black-crested titmouse X X 9 40 53 11 5 5 123

verdin X X 2 3 6 1 1 1 14

Carolina wren X X 53 78 93 57 46 29 356

Bewick's wren X X 4 4 5 2 7 3 25

northern mockingbird X X 30 42 53 31 35 36 227

long-billed thrasher X 1 1 2

curve-billed thrasher X X 2 3 1 3 2 11

European starling X X 9 18 22 12 12 12 85

yellow-breasted chat X 1 1

olive sparrow X 11 11

lark sparrow X X 2 1 1 4

pyrrhuloxia X X 1 2 1 4

blue grosbeak X X 7 7

indigo bunting X 2 2

painted bunting X X 23 10 33

dicksissel X X 25 4 6 35

red-winged blackbird X X 14 30 7 5 1 3 60
326

Appendix H (continued). Relative abundance and distribution of breeding bird species observed during Scully (2006). Bold species indicate a 

species that was observed at one of the point count locations.

Species Observed Number of Times Detected

Species

City of San 

Antonio (18)

Rancho de las 

Cabras (7) Jan Mar May Jul Sep Nov Total

great-tailed grackle X 50 68 71 51 28 34 302

bronzed cowbird X 1 1

brown-headed cowbird X X 6 11 17 7 3 44

orchard oriole X 4 4

Bullock's oriole X 0

house finch X X 5 6 13 7 8 8 47

lesser goldfinch X 2 1 1 4

house sparrow X 6 14 27 15 5 9 76

Total Number of Detections n/a n/a 424 714 954 522 416 313 3343

Species Observed Total 61 52

Species Observed at Points 57 49

Grand Total 68
327

Appendix I. Breeding bird species and the number of detections during 10-minute surveys of 40 

randomly located point locations on San Antonio Missions National Historical Park (Table modified from 

Twedt 2013).

Common Name 2010 2011 2012

American Crow 5 12 17

ash-throated flycatcher 1

barred owl 1 1

barn swallow 1 18 5

black-bellied whistling duck 2 3

brown-crested flycatcher 1

black-chinned hummingbird 1 3 1

black-crested titmouse 34 19 23

Bewick's wren 3 3

brown-headed cowbird 11 26 11

blue grosbeak 2 3

blue jay 2 5 3

black vulture 2 3

Bullock's oriole 2 2

Carolina chickadee 6 3 7

Carolina wren 38 64 76

cave swallow 3 11 11

chimney swift 6 4

cliff swallow 35 9 18

common nighthawk 1

crested caracara 1

dickcissel 1

Eurasian collared-dove 1

European starling 22 14 12

great crested flycatcher 5 7 11

golden-fronted woodpecker 7 22 17

greater roadrunner 2 1

great-tailed grackle 21 37 27

house finch 1 10 12

house sparrow 3 20 18

indigo bunting 1

Inca dove 7 4
328

Appendix I (continued). Breeding bird species and the number of detections during 10-minute surveys 

of 40 randomly located point locations on San Antonio Missions National Historical Park (Table modified 

from Twedt 2013).

Common Name 2010 2011 2012

killdeer 3 1

long-billed thrasher 2

ladder-backed woodpecker 4 15 12

lesser goldfinch 1 4 5

lesser nighthawk 1

loggerhead shrike 1 1

mallard 5 2

mourning dove 6 15 10

northern mockingbird 19 65 63

olive sparrow 3 4 2

orchard oriole 2

painted bunting 9 20 20

purple martin 1 10 10

pyrrhuloxia 1

rock pigeon 6 7

red-shouldered hawk 7 11 1

red-tailed hawk 1 1 2

red-winged blackbird 3 6 1

scissor-tailed flycatcher 2 20 11

turkey vulture 6 1

verdin 1 1

western kingbird 2 7 5

white-eyed vireo 24 34 27

wild turkey 1

white-tipped dove 1

white-winged dove 3 12 22

yellow-breasted chat 3

yellow-billed cuckoo 3 3 11

Individuals detected 301 556 508

Species detected 42 48 47

Total Species detected 60
329

Appendix J. Resident bird species observed in SAAN from 1985-2013.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

Cooper's hawk Accipiter cooperii X X X X

sharp-shinned hawk Accipiter striatus X X X X

Swainson's hawk Buteo swainsoni X X X X

northern harrier Circus cyaneus X X X

osprey, western osprey Pandion haliaetus X X X X

wood duck Aix sponsa X X

northern pintail Anas acuta X X

American wigeon Anas americana X

northern shoveler Anas clypeata X X X

Eurasian teal, green-winged teal Anas crecca X X

gadwall Anas strepera X X X

lesser scaup Aythya affinis X X

ring-necked duck Aythya collaris X X

hooded merganser Lophodytes cucullatus X X

ruddy duck Oxyura jamaicensis X

rufous hummingbird Selasphorus rufus X X

common poorwill Phalaenoptilus nuttallii X X

European herring gull, herring gull Larus argentatus X

ring-billed gull Larus delawarensis X X

Bonaparte's gull Larus philadelphia X X

forster's tern Sterna forsteri X X

ae'o, black-necked stilt, hawaiian stilt Himantopus mexicanus X X
330

Appendix J (continued). Resident bird species observed in SAAN from 1985-2013.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

American avocet Recurvirostra americana X X

spotted sandpiper Actitis macularia X X X

least sandpiper Calidris minutilla X X X

Wilson's snipe Gallinago delicata X X

long-billed dowitcher Limnodromus scolopaceus X X X

Scolopax minor X X

lesser yellowlegs Tringa flavipes X X X X

greater yellowlegs Tringa melanoleuca X X X

belted kingfisher Ceryle alcyon X X X

green kingfisher Chloroceryle americana X X X

ringed kingfisher Ceryle torquata X

peregrine falcon Falco peregrinus X X

American kestrel Falco sparverius X X X X

American coot Fulica americana X X X

cedar waxwing Bombycilla cedrorum X X X X

northern cardinal Cardinalis cardinalis X X X X

brown creeper Certhia americana X X

grasshopper sparrow Ammodramus savannarum X X

dark-eyed junco Junco hyemalis X X X

Lincoln's sparrow Melospiza lincolnii X X X X

savannah sparrow Passerculus sandwichensis X X X

spotted towhee Pipilo maculatus X X X
331

Appendix J (continued). Resident bird species observed in SAAN from 1985-2013.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

vesper sparrow Pooecetes gramineus X X X X

chipping sparrow Spizella passerina X X X X

field sparrow Spizella pusilla X X X X

white-throated sparrow Zonotrichia albicollis X X X X

white-crowned sparrow Zonotrichia leucophrys X X X X

American goldfinch Carduelis tristis X X X X

northern rough-winged swallow Stelgidopteryx serripennis X X

Brewer's blackbird Euphagus cyanocephalus X X

common grackle Quiscalus quiscula X X X X

eastern meadowlark Sturnella magna X X X X

western meadowlark Sturnella neglecta X X X

gray catbird, grey catbird Dumetella carolinensis X X X

brown thrasher Toxostoma rufum X X

American pipit, buff-bellied pipit Anthus rubescens X X X

yellow-rumped warbler Dendroica coronata X X X X

common yellowthroat Geothlypis trichas X X

black-and-white warbler Mniotilta varia X X X

orange-crowned warbler Vermivora celata X X X X

blue-gray gnatcatcher Polioptila caerulea X X X X

ruby-crowned kinglet Regulus calendula X X X X

golden-crowned kinglet Regulus satrapa X X X

cactus wren Campylorhynchus brunneicapillus X
332

Appendix J (continued). Resident bird species observed in SAAN from 1985-2013.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

winter wren Troglodytes troglodytes X X X

hermit thrush Catharus guttatus X X X X

eastern bluebird Sialia sialis X X X X

American robin Turdus migratorius X X X X

vermilion flycatcher Pyrocephalus rubinus X X X

eastern phoebe Sayornis phoebe X X X X

Say's phoebe Sayornis saya X X

Couch's kingbird Tyrannus couchii X X

solitary vireo, blue-headed vireo Vireo solitarius X X X X

great egret Ardea alba X X X X

great blue heron Ardea herodias X X X X

cattle egret, western cattle egret Bubulcus ibis X X X

green heron Butorides virescens X X X X

little blue heron Egretta caerulea X X X

snowy egret Egretta thula X X X

tricolored heron Egretta tricolor X X

yellow-crowned night heron, yellow-crowned night-heron Nyctanassa violacea X X X X

black-crowned night heron, black-crowned night-heron Nycticorax nycticorax X X X

American white pelican Pelecanus erythrorhynchos X X

northern flicker Colaptes auratus X X X X

yellow-bellied sapsucker Sphyrapicus varius X X X

black-necked grebe, eared grebe Podiceps nigricollis X
333

Appendix J (continued). Resident bird species observed in SAAN from 1985-2013.

Common Names Scientific Name

NPS 

(2014)

Coonan 

(1987)

Scully 

(2006)

Twedt 

(2013)

pied-billed grebe Podilymbus podiceps X X X

least grebe Tachybaptus dominicus X X

monk parakeet Myiopsitta monachus X X X

Neotropic cormorant Phalacrocorax brasilianus X X X

91 40 81 56
334

Appendix K. Bird species and number detected during 90 area search survey visits to 40 randomly 

located survey locations in SAAN during winters of 2010-2011 (n=30 visits), 2011-12 (n=30 visits), and 

2012-2013 (n=30 visits). “All” detections includes birds detected at any distance from plot center 

(including flyovers), whereas “50-m Radius” includes only birds < 50m from plot center when first detected 

(Appendix modified from Twedt 2013).

Common Name

All 50-m Radius

Number 

Points

Number 

Individuals

Number 

Points

Number 

Individuals

American coot 1 1

American goldfinch 37 283 18 182

American kestrel 4 4 1 1

American pipit 7 64

American robin 2 2

blue-gray gnatcatcher 6 9 5 8

blue-headed vireo 3 3 2 2

cedar waxwing 4 74

chipping sparrow 2 42 2 42

common grackle 1 12 1 12

Cooper's hawk 2 2

eastern bluebird 12 29 4 13

eastern meadowlark 7 78 4 29

eastern phoebe 37 49 25 35

gadwall 9 47 1 2

great blue heron 9 9 4 4

green kingfisher 1 1

great egret 14 24 1 1

greater yellowlegs 4 4

hermit thrush 34 64 29 48

long-billed dowitcher 2 4 1 1

little blue heron 2 2 1 1

least sandpiper 6 101

lesser yellowlegs 1 2

Lincoln's sparrow 15 24 13 21

neotropic cormorant 13 22

northern cardinal 72 261 59 136

northern flicker 23 32 8 9
335

Appendix K (continued). Bird species and number detected during 90 area search survey visits to 40 

randomly located survey locations in SAAN during winters of 2010-2011 (n=30 visits), 2011-12 (n=30 

visits), and 2012-2013 (n=30 visits). “All” detections includes birds detected at any distance from plot 

center (including flyovers), whereas “50-m Radius” includes only birds < 50m from plot center when first 

detected (Appendix modified from Twedt 2013).

Common Name

All 50-m Radius

Number 

Points

Number 

Individuals

Number 

Points

Number 

Individuals

northern harrier 2 2 1 1

northern shoveler 1 4

orange-crowned warbler 21 31 20 28

osprey 2 2

pied-billed grebe 3 6 1 1

ruby-crowned kinglet 41 74 32 53

savannah sparrow 9 121 8 58

dark-eyed junco 1 15 1 15

snowy egret 7 12 1 1

spotted sandpiper 5 6 2 2

spotted towhee 11 16 9 11

sharp-shinned hawk 4 4 3 3

vermillion flycatcher 1 1

vesper sparrow 5 17 3 10

white-crowned sparrow 4 80 1 5

western meadowlark 3 42 1 1

winter wren 2 2 1 1

white-throated sparrow 3 21 3 21

yellow-bellied sapsucker 1 1 1 1

yellow-rumped warbler 40 226 34 193

Totals 496 1932 301 952
336

Appendix L. Resident bird species and number detected during 10-minute surveys of 40 randomly 

located point locations in SAAN during the breeding season May-June 2010 (n = 20 counts), 2011 (n = 30 

counts), and 2012 (n = 30 counts). Birds for which no detection distance was recorded (i.e., FLYOVERS) 

are not reported in table. * indicates a resident species that was observed in the breeding season but not 

in the winter surveys (appendix modified from Twedt 2013).

Common Name 2010 2011 2012

black-crowned night-heron* 1

blue-headed vireo 1

black-necked stilt* 1

cattle egret* 3 2

chipping sparrow 1

eastern bluebird 1 2

eastern phoebe 1 1

field sparrow* 2

great egret 2 8 2

green heron* 1 1

little blue heron 1

monk parakeet* 1

Neotropic cormorant 1 3 2

northern cardinal 79 109 115

snowy egret 3 2

spotted sandpiper 1

Swainson's hawk* 1

yellow-crowned night-heron* 1 2 2

Individuals detected 88 136 129

Species detected 8 13 10
337

Appendix M. Resident bird species abundance by season for the San Juan Woods (SAJU) and Espada 

Labores (ESPA) land tracts, SAAN, 1985-1986 (Appendix modified from Coonan 1987).

Species Area Fall Winter Spring

Early 

Summer

Late 

Summer

great blue heron SAJU 0.7

ESPA 1.6 1 0.2 0.2

great egret SAJU

ESPA 1

green heron SAJU 0.7 1.5 0.7 1.5

ESPA 0.2 0.2 0.8

yellow-crowned night heron SAJU

ESPA 0.2

osprey SAJU

ESPA 0.2

sharp-shinned hawk SAJU

ESPA 0.2

Cooper's hawk SAJU

ESPA 0.2

Swainson's hawk SAJU

ESPA 0.4

American kestrel SAJU 2.2 2.9

ESPA 1.2 1

peregrine falcon SAJU 0.7

ESPA 0.3

lesser yellowlegs SAJU

ESPA 0.2 0.2

rufous hummingbird SAJU 0.7

ESPA 1

belted kingfisher SAJU 0.7

ESPA 0.4 0.4 1

yellow-bellied sapsucker SAJU 0.7

ESPA
338

Appendix M (continued). Resident bird species abundance by season for the San Juan Woods (SAJU) 

and Espada Labores (ESPA) land tracts, SAAN, 1985-1986 (Appendix modified from Coonan 1987).

Species Area Fall Winter Spring

Early 

Summer

Late 

Summer

northern flicker SAJU 1.5 0.7

ESPA 0.4

eastern phoebe SAJU 3.7 1.5 1.5

ESPA 0.6 2.4 0.2 0.2

brown creeper SAJU 0.7 0.7

ESPA

golden-crowned kinglet SAJU 1.5 6.6 0.7

ESPA 1 2 1.4

ruby-crowned kinglet SAJU 5.2 8.8 1

ESPA 1 3.6 0.4

blue-gray gnatcatcher SAJU 4.4 2.9

ESPA 0.4 1.2 1.8

eastern bluebird SAJU

ESPA 1.2 4.4 0.2

hermit thrush SAJU 0.7 3

ESPA

American robin SAJU 1.5 24.3

ESPA 7.4 12.5 1.6

gray catbird SAJU 0.7

ESPA

brown thrasher SAJU

ESPA 0.2 0.4

cedar waxwing SAJU 0.7 16.2 8.1

ESPA 12.9 6.9

solitary vireo SAJU 2.2

ESPA 0.2

orange-crowned warbler SAJU 2.2

ESPA 0.2
339

Appendix M (continued). Resident bird species abundance by season for the San Juan Woods (SAJU) 

and Espada Labores (ESPA) land tracts, SAAN, 1985-1986 (Appendix modified from Coonan 1987).

Species Area Fall Winter Spring

Early 

Summer

Late 

Summer

yellow-rumped warbler SAJU 13.2 28.7 2.9

ESPA 0.8 6.2 2

black-and-white warbler SAJU

ESPA

northern cardinal SAJU 19.9 16.2 44.9 38.2 33.8

ESPA 10.7 15.7 21.5 21.1 16.9

chipping sparrow SAJU

ESPA 0.4

field sparrow SAJU

ESPA 2.4 0.4 2.4

vesper sparrow SAJU 1.5

ESPA 2.8 17.1 2.2

Lincoln's sparrow SAJU 0.7 2.9

ESPA 0.2 1.8 2

white-throated sparrow SAJU 0.7

ESPA

white-crowned sparrow SAJU 1.5 1.5 1.5

ESPA 0.4

eastern meadowlark SAJU 1.5

ESPA 4 1.4 1.2

common grackle SAJU

ESPA 1.4 0.4 0.6

American goldfinch SAJU

ESPA 0.4 7.2 0.4

Number of Sp. (Resident) SAJU 13 21 10 3 5

ESPA 20 24 18 5 9
340

Appendix N. Relative abundance and distribution of resident bird species observed during Scully (2006). 

Bold species indicate a species that was observed at one of the point count locations.

Species

Species Observed Number of Times Detected

City of San 

Antonio 

(18)

Rancho de 

las Cabras 

(7) Jan Mar May Jul Sep Nov Total

wood duck X 1 1

Gadwall X X 6 2 8

northern shoveller X 0

northern pintail X 0

green-winged teal X 3 3

ring-necked duck X 0

lesser scaup X 0

hooded merganser X 1 1

least grebe X 0

pied-billed grebe X 2 1 3

American white pelican X 1 1

Neotropical cormorant X 1 2 3 2 8

great blue heron X X 8 4 1 5 4 4 26

great egret X X 12 12 26 21 10 9 90

snowy egret X X 6 7 8 8 10 9 48

little blue heron X X 1 3 6 8 4 3 25

tri-colored heron X 0

cattle egret X X 1 9 12 6 28

green heron X X 2 5 3 10

black-crowned night heron X 1 1 2

yellow-crowned night heron X 7 3 10

Osprey X 5 1 4 10

northern harrier X 3 3

sharp-shinned hawk X X 2 1 3

Cooper's hawk X X 1 1

Swainson's hawk X X 1 1

American kestrel X X 1 1 2
341

Appendix N (continued). Relative abundance and distribution of resident bird species observed during 

Scully (2006). Bold species indicate a species that was observed at one of the point count locations.

Species

Species Observed Number of Times Detected

City of San 

Antonio 

(18)

Rancho de 

las Cabras 

(7) Jan Mar May Jul Sep Nov Total

American coot X 0

American avocet X 1 1

greater yellowlegs X 2 2 3 7

lesser yellowlegs X 1 1

spotted sandpiper X 5 3 6 2 3 4 23

least sandpiper X 1 1 3 5

long-billed dowitcher X 1 1

Wilson's snipe X 0

American woodcock X 0

Bonaparte's gull X 0

ring-billed gull X 7 1 8

Forster's tern X 0

monk parakeet X 1 1

common poorwill X 0

ringed kingfisher X 0

belted kingfisher X 3 3 1 5 7 19

green kingfisher X X 1 2 2 5

northern flicker X X 1 1

eastern phoebe X X 12 5 1 10 28

Say's phoebe X 1 1

Vermillion flycatcher X 2 2

Couch's kingbird X 1 2 3

blue-headed vireo X 0

northern rough-winged swallow X 0

winter wren X 0

golden-crowned kinglet X X 1 1

ruby-crowned kinglet X X 24 22 15 61
342

Appendix N (continued). Relative abundance and distribution of resident bird species observed during 

Scully (2006). Bold species indicate a species that was observed at one of the point count locations.

Species

Species Observed Number of Times Detected

City of San 

Antonio 

(18)

Rancho de 

las Cabras 

(7) Jan Mar May Jul Sep Nov Total

blue-gray gnatcatcher X X 1 10 1 2 1 15

eastern bluebird X X 1 1 2 4

hermit thrush X X 3 3 6

American robin X X 7 1 9 17

gray catbird X 1 1

American pipit X 13 8 21

cedar waxwing X X 7 1 4 12

orange-crowned warbler X X 6 5 11

yellow-rumped warbler X X 19 4 14 37

black-and-white warbler X X 1 1

common yellowthroat X X 2 1 3

spotted towhee X X 1 1 2 4

chipping sparrow X 1 1

field sparrow X 0

vesper sparrow X X 2 1 3

savannah sparrow X X 6 6 2 14

grasshopper sparrow X 0

Lincoln's sparrow X X 4 7 1 3 15

white-throated sparrow X X 4 4 2 10

white-crowned sparrow X X 3 1 4

dark-eyed junco X 0

northern cardinal X X 104 192 182 124 46 26 674

eastern meadowlark X X 0

western meadowlark X X 4 1 5

Brewer's blackbird X 2 2

common grackle X X 3 6 3 12

American goldfinch X X 10 8 26 44
343

Appendix N (continued). Relative abundance and distribution of resident bird species observed during 

Scully (2006). Bold species indicate a species that was observed at one of the point count locations.

Species

Species Observed Number of Times Detected

City of San 

Antonio 

(18)

Rancho de 

las Cabras 

(7) Jan Mar May Jul Sep Nov Total

Total Number of Detections n/a n/a 308 321 260 191 98 190 1368

Species Observed Total 74 43

Species Observed at Points 56 32

Grand Total 81

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