National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

Plant Community Composition and Structure 

Monitoring for Agate Fossil Beds National Monument 

2011-2015 Summary Report

Natural Resource Report NPS/NGPN/NRR—2016/1198
ON THIS PAGE

Photograph of riparian long-term monitoring plot 261 at Agate Fossil Beds National Monument, 2015.

Photograph courtesy of the National Park Service.

ON THE COVER

Photograph of plant community monitoring at Agate Fossil Beds National Monument, 2015.

Photograph courtesy of the National Park Service.
Plant Community Composition and Structure 

Monitoring for Agate Fossil Beds National 

Monument 

2011-2015 Summary Report

Natural Resource Report NPS/NGPN/NRR—2016/1198

Isabel W. Ashton

Christopher J. Davis

National Park Service

Northern Great Plains Inventory & Monitoring Network

231 East St. Joseph Street

Rapid City, SD 57701

April 2016

U.S. Department of the Interior

National Park Service

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii

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Please cite this publication as:

Ashton, I. W. and C. J. Davis. 2016. Plant community composition and structure monitoring for 

Agate Fossil Beds National Monument: 2011-2015 summary report. Natural Resource Report

NPS/NGPN/NRR—2016/1198. National Park Service, Fort Collins, Colorado.

NPS 165/132284, April 2016 
iii

Contents 

Page

Figures...................................................................................................................................................iv

Tables.....................................................................................................................................................v

Executive Summary..............................................................................................................................vi

Acknowledgments...............................................................................................................................viii

Introduction............................................................................................................................................1

Methods..................................................................................................................................................2

NGPN and NGPFire Monitoring Plots 2011-2015 ........................................................................2

Other Monitoring Plots (1997-2015)..............................................................................................5

Data Management and Analysis.....................................................................................................6

Reporting on Natural Resource Condition .....................................................................................7

Results and Discussion ..........................................................................................................................9

Status & Trends in Community Composition and Structure of AGFO Prairies ............................9

Species Richness, Diversity, and Evenness.............................................................................11

The Influence of Climate and Fire on Plant Community Structure and Diversity .......................14

Rare Plants....................................................................................................................................18

Fossil Hills Trail Paving Project...................................................................................................19

The Status of Riparian Vegetation in AGFO ...............................................................................21

Conclusion ...........................................................................................................................................24

Literature Cited ....................................................................................................................................26

Appendix A: List of plant species found at AGFO 1998-2015 ...........................................................29
iv

Figures 

Page

Figure 1. Map of Agate Fossil Beds National Monument (AGFO) plant community 

monitoring plots, 1997-2015..................................................................................................................3

Figure 2. Long-term monitoring plot layout used for sampling vegetation in Agate Fossil 

Beds National Monument. .....................................................................................................................4

Figure 3. The Northern Great Plains Inventory & Monitoring vegetation crew used pointintercept (left and center panel) and quadrats (right panel) to document plant diversity 

and abundance........................................................................................................................................4

Figure 4. Average cover by lifeform of native (green) and exotic (red) plants recorded in 

monitoring plots in Agate Fossil Beds National Monument (1998-2015).............................................9

Figure 5. The average absolute cover of the 10 most common native plants recorded at 

Agate Fossil Beds National Monument in 1998-2015.........................................................................10

Figure 6. Trends in the relative cover of annual bromes in Agate Fossil Beds National 

Monument from 1998-2015.................................................................................................................11

Figure 7. Trends in native species richness and evenness in Agate Fossil Beds National 

Monument, 1998-2015.........................................................................................................................13

Figure 8. The relationship between native species richness and the relative cover of 

annual bromes in long-term monitoring plots in National Park units of the Northern Great 

Plains, 1998-2015. ...............................................................................................................................14

Figure 9. The total annual precipitation anomaly from 1998-2015 for Agate Fossil Beds 

National Monument .............................................................................................................................15

Figure 10. A long-term monitoring plot in Agate Fossil Beds National Monument in 

2012, during a severe drought, and 2014 a wet year............................................................................16

Figure 11. Map of recent fire history at Agate Fossil Beds National Monument...............................16

Figure 12. Native species richness (left panel) and relative percent cover of exotic plants 

(right panel) across plots with different fire histories..........................................................................17

Figure 13. Photographs of two rare species found in plant community monitoring plots at 

Agate Fossil Beds National Monument ...............................................................................................19

Figure 14. Native species richness (A), exotic species relative cover (B), and litter cover 

(C) in intact native mixed-grass prairie and disturbed prairie along the Fossil Hill Trail at 

Agate Fossil Beds National Monument (mean ± standard error of the mean).....................................20

Figure 15. Native species richness and exotic species relative cover in disturbed prairie 

plots were lower in 2013 but had returned to levels similar to 18-year AGFO averages by 

2014......................................................................................................................................................20

Figure 16. Location of 17 riparian monitoring plots in Agate Fossil Beds National 

Monument, 2012-2015 and estimated pale yellow iris infestation in 2012 .........................................21
v

Tables 

Page

Table ES-1. Natural resource condition summary table for plant communities in Agate 

Fossil Beds National Monument (AGFO) ...........................................................................................vii

Table 1. Exotic species surveyed for at Agate Fossil Beds National Monument as part of 

the early detection and rapid response program within the Northern Great Plains 

Network..................................................................................................................................................5

Table 2. Definitions of state and global species conservation status ranks...........................................7

Table 3. Key to the symbols used in the Natural Resource Condition Table........................................8

Table 4. Average plant species richness in monitoring plots at Agate Fossil Beds 

National Monument from 1998 to 2015. Values represent means ± one standard error. ....................11

Table 5. Rare species occurrence in Agate Fossil Beds National Monument sampling 

plots from 1998-2015...........................................................................................................................18

Table 6. The relative percent cover of pale yellow iris in monitoring plots at Agate Fossil 

Beds National Monument 2012-2015..................................................................................................23

Table 7. Natural resource condition summary table of plant communities in Agate Fossil 

Beds National Monument (AGFO)......................................................................................................25
vi

Executive Summary

The Northern Great Plains Inventory & Monitoring Program and Fire Effects Program have been 

monitoring vegetation in Agate Fossil Beds National Monument for over 18 years. While methods 

have changed slightly, this report summarizes data from over 80 locations from 1998-2015. We use 

these data to explore status and trends in upland and riparian plant communities, the occurrence of 

rare plants, and the effects of the Fossil Hills trail installation on the surrounding vegetation. A 

summary of the current condition (2011-2015) and trends (based on 1998-2015) in plant 

communities at Agate Fossil Beds NM (AGFO) is found in Table ES-1 below. 

1. What is the current status of plant community composition and structure of AGFO 

grasslands (species richness, cover, and diversity) and how has this changed from 1998 to 

2015? 

Native grasses, such as needle and thread, sand reed, and western wheatgrass, are abundant 

and the dominant component of the prairie at AGFO. Native plant diversity is at a moderate 

level compared to other grasslands in the region (Table 7), but diversity is spatially variable. 

We found no significant trends in native diversity or evenness from 1998 to 2015, but both 

may become threatened if cover of annual invasive brome grasses increases, as we’ve 

observed in other Northern Great Plains Inventory and Monitoring units (Figure 8). 

2. How do trends in grassland condition correlate with climate and fire history?

Native species richness increased in years with more rainfall and a hot dry year in 2012 

corresponded to large declines in native species richness and an increase in exotic species 

cover. Plots that had not burned in 5 or 6 years had a higher number of native species and a 

lower cover of exotics than sites that burned more recently and when compared to AGFO

averages (Figure 12). This suggests that prescribed fire can benefit the mixed-grass prairie in 

AGFO, but it may take 5 or more years to see the positive effects following a burn.

3. What, if any, rare plants were found in AGFO long-term monitoring plots? 

We identified 22 rare plant species in AGFO between 1998 and 2015; seven of these are 

considered critically imperiled within Nebraska. We recommend monitoring of rare plant 

populations and more targeted surveys of rare plant species be completed when funds are 

available. 

4. How did installation of the AGFO Fossil Hills Trail affect the adjacent prairie?

The disturbed prairie adjacent to the Fossil Hills Trail is very similar to the native prairie in 

other parts of AGFO. This suggests that the prairie in AGFO is resilient and can recover 

from a moderate level of disturbance. We suggest continued monitoring of these plots to 

ensure that any increase in exotic species abundance is detected so appropriate control 

measures can be taken. 

5. What is the composition and structure of the riparian corridor at AGFO?

The riparian corridor in AGFO is a fairly diverse assemblage of riparian species such as 

sedges, willows, and cattails. It is, however, more invaded than the upland areas of AGFO
vii

and threatened by high cover of Kentucky bluegrass and pale yellow iris. Since riparian 

monitoring began in 2012, we have not detected a significant change in the cover of pale 

yellow iris. Continued monitoring is necessary to determine if exotic treatment is effective 

over the long-term.

Table ES-1. Natural resource condition summary table for plant communities in Agate Fossil Beds 

National Monument (AGFO). Current values are based on data from 2011-2015 and trends are based on 

data from 1998-2015. 

Indicator of 

Condition

Specific 

Measures

Current

Value 

(mean ± SE)

Reference 

Condition 

and Data 

Source

Condition 

Status/Trend

Rationale for

Resource Condition

Upland Plant 

Community 

Structure and 

Composition

Native species 

richness (1m2

quadrats) 

7.3 ± 0.5

species

3-15 

species 

AGFO plays a vital role in 

protecting and managing some of 

the last remnants of native mixedgrass prairie in the region. The 

monument is characterized by 

moderate native species 

richness, but average richness is 

within a natural range of 

variability (Symstad and Jonas 

2014). The lowest native diversity 

is found near the road. Native 

evenness has not changed since 

monitoring began in 1998. 

Evenness

(native spp. 

point-intercept 

transects)

0.70 ± 0.01 To be 

determined

Relative cover 

of exotic 

species 

17.6 ± 2.5% < 10 % 

cover

AGFO maintains a mixed-grass 

prairie with moderate exotic plant 

cover and a fair diversity of native 

plants. Annual invasive bromes 

are not currently abundant in 

AGFO, but active management 

may be required to keep such low 

cover.

Annual brome 

cover 

7.4 ± 1.9% < 10 % 

cover

Riparian Plant 

Community 

Structure and 

Composition 

Native species 

richness 

(50 m pointintercept

transect)

9.6 ± 1.0 To be 

determined

The riparian areas of AGFO had 

levels of diversity similar to the 

upland areas.

Relative cover 

of exotic 

species

28.3 ± 2.0% ≤10 % 

cover

The relative cover of exotic 

species in the riparian areas of 

AGFO was very high. Exotic 

control efforts should be focused 

in this area to restore native plant 

diversity and ecological integrity.

Pale yellow iris has invaded 

riparian areas throughout the 

monument. It had a patchy 

distribution and was absent in 

some sites while accounting for 

over 50% in others

Relative cover 

of pale yellow 

iris 

11.5 ± 2.4% ≤10 % 

cover
viii

Acknowledgments 

We thank the authors of the NGPN Plant Community Monitoring Protocol, particularly A. Symstad, 

for outstanding guidance on data collection and reporting. Thank you to the staff at AGFO for 

providing logistical support and performing safety checks. The NGPN and NGPFire vegetation field 

crews collected all the data included in this report. We thank D. Swanson for providing data on fire 

history and A. Weaver for helping with the maps for this report. Comments from J. Hill, R. Manasek, 

and J. Handley improved this manuscript.
1

Introduction 

During the last century, much of the prairie within the Northern Great Plains has been plowed for 

cropland, planted with non-natives to maximize livestock production, or otherwise developed,

making it one of the most threatened ecosystems in the United States. Within Nebraska, greater than 

77% of the area of native mixed grass prairie has been lost since European settlement (Samson and 

Knopf 1994). The National Park Service (NPS) plays an important role in preserving and restoring 

some of the last pieces of intact prairies within its boundaries. The stewardship goal of the NPS is to 

“preserve ecological integrity and cultural and historical authenticity” (NPS 2012); however, 

resource managers struggle with the grim reality that there have been fundamental changes in the 

disturbance regimes, such as climate, fire, and grazing by large, native herbivores, that have 

historically maintained prairies and there is the continual pressure of exotic invasive species. Longterm monitoring in national parks is essential to sound management of prairie landscapes because it 

can provide information on environmental quality and condition, benchmarks of ecological integrity, 

and early warning of declines in ecosystem health.

Agate Fossil Beds National Monument (AGFO) was established in 1965 to protect and preserve a 

large concentration of ancient mammal fossils. The monument contains 2,270 acres of native mixedgrass prairie intersected by riparian vegetation along the Niobrara River. Vegetation monitoring 

began in AGFO in 1998 by the Heartland Inventory & Monitoring Program (James 2010a) and the 

Northern Great Plains Fire Ecology Program (FireEP; Wienk et al. 2011). In 2010, AGFO was 

incorporated into the Northern Great Plains Inventory & Monitoring Network (NGPN). At this time, 

vegetation monitoring protocols and plot locations were shifted to better represent the entire 

monument and to coordinate efforts with the FireEP (Symstad et al. 2012b), and sampling efforts 

began in 2011(Ashton et al. 2011). In 2012, the NGPN began monitoring an additional 17 plots 

within the riparian corridor to assess riparian condition. In this report, we use the data from 2011-

2015 to assess the current condition of AGFO vegetation and the data from 1998-2015 are used to 

look at longer-term trends. 

Using 18 years of plant community monitoring data in AGFO, we explore the following questions:

1. What is the current status of plant community composition and structure of AGFO grasslands

(species richness, exotic plant cover, and diversity) and how has this changed from 1998-2015? 

2. How do trends in grassland condition correlate with climate and fire history?

3. What, if any, rare plants were found in AGFO long-term monitoring plots? 

4. How did installation of the AGFO Fossil Hills Trail affect the adjacent prairie?

5. What is the composition and structure of the riparian corridor at AGFO?
2

Methods 

Three different methods and protocols have been used to monitor long-term vegetation plots at 

AGFO since 1997: the NGPN monitoring protocol (Symstad et al. 2012b, a), the Fire Monitoring

Handbook (NPS 2003), and the Heartland Vegetation Monitoring Protocol (James et al. 2009). 

Below, we briefly describe all three methods, but focus on the NGPN monitoring protocol, which is 

the current standard and was used to collect most of the data in this report. For more detail on any of 

the methods, please see the protocol publications (cited above). 

NGPN and NGPFire Monitoring Plots 2011-2015

The NGPN and NGPFire implemented a survey to monitor plant community structure and 

composition in AGFO using a spatially balanced probability design (Generalized Random 

Tessellation Stratified [GRTS]; Stevens and Olsen 2003, 2004). Using a GRTS design, NGPN 

selected 16 randomly located sites within the upland grasslands of AGFO to become Plant 

Community Monitoring plots (PCM plots; Figure1). The NGPN visits 6 PCM plots every year using 

a rotating sampling scheme where three sites were visited in the previous year and three sites are new 

visits. After five years (2011-2015), most of the PCM plots were visited at least twice during the first

weeks of June. When a PCM plot fell within an active burn unit, NGPFire added additional visits 

based on a 1, 2, 5, and 10 year sampling schedule. NGPFire also established and monitored a number 

of new sites focused in active burn units (Fire FPCM plots) using the same GRTS sampling schema.

From 2011-2015, 16 FPCM plots were established. Finally, using the same set of random sites, 

NGPN selected 17 additional plots that fell within the riparian zone along the Niobrara River. These 

were monitored in 2012-2015 to assess the condition of riparian condition.

At each of the grassland sites we visited, we recorded plant species cover and frequency in a 

rectangular, 50 m x 20 m (0.1 ha), permanent plot (Figure 2). Data on ground cover and herb-layer (≤ 

2 m) height and plant cover were collected on two 50 m transects (the long sides of the plot) using a 

point-intercept method (Figure 3). At 100 locations along the transects (every 0.5 m) a pole was 

dropped to the ground and all species that touched the pole were recorded, along with ground cover, 

and the height of the canopy (Figure 3). Using this method, absolute canopy cover can be greater 

than 100% (particularly in wet years and productive sites) because we record multiple layers of 

plants. Species richness data from the point-intercept method were supplemented in the 16 PCM

plots with species presence data collected in five sets of nested square quadrats (0.01 m2

, 0.1 m2, 1 

m2

, and 10 m2) located systematically along each transect (Figure 2). 
3

Figure 1. Map of Agate Fossil Beds National Monument (AGFO) plant community monitoring plots, 1997-

2015. Sixteen PCM plots (red) were established by the Northern Great Plains Inventory & Monitoring 

Program (NGPN) and 16 (blue) FPCM plots were established by the Fire Effects Program (NGPFire) 

between 2011 and 2015. Ten LPCM plots were established by the Heartland Monitoring Network (pink) 

representing restored and native mixed-grass prairie. Seventeen plots were visited by the NGPN to 

monitor riparian forest condition (yellow). A few additional FMH plots (green) were monitored from 1997-

2011 by NGPFire. There are a total of 64 monitoring plots. 
4

Figure 2. Long-term monitoring plot layout used for sampling vegetation in Agate Fossil Beds National 

Monument.

Figure 3. The Northern Great Plains Inventory & Monitoring vegetation crew used point-intercept (left and 

center panel) and quadrats (right panel) to document plant diversity and abundance. 

NGPN completed a survey of the riparian zone in AGFO in August of 2012-2015 using a set of 17 

randomly located sites. In this case, vegetation was measured using the point-intercept method, as 
5

described above, but it was measured along only one 50 m transect that ran perpendicular to the river 

channel. These plots were not permanently marked and were relocated using GPS coordinates.

At all PCM plots, but not the FPCM plots, we also surveyed the area for common disturbances and 

target species of interest to AGFO. Common disturbances can include such things as rodent mounds, 

improvised and animal trails, and fire. For all plots, the type and severity of the disturbances were 

recorded. We also surveyed the area for exotic species that have the potential to spread into the 

monument and cause significant ecological impacts (Table 1). These species were chosen in 

collaboration with the Midwest Invasive Plant Network, the Exotic Plant Management Team, 

resource managers, and local weed experts. For each target species that was present at a site, an 

abundance class was given on a scale from 1-5 where 1 = one individual, 2 = few individuals, 3 = 

cover of 1-5%, 4 = cover of 5-25%, and 5 = cover > 25% of the plot. The information gathered from 

this procedure is critical for early detection and rapid response to such threats. 

Table 1. Exotic species surveyed for at Agate Fossil Beds National Monument as part of the early 

detection and rapid response program within the Northern Great Plains Network.

Scientific Name Common Name Habitat

Alliaria petiolata garlic mustard Riparian

Polygonum cuspidatum; P. sachalinense; P. x bohemicum knotweeds Riparian

Pueraria montana var. lobata kudzu Riparian

Iris pseudacorus yellow iris Riparian

Ailanthus altissima tree of heaven Riparian

Lepidium latifolium perennial pepperweed Riparian

Arundo donax giant reed Riparian

Rhamnus cathartica common buckthorn Riparian

Heracleum mantegazzianum giant hogweed Riparian

Centaurea solstitialis yellow star thistle Upland

Hieracium aurantiacum; H. caespitosum orange and meadow hawkweed Upland

Isatis tinctoria Dyer's woad Upland

Taeniatherum caput-medusae medusahead Upland

Chondrilla juncea rush skeletonweed Upland

Gypsophila paniculata baby's breath Upland

Centaurea virgata; C.diffusa knapweeds Upland

Linaria dalmatica; L. vulgaris toadflax Upland

Euphorbia myrsinites & E. cyparissias myrtle spurge Upland

Dipsacus fullonum & D. laciniatus common teasel Upland

Salvia aethiopis Mediterranean sage Upland

Ventenata dubia African wiregrass Upland

Other Monitoring Plots (1997-2015)

In 1997, NGPFire began monitoring plots within AGFO to evaluate the effectiveness of prescribed 

burns. Starting in 1998, data collection followed the NPS National Fire Ecology Program protocols 

(NPS 2003): in grassland plots vegetation cover and height data were collected using a pointintercept method, with 100 points evenly distributed along a single 30 m transect. NGPFire plot 

locations were located randomly within major vegetation types within areas planned for prescribed 
6

burning (burn units) in the near future. The plots were then sampled 1, 2, 5, and 10 years after a 

prescribed burn. The data were not collected using these protocols in 2010, so this year was excluded 

from analyses. Hereafter, we refer to these plots as Fire Monitoring Handbook (FMH) plots. These 

FMH plots are being retired after the10 year visit (e.g. the rebar will be removed) and replaced with 

the FPCM plots described above. 

The Heartland Inventory & Monitoring Program also established a number of plots in 1997. Plant 

frequency was measured using circular subplots as described in the Heartland Networks’ vegetation 

monitoring protocol (James et al. 2009). The data and a summary of results from these plots are 

described in detail by James (2010b). In 2009, 2013 and 2014, a subset of these plots (called Legacy 

Plant Community Monitoring Plots, LPCMs) was revisited by NGPN and point-intercept data was 

also collected using the methods described above. In this report, we present the point-intercept from 

the three survey years, but do not report frequency. These plots were chosen to revisit because they 

were established to evaluate the disturbance caused by a trail installation. Three plots were 

established adjacent to the trail in areas of prairie impacted by construction disturbance (LPCM_2, 3 

and 7) and two plots were established nearby in undisturbed native prairie (LPCM_4 and 5).

Data Management and Analysis

We used FFI (FEAT/FIREMON Integrated; http://frames.gov/ffi/) as the primary software 

environment for managing our sampling data. FFI is used by a variety of agencies (e.g., NPS, USDA 

Forest Service, U.S. Fish and Wildlife Service), has a national-level support system, and generally 

conforms to the Natural Resource Database Template standards established by the Inventory and

Monitoring Program. 

Species scientific names, codes, and common names are from the USDA Plants Database (USDANRCS 2015). However, nomenclature follows the Integrated Taxonomic Information System (ITIS) 

(http://www.itis.gov). In the few cases where ITIS recognizes a new name that was not in the USDA 

PLANTS database, the new name was used, and a unique plant code was assigned. This report uses 

common names after the first occurrence in the text, but scientific names can be found in Appendix 

A. 

After data for the sites were entered, 100% of records were verified to the original data sheet to 

minimize transcription errors. A further 10% of records were reviewed a second time. After all data 

were entered and verified, automated queries were used to check for errors in the data. When errors 

were caught by the crew or the automated queries, changes were made to the original datasheets 

and/or the FFI database as needed. Summaries were produced using the FFI reporting and query tools 

and statistical summaries, and graphics were generated using R software (version 3.2.2).

Plant life forms (e.g., shrub, forb) were based on definitions from the USDA Plants Database 

(USDA-NRCS 2015). The conservation status ranks of plant species in Nebraska is determined by 

the Nebraska Natural Heritage Program (NENHP). For the purpose of this report, a species was 

considered rare if its conservation status rank was S1, S2, or S3. See Table 2 for a detailed definition 

of each conservation status rank.
7

Table 2. Definitions of state and global species conservation status ranks*.

Status 

Rank Category Definition

S1/G1 Critically imperiled Due to extreme rarity (5 or fewer occurrences) or other factor(s) making it 

especially vulnerable to extirpation.

S2/G2 Imperiled Due to rarity resulting from a very restricted range, very few populations (often 20 

or fewer), steep declines, or other factors making it very vulnerable to extirpation.

S3/G3 Vulnerable Due to a restricted range, relatively few populations (often 80 or fewer), recent 

widespread declines, or other factors making it vulnerable to extirpation. 

S4/G4 Apparently secure Uncommon but not rare; some cause for concern due to declines or other factors.

S5/G5 Secure Common, widespread and abundant.

S#S#/

G#G#

Range rank

(e.g. S2S3)

Used to indicate uncertainty about the status of the species or community. 

Ranges cannot skip more than one rank.

*Adapted from NatureServe status assessment table (http://www.natureserve.org/conservationtools/conservation-status-assessment)

We measured diversity at the plots in two ways: species richness and Pielou’s Index of Evenness. 

Species richness is simply a count of the species recorded in an area. Peilou’s Index of Evenness, J’, 

measures how even abundances are across taxa and ranges between zero and one; values near zero 

indicate dominance by a single species and values near one indicate nearly equal abundance of all 

species present. Plant richness was calculated for each plot using the total number of species 

intersected along the transects. Average height was calculated as the average height per plot using all 

species intersected on the transects. 

Climate data from the Agate 3E, Nebraska weather station (GHCND:USC00250030) were 

downloaded from NOAA’s online database (NOAA 2015). Fire history maps were compiled for 

AGFO and cross-referenced with plot locations. For each time data were collected at a plot (i.e., plot 

visit), we determined the number of years since the plot had burned and the number of fires recorded 

for that plot. For plots where no burns were recorded, we calculated the difference between the year 

of data collection and the oldest fire recorded in AGFO. This is likely an underestimate of the true 

time since it burned because fires were infrequent prior to the 1980s.

Reporting on Natural Resource Condition

Results were summarized in a Natural Resource Condition Table based on the templates from the 

State of the Park report series (http://www1.nrintra.nps.gov/im/stateoftheparks/index.cfm). The goal 

is to improve park priority setting and to synthesize and communicate complex park condition 

information to the public in a clear and simple way. By focusing on specific indicators, such as exotic 

species cover, it will also be possible and straightforward to revisit the metric in subsequent years. 

The status and trend of each indicator is scored and assigned a corresponding symbol based on the 

key found in Table 3.
8

We chose a set of indicators and specific measures that can describe the condition of vegetation in 

the Northern Great Plains and the status of exotic plant invasions. The measures include: absolute 

herb-layer canopy cover, native species richness, evenness, relative cover of exotic species, and 

annual brome cover. Reference values were based on descriptions of historic condition and variation, 

past studies, and/or management targets. Current park unit condition was compared to a reference 

value, and status was scored as good condition, warrants moderate concern, or warrants significant 

concern based on this comparison (Table 3). Good condition was applied to values that fell within the 

range of the reference value, and significant concern was applied to conditions that fell outside the 

bounds of the reference value. In some cases, reference conditions can be determined only after we 

have accumulated more years of data. When this is the case, we refer to these as “To be determined” 

and estimate condition based on our professional judgment.

Table 3. Key to the symbols used in the Natural Resource Condition Table. The background color 

represents the current status, the arrow summarizes the trend, and the thickness of the outside line 

represents the degree of confidence in the assessment. A symbol that does not contain an arrow 

indicates that there is insufficient information to assess a trend. Based on the State of the Park reports 

(http://www.nps.gov/stateoftheparks/).

Condition Status Trend in Condition

Confidence in 

Assessment

Warrants 

Significant Concern Condition is Improving High

Warrants 

Moderate Concern Condition is Unchanging Medium

Resource is in Good 

Condition Condition is Deteriorating Low
9

Results and Discussion

Status & Trends in Community Composition and Structure of AGFO Prairies

There are 453 plant species on the AGFO species list and we found 277 plant species in monitoring 

plots from 1998-2015 at AGFO (Appendix A). Graminoids, which includes grasses, sedges, and 

rushes, accounted for most of the vegetative cover at AGFO, but forbs, shrubs and subshrubs were 

also present (Figure 4). We found 47 exotic plant species at AGFO, all of which were forbs or 

graminoids. Exotic graminoids were particularly abundant (Figure 4). The shrubs and subshrubs were 

all native species.

Figure 4. Average cover by lifeform of native (green) and exotic (red) plants recorded in monitoring plots 

in Agate Fossil Beds National Monument (1998-2015). Absolute cover can be greater than 100% 

because the point-intercept methods records layers of overlapping vegetation. 

Needle and thread (Heterostipa comata), prairie sand reed (Calamovilfa longifolia), Western 

wheatgrass (Pascopyrum smithii), and slender wheatgrass (Elymus trachycaulus) were the most 

abundant native grasses and averaged between 8 and 25% absolute cover (Figure 5). There were no 

exotic species in the 10 most common plants in AGFO (Figure 5). There is also no evidence that 

exotic cover has increased since 1998 (F1,52 =0.65 P=0.42), but exotic species are still a concern. The 

cover of exotic species in 2011-2015 averaged 17.6 ± 2.5% (mean ± standard error) and it was 16.4 ± 

2.5% for the entire period of record. Kentucky bluegrass (Poa pratensis), prickly Russian thistle 

(Salsola tragus), cheatgrass (Bromus tectorum) and Japanese brome (B. japonicus) were the most 

pervasive exotics at AGFO. We found no targeted early detection species (Table 1) in the upland 

areas of AGFO. Cheatgrass and Japanese brome are both Eurasian, annual grasses that have been a 

part of the NGP landscape for more than a century, but their invasion in the region has accelerated 
10

since 1950 (Schachner et al. 2008). The presence of annual bromes in mixed grass prairie is 

associated with decreased productivity and altered nutrient cycling (Ogle et al. 2003). There is strong 

evidence from regions further west that cheatgrass alters fire regimes and the persistence of native 

species (D'Antonio and Vitousek 2003). From 1998 to 2015, the average relative cover of annual 

bromes was 5.8 ± 1.5% and the average for the last 5 years was 7.4 ± 1.9%. While the cover of 

annual bromes has not been increasing over time in AGFO (R2

=0.19, F1,52 =0.29 P=0.59; Figure 6), 

there is evidence that annual bromes are increasing within other National Park units in the region 

(unpublished data).

Figure 5. The average absolute cover of the 10 most common native plants recorded at Agate Fossil 

Beds National Monument in 1998-2015. Bars represent means ± one standard error. All of the 10 most 

common plants were native species.
11

Figure 6. Trends in the relative cover of annual bromes in Agate Fossil Beds National Monument from 

1998-2015. Points represent mean ± one standard errors and sample size is to the right of the point. 

Years with fewer than three monitoring plots were excluded from the graph. The shaded area highlights 

the period from 2011-2015 when sampling methods were consistent and distribution of plots was more 

even and consistent across years. The dashed line represents the maximum and minimum cover values 

for each year. 

Species Richness, Diversity, and Evenness 

One of the ways for the NPS to measure effectiveness of actions to achieve its mission of ‘preserving

ecological integrity’ is to examine trends in native plant diversity and evenness within park unit 

boundaries. Average species richness has been measured by point-intercept since 1998 and in 1 m2

and 10 m2 quadrats since 2011 (Table 4). 

Table 4. Average plant species richness in monitoring plots at Agate Fossil Beds National Monument

from 1998 to 2015. Values represent means ± one standard error. 

Point-intercept

(1998-2015; n=47)

1 m2 quadrats

(2011-2015, n=31)

10 m2 quadrats

(2011-2015, n=31)

Species richness 11.8 ± 0.6 8.7 ± 0.6 14.8 ± 0.9

Native species richness 9.8 ± 0.6 7.3 ± 0.5 12.2 ± 0.8

Exotic species richness 2.8 ± 0.2 1.4 ± 0.2 2.5 ± 0.3

Graminoid species richness 6.0 ± 0.2 3.6 ± 0.2 4.7 ± 0.2

Forb species richness 5.0 ± 0.4 4.5 ± 0.4 8.9 ± 0.6

While there was some variation across the monument, the plots we visited in AGFO tended to have a 

moderate diversity of native plants compared to other mixed-grass prairies. Species richness in the 

mixed-grass prairie is determined by numerous factors including fire regime, grazing, disturbance, 

and weather fluctuations (Symstad and Jonas 2011). While it is difficult to define a reference 
12

condition for species richness, which naturally varies considerably across both space and time, the 

natural range of variation over long-time periods may be a good starting point (Symstad and Jonas 

2014). Long-term records of species diversity in mixed-grass prairie from a relatively undisturbed 

site in Kansas varied between 3 and 15 species per square meter over the course of 30 years 

(Symstad and Jonas 2014). Compared to this, AGFO is within the natural range (7 species). Only one 

site, PCM_005 (Figure 1; middle) fell below this reference condition. This site is very close to the 

road and was likely impacted by construction. The most diverse plot, AGFO_PCM_012 (Figure 1; 

southeast), averaged 10.2 species.

We did not find any directional change in species richness or evenness over time (Figure 8). Native 

species richness in 1m2 quadrats was consistent from 2011 to 2015; it ranged from a low in 2012 of 

4.5 ± 0.6 (a drought year) to a high of 9.5 ± 0.9 in 2014 (a wet year). In the longer record from pointintercept data (1998-2015; Figure 7: top) annual average native richness ranged between 7 and 14 

species. Annual average evenness of native species ranged from 0.62 to 0.72 during this time period, 

indicating the plots were not strongly dominated by a single species (Figure 7: bottom). There is a 

great deal of variation in species richness and evenness among sites within AGFO (dashed lines in 

Figure 7 represent the maximum and minimum values) which makes long-term trends in these 

metrics difficult to detect.

There is evidence from other regions that annual bromes can affected persistence of native species 

(D'Antonio and Vitousek 2003). In AGFO and other nearby Northern Great Plains parks, there is a 

negative correlation between the cover of annual bromes and native species richness (Figure 9; 

F1,551=36.5, P<0.0001). If the cover of annual bromes in AGFO increases over time, we expect there 

will be a corresponding decline in native species richness. 

Disturbance from grazing, fire, and humans affects plant community structure and composition in 

mixed-grass prairie. We estimated the approximate area affected by natural and human disturbances 

at each site we visited in 2011-2015 by surveying the area for ~ 5 minutes at the end of the plot visit. 

The most common disturbance was from rodents (e.g. pocket gophers) and it was widespread,

occurring in 21 plots. There was also evidence of prescribed fires and off-road use, but this occurred 

in fewer plots (7 and 6 plots, respectively). We found no correlation with total disturbance, small or 

large animal disturbance and native richness or exotic cover. As more monitoring data are collected 

in future years, we may be able to better explore the statistical relationship between these metrics and 

disturbance. 
13

Figure 7. Trends in native species richness and evenness in Agate Fossil Beds National Monument, 

1998-2015. Data are means ± one standard error. The dashed line indicates the maximum and minimum 

values for each year.
14

Figure 8. The relationship between native species richness and the relative cover of annual bromes in 

long-term monitoring plots in National Park units of the Northern Great Plains, 1998-2015. 

The Influence of Climate and Fire on Plant Community Structure and Diversity

Climate

The Northern Great Plains has a continental climate, with hot summers and very cold winters. The 

30-year normal temperatures at a nearby weather station, Agate 3E, Nebraska ranged from average 

minimum monthly temperatures in December of 7.8° F to maximum monthly July temperatures of 

88.7° F (based on 1980-2010). The 30-year normal annual precipitation totals 14.37 inches. Annual 

precipitation at AGFO in 1998-2015 was variable and ranged between 4.5 and 21.3 inches, in 2012 

and 2009, respectively. There were dry years in the early 2000s, 2006-2008, and in 2012 (Figure 10). 

The last two years have been much wetter than average. The native vegetation is adapted to this 

variation, and productivity responds strongly to decreases in spring and summer precipitation (Yang 

et al. 1998, Smart et al. 2007). Species richness and diversity in regional grasslands are also sensitive 

to temperature and precipitation fluctuation, but the response is complex and less predictable (Jonas 

et al. 2015).
15

Figure 9. The total annual precipitation anomaly from 1998-2015 for Agate Fossil Beds National 

Monument. Positive values (blue) represent years wetter than and negative values (red) years drier than 

the 1981-2010 average. The anomaly is measured in inches and based on data from a nearby weather 

station.

We found that native species richness increased in response to increasing precipitation (F1,52=11.1, 

P<0.001). Plant height and exotic cover also responded to precipitation (F1,52=4.2, P=0.047, 

F1,52=6.2, P=0.016, for height and cover respectively) and maximum temperature (F1,52=7.8, 

P=0.007, F1,52=13.8, P<0.001). However, the response was driven by 2012, an extremely hot and dry 

year (Figure 10). When 2012 was excluded from analysis neither height nor exotic cover showed a 

significant response to temperatures or precipitation. Similarly, native species richness declined in 

2012 when average maximum temperatures were very hot, but otherwise there was no significant 

response over this time period. Continued monitoring and a longer time series of vegetation data and 

climate will allow us to determine whether the response to the 2012 drought is typical.
16

Figure 10. A long-term monitoring plot in Agate Fossil Beds National Monument in 2012, during a severe 

drought, and 2014 a wet year. 

Fire History

Historically, fire was a common disturbance in Northern Great Plains grasslands, with natural fire

return intervals of 9-12 years (Guyette et al. 2015). Natural fires have been suppressed for most of 

the last century, but the use of prescribed burning in Northern Great Plains parks to mitigate the 

effects of the absence of natural fires has increased over time since its start at Wind Cave NP in 1973 

(Wienk et al. 2011). As of 2015, there is a mosaic of recently burned and unburned areas at AGFO

(Figure 11).

Figure 11. Map of recent fire history at Agate Fossil Beds National Monument. 
17

The effects of specific prescribed burns on vegetation and fuel loads and more details about fires at 

AGFO can be found in past NGPFire annual reports (see http://www.nps.gov/ngpfire/docs.htm). 

Here, we were interested in determining the relationship between fire history and vegetation. We 

compared two vegetation metrics, native species richness and relative cover of exotic plants, with the 

length of time between the data collection at a plot and the most recent fire at that plot (years since 

fire). For example, a site that burned in the spring and then was visited in the summer would be 0 

years since fire. We excluded plots that had not burned from this analysis, because we do not have 

confidence in the historical fire record (pre-1980s). 

We found a strong positive relationship between native richness and years since fire (Figure 12;

F1,32=32.6, P<0.0001). Exotic species cover declined significantly as years since fire increased

(Figure 12; F1,32=4.8, P=0.036). Annual bromes show a similar pattern, but it is not significant. Plots 

that had not burned in 5 or 6 years had a higher number of native species and a lower cover of exotics 

than sites that burned more recently and when compared to AGFO averages. This suggests that 

prescribed fire can benefit the mixed-grass prairie in AGFO, but it may take 5 or more years to see 

the positive effects.

Figure 12. Native species richness (left panel) and relative percent cover of exotic plants (right panel)

across plots with different fire histories. Observations vary between plots that have recently burned (0 

years since fire) and plots that had burned 6 years previously (6 years since fire). Bars represent means ±

one standard error and sample sizes range from 3 to 9 plots. The dashed line indicates the average 

native species richness and relative percent cover of exotic species of all plots in AGFO. 

The best approach to reducing exotic species abundance in AGFO will likely include burning; 

however there may also be a need for targeted herbicides and seeding of native species. Ongoing 

research on this topic and an upcoming adaptive management initiative for annual brome control in 

NGPN units should provide more data and guidance to help with these management decisions. 
18

Rare Plants 

While repeating rare plant surveys and locating rare species is not the focus of NGPN plant 

community monitoring, we identified 40 rare plant species in AGFO from 1998 to 2015. Of these 

species, 22 were S3S5 species (vulnerable to secure) whose vulnerability rank is low and uncertain 

and won’t be discussed here (see Appendix A for S3S5 species). Seven critically imperiled (S1) 

species were observed mostly in very low frequencies and abundances with the exception of slender 

wheatgrass (Elymus trachycaulus), which was observed in 42 plots with 8% mean cover (Table 5).

Other more commonly observed rare species included aridland goosefoot (Chenopodium dessicatum, 

S2S4), longbracted plantain (Plantago patagonica S2S4), and hairy goldenaster (Heterotheca villosa, 

S1). Most rare species we observed were in fewer than 5 plots and had less than 0.01% mean cover 

(Table 5; Figure 13). All rare species we observed in AGFO are classified as apparently secure or 

secure (G4 or G5) at the global scale, but are rare in Nebraska, generally because these species exist 

on the edge of their global range in the state.

Table 5. Rare species occurrence in Agate Fossil Beds National Monument sampling plots from 1998-

2015. Status ranks are based on Nebraska Natural Heritage Program designations. Plot count is the 

number of unique plots a species was recorded in across all years. Mean cover is the average cover of 

that species across all years in plots where cover measurements were recorded.

Species Common Name

State 

Rank

Global 

Rank

Plot 

Count

Mean 

Cover (%)

Astragalus agrestis purple milkvetch S1 G5 1 0.00

Elymus lanceolatus thickspike wheatgrass S1 G5 1 0.00

Elymus trachycaulus slender wheatgrass S1 G5 42 8.00

Eriogonum cernuum nodding buckwheat S1 G5 3 <0.01

Heterotheca villosa hairy goldenaster S1 G5 7 0.01

Symphoricarpos albus common snowberry S1 G5 1 0.00

Symphyotrichum falcatum white prairie aster S1 G5 1 <0.01

Euphorbia missurica prairie sandmat S1S3 G5 1 0.00

Erigeron ochroleucus buff fleabane S2 G5 3 0.00

Fritillaria atropurpurea spotted fritillary S2 G5 2 0.00

Phacelia hastata silverleaf phacelia S2S3 G5 1 0.00

Dieteria canescens hoary tansyaster S2S4 G5 1 0.00

Carex hallii deer sedge S2S4 G4 5 0.00

Chenopodium desiccatum aridland goosefoot S2S4 G5 13 0.29

Cryptantha fendleri sanddune cryptantha S2S4 G5 4 0.00

Physaria reediana Reed's twinpod S2S4 G4 2 0.00

Plantago patagonica longbracted plantain S2S4 G5 14 0.03

Sphenopholis obtusata prairie wedgescale S2S4 G5 10 0.00
19

Figure 13. Photographs of two rare species found in plant community monitoring plots at Agate Fossil 

Beds National Monument. Left: purple milkvetch (Astragalus agrestis S1); Right: spotted fritillary (Fritillaria 

atropurpurea S2). Both species were observed in very low frequencies.

We recommend monitoring of known rare plant populations and a formal rare plant survey be 

conducted when funds are available. A full rare plant survey will be more likely to thoroughly and 

accurately quantify the status of rare plants found in AGFO. Any future construction efforts that 

could disturb native vegetation (e.g. trail building), should avoid damaging species considered rare in 

Nebraska.

Fossil Hills Trail Paving Project

Fossil Hills Trail is a paved walkway that connects the AGFO visitor center with University and 

Carnegie Hills. Construction work on the trail was completed in 2007 and resulted in areas of 

disturbance to native mixed-grass prairie along the trail corridor. We collected data from three plots 

installed in disturbed prairie habitat and two plots in nearby undisturbed native prairie to evaluate the 

recovery of the disturbed sites. All of the monitoring sites were impacted by a prescribed fire in May 

2009 (James 2009). 

There was no statistically significant difference in native species richness (Figure 14; F2,6=0.11, 

P=0.898) or exotic species relative cover (Figure 14; F1,6=0.70, P=0.533) between disturbed and 

undisturbed native prairie habitat from 2009-2014. Native species richness in both disturbed and 

undisturbed habitat was typically equal to, or greater than, the 18-year average native species 

richness across all plots in AGFO, except in disturbed prairie plots in 2013, which followed a 

drought year (Figure 9; Figure 15). Exotic species relative cover was less than, or equal to, the

average exotic species relative cover across the entire monument. Litter cover was greater in 

disturbed prairie plots from 2009-2014 (Figure 14; F1,6=8.2, P=0.029), and was greater than the 18-

year average litter cover in AGFO in 2013 and 2014 in disturbed prairie plots.
20

Figure 14. Native species richness (A), exotic species relative cover (B), and litter cover (C) in intact 

native mixed-grass prairie and disturbed prairie along the Fossil Hill Trail at Agate Fossil Beds National 

Monument (mean ± standard error of the mean). The dashed line indicates the average value for each 

respective table’s attribute across all plots in the park. 

Figure 15. Native species richness and exotic species relative cover in disturbed prairie plots were lower 

in 2013 but had returned to levels similar to 18-year AGFO averages by 2014. This variation was likely in 

response to drought conditions in 2012, and comparing images of plot LPCM_07 in 2013 and 2014 

clearly shows the difference in plant community condition in those years.

2013 2014
21

Native plant richness is similar in both disturbed and undisturbed plot types and is generally higher in 

those plots than the AGFO average; however, there are exotic species present in both plot types and 

there is greater litter cover in disturbed prairie plots. Increased litter cover is associated with a greater 

risk of exotic brome invasion in Northern Great Plains National Park units (unpublished data), and 

we suggest continued monitoring of these plots to ensure that any increase in exotic species 

abundance is detected so appropriate control measures can be taken. 

The Status of Riparian Vegetation in AGFO

Wetlands along the Niobrara River cover approximately 234 acres within AGFO, or 8% of the 

monument (Gitzen et al. 2010). We visited 17 riparian monitoring plots in AGFO between 2012 and 

2015 (Figure 16) to estimate the current condition of the plant community and to provide some field 

data on the extent of pale yellow iris (Iris pseudacorus) invasion.

Figure 16. Location of 17 riparian monitoring plots in Agate Fossil Beds National Monument, 2012-2015 

and estimated pale yellow iris infestation in 2012.The land cover classification was developed by the 

NGPN in 2012 from 0.6 meter, WorldView-2 satellite imagery collected on June 4, 2012 and refined using 

field training data sets acquired on June 21, 2012.

We found 88 plant species in the riparian area, and 15 of these were exotic species. Many of the most 

common species were native graminoids (Figure 17) including woolly sedge (Carex pellita), Baltic 

rush (Juncus balticus), broadleaf cattail (Typha latifolia) and western wheatgrass (Pascopyrum 

smithii). Common exotic species included Kentucky bluegrass (Poa pratensis) and pale yellow iris 

(Iris pseudacorus). Species richness in the riparian areas was comparable to that of the upland areas. 

Total species richness averaged 12.2 ± 1.2 species. On average, we recorded 9.6 ± 1.0 native species 

on each transect. Exotic cover was high, averaging 28.3 ± 2.0 % across the riparian areas of the 

monument from 2012 to 2015 (Table 8). Kentucky bluegrass occurred in 12 of 17 plots and averaged 

over 10.0 ± 1.6 % relative cover throughout the riparian area (Table 8). 
22

Figure 17. The average absolute cover of the 10 most common native (green) and exotic (red) riparian 

plants recorded at Agate Fossil Beds National Monument in 2015. Bars represent means ± standard 

errors. Kentucky bluegrass and pale yellow iris were the most common exotic species. 

In 2012, it was estimated that 57 acres of the riparian corridor were infested with pale yellow iris 

(Figure 16). Pale yellow iris is an Eurasian species that typically grows in temperate freshwater and 

brackish marsh communities (Sutherland 1990). Its showy flower has made it a favorite ornamental 

plant and it is now considered invasive across much of North America. Pale yellow iris has the 

potential to uplift sediments, alter habitat, reduce diversity of native species, and these changes favor 

its continued spread (Thomas 1980). It was first introduced in the Niobrara basin in 1906 upstream of 

AGFO in a manmade, spring fed pond on Agate Springs Ranch. 
23

Pale yellow iris was very abundant and found in 11 of 17 sites, averaging 11.5 ± 2.4% relative cover 

in the riparian area. The distribution of the pale yellow iris is not continuous (i.e., it is not in high 

abundance at neighboring sites); instead it appears to be patchy across the riparian area (Figure 16), 

most often appearing in the wetter sites with the cattails. This patchiness may present a challenge to 

future control efforts. The abundance of pale yellow iris has stayed fairly constant over the 4 year 

monitoring period (Table 8), despite some control efforts in 2015. Future monitoring will be 

necessary to determine the effectiveness of the treatment program over time. 

Table 6. The relative percent cover of pale yellow iris in monitoring plots at Agate Fossil Beds National 

Monument 2012-2015. 

Year

Number 

of plots

Relative cover 

of exotic 

species

(% mean ± se)

Relative cover 

of Kentucky 

bluegrass

(% mean ± se)

Relative cover 

of yellow iris

(% mean ± se)

Minimum 

relative cover 

of yellow iris 

(%)

Maximum 

relative cover 

of yellow iris 

(%)

2012 12 28.1 ± 4.7 11.9 ± 3.6 11.4 ± 5.1 0 48.2

2013 11 31.0 ± 5.0 9.8 ± 3.9 10.6 ± 6.0 0 57.1

2014 12 31.9 ± 3.9 10.1 ± 3.2 14.1 ± 5.9 0 54.3

2015 17 24.2 ± 3.3 8.7 ± 2.8 10.1 ± 3.3 0 40.4
24

Conclusion

The Northern Great Plains Inventory & Monitoring Program and Fire Effects Program have been 

monitoring vegetation in Agate Fossil Beds National Monument for over 18 years. While methods 

have changed slightly, this report summarizes data from over 64 locations from 1998-2015. Below, 

we list the questions we asked and provide a summarized answer, for more details see the Results 

and Discussion section. We conclude with a Natural Resource Condition Table (Table 9) that 

summarizes the current status and trends in a few key vegetation metrics. 

1. What is the current status of plant community composition and structure of AGFO 

grasslands (species richness, cover, and diversity) and how has this changed from 1998 to 

2015? 

Native grasses, such as needle and thread, sand reed, and western wheatgrass, are abundant 

and the dominant component of the prairie at AGFO. Native plant diversity is at a moderate 

level compared to other grasslands in the region (Table 7), but diversity is spatially variable. 

We found no significant trends in native diversity or evenness from 1998 to 2015, but both 

may become threatened if cover of annual invasive brome grasses increases, as we’ve 

observed in other Northern Great Plains Inventory and Monitoring units (Figure 8). 

2. How do trends in grassland condition correlate with climate and fire history?

Native species richness increased in years with more rainfall and a hot dry year in 2012 

corresponded to large declines in native species richness and an increase in exotic species 

cover. Plots that had not burned in 5 or 6 years had a higher number of native species and a 

lower cover of exotics than sites that burned more recently and when compared to AGFO 

averages (Figure 12). This suggests that prescribed fire can benefit the mixed-grass prairie in 

AGFO, but it may take 5 or more years to see the positive effects following a burn.

3. What, if any, rare plants were found in AGFO long-term monitoring plots? 

We identified 22 rare plant species in AGFO between 1998 and 2015; seven of these are 

considered critically imperiled within Nebraska. We recommend monitoring of rare plant 

populations and more targeted surveys of rare plant species be completed when funds are 

available. 

4. How did installation of the AGFO Fossil Hills Trail affect the adjacent prairie?

The disturbed prairie adjacent to the Fossil Hills Trail is very similar to the native prairie in 

other parts of AGFO. This suggests that the prairie in AGFO is resilient and can recover 

from a moderate level of disturbance. We suggest continued monitoring of these plots to 

ensure that any increase in exotic species abundance is detected so appropriate control 

measures can be taken. 

5. What is the composition and structure of the riparian corridor at AGFO?

The riparian corridor in AGFO is a fairly diverse assemblage of riparian species such as 

sedges, willows, and cattails. It is, however, more invaded than the upland areas of AGFO

and threatened by high cover of Kentucky bluegrass and pale yellow iris. Since riparian 
25

monitoring began in 2012, we have not detected a significant change in the cover of pale 

yellow iris. Continued monitoring is necessary to determine if exotic treatment is effective 

over the long-term.

Table 7. Natural resource condition summary table of plant communities in Agate Fossil Beds National 

Monument (AGFO). Current values are based on data from 2011-2015 and trends are based on data 

from 1998-2015. 

Indicator of 

Condition

Specific 

Measures

Current

Value 

(mean ± SE)

Reference 

Condition 

and Data 

Source

Condition 

Status/Trend

Rationale for

Resource Condition

Upland Plant 

Community 

Structure and 

Composition

Native species 

richness (1m2

quadrats) 

7.3 ± 0.5

species

3-15 

species 

AGFO plays a vital role in 

protecting and managing some of 

the last remnants of native mixedgrass prairie in the region. The 

monument is characterized by 

moderate native species 

richness, but average richness is 

within a natural range of 

variability (Symstad and Jonas 

2014). The lowest native diversity 

is found near the road. Native 

evenness has not changed since 

monitoring began in 1998. 

Evenness

(native spp. 

point-intercept 

transects)

0.70 ± 0.01 To be 

determined

Relative cover 

of exotic 

species 

17.6 ± 2.5% < 10 % 

cover

AGFO maintains a mixed-grass 

prairie with moderate exotic plant 

cover and a fair diversity of native 

plants. Annual invasive bromes 

are not currently abundant in 

AGFO, but active management 

may be required to keep such low 

cover.

Annual brome 

cover 

7.4 ± 1.9% < 10 % 

cover

Riparian Plant 

Community 

Structure and 

Composition 

Native species 

richness 

(50 m pointintercept

transect)

9.6 ± 1.0 To be 

determined

The riparian areas of AGFO had 

levels of diversity similar to the 

upland areas.

Relative cover 

of exotic 

species

28.3 ± 2.0% ≤10 % 

cover

The relative cover of exotic 

species in the riparian areas of 

AGFO was very high. Exotic 

control efforts should be focused 

in this area to restore native plant 

diversity and ecological integrity.

Pale yellow iris has invaded 

riparian areas throughout the 

monument. It had a patchy 

distribution and was absent in 

some sites while accounting for 

over 50% in others

Relative cover 

of pale yellow 

iris 

11.5 ± 2.4% ≤10 % 

cover
26

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29

Appendix A: List of plant species found at AGFO 1998-2015

Below is a list of all the plant species found in AGFO long-term plant community monitoring plots. 

The species are grouped by plant family. An “X” in the exotic column means that species is not 

native to the park or, in the case where only the genus was identified, there are some species within 

that genus that are exotic. Species considered to be rare in Nebraska are marked in the final column 

and the state conservation ranks are provided. Conservation rank definitions are in Table 2 of the 

report. 

Family Code Scientific Name Common Name Exotic Rare

Agavaceae YUGL Yucca glauca soapweed yucca

Alismataceae SACU Sagittaria cuneata arumleaf arrowhead

Amaranthaceae AMAR Amaranthus arenicola sandhill amaranth

Anacardiaceae RHTR Rhus trilobata skunkbush sumac

Apiaceae

CIMA2 Cicuta maculata spotted water hemlock S3S5

CYGL99 Cymopterus glomeratus plains springparsley

LOOR Lomatium orientale Northern Idaho biscuitroot

MUTE3 Musineon tenuifolium slender wildparsley

Asclepiadaceae

ASIN Asclepias incarnata swamp milkweed

ASSP Asclepias speciosa showy milkweed

ASVI Asclepias viridiflora green comet milkweed

Asteraceae

AMAC2 Ambrosia acanthicarpa flatspine burr ragweed

AMBRO Ambrosia spp. ragweed X

AMPS Ambrosia psilostachya Cuman ragweed

AMTR Ambrosia trifida great ragweed

ARDR4 Artemisia dracunculus tarragon

ARFR4 Artemisia frigida fringed sagewort

BIFR Bidens frondosa devil's beggartick

BREU Brickellia eupatorioides false boneset

CIAR4 Cirsium arvense Canada thistle X

CICA11 Cirsium canescens prairie thistle

CIFL Cirsium flodmanii Flodman's thistle

CIRSI Cirsium spp. thistle X

COCA5 Conyza canadensis horseweed

CYXA Cyclachaena xanthifolia giant sumpweed

DICA18 Dieteria canescens hoary tansyaster S2S4

DYPA Dyssodia papposa fetid marigold

ERBE2 Erigeron bellidiastrum western daisy fleabane

EROC Erigeron ochroleucus buff fleabane S2

ERPU2 Erigeron pumilus shaggy fleabane

ERST3 Erigeron strigosus prairie fleabane
30

Family Code Scientific Name Common Name Exotic Rare

GUSA2 Gutierrezia sarothrae broom snakeweed

HEAN3 Helianthus annuus common sunflower

HELIA3 Helianthus spp. sunflower X

HEPE Helianthus petiolaris prairie sunflower

HEVI4 Heterotheca villosa hairy false goldenaster S1

HYFI Hymenopappus filifolius fineleaf hymenopappus

LASE Lactuca serriola prickly lettuce X

LAPU Lactuca pulchella blue lettuce X

LIPU Liatris punctata dotted blazing star

LYJU Lygodesmia juncea rush skeletonplant

MATA2 Machaeranthera 

tanacetifolia tanseyleaf tansyaster S3S5

MUOB99 Mulgedium oblongifolium blue lettuce

PACA15 Packera cana woolly groundsel

RACO3 Ratibida columnifera upright prairie coneflower

SERI2 Senecio riddellii Riddell's ragwort

SOAR2 Sonchus arvensis field sowthistle X

SOCA6 Solidago canadensis Canada goldenrod S3S5

SOGI Solidago gigantea giant goldenrod

SOMI2 Solidago missouriensis Missouri goldenrod

SOMO Solidago mollis velvety goldenrod

SYER Symphyotrichum ericoides white heath aster S3S5

SYFA Symphyotrichum falcatum white prairie aster S1

SYLA6 Symphyotrichum 

lanceolatum white panicle aster

SYMPH4 Symphyotrichum spp. aster

TAOF Taraxacum officinale common dandelion X

TEAC Tetraneuris acaulis stemless four-nerve daisy

TOEX2 Townsendia exscapa stemless Townsend daisy S3S5

TOGR Townsendia grandiflora largeflower Townsend daisy S3S5

TRDU Tragopogon dubius yellow salsify X

XAGR99 Xanthisma grindelioides rayless tansyaster

XASP99 Xanthisma spinulosum lacy tansyaster

Boraginaceae

CRCA8 Cryptantha cana mountain cryptantha

CRCE Cryptantha celosioides buttecandle

CRFE3 Cryptantha fendleri sanddune cryptantha S2S4

CRMI5 Cryptantha minima little cryptantha

CRTH Cryptantha thyrsiflora calcareous cryptantha S3S5

LAOC3 Lappula occidentalis flatspine stickseed

LASQ Lappula squarrosa European stickseed X
31

Family Code Scientific Name Common Name Exotic Rare

LICA13 Lithospermum 

caroliniense Carolina puccoon

LIIN2 Lithospermum incisum narrowleaf stoneseed

Brassicaceae

ALDE Alyssum desertorum desert madwort X

ARHO2 Arabis holboellii Holboell's rockcress

BOHO99 Boechera holboellii Holboell's rockcress

BRASS2 Brassica spp. mustard X

BOCO4 Boechera collinsii Collins' rockcress

CAMI2 Camelina microcarpa littlepod false flax X

DEPI Descurainia pinnata western tansymustard S3S5

DESO2 Descurainia sophia herb sophia X

DRRE2 Draba reptans Carolina draba

ERCA14 Erysimum capitatum sanddune wallflower

LEDE Lepidium densiflorum common pepperweed

PHLU99 Physaria ludoviciana foothill bladderpod

PHRE8 Physaria reediana alpine bladderpod S2S4

SIAL2 Sisymbrium altissimum tall tumblemustard X

THAR5 Thlaspi arvense field pennycress X

Cactaceae

ESVI2 Escobaria vivipara spinystar

MAHEM2 Mammillaria heyderi var. 

meiacantha little nipple cactus

OPFR Opuntia fragilis brittle pricklypear

OPMA2 Opuntia macrorhiza twistspine pricklypear

OPPO Opuntia polyacantha plains pricklypear

Capparaceae PODO3 Polanisia dodecandra redwhisker clammyweed

Caprifoliaceae

SYAL Symphoricarpos albus common snowberry S1

SYOC Symphoricarpos 

occidentalis western snowberry

Caryophyllaceae

ERHO13 Eremogone hookeri Hooker's sandwort S3S5

PADE4 Paronychia depressa spreading nailwort

SIDR Silene drummondii Drummond's campion X

SILEN Silene spp. catchfly

Chenopodiaceae

CHAL7 Chenopodium album lambsquarters X

CHBE4 Chenopodium berlandieri pitseed goosefoot

CHDE Chenopodium desiccatum aridland goosefoot S2S4

CHENO Chenopodium spp. goosefoot X

CHFR3 Chenopodium fremontii Fremont's goosefoot

CHPR5 Chenopodium pratericola desert goosefoot

CHSI2 Chenopodium simplex mapleleaf goosefoot

CORIS Corispermum spp. bugseed X

KOSC Kochia scoparia burningbush, kochia X
32

Family Code Scientific Name Common Name Exotic Rare

KRLA2 Krascheninnikovia lanata winterfat S3S5

SALSO Salsola spp. Russian thistle X

SATR12 Salsola tragus prickly Russian thistle X

Cleomaceae PESE99 Peritoma serrulata Rocky Mountain beeplant

Commelinaceae TRBR Tradescantia bracteata longbract spiderwort

TROC Tradescantia occidentalis prairie spiderwort

Cucurbitaceae ECLO Echinocystis lobata wild cucumber

Cyperaceae

CADU6 Carex duriuscula needleleaf sedge

CAFI Carex filifolia threadleaf sedge

CAHA3 Carex hallii deer sedge S2S4

CAHY4 Carex hystericina bottlebrush sedge

CAIN9 Carex inops sun sedge

CANE2 Carex nebrascensis Nebraska sedge

CAPE42 Carex pellita woolly sedge

CAPR5 Carex praegracilis clustered field sedge

CAREX Carex spp. sedge

ELER Eleocharis erythropoda bald spikerush

SCPU10 Schoenoplectus pungens common threesquare

SCTA2 Schoenoplectus 

tabernaemontani softstem bulrush

Equisetaceae EQLA Equisetum laevigatum smooth horsetail

Euphorbiaceae

CHGL13 Chamaesyce 

glyptosperma ribseed sandmat X

EUGL3 Euphorbia glyptosperma ribseed sandmat X

EURO5 Euphorbia robusta horned spurge X

EUSE4 Euphorbia serpens matted sandmat

CRTE4 Croton texensis Texas croton

EUBR Euphorbia brachycera horned spurge

EUMI5 Euphorbia missurica prairie sandmat S1S3

EUPHO Euphorbia spp. spurge, sandmat X

Fabaceae

ASAD11 Astragalus adsurgens prairie milkvetch

ASAG2 Astragalus agrestis purple milkvetch S1

ASCE Astragalus ceramicus painted milkvetch

ASCR2 Astragalus crassicarpus groundplum milkvetch

ASLA27 Astragalus laxmannii Laxmann's milkvetch

ASLO4 Astragalus lotiflorus lotus milkvetch

ASMI10 Astragalus missouriensis Missouri milkvetch

ASMO7 Astragalus mollissimus woolly locoweed

ASSE5 Astragalus sericoleucus silky milkvetch

ASSP6 Astragalus spatulatus tufted milkvetch
33

Family Code Scientific Name Common Name Exotic Rare

ASTRA Astragalus spp. milkvetch

DACA7 Dalea candida white prairie clover

DAEN Dalea enneandra nineanther prairie clover

DALEA Dalea spp. prairie clover

DAPU5 Dalea purpurea purple prairie clover S3S5

GLLE3 Glycyrrhiza lepidota American licorice

LAPO2 Lathyrus polymorphus manystem pea

LUAR3 Lupinus argenteus silvery lupine

LUPIN Lupinus spp. lupine

LUPL Lupinus plattensis Nebraska lupine

LUPU Lupinus pusillus rusty lupine

MELU Medicago lupulina black medick X

MEOF Melilotus officinalis yellow sweetclover X

MESA Medicago sativa alfalfa X

OXLA3 Oxytropis lambertii purple locoweed

OXSE Oxytropis sericea white locoweed

PEAR6 Pediomelum argophyllum silverleaf Indian breadroot

PEES Pediomelum esculentum large Indian breadroot

PSLA3 Psoralidium lanceolatum lemon scurfpea

PSTE5 Psoralidium tenuiflorum slimflower scurfpea

THRH Thermopsis rhombifolia golden pea

Grossulariaceae RIAM2 Ribes americanum American black currant

Hydrophyllaceae ELNY Ellisia nyctelea Aunt Lucy

PHHA Phacelia hastata silverleaf phacelia S2S4

Iridaceae IRPS Iris pseudacorus pale yellow iris X

Juncaceae JUBA Juncus balticus Baltic rush

JUNCU Juncus spp. rush X

Lamiaceae

HEDR Hedeoma drummondii Drummond's false pennyroyal

HEHI Hedeoma hispida rough false pennyroyal

LYAM Lycopus americanus American water horehound

LYAS Lycopus asper rough bugleweed

MEAR4 Mentha arvensis wild mint

SCLA2 Scutellaria lateriflora blue skullcap

Lemnaceae LEMI3 Lemna minor common duckweed S3S5

Lentibulariaceae UTRIC Utricularia spp. bladderwort

Liliaceae

ALTE Allium textile textile onion

CANU3 Calochortus nuttallii sego lily

FRAT Fritillaria atropurpurea spotted fritillary S2

MAST4 Maianthemum stellatum starry false lily of the valley

Linaceae LIRI Linum rigidum stiffstem flax
34

Family Code Scientific Name Common Name Exotic Rare

Loasaceae MEDE2 Mentzelia decapetala tenpetal blazingstar

Malvaceae SPCO Sphaeralcea coccinea scarlet globemallow

Melanthiaceae TOVE2 Toxicoscordion 

venenosum

meadow deathcamas

Nyctaginaceae

ABFR2 Abronia fragrans snowball sand verbena

MIHI Mirabilis hirsuta hairy four o'clock

MILI3 Mirabilis linearis narrowleaf four o'clock

Onagraceae

EPLE2 Epilobium leptophyllum bog willowherb

GAPA6 Gaura parviflora velvetweed X

OEAL Oenothera albicaulis whitest evening primrose

OENU Oenothera nuttallii Nuttall's evening-primrose

OESE3 Oenothera serrulata yellow sundrops

OESU99 Oenothera suffrutescens scarlet beeblossom

Orobanchaceae ORFA Orobanche fasciculata clustered broomrape

Papaveraceae ARPO2 Argemone polyanthemos crested pricklypoppy

Pinaceae PIPU Picea pungens blue spruce

Plantaginaceae PLER Plantago eriopoda redwool plantain S3S5

PLPA2 Plantago patagonica woolly plantain S2S4

Poaceae

ACHY Achnatherum hymenoides Indian ricegrass

ANGE Andropogon gerardii big bluestem

ANHA Andropogon hallii sand bluestem

ARPU9 Aristida purpurea purple threeawn S3S5

BOCU Bouteloua curtipendula sideoats grama

BOGR2 Bouteloua gracilis blue grama

BRIN2 Bromus inermis smooth brome X

BRJA Bromus japonicus Japanese brome X

BROMU Bromus spp. brome X

BRTE Bromus tectorum cheatgrass X

CALO Calamovilfa longifolia prairie sandreed

CAST36 Calamagrostis stricta slimstem reedgrass

DISP Distichlis spicata saltgrass

ELEL5 Elymus elymoides squirreltail

ELLA3 Elymus lanceolatus thickspike wheatgrass S1

ELRE4 Elymus repens quackgrass X

ELTR7 Elymus trachycaulus slender wheatgrass S1

ELYMU Elymus spp. wildrye X

FEOC Festuca occidentalis western fescue

GLST Glyceria striata fowl mannagrass

HECO26 Hesperostipa comata needle and thread

HOJU Hordeum jubatum foxtail barley
35

Family Code Scientific Name Common Name Exotic Rare

KOMA Koeleria macrantha prairie Junegrass

LEOR Leersia oryzoides rice cutgrass

MUAS Muhlenbergia asperifolia scratchgrass, alkali muhly

MUCU3 Muhlenbergia cuspidata plains muhly

MUHLE Muhlenbergia spp. muhly

MUME2 Muhlenbergia mexicana Mexican muhly

MUPA99 Muhlenbergia paniculata tumblegrass

MUPU2 Muhlenbergia pungens sandhill muhly

MURA Muhlenbergia racemosa marsh muhly

NAVI4 Nassella viridula green needlegrass

PACA6 Panicum capillare witchgrass S3S5

PANIC Panicum spp. panicgrass X

PASM Pascopyrum smithii western wheatgrass

PAVI2 Panicum virgatum switchgrass

POCO Poa compressa Canada bluegrass X

POPA2 Poa palustris fowl bluegrass

POPR Poa pratensis Kentucky bluegrass X

POSE Poa secunda Sandberg bluegrass

SCSC Schizachyrium scoparium little bluestem

SONU2 Sorghastrum nutans Indiangrass

SPCR Sporobolus cryptandrus sand dropseed

SPGR Spartina gracilis alkali cordgrass

SPOB Sphenopholis obtusata prairie wedgescale S2S4

SPPE Spartina pectinata prairie cordgrass

THIN6 Thinopyrum intermedium intermediate wheatgrass X

VUOC Vulpia octoflora sixweeks fescue

Polemoniaceae PHAN4 Phlox andicola prairie phlox

PHHO Phlox hoodii spiny phlox

Polygonaceae

ERAN4 Eriogonum annuum annual buckwheat

ERCE2 Eriogonum cernuum nodding buckwheat S1

ERFL4 Eriogonum flavum alpine golden buckwheat

ERPA9 Eriogonum pauciflorum fewflower buckwheat S3S5

FACO Fallopia convolvulus black bindweed X

PEAM8 Persicaria amphibia longroot smartweed S3S5

PELA22 Persicaria lapathifolia curlytop knotweed

POAV Polygonum aviculare prostrate knotweed X

PORA3 Polygonum ramosissimum bushy knotweed

RUVE2 Rumex venosus veiny dock

Potamogetonaceae POTAM Potamogeton pondweed

Rosaceae ROWO Rosa woodsii Woods' rose
36

Family Code Scientific Name Common Name Exotic Rare

Rubiaceae GATI Galium tinctorium stiff marsh bedstraw

Salicaceae

SAER Salix eriocephala Missouri River willow S3S5

SAIN3 Salix interior sandbar willow

SALIX Salix spp. willow

Santalaceae COUM Comandra umbellata bastard toadflax

Scrophulariaceae

CASE5 Castilleja sessiliflora Great Plains Indian paintbrush

PEAL2 Penstemon albidus white penstemon

PEAN4 Penstemon angustifolius broadbeard beardtongue

PEER Penstemon eriantherus fuzzytongue penstemon S3S5

VEAN2 Veronica anagallisaquatica water speedwell

VETH Verbascum thapsus common mullein X

Solanaceae

PHHI8 Physalis hispida prairie groundcherry

PHVI5 Physalis virginiana Virginia groundcherry

PHYSA Physalis spp. groundcherry

SOTR Solanum triflorum cutleaf nightshade S3S5

Sparganiaceae SPEU Sparganium eurycarpum broadfruit bur-reed

Typhaceae TYAN Typha angustifolia narrowleaf cattail

TYLA Typha latifolia broadleaf cattail

Urticaceae PAPE5 Parietaria pensylvanica Pennsylvania pellitory

URDI Urtica dioica stinging nettle

Verbenaceae VEHA2 Verbena hastata swamp verbena

Violaceae VINU2 Viola nuttallii Nuttall's violet, yellow prairie 

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