National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

Plant Community Composition and Structure Monitoring 

for Fort Laramie National Historic Site

2011-2015 Summary Report

Natural Resource Report NPS/NGPN/NRR—2016/1149
ON THIS PAGE

Photograph of long-term monitoring plot PCM_007 at Fort Laramie National Historic Site, 2015.

Photograph courtesy of the National Park Service.

ON THE COVER

Long-term monitoring plot PCM-070 at Fort Laramie National Historic Site, 2014

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

Monitoring for Fort Laramie National Historic Site

2011-2015 Summary Report

Natural Resource Data Series NPS/NGPN/NRR—2016/1149

Isabel W. Ashton

Christopher J. Davis

National Park Service

Northern Great Plains Inventory & Monitoring Network

231 E. St. Joseph Street

Rapid City, SD 57701

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, 

Colorado, publishes a range of reports that address natural resource topics. These reports are of 

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This report is available in digital format from the Northern Great Plains Inventory & Monitoring 

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report in a format optimized for screen readers, please email irma@nps.gov.

Please cite this publication as:

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

Laramie National Historic Site: 2011-2015 summary report. Natural Resource Report 

NPS/NGPN/NRR—2016/1149. National Park Service, Fort Collins, Colorado.

NPS XXXXX NPS 375/131819 , Month 2016 , March 2016
iii

Contents 

Page

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

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

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

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

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

Methods..................................................................................................................................................3

Sample Design................................................................................................................................3

Plot Layout and Sampling ..............................................................................................................3

Data Management and Analysis.....................................................................................................5

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

Results and Discussion ..........................................................................................................................8

Status & Trends in Community Composition and Structure of FOLA Prairies.............................8

Species Richness, Diversity, and Evenness.............................................................................12

The Influence of Climate on Plant Community Structure and Diversity .....................................15

Rare Plants....................................................................................................................................16

The Status of Riparian Forests in FOLA......................................................................................17

Exotic Species in Riparian Forests..........................................................................................21

Conclusion ...........................................................................................................................................23

Literature Cited ....................................................................................................................................25

Appendix A: List of plant species found in 2011-2015 at FOLA........................................................27

Appendix B: Natural Resource Condition Maps of Exotic Species at FOLA.....................................33
iv

Figures 

Page

Figure 1. Map of Fort Laramie National Historic Site and plant community monitoring 

plots........................................................................................................................................................2

Figure 2. Long-term monitoring plot layout used for sampling vegetation in Fort Laramie 

National Historic Site.............................................................................................................................4

Figure 3. The Northern Great Plains Inventory & Monitoring vegetation crew used pointintercept (left 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 Fort Laramie National Historic Site (2011-2015). .................................................8

Figure 5. The average absolute cover of the 10 most common native (green) and exotic 

(red) plants recorded at Fort Laramie National Historic Site, 2011-2015. ............................................9

Figure 6. Trends in the relative cover of exotic plants, smooth brome, and cheatgrass in 

Fort Laramie National Historic Site from 2011-2015............................................................................9

Figure 7. A photograph of long-term monitoring plot FOLA_PCM_009 which has a 

moderate diversity of native plant species. ..........................................................................................13

Figure 8. Trends in native species richness and evenness in Fort Laramie National 

Historic Site, 2011-2015. .....................................................................................................................14

Figure 9.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. ...............................................................................................................................15

Figure 10. The total annual precipitation anomaly from 2000-2015 for Fort Laramie 

National Historic Site...........................................................................................................................16

Figure 11. Photograph of Emory’s sedge (Carex emoryi), a critically imperiled (S1) 

species in Wyoming found in plant community monitoring plots at Fort Laramie National 

Historic Site. ........................................................................................................................................17

Figure 12. Map of the plant community types within the riparian area in Fort Laramie 

National Historic Site and the location of 20 long-term monitoring plots (red). Vegetation 

classification is based on the NPS Vegetation Mapping Program report (TNC 1998)........................18

Figure 13.Size-class proportions of cottonwood (Populus) and willow (Salix) trees in 

riparian forests along the North Platte River in Nebraska in the 1850-1880s (bottom 

panels; from Johnson 1994) and along the Laramie and North Platte River in Fort 

Laramie National Historic Site (top panel)..........................................................................................21
v

Tables

Page

Table E-1. Natural resource condition summary table for plant communities in Fort 

Laramie National Historic Site (FOLA). .............................................................................................vii

Table 1. Exotic species surveyed for at Fort Laramie National Historic Site as part of the 

early detection and rapid response program within the Northern Great Plains Network. .....................5

Table 2. Definitions of rare species conservation status ranks.( S: state ranks, G: global 

ranks)......................................................................................................................................................6

Table 3. Key to the symbols used in the Natural Resource Condition Table........................................7

Table 4. Exotic plant species found in vegetation monitoring plots in 1986, 1998, 2000, 

and 2011-2015 .....................................................................................................................................10

Table 5. Average plant species richness in monitoring plots at Fort Laramie National 

Historic Site from 2011 to 2015...........................................................................................................12

Table 6. Rare species occurrence in Fort Laramie National Historic Site from 1998-2015 ...............17

Table 7. Tree and tall shrub occurrence in 2014 at 20 plots in Fort Laramie National 

Historic Site. ........................................................................................................................................19

Table 8. Tree basal area and density by size class for dominant tree and shrub species in 

the riparian forest of Fort Laramie National Historic Site ...................................................................20

Table 9. Exotic species detected in 20 riparian plots in Fort Laramie National Historic 

Site and their corresponding abundance, cover class, and estimated percent cover. ...........................22

Table 10. Natural resource condition summary table for plant communities in Fort 

Laramie National Historic Site (FOLA). .............................................................................................24
vi

Executive Summary

The Northern Great Plains Inventory & Monitoring Program has been monitoring vegetation in Fort 

Laramie National Historic Site since 2011. This report summarizes those data from 30 locations 

monitored from 2011-2015. We use these data to explore status and trends in upland and riparian 

plant communities and the occurrence of rare plants. A summary of the current condition (2011-

2015) and short-term trends in plant communities at Fort Laramie is found in Table E-1. 

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

grasslands (species richness, cover, and diversity) and how has this changed from 2011-

2015? 

FOLA plays a vital role in protecting and managing some of the last remnants of native prairie in 

the area. Native grasses, such western wheatgrass and needle and thread, are abundant in some 

sites, but many areas have a high cover of exotic plants. Native plant diversity is at a low level 

compared to other grasslands in the region (Table 10), but diversity is spatially variable. 

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

threatened by the increasing cover of annual bromes (Table 10). Annual bromes are the most 

abundant exotic plant species in FOLA and present the largest challenge to FOLA. Continued 

control efforts will be necessary to maintain native prairie within FOLA. 

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

Native diversity tended to increase in wet years. The large variability in the climate of FOLA has 

made it difficult to discern strong patterns linking temperature, precipitation, and plant 

community structure (e.g. exotic cover, diversity). A longer time series of vegetation data will 

make it easier to elucidate trends in the future. 

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

We identified 1 rare plant species in FOLA between 2011 and 2015. This plant is found in such 

low abundance and in such few plots, it will take many years to determine any trends in rare plant 

cover. Since to our knowledge, the last rare plant survey was completed in 2004, we recommend 

targeted surveys of rare plant species be considered when funds are available.

4. What is the composition and structure of riparian forests at FOLA?

The riparian forest in FOLA is a fairly diverse assemblage of cottonwood, willow species, honey 

locust (Gleditsia triacanthos), and green ash. Cottonwoods of all age classes are present (Table 

10). Exotic species are common in the understory of the riparian forest, and the current control 

measures may help reduce their abundance in the future. Young cottonwoods have successful 

established in 40% of the monitoring plots. This suggests that the successional transition to green 

ash and box elder dominated forests may be slow. 
vii

Table E-1. Natural resource condition summary table for plant communities in Fort Laramie National 

Historic Site (FOLA).

Indicator of 

Condition

Specific 

Measures

2014

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)

4.3 ± 0.3

species

3-15 

species (1)

FOLA plays a vital role in 

protecting and managing 

some of the last remnants of 

native prairie and riparian 

forests in the region. The park 

is characterized by low native 

species richness, which 

should be a moderate 

concern. Native species 

richness and evenness vary 

from year to year, but there is

not a significant trend since 

monitoring began in 2011. 

Native evenness 

(point-intercept 

transects)

0.75 ± 0.02 To be 

determined

Exotic Plant 

Early 

Detection 

and 

Management

Relative cover of 

exotic species 45.3 ± 4.5 % < 10% 

cover

The sites in FOLA had a high 

cover of exotic species. None 

of the sites had <10% cover

of exotic plants. Cheatgrass 

was the most abundant exotic 

species, and more research 

on effective management 

strategies is greatly needed.

Annual brome 

cover 

25.9 ± 4.4% < 10% 

cover

Riparian 

Forest

Plains 

cottonwood 

stand seral 

stage 

Lateintermediate 

seral stage

Mixture of 

seral 

stages (2)

The riparian forests of FOLA 

are currently a mosaic of 

areas dominated by willow, 

cottonwood, and ash with an 

understory of many exotic 

plants. As cottonwood forests 

age in FOLA, green ash and 

box elder are likely to become 

more dominant. Eight of 20 

plots had evidence of young 

cottonwoods and a majority of 

plots had large densities of 

other native tree and shrub 

seedlings in the understory. 

Forest surveys will be 

repeated every 5 years in 

FOLA and this will allow us to 

detect trends in condition. 

Percent of 20 

riparian plots 

with native 

deciduous 

seedlings

70% To be 

determined

References, Notes, and Data Sources: 1. Symstad and Jonas (2014) 2. Uresk (2015) 
viii

Acknowledgments 

We thank all 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 FOLA, 

particularly M. Evans, for help in the field. The 2011-2015 NGPN vegetation field crews collected 

all the data included in this report. Thanks to A. Weaver for assistance with maps. Comments from 

M. Neubert, M. Evans, and J. Handley improved this report. 
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. 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); 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. Long-term 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. 

Fort Laramie National Historic Site (FOLA), established in 1938 to protect and preserve the wellknown military post, covers 833 acres on the boundary of the northern mixed-grass and short-grass 

prairie region (Lauenroth et al. 1999). The park is a mosaic of disturbed old-fields, riparian forests, 

and native prairie and is host to 376 plant species (Heidel 2004). The Northern Great Plains 

Inventory & Monitoring Program (NGPN) began vegetation monitoring at FOLA in 2011 (Ashton et 

al. 2012). A total of 30 plots were established in FOLA (Figure 1); 15 plots were randomly 

distributed throughout the park to better study herbaceous plant communities, 15 plots were 

established in the riparian forest to assess forest condition, and 5 plots were used to study both forest 

condition and herbaceous plant communities. 

Using 5 years of plant community monitoring data in FOLA, we explore the following questions: 

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

(species richness, cover, and diversity) and how has this changed from 2011-2015? 

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

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

4. What is the composition and structure of riparian forests at FOLA?
2

Figure 1. Map of Fort Laramie National Historic Site and plant community monitoring plots. The blue area 

represents the riparian area of the park. There are three different types of monitoring plots: upland 

herbaceous (red), riparian woody plots (yellow)
3

Methods 

The NGPN Plant Community Composition and Structure Monitoring Protocol (Symstad et al. 2012b, 

a) was used to monitor long-term vegetation plots at FOLA. Below, we briefly describe the general 

approach but for those interested in more detail please see Symstad et al. 2012a, available at 

http://science.nature.nps.gov/im/units/ngpn/monitor/plants.cfm. 

Sample Design

We implemented a survey to monitor plant community structure and composition in FOLA using a 

spatially balanced probability design (Generalized Random Tessellation Stratified [GRTS]; Stevens 

and Olsen 2003, 2004). Using a GRTS design, we selected 15 randomly located sites within FOLA 

(Figure 1). We visited 6 sites every year, and after five years (2015) we had visited all 15 sites twice

(or attempted to). Visits were made during the first week of June. 

In 2014, we used the GRTS design to select 20 plots within riparian forest communities at FOLA. 

The riparian corridor was delineated in the field and defined as everything below the highest river 

terrace (Figure 1). It comprised approximately 29% of the park. Four of the previously selected plots 

fell within the riparian forest, so these were used (dual plots) and 16 new plots were selected (Figure 

1).

Plot Layout and Sampling

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, herb-layer 

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

a point-intercept method (Figure 3). Species richness data from the point-intercept method were 

supplemented 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). 

When woody species were also present (e.g. the plots in the riparian area), tree regeneration and tall 

shrub density data were collected within a 10 m radius subplot centered in the larger 50 m x 20 m 

plot (Figure 2). Trees with diameter at breast height (DBH) > 15 cm, located within the entire 0.1 ha 

plot, were mapped and tagged. For each tree, the species, DBH, status, and condition (e.g., leafdiscoloration, insect-damaged, etc.) were recorded. 

To increase the number of forested plots and our understanding of riparian forest condition, NGPN 

completed a survey in the last week of August 2014 using a set of 20 forested sites. In this case, 

seedlings and poles were measured as described above, but larger trees (DBH >15cm) were not

tagged and only measured within the 10 m radius subplot. Dead and downed woody fuel load data 

were collected at these forested plots on two perpendicular, 100 ft (30.49 m) transects with midpoints 

at the center of the plot (Figure 2), following Brown’s Line methods (Brown 1974, Brown et al. 

1982). The fuels data were not reported because grasses dominated the fuel layer. This forest survey 

will be repeated every 5 years (e.g. 2019, 2024, etc.).
4

Figure 2. Long-term monitoring plot layout used for sampling vegetation in Fort Laramie National Historic 

Site.

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

panel) and quadrats (right panel) to document plant diversity and abundance. These photographs were 

taken at Scotts Bluff National Monument, but the same methods were used at Fort Laramie NHS. 
5

At all plots, we surveyed the area for common disturbances and target species of interest to the park. 

Common disturbances included such things as flooding, rodent mounds, and animal trails. 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 park and cause significant ecological impacts (Table 

1). These species were chosen in collaboration with the Midwest Invasive Plant Network, the Exotic 

Plant Management Team, park 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 Fort Laramie National Historic Site 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

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. 
6

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., subshrub, forb) were based on definitions for each species from the USDA 

Plants Database (USDA-NRCS 2015). The conservation status ranks of plant species in FOLA were 

based on the species list maintained by the Wyoming Natural Diversity Database (WYNDD), and for 

the purpose of this report, a species was considered rare if it was S1, S2, or S3. See Table 2 for a 

detailed description of conservation ranks.

Table 2. Definitions of rare species conservation status ranks.( S: state ranks, G: global 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 from the state/province.

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.

S3G3 Vulnerable Due to a restricted range, relatively few populations (often 80 or fewer), recent 

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

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.

We measured diversity at the plots in 2 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. It ranges between 0 and 1; values near 0 indicate 

dominance by a single species and values near 1 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 Old Fort Laramie, WY weather station were downloaded from NOAA’s online 

database (NOAA 2015). 
7

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.

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: 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 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”, or 

TBD, 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
8

Results and Discussion

Status & Trends in Community Composition and Structure of FOLA Prairies 

We found 200 plant species from 2011-2015 at FOLA (Appendix A). Graminoids, which includes 

grasses, sedges, and rushes, accounted for most of the vegetative cover at FOLA, but forbs, shrubs 

and subshrubs (defined as a low-growing shrub usually under 0.5m) were also present (Figure 4). We 

found 50 exotic plant species at FOLA, and 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 Fort Laramie National Historic Site (2011-2015). 

Western wheatgrass (Pascopyrum smithii), needle and thread (Heterostipa comata), sand dropseed 

(Sporobulus cryptandrus) and blue grama (Bouteloua gracilis) were the most abundant native grasses 

and averaged between 5 and 15% absolute cover (Figure 5). Cheatgrass (Bromus tectorum) and 

smooth brome (B. inermis) were the most pervasive exotics at FOLA. Cheatgrass is a Eurasian, 

annual grass that has been a part of the Northern Great Plains landscape for more than a century, but 

its invasion in the region has accelerated 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 2011-2015, the 

average relative cover of cheatgrass was 25.9 ± 4.4% (mean ± standard error; Figure 6). Smooth 

brome is related to cheatgrass, but differs in that it is a perennial grass that was widely planted for 

forage and along roads. Smooth brome can form monocultures and reduce native plant abundance 

and diversity, and this may be due in part to its ability alter soil nutrient dynamics (Vinton and 

Goergen 2006). While smooth brome and cheatgrass were the most abundant, many other exotic 

species were found yielding an average cover of all exotic species to be 45 ± 4.5 %. Maps of 

cheatgrass and smooth brome occurrence can be found in Appendix B.
9

Figure 5. The average absolute cover of the 10 most common native (green) and exotic (red) plants 

recorded at Fort Laramie National Historic Site, 2011-2015. Bars represent means ± standard errors.

Figure 6. Trends in the relative cover of exotic plants, smooth brome, and cheatgrass in Fort Laramie 

National Historic Site from 2011-2015. Points represent means ± standard errors, n=6. 

It is difficult to distinguish trends from a 5 year dataset, but historical vegetation data from FOLA 

can provide some evidence of whether exotic cover has changed over time. The vegetation 

management plan for FOLA (Jones and Tebben 2002) summarized the proportion of plots where 

exotic species were found in three different surveys completed in 1986 (Olmstead and Perez), 1998

(TNC), and 2000 (Fertig). Table 4 summarizes the data from Jones and Tebben (2002) and compares 

it to the proportion of plots where exotic species were found by NGPN. Data is represented as the 

proportions of plots survey with the target species, because the sample size varied across the years. 
10

Many of the exotic species we encountered were present in the park in 1986, including cheatgrass, 

quackgrass, and kochia, at a similar rate as seen in 2011-2015. Since 1986 and 1998, the proportion 

of plots infested with smooth brome, crested wheatgrass, Canada thistle, prickly lettuce, and prickly 

Russian thistle has close to doubled. Future monitoring will allow us to better quantify these 

increases and determine whether they are statistically significant. 

Table 4. Exotic plant species found in vegetation monitoring plots in 1986, 1998, 2000, and 2011-2015. 

The historic data were copied from Jones and Tebben 2002. The 2011-2015 data were from the NGPN 

monitoring plots. The values represent the percent of plots where the exotic species was present. An “X” 

indicates presence within the park. 

Common name Scientific Name

1986

(n=16)

1998

(n=32)

2000 (based 

on species list 

for park)

2011-2015

(n=15 or 

* 30 plots)

crested wheatgrass † Agropyron cristatum 6 13

creeping bentgrass Agrostis stolonifera X

pale madwort Alyssum alyssoides 6

desert madwort Alyssum desertorum 47

mat amaranth Amaranthus blitoides 13

Absinthium * Artemisia absinthium 3

biennial wormwood Artemisia biennis 20

smooth brome † Bromus inermis 34 X 67

Japanese brome * Bromus japonicus 22 X 27

Cheatgrass * Bromus tectorum 56 53 X 57

littlepod false flax † Camelina microcarpa 9 47

shepard's purse Capsella bursa-pastoris X

musk thistle Carduus nutans X

lambsquarters Chenopodium album 7

Canada thistle * † Cirsium arvense 16 X 30

bull thistle Cirsium vulgare 7

field bindweed Convolvulus arvensis X 27

gypsyflower* Cynoglossum officinale 20

herb sophia Descurainia sophia X 67

barnyardgrass Echinochloa crus-galli 13

Russian olive* Elaeagnus angustifolia X 7

quackgrass Elymus repens 38 6 X 33

stinkgrass Eragrostis cilianensis X

roundfruit rush Juncus compressus 13

burningbush, kochia * † Kochia scoparia 19 X 33

prickly lettuce † Lactuca serriola 19 6 X 80

* Indicates 2011-2015 species that were surveyed in 30 plots (15 plots were typically searched).

† Those species, also in bold, that appear in a substantially greater proportion of plots in recent 

years.
11

Table 4 (continued). Exotic plant species found in vegetation monitoring plots in 1986, 1998, 2000, and 

2011-2015. The historic data were copied from Jones and Tebben 2002. The 2011-2015 data were from 

the NGPN monitoring plots. The values represent the percent of plots where the exotic species was 

present. An “X” indicates presence within the park. 

Common name Scientific Name

1986

(n=16)

1998

(n=32)

2000 (based 

on species list 

for park)

2011-2015

(n=15 or 

* 30 plots)

field pepperweed Lepidium campestre 7

clasping pepperweed Lepidium perfoliatum X

butter and eggs Linaria vulgaris X

perennial ryegrass Lolium perenne X

black medick Medicago lupulina X 27

alfalfa Medicago sativa 13

yellow sweetclover* † Melilotus officinalis 6 X 43

catnip Nepeta cataria 3 X 20

Scotch cottonthistle * Onopordum acanthium X 37

pearl millet Pennisetum glaucum X

spotted ladysthumb Persicaria maculosa X 7

reed canarygrass * Phalaris arundinacea 10

timothy Phleum pratense 25 13

common plantain Plantago major X

Canada bluegrass Poa compressa 13

Kentucky bluegrass † Poa pratensis 25 19 X 40

curlytop knotweed Polygonum lapathifolium X

annual rabbitsfoot grass Polypogon monspeliensis X

purslane Portulaca oleracea X

curly dock Rumex crispus X 13

narrowleaf dock Rumex stenophyllus X

crack willow Salix fragilis 7

slender Russian thistle Salsola collina X 13

prickly Russian thistle * † Salsola tragus 31 X 70

green bristlegrass Setaria viridis 13 X 7

tall tumblemustard * † Sisymbrium altissimum 9 X 47

field sowthistle Sonchus arvensis X

five-stamen tamarisk * Tamarix chinensis X 3

common dandelion † Taraxacum officinale 6 6 60

field pennycress Thlaspi arvense 9 13

yellow salsify † Tragopogon dubius 38 73

* Indicates 2011-2015 species that were surveyed in 30 plots (15 plots were typically searched).

† Those species, also in bold, that appear in a substantially greater proportion of plots in recent 

years.
12

Table 4 (continued). Exotic plant species found in vegetation monitoring plots in 1986, 1998, 2000, and 

2011-2015. The historic data were copied from Jones and Tebben 2002. The 2011-2015 data were from 

the NGPN monitoring plots. The values represent the percent of plots where the exotic species was 

present. An “X” indicates presence within the park. 

Common name Scientific Name

1986

(n=16)

1998

(n=32)

2000 (based 

on species list 

for park)

2011-2015

(n=15 or 

* 30 plots)

puncture vine Tribulus terrestris X

strawberry clover Trifolium fragiferum X 20

narrowleaf cattail Typha angustifolia 7

common mullein * Verbascum thapsus X 30

* Indicates 2011-2015 species that were surveyed in 30 plots (15 plots were typically searched).

† Those species, also in bold, that appear in a substantially greater proportion of plots in recent 

years.

Species Richness, Diversity, and Evenness 

One of the ways for the NPS to measure effectiveness at the mission to ‘preserve ecological 

integrity’ is to examine trends in native plant diversity and evenness within their boundaries. Average 

species richness has been measured by point-intercept and in 1 m2 and 10 m2 quadrats since 2011 

(Table 5).

Table 5. Average plant species richness in monitoring plots at Fort Laramie National Historic Site from 

2011 to 2015. Values represent means ± standard errors. 

Attribute Point-intercept 1 m2 quadrats 10 m2 quadrats

Species richness 14 ± 1.4 7 ± 0.4 12 ± 0.7

Native species richness 9 ± 1.1 4 ± 0.3 7 ± 0.6

Exotic species richness 5 ± 0.6 3 ± 0.2 4 ± 0.3

Graminoid species richness 6 ± 0.5 3 ± 0.2 4 ± 0.2

Forb species richness 6 ± 0.8 3 ± 0.3 6 ± 0.5

While there was some variation across sites, the plots we visited in FOLA tended to have a low 

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, prairie dog disturbance, and 

weather fluctuations (Symstad and Jonas 2011). In FOLA, there is also a mixed history of past landuse practices that have affected current species richness. While it is difficult to define a reference 

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 vary between 3 and 15 species per square meter over the course of 30 years (Symstad 

and Jonas 2014). Compared to this, FOLA is within the natural range (4 species) but is on the low 

end of the range. Some sites, such as PCM_002, 003, 070, and 068 (Figure 1), fall below this 
13

reference condition. In contrast, the most diverse plots, FOLA_PCM_069, 011, 09 (Figure 7) have 

greater than 7 native species per square meter. 

Figure 7. A photograph of long-term monitoring plot FOLA_PCM_009 which has a moderate diversity of 

native plant species. 

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

richness in 1m2 quadrats was consistent from 2011 to 2015 and ranged from a low in 2012 of 3.2 ± 

0.64 (a drought year) to a high of 4.8 ± 1.02 in 2011 (a wet year). From 2011-2015, we recorded 

between 1 and 20 native species along the point-intercept transects (Figure 8: top). There was no 

trend in Peilou’s Index of Evenness, J’, which measures how even abundances are across taxa 

(Figure 8). There is a great deal of variation in species richness and evenness across sites within the 

park (dashed lines in Figure 8represent the maximum and minimum values) which makes detecting 

long-term trends difficult. 
14

Figure 8. Trends in native species richness and evenness in Fort Laramie National Historic Site, 2011-

2015. Data are means ± one standard error. The dashed line indicates the range of values across the 

entire data set. 

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

(D'Antonio and Vitousek 2003). In the 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 high cover of annual bromes in FOLA persists or increases, we expect there will be a 

corresponding decline in native species richness over time. 
15

Figure 9.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. 

Disturbance from grazing, flooding, and humans can affect plant community structure and 

composition in prairie. We measured the approximate area affected by natural and human 

disturbances at each site we visited between 2011-2015. The most common disturbance was from 

small rodents, but there was also evidence of deer trails, grazing, and flooding. 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. 

The Influence of Climate on Plant Community Structure and Diversity

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, Old Fort Laramie, ranged from average 

minimum monthly temperatures in December of 10.8° F to maximum monthly July temperatures of 

88.4° F (based on 1981-2010). The 30-year normal annual precipitation totals 15.79 inches. Annual 

precipitation at FOLA in 2011-2015 was variable and ranged between 6.2 and 17.0 inches, in 2012 

and 2015, respectively. There were dry years in the early 2000s, 2006-2008, and in 2012-2013 

(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 increases in summer precipitation (Yang et al. 

1998). 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).
16

Figure 10. The total annual precipitation anomaly from 2000-2015 for Fort Laramie National Historic Site. 

Positive values (blue) represent years wetter than and negative values (red) are drier than the 1981-2010 

normal. The anomaly is measured in inches and based on data from a nearby weather station. 

A longer time series of vegetation data is needed to elucidate trends and correlations with climate

because of the large variation in annual temperature and precipitation patterns at FOLA. It is very 

likely that the large drought in 2012 contributed to the declines in both native species richness 

(Figure 8) and exotic species cover seen in that year (Figure 6). Native species richness and exotic 

cover increased in the subsequent wetter years. 

Rare Plants 

A review of rare plant observations in FOLA was completed in 2000 (Fertig 2000) and a floristic 

inventory of FOLA was conducted in 2004 (Heidel 2004). While repeating a floristic inventory and 

locating rare species was not the focus of this study, two rare plant species were observed within 

vegetation monitoring plots at FOLA. 

We identified one rare sedge species, Emory’s sedge (Carex emoryi; Figure 11) in FOLA between 

1998 and 2015 (Table 6). Emory’s sedge was observed once in 2013 in a single plot. It is critically 

imperiled (S1) in the state of Wyoming, but is globally secure (G5); the result of the species existing

on the edge of their global distribution range in Fort Laramie National Historic Site.
17

Figure 11. Photograph of Emory’s sedge (Carex emoryi), a critically imperiled (S1) species in Wyoming

found in plant community monitoring plots at Fort Laramie National Historic Site.

Table 6. Rare species occurrence in Fort Laramie National Historic Site from 1998-2015. Status ranks are 

based on Wyoming Natural Diversity Database 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 (%)

Carex emoryi Emory’s sedge S1 G5 1 0.05

The Status of Riparian Forests in FOLA

In 2014, the NGPN established 20 plots in the forested area along the Laramie River to monitor 

status and trends in lowland riparian forest condition (Figure 12). The 2014 data provide a baseline 

dataset for future surveys; we plan to revisit the same plots every five years (e.g. 2019, 2024, etc.). 

The riparian lowland forest in Fort Laramie NHS is small (~234 acres), and comprises about 28% of 

the park. The forest is fairly open and dominated by plains cottonwood (Populus deltoides), 

narrowleaf willow (Salix exiqua), and bare sand flats (TNC 1998) The 20 monitoring plots were 

chosen randomly within the riparian corridor and most fall within the cottonwood community type.
18

Figure 12. Map of the plant community types within the riparian area in Fort Laramie National Historic 

Site and the location of 20 long-term monitoring plots (red). Vegetation classification is based on the NPS 

Vegetation Mapping Program report (TNC 1998).

In 2014, we found 9 species of tree or tall shrub in 18 riparian forest plots at FOLA (Table 7); 2 plots

(PCM-083 and 074) did not have any tree or tall shrub species present. Our data were consistent with 

the 1990’s vegetation map and the most common tree species were cottonwood, peachleaf willow, 

and green ash (Table 7). Mature cottonwood trees were found in higher average densities than other 

species (Table 8). Younger cottonwood trees were also fairly common, but seedlings were found in 

only 4 sites (Table 7; Sites: 066, 069, 073, 087). Mature green ash (Fraxinius pennsylvanica) trees 

were found in only 5 sites (Table 7), and the average density was less than half that of cottonwood 

trees (Table 8). As riparian forests along the North Platte age, cottonwood and willow forests are 

most often replaced with green ash and box elder (Acer negundo)forests (Johnson 1994). In 2014, we 

found numerous poles and seedlings of green ash, but box elder is still uncommon. Future monitoring 

is needed to determine if these cottonwood and willow stands will soon become dominated by green 

ash.
19

Table 7. Tree and tall shrub occurrence in 2014 at 20 plots in Fort Laramie National Historic Site.

Species Name Common Name

Number of plots 

with trees

(DBH > 15 cm)

Number of plots 

with poles

(2.5 cm ≤ DBH ≤ 15 

cm)

Number of plots 

with seedlings 

(height < 137 cm)

Populus deltoides plains cottonwood 12 8 4

Salix amygdaloides peachleaf willow 6 2 2

Fraxinus pennsylvanica green ash 5 3 9

Gleditsia triacanthos honey locust 1 1 3

Salix fragilis (exotic) crack willow 1 0 1

Acer negundo boxelder 0 1 1

Prunus virginiana chokecherry 0 1 3

Salix exigua narrowleaf willow 0 4 6

Shepherdia argentea silver buffaloberry 0 2 2

Since the mid to late 1880’s, riparian forests have expanded along the North Platte as a result of the 

construction of dams and the resulting changes in water flow (Johnson 1994). Willows and 

cottonwoods have thrived because low flows in June allow for sufficient recruitment and lower peak 

flows and reduced ice scour reduce tree mortality. We compared our 2014 data to forest composition 

in the late 1850s to late 1880s (copied from Johnson 1994). The data from the 1850s to late1880s 

encompasses a greater area and thus a greater number of total trees, but the shape of the histogram 

reveals that cottonwood and willow age structure in 2014 is fairly similar to the past (Figure 13). 

This suggests that new cottonwoods are being established. There were relatively fewer willow trees 

in the 10 cm size class in 2014 than the past. It is unclear, however, if the establishment of young 

cottonwoods is sufficient to maintain a cottonwood forest in this area. Jones (2007) conducted a 

survey of riparian forests in Fort Laramie NHS in 2006. He mapped cottonwood seedling and sapling 

patches along the entire length of the riparian corridor. He found 33 seedlings patches and numerous 

saplings, but many of the seedlings were root sprouts and it was unclear if these patches were being 

established frequently enough to maintain cottonwood forests (Jones 2007). Since 2006, there have

been a few flood years (e.g. 2010 and 2014) that have likely allowed cottonwood seedlings to 

germinate and persist. A metric developed to classify cottonwood stand successional status indicates 

that FOLA riparian areas are primarily composed of late-intermediate seral stage cottonwood stands, 

indicating at least some cottonwood seedling recruitment is occurring in these plots (Uresk 2015).We 

plan to resurvey the FOLA riparian plots in 2019 and at that time, we may be able to determine 

whether cottonwoods are persisting and document effects of the large flood event in 2015. 

If the goal is to maintain cottonwood forests and willows along this section of the Laramie and Platte 

Rivers, management interventions such as watering, bank stabilization, and fencing could ensure that 

the young trees which are currently present survive to maturity. 
20

Table 8. Tree basal area and density by size class for dominant tree and shrub species in the riparian 

forest of Fort Laramie National Historic Site. (Values: mean across 20 riparian forest monitoring ±

standard error of the mean)

Species Indicator Value

Plains cottonwood

Basal Area (m2/ ha) 7.18 ± 2.15

Tree Density (stems/ha) 87.54 ± 30.73

Pole Density (stems/ha) 28.66 ± 11.06

Seedling Density (stems/ha) 784.53 ± 544.99

Snag Density (stems/ha) 20.90 ± 14.78

Green ash

Basal Area (m2/ ha) 5.86 ± 4.52

Tree Density (stems/ha) 33.94 ± 21.20

Pole Density (stems/ha) 15.92 ± 9.94

Seedling Density (stems/ha) 36.60 ± 11.14

Snag Density (stems/ha) 20.70 ± 14.29

Willow species

Basal Area (m2/ ha) 3.89 ± 2.70

Tree Density (stems/ha) 19.24 ± 10.47

Pole Density (stems/ha) 35.03 ± 15.65

Seedling Density (stems/ha) 4048.38 ± 1618.05

Snag Density (stems/ha) 9.55 ± 5.71

Honey locust

Basal Area (m2/ ha) 0.01 ± 0.01

Tree Density (stems/ha) 7.96 ± 7.96

Pole Density (stems/ha) 7.96 ± 7.96

Seedling Density (stems/ha) 224.38 ± 159.38

Snag Density (stems/ha) 4.78 ± 3.48

Deciduous shrubs

Basal Area (m2/ ha) 0.09 ± 0.06

Tree Density (stems/ha) 0.00 ± 0.00

Pole Density (stems/ha) 35.03 ± 28.76

Seedling Density (stems/ha) 1940.38 ± 1537.88

Snag Density (stems/ha) 4.78 ± 3.48

Boxelder

Basal Area (m2/ ha) 0.45 ± 0.45

Tree Density (stems/ha) 0.00 ± 0.00

Pole Density (stems/ha) 1.59 ± 1.59

Seedling Density (stems/ha) 1.59 ± 1.59

Snag Density (stems/ha) 0.00 ± 0.00

Crack willow

(exotic)

Basal Area (m2/ ha) 0.03 ± 0.03

Tree Density (stems/ha) 0.40 ± 0.40

Pole Density (stems/ha) 0.00 ± 0.00

Seedling Density (stems/ha) 7.96 ± 7.96

Snag Density (stems/ha) 0.00 ± 0.00
21

Figure 13.Size-class proportions of cottonwood (Populus) and willow (Salix) trees in riparian forests along 

the North Platte River in Nebraska in the 1850-1880s (bottom panels; from Johnson 1994) and along the 

Laramie and North Platte River in Fort Laramie National Historic Site (top panel). Labels in wedges 

indicate diameter-at-breast-height (DBH) class categories, and each number is the upper limit of that 

range (e.g. diameter class 10 includes individuals >5 cm and ≤10 cm). 

Exotic Species in Riparian Forests

The understory of the riparian forests in FOLA is a mix of native and exotic grasses and shrubs. The 

focus of the 2014 survey was woody species, but field crews also surveyed for the presence of exotic 

species of management concern (e.g. musk thistle, Russian olive) and potential early invaders (Table 

1). Smooth brome (B. inermis) is widespread in this area, but the 2014 survey did not include it, 

probably because it was assumed to be abundant. Canada thistle and prickly Russian thistle were

each found in half of the 20 plots (Table 9). On average, 2 exotic species were found in each plot. We 

did not find any early detection species. Where Japanese brome, reed canarygrass, and yellow 

sweetclover were found, they were in very high abundance (>25% cover)

The NGP Exotic Plant Management Team (EMPT) is aware of the high density and cover of exotic 

plants in the riparian forest and much of their control efforts were concentrated in this area during the 

2015 field season (Hauk 2016). The EPMT focused on the control of musk thistle, Canada thistle, 

and Scotch cottonthistle. They have also continued to remove Russian olive and tamarisk as they are 

found to keep their spread under control. 
22

Table 9. Exotic species detected in 20 riparian plots in Fort Laramie National Historic Site and their 

corresponding abundance, cover class, and estimated percent cover. 

Species Common Name

Number 

of Plots

Average 

Cover Class

Estimated 

Cover (%)

Cirsium arvense Canada thistle 10 2.50 ± 0.17 1-5

Salsola tragus prickly Russian thistle 10 3.20 ± 0.39 1-5

Onopordum acanthium Scotch cottonthistle 8 2.25 ± 0.25 <5

Verbascum thapsus common mullein 8 2.00 ± 0.19 <1

Cynoglossum officinale houndstongue 5 2.20 ± 0.37 <5

Bromus japonicus Japanese brome 3 5.00 ± 0.00 >25%

Bromus tectorum cheatgrass 3 4.34 ± 0.67 5-25

Elaeagnus angustifolia Russian olive 2 2.00 ± 0.00 <1

Kochia scoparia burningbush; kochia 2 2.50 ± 0.50 <5

Artemisia absinthium absinth wormwood 1 2.00 ± 0.00 <1

Melilotus officinalis yellow sweetclover 1 5.00 ± 0.00 >25%

Phalaris arundinacea reed canarygrass 1 5.00 ± 0.00 >25%

Sisymbrium altissimum tall tumblemustard 1 3.00 ± 0.00 1-5

Tamarix chinensis five-stamen tamarisk 1 1.00 ± 0.00 <1
23

Conclusion

The Northern Great Plains Inventory & Monitoring Program has been monitoring vegetation in Fort 

Laramie National Historic Site for 5 years. This report summarizes data from 30 locations from 

2011-2015. 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 10) 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 FOLA

grasslands (species richness, cover, and diversity) and how has this changed from 2011-

2015? 

FOLA plays a vital role in protecting and managing some of the last remnants of native prairie in 

the area. Native grasses, such western wheatgrass and needle and thread, are abundant in some 

sites, but many areas have a high cover of exotic plants. Native plant diversity is at a low level 

compared to other grasslands in the region (Table 10), but diversity is spatially variable. 

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

threatened by the increasing cover of annual bromes (Table 10). Annual bromes are the most 

abundant exotic plant species in FOLA and present the largest challenge to FOLA. Continued 

control efforts will be necessary to maintain native prairie within FOLA. 

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

Native diversity tended to increase in wet years. The large variability in FOLA’s climate has 

made it difficult to discern strong patterns linking temperature, precipitation, and plant 

community structure (e.g. exotic cover, diversity). A longer time series of vegetation data will 

make it easier to elucidate trends in the future. 

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

We identified 1 rare plant species in FOLA between 2011 and 2015. This plant is found in such 

low abundance and in such few plots, it will take many years to determine any trends in rare plant 

cover. Since to our knowledge, the last rare plant survey was completed in 2004, we recommend 

targeted surveys of individual rare plant species be considered when funds are available.

4. What is the composition and structure of riparian forests at FOLA?

The riparian forest in FOLA is a fairly diverse assemblage of cottonwood, willow species, honey 

locust (Gleditsia triacanthos), and green ash. Cottonwoods of all age classes are present (Table 

10). Exotic species are common in the understory of the riparian forest, and the current control 

measures may help reduce their abundance in the future. Young cottonwoods have successful 

established in 40% of the monitoring plots. This suggests that the successional transition to green 

ash and box elder dominated forests may be slow. 
24

Table 10. Natural resource condition summary table for plant communities in Fort Laramie National 

Historic Site (FOLA).

Indicator of 

Condition

Specific 

Measures

2014

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)

4.3 ± 0.3

species

3-15 

species 

FOLA plays a vital role in 

protecting and managing 

some of the last remnants of 

native prairie and riparian 

forests in the region. The park 

is characterized by low native 

species richness which should 

be a moderate concern.

Native species richness and 

evenness vary from year to 

year, but there is not a 

significant trend since 

monitoring began in 2011. 

Native evenness 

(point-intercept 

transects)

0.75 ± 0.02 To be 

determined

Exotic Plant 

Early 

Detection 

and 

Management

Relative cover of 

exotic species 45.3 ± 4.5 % < 10% 

cover

The sites in FOLA had a high 

cover of exotic species. None 

of the sites had <10% cover

of exotic plants. Cheatgrass 

was the most abundant exotic 

species, and more research 

on effective management 

strategies is greatly needed.

Annual brome 

cover 

25.9 ± 4.4% < 10% 

cover

Riparian 

Forest

Plains 

cottonwood 

stand seral 

stage 

Lateintermediate 

seral stage

Mixture of 

seral 

stages (2)

The riparian forests of FOLA 

are currently a mosaic of 

areas dominated by willow, 

cottonwood, and ash with an 

understory of many exotic 

plants. As cottonwood forests 

age in FOLA, green ash and 

box elder are likely to become 

more dominant. Eight of 20 

plots had evidence of young 

cottonwoods and a majority of 

plots had large densities of 

other native tree and shrub 

seedlings in the understory. 

Forest surveys will be 

repeated every 5 years in 

FOLA and this will allow us to 

detect trends in condition. 

Percent of 20 

riparian plots 

with native 

deciduous 

seedlings

70% To be 

determined

References, Notes, and Data Sources: 1. Symstad and Jonas (2014) 2. Uresk (2015) 
25

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Appendix A: List of plant species found in 2011-2015 at FOLA

Family Code Scientific Name Common Name Exotic Rare

Aceraceae ACNE2 Acer negundo boxelder

Agavaceae YUGL Yucca glauca soapweed yucca

Amaranthaceae AMBL Amaranthus blitoides mat amaranth X

Anacardiaceae RHTR Rhus trilobata skunkbush sumac

TORY Toxicodendron rydbergii western poison ivy

Apiaceae LOFO Lomatium foeniculaceum desert biscuitroot

Apocynaceae APCA Apocynum cannabinum Indianhemp

Asclepiadaceae ASSP Asclepias speciosa showy milkweed

ASVI Asclepias viridiflora green comet milkweed

Asteraceae

AMPS Ambrosia psilostachya Cuman ragweed

AMTO3 Ambrosia tomentosa skeletonleaf burr ragweed

ARAB3 Artemisia absinthium absinth wormwood X

ARBI2 Artemisia biennis biennial sagewort X

ARCA12 Artemisia campestris field sagewort

ARDR4 Artemisia dracunculus tarragon

ARFI2 Artemisia filifolia sand sagebrush

ARFR4 Artemisia frigida fringed sagewort

ARLU Artemisia ludoviciana white sagebrush

BIFR Bidens frondosa devil's beggartick

BITR Bidens tripartita threelobe beggarticks

CIAR4 Cirsium arvense Canada thistle X

CICA11 Cirsium canescens prairie thistle X

CIFL Cirsium flodmanii Flodman's thistle

CIVU Cirsium vulgare bull thistle X

COCA5 Conyza canadensis horseweed

CYXA Cyclachaena xanthifolia giant sumpweed

ERIGE2 Erigeron spp. fleabane

EUOC4 Euthamia occidentalis western goldentop

GNPA Gnaphalium palustre western marsh cudweed

GRSQ Grindelia squarrosa curlycup gumweed

HEAN3 Helianthus annuus common sunflower

HELIA3 Helianthus spp. sunflower

HEPE Helianthus petiolaris prairie sunflower

HEVI4 Heterotheca villosa hairy false goldenaster

LASE Lactuca serriola prickly lettuce X

LYJU Lygodesmia juncea rush skeletonplant

MATA2 Machaeranthera tanacetifolia tanseyleaf tansyaster

MUOB99 Mulgedium oblongifolium blue lettuce
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Family Code Scientific Name Common Name Exotic Rare

ONAC Onopordum acanthium Scotch cottonthistle X

PACA15 Packera cana woolly groundsel

PAPL12 Packera plattensis prairie groundsel

RACO3 Ratibida columnifera upright prairie coneflower

SERI2 Senecio riddellii Riddell's ragwort

SYER Symphyotrichum ericoides white heath aster

SYLA6 Symphyotrichum lanceolatum white panicle aster

TAOF Taraxacum officinale common dandelion X

THME Thelesperma megapotamicum Hopi tea greenthread

TRDU Tragopogon dubius yellow salsify X

XAST Xanthium strumarium rough cockleburr

Boraginaceae

CRCE Cryptantha celosioides buttecandle

CRMI5 Cryptantha minima little cryptantha

CYOF Cynoglossum officinale houndstongue X

LAOC3 Lappula occidentalis flatspine stickseed

LIIN2 Lithospermum incisum narrowleaf stoneseed

Brassicaceae

ALDE Alyssum desertorum desert madwort X

CAMI2 Camelina microcarpa littlepod false flax X

DEPI Descurainia pinnata western tansymustard

DESO2 Descurainia sophia herb sophia X

DRRE2 Draba reptans Carolina draba

LECA5 Lepidium campestre field pepperweed X

LEDE Lepidium densiflorum common pepperweed

SIAL2 Sisymbrium altissimum tall tumblemustard X

THAR5 Thlaspi arvense field pennycress X

Cactaceae

ESVI2 Escobaria vivipara spinystar

OPFR Opuntia fragilis brittle pricklypear

OPMA2 Opuntia macrorhiza twistspine pricklypear

OPPO Opuntia polyacantha plains pricklypear

Capparaceae PODO3 Polanisia dodecandra redwhisker clammyweed

Caprifoliaceae SYOC Symphoricarpos occidentalis western snowberry

Chenopodiaceae

CHAL7 Chenopodium album lambsquarters X

CHBE4 Chenopodium berlandieri pitseed goosefoot X

CHENO Chenopodium spp. goosefoot X

CHFR3 Chenopodium fremontii Fremont's goosefoot

KOSC Kochia scoparia burningbush, kochia X

KRLA2 Krascheninnikovia lanata winterfat

SACO8 Salsola collina slender Russian thistle X

SATR12 Salsola tragus prickly Russian thistle X

Commelinaceae TROC Tradescantia occidentalis prairie spiderwort
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Family Code Scientific Name Common Name Exotic Rare

Convolvulaceae COAR4 Convolvulus arvensis field bindweed X

IPLE Ipomoea leptophylla bush morning-glory

Cyperaceae

CADU6 Carex duriuscula needleleaf sedge

CAEM2 Carex emoryi Emory's sedge S1

CAFI Carex filifolia threadleaf sedge

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

CYSQ Cyperus squarrosus bearded flatsedge

ELAC Eleocharis acicularis needle spikerush

ELPA3 Eleocharis palustris common spikerush

SCPU10 Schoenoplectus pungens common threesquare

SCTA2 Schoenoplectus 

tabernaemontani softstem bulrush

Elaeagnaceae ELAN Elaeagnus angustifolia Russian olive X

SHAR Shepherdia argentea silver buffaloberry

Equisetaceae EQLA Equisetum laevigatum smooth horsetail

Euphorbiaceae

CRTE4 Croton texensis Texas croton

EUPHO Euphorbia spp. spurge, sandmat X

EUGL3 Euphorbia glyptosperma ribseed sandmat

EUSE5 Euphorbia serpyllifolia thymeleaf sandmat

Fabaceae

AMFR Amorpha fruticosa desert false indigo

DACA7 Dalea candida white prairie clover

GLLE3 Glycyrrhiza lepidota American licorice

GLTR Gleditsia triacanthos honeylocust

LAPO2 Lathyrus polymorphus manystem pea

LUPU Lupinus pusillus rusty lupine

MELU Medicago lupulina black medick X

MEOF Melilotus officinalis yellow sweetclover X

MESA Medicago sativa alfalfa X

PEES Pediomelum esculentum large Indian breadroot

PSTE5 Psoralidium tenuiflorum slimflower scurfpea

TRFR2 Trifolium fragiferum strawberry clover X

Fumariaceae COCU2 Corydalis curvisiliqua curvepod fumewort

Grossulariaceae RIAU Ribes aureum golden currant

RICE Ribes cereum wax currant

Hydrophyllaceae ELNY Ellisia nyctelea Aunt Lucy
30

Family Code Scientific Name Common Name Exotic Rare

Juncaceae JUBA Juncus balticus Baltic rush

JUCO Juncus compressus roundfruit rush X

Lamiaceae

LYAM Lycopus americanus American water horehound

LYAS Lycopus asper rough bugleweed

MEAR4 Mentha arvensis wild mint

NECA2 Nepeta cataria catnip X

TECA3 Teucrium canadense Canada germander

Lemnaceae LETU2 Lemna turionifera turion duckweed

Liliaceae ALTE Allium textile textile onion

Loasaceae MEDE2 Mentzelia decapetala tenpetal blazingstar

Malvaceae SPCO Sphaeralcea coccinea scarlet globemallow

Nyctaginaceae MIHI Mirabilis hirsuta hairy four o'clock

MILI3 Mirabilis linearis narrowleaf four o'clock

Oleaceae FRPE Fraxinus pennsylvanica green ash

Onagraceae

OEAL Oenothera albicaulis whitest evening-primrose

OECU2 Oenothera curtiflora velvetweed

OENOT Oenothera spp. evening-primrose

OESE3 Oenothera serrulata yellow sundrops

OESU99 Oenothera suffrutescens scarlet beeblossom

OEVI Oenothera villosa hairy evening primrose

Papaveraceae ARPO2 Argemone polyanthemos crested pricklypoppy

Plantaginaceae PLMA2 Plantago major common plantain

PLPA2 Plantago patagonica woolly plantain

Poaceae

ACHY Achnatherum hymenoides Indian ricegrass

AGCR Agropyron cristatum crested wheatgrass X

AGST2 Agrostis stolonifera creeping bentgrass

ARPU9 Aristida purpurea purple threeawn

BOCU Bouteloua curtipendula sideoats grama

BODA2 Bouteloua dactyloides buffalograss

BOGR2 Bouteloua gracilis blue grama

BRIN2 Bromus inermis smooth brome X

BRJA Bromus japonicus Japanese brome X

BRTE Bromus tectorum cheatgrass X

CALO Calamovilfa longifolia prairie sandreed

ECCR Echinochloa crus-galli barnyardgrass X

ELCA4 Elymus canadensis Canada wildrye

ELRE4 Elymus repens quackgrass X

ELTR7 Elymus trachycaulus slender wheatgrass

HECO26 Hesperostipa comata needle and thread

HOBR2 Hordeum brachyantherum meadow barley
31

Family Code Scientific Name Common Name Exotic Rare

KOMA Koeleria macrantha prairie Junegrass

MUPA99 Muhlenbergia paniculata tumblegrass

NAVI4 Nassella viridula green needlegrass

PACA6 Panicum capillare witchgrass

PASM Pascopyrum smithii western wheatgrass

PAVI2 Panicum virgatum switchgrass

PHAR3 Phalaris arundinacea reed canarygrass X

PHPR3 Phleum pratense timothy X

POCO Poa compressa Canada bluegrass X

POPR Poa pratensis Kentucky bluegrass X

PSSP6 Pseudoroegneria spicata bluebunch wheatgrass

SCSC Schizachyrium scoparium little bluestem

SEVI4 Setaria viridis green bristlegrass X

SPCR Sporobolus cryptandrus sand dropseed

SPPE Spartina pectinata prairie cordgrass

VUOC Vulpia octoflora sixweeks fescue

Polygonaceae

ERAN4 Eriogonum annuum annual buckwheat

EREF Eriogonum effusum spreading buckwheat

PEAM8 Persicaria amphibia longroot smartweed

PEMA24 Persicaria maculosa spotted ladysthumb X

PERSI99 Persicaria spp. smartweed X

PELA22 Persicaria lapathifolia curlytop knotweed

RUCR Rumex crispus curly dock X

RUMEX Rumex spp. dock X

Ranunculaceae RACY Ranunculus cymbalaria alkali buttercup

Rosaceae

POSU25 Potentilla supina Paradox cinquefoil

PRAM Prunus americana American plum

PRVI Prunus virginiana chokecherry

ROAR3 Rosa arkansana prairie rose

Rubiaceae GAAP2 Galium aparine stickywilly

GATR3 Galium triflorum fragrant bedstraw

Salicaceae

POAN3 Populus angustifolia narrowleaf cottonwood

PODE3 Populus deltoides eastern cottonwood

SAAM2 Salix amygdaloides peachleaf willow

SAEX Salix exigua narrowleaf willow

SAFR Salix fragilis crack willow X

Scrophulariacea

e

VEAN2 Veronica anagallis-aquatica water speedwell

VETH Verbascum thapsus common mullein X

Solanaceae PHLO4 Physalis longifolia longleaf groundcherry
32

Family Code Scientific Name Common Name Exotic Rare

SORO Solanum rostratum buffalobur nightshade

Tamaricaceae TACH2 Tamarix chinensis five-stamen tamarisk X

Typhaceae TYAN Typha angustifolia narrowleaf cattail X

Urticaceae PAPE5 Parietaria pensylvanica Pennsylvania pellitory

Verbenaceae

PHCU3 Phyla cuneifolia wedgeleaf

VEBR Verbena bracteata bigbract verbena

VEHA2 Verbena hastata swamp verbena

Vitaceae PAVI5 Parthenocissus vitacea woodbine

VIRI Vitis riparia riverbank grape
33

Appendix B: Natural Resource Condition Maps of Exotic 

Species at FOLA

The maps below illustrate the abundance of cheatgrass (Bromus tectorum) and smooth brome (B. 

inermis) in monitoring plots at Fort Laramie National Historic Site. Red indicates relative cover of 

>13 % and is a significant concern. 
The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific 

and other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and 

affiliated Island Communities.

NPS 375/128115, March 2016
National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

1201 Oakridge Drive, Suite 150

Fort Collins, CO 80525

www.nature.nps.gov

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