Features

Gap Analysis of the Flora of Wyoming

Walter Fertig and Robert Thurston

Department of Botany, University of Wyoming, Laramie

Beginning with the establishment of Yellowstone National Park in 1872, nearly 10% of the state of Wyoming has been set aside as GAP status 1 or 2 lands.  Most of these areas were initially protected for their scenic, historic, or recreational values rather than for conserving biodiversity, and they tend to be concentrated in the Greater Yellowstone Ecosystem and other high-elevation areas (Figure 1).  The Wyoming GAP Project used modeled distributions of 445 terrestrial vertebrate species and 42 land cover types to assess the effectiveness of status 1 and 2 lands in conserving the state's biodiversity.  Not surprisingly, the gap analysis revealed high levels of protection for species and cover types found in montane and alpine habitats and minimal protection for elements in low-elevation areas of eastern and southern Wyoming (Merrill et al. 1996).

Figure 1.  Revised GAP land status map of Wyoming with Research Natural Areas, Nature Conservancy preserves and easements, and BLM Areas of Critical Environmental Concern established since publication of the original state land status map in Merrill et al. (1996).

Vascular plant species were not included in the initial Wyoming Gap Analysis, nor have they traditionally been assessed in other states.
However, state or regional floras may be more useful probes of biodiversity protection than vertebrates or land cover types. Because of their high levels of species richness, endemism, and habitat specialization, plants are a useful proxy for total biodiversity.  Being sessile organisms, plants are also easier to map and positively locate in different GAP land management areas.  Finally, large data sets of point locations are available for plants from herbarium records and floristic checklists.

With funding from National GAP, we used dot distribution and modeled habitat maps to conduct the first gap analysis of the flora of Wyoming.  Location points were derived for 2,770 of the state's 2,800 vascular plant taxa (Dorn 2001) from the digital specimen database of the Rocky Mountain Herbarium (www.uwyo.edu/botany/herb.htm), the state natural heritage program (www.uwyo.edu/wyndd), and available checklists for special management areas (Fertig 2000, 2001; Fertig and Oblad 2000; Heidel and Fertig 2001; Shaw 1992; Whipple 2000, 2001).  All duplicate records (representing the same collector or locality) were eliminated, leaving a final data set of 208,659 points.  These points were overlaid on the state GAP land status coverage to determine the number and percentage of points of each species in the four land status categories.  The same values were calculated with the state's flora subdivided by major biome types (alpine, eastern deciduous forest, Great Plains grasslands, Rocky Mountain forest, intermountain desert steppe, and wetlands), and for non-native and rare species.  The land status coverage was modified from Merrill et al. (1996) to include new Research Natural Areas, Nature Conservancy  (TNC) preserves and easements, and BLM Areas of Critical Environmental Concern (ACECs) established since 1996 (Figure 1).

Potential distribution maps were created for 100 plant species based on correlations between selected environmental variables and known plant locations in Wyoming and adjacent states (Fertig 1999).  Digital versions of these models were overlaid with the revised land status layer to derive the percentage of area in Wyoming falling in each of the four GAP categories.

Based on our revised land status coverage, the total area of Wyoming under GAP status 1 or 2 management is 26,695 km² (10.55% of the state).  These lands contain at least one population for 2,261 of the state's 2,770 plant species that we examined (81.62%) (Table 1).  1,263 of these taxa (45.6%) have at least five or more populations in status 1 or 2 lands, and 1,557 taxa (56.21%) have over 10% of their known populations under protection.  Alpine species are the best represented, with 158 of 163 taxa (96.93%) being found at least once in GAP 1 or 2 areas and 107 taxa (65.64%) having at least 50% of their populations protected.  Wetland and Rocky Mountain forest plants are also relatively well protected, with 87.86-90.54% of their species present at least once in status 1 or 2 lands.  By contrast, plants of the eastern deciduous forest, intermountain desert steppe, and Great Plains grasslands have only 72.52-77.68% of their species minimally represented in GAP 1 or 2 areas.  Although only 40 of 52 eastern deciduous forest species occur in protected sites, 37 of these (71.16%) have at least 10% of their populations in preserves.  Of 261 intermountain desert steppe taxa in protected areas, only 90 (26.79%) have at least 10% of their populations represented.  Plants of the Great Plains have the lowest levels of protection, with only 293 of 404 species present on protected lands and less than 15% of the flora having over 10% of their populations preserved (Table 1).

The state natural heritage program recognizes 522 plant taxa of "special concern" (Fertig and Beauvais 1999).  Of these species, 196 (37.55%) currently receive no protection in GAP 1 or 2 areas of Wyoming.  The percentage of unprotected rare species in Wyoming is just over twice as high as the percentage of unprotected taxa in the state flora as a whole.
Only 230 rare plant species (44.06%) have at least 25% of their known occurrences in preserves (Table 1).

Conversely, 366 non-native plant taxa have been documented for the flora of Wyoming, of which 211 (57.45%) occur at least once in status 1 or 2 lands.  Fifty-two of these species (14.21%) have more than 25% of their known occurrences in highly protected areas. 

For 100 modeled species we found little overall difference in the average percentage of a species' predicted area within status 1 or 2 lands and the average percentage of known populations of the same species in the protected areas (21.03% vs. 20.97%, respectively, Table 2).
Individual models and dot distribution maps could differ significantly, however, with modeled ranges typically overpredicting protection for many alpine, Rocky Mountain forest, and wetland species, and point maps doing the same for eastern deciduous forest taxa and rare plants. 

Models are a useful tool for identifying new areas of potential habitat for species of high management interest (Fertig 1999) but should not substitute for ground-based confirmation of presence in protected areas.  Point-based coverages have limitations too in that they may reflect unequal or biased sampling (with private lands being especially underrepresented).  Use of species lists may also suffer from unequal sampling intensity and possible misidentifications.  In Wyoming, TNC easements, state Wildlife Habitat Management Areas, ACECs, and national forest wilderness and special interest areas outside the Greater Yellowstone area are especially undersampled at present and may provide better levels of protection than currently detected.  As with all gap analyses, care must be taken in presuming that presence in a protected area equates with adequate management, minimum viable population size, and occurrence of necessary ecological conditions for any given species.

The use of vascular plants to identify patterns in overall biodiversity protection corroborates the findings of other gap analyses using terrestrial vertebrates and land cover types (Merrill et al. 1996; Scott et al. 2001).  We find that alpine and montane upland and wetland species have much higher representation in GAP status 1 or 2 lands in Wyoming than taxa from the Great Plains, eastern deciduous forest, and intermountain desert steppe.  Rare species are also twice as likely to be absent from the existing protected areas network as wide-ranging species.  Floras confer additional advantages for gap analysis because their high species richness, mix of habitat generalist and specialist taxa, and large pool of location information contribute to a more robust data set than vertebrate faunas or coarse vegetation types.  By determining the protection status of individual plant species, conservationists have a precise tool for identifying and prioritizing biome types, geographic areas, and suites of species that are underrepresented in the protected areas network.

Literature Cited

Dorn, R.D.  2001.  Vascular plants of Wyoming, third edition.  Mountain West Publishers, Cheyenne, Wyoming.  412 pp.

Fertig, W.  1999.  Predictive modeling of rare plant species.  Gap Analysis Bulletin 8:18-19.

Fertig, W.  2000.  Vascular plant species checklist and rare plants of Fossil Butte National Monument. Wyoming Natural Diversity Database, Laramie, Wyoming.  52 pp.

Fertig, W.  2001.  Known and potential vascular plant flora of Fort Laramie National Historic Site.  Wyoming Natural Diversity Database, Laramie, Wyoming.  19 pp.

Fertig, W. and G. Beauvais.  1999.  Wyoming plant and animal species of special concern.  Wyoming Natural Diversity Database, Laramie, Wyoming.  36 pp.

Fertig, W. and B. Oblad. 2000.  Protection status and checklist of the vascular plant flora of the Wyoming Black Hills.
Wyoming Natural Diversity Database, Laramie, Wyoming.  54 pp.

Heidel, B. and W. Fertig.  2001.  Vascular plant species checklist of Bighorn Canyon National Recreation Area, Montana and Wyoming.  Wyoming Natural Diversity Database, Laramie, Wyoming.  76 pp.

Merrill, E.H., T.W. Kohley, M.E. Herdendorf, W.A. Reiners, K.L. Driese, R.W. Marrs, and S.H. Anderson.  1996.  The Wyoming Gap Analysis Project final report.
Department of Zoology and Physiology, Department of Botany, and Wyoming Cooperative Fish and Wildlife Research Unit, University of Wyoming, Laramie, Wyoming.  109 pp. + appendices.

Scott, J.M., F.W. Davis, R.G. McGhie, R.G. Wright, C. Groves, and J. Estes.  2001.  Nature reserves: Do they capture the full range of America's biological diversity?  Ecological Applications 11(4):999-1007.

Shaw, R.J.  1992.  Annotated checklist of the vascular plants of Grand Teton National Park and Teton County, Wyoming.  Grand Teton Natural History Association, Moose, Wyoming.  92 pp.

Whipple, J.J. 2000. Draft vascular plant species list, Yellowstone National Park. Yellowstone National Park, Wyoming. 49 pp.

Whipple, J.J. 2001.  Annotated checklist of exotic vascular plants in Yellowstone National Park.  Western North American Naturalist 61(3):336-346.