Mapping Wildlife Habitat in the Lewis Creek Watershed

Personnel: David E. Capen, Lisa Osborn, Sean MacFaden, Reed Sims

Cooperators: Natural Resource Conservation Service

Introduction

As part of a special USDA research project to demonstrate GIS applications for natural resource assessment and community planning, a land-cover/land-use (LCLU) GIS coverage was developed for the Lewis Creek Watershed in northwestern Vermont. This watershed lies within Chittenden and Addison Counties in Vermont and encompasses portions of seven towns: Charlotte, Hinesburg, Monkton, Starksboro, Ferrisburg, Bristol, and Huntington. To complement the LCLU coverage, a list of wildlife species that were expected to occur in the region of the watershed was compiled. For each species, habitat(s) where the species would be likely to occur and related habitat associations to one of twelve classes of land cover or land use were identified. The resulting "species-habitat" matrix, when linked with the LCLU coverage in a GIS, can be used to predict the distribution of wildlife species within the watershed.

Land Use/Land Cover Mapping

The primary source for LCLU was Vermont's unique resource of 1:5000 digital orthophotos, which have been produced over a six-year period, 1995-2000. Photographs for Addison County were taken in early spring 1995; those for Chittenden County were recorded in spring 1999. The Vermont Digital Orthophoto Quads (DOQs) are available from the Vermont Mapping Program

The LCLU coverage was developed by on-screen digitizing using ArcInfo GIS. The high-resolution DOQs allowed us to delineate 0.01 acres as the minimum mapping unit. Polygons were labeled at intervals throughout the digitizing process. Land-use/land-cover classes and codes were those recommended by the Technical Advisory Committee of Vermont Center for Geographic Information (VCGI), and are available from (VCGI). These codes are an expansion of the U.S.G.S. LCLU categories developed by Anderson et al. (1976) for use with remotely sensed images. Initially, we labeled 30 different classes were labeled, but when the two coverages were joined the number of classes were consolidated, because the main function of the coverage was as a tool for wildlife habitat analysis and many of the remaining codes were for different types of developed areas. The final result was twelve land cover classes.

Figure 1: Twelve-class land-cover map for the Lewis Creek Watershed, Vermont

Figure 2. Close-up of 12-class land-cover map for the Lewis Creek Watershed, Vermont

There has been no assessment of the accuracy of the LCLU coverage, although it is believed to be quite accurate because of the detail visible on the DOQs.

Habitat Conservation Planning

Experienced conservation planners, with an understanding of wildlife habitat, would design a habitat conservation plan for a watershed that would provide a diversity of land-cover types maintained in a configuration that would allow movement of animals within and among different habitat types. The most important component of such a plan would be "connectivity," the antithesis of habitat fragmentation. Whether land-cover types are open fields, forest, wetlands, rivers, or ponds, the most important feature in a habitat conservation plan is connectivity. If habitat connectivity is achieved in only a single land-cover type, such as forest, however, species that prefer a mix of habitat types might not be present or might not survive adequately.

In most Vermont landscapes, ownership patterns make comprehensive planning for wildlife difficult, and ideal conservation plans are rarely achieved. Fragmentation of habitat is the most serious threat, but just as important is the fact that areas most suitable for agriculture and human settlement also are often the highest quality wildlife habitat. Thus, acres conserved for wildlife too often are those that remain after the most productive sites are developed.

Species-Habitat Matrix

One approach for assuring that a diversity of wildlife is conserved within a conservation district, such as a watershed, is to compile a list of wildlife species that would be expected to occur in the watershed, identify areas where these species occur, and be certain that adequate amounts of habitat for all species are conserved. To provide for this approach in the Lewis Creek watershed, a matrix of species for the watershed and habitats that relate to the LULC mapping were compiled.

A list of wildlife species-amphibians, birds, mammals, and reptiles-thought to be present in the Lewis Creek watershed was developed. This list was modified from a more comprehensive database of terrestrial vertebrates in Vermont and New Hampshire compiled for the New England Gap Analysis Project. For each species in this list, the LCLU classes where the species could be found were indicated. The species-habitat matrix does not project "preferred" habitat, but rather all habitat classes that would fall within the normal home range of a species. Thus, a wide-ranging mammal, such as a coyote, would be associated with most of the habitat (LCLU) classes in the database.

Figure 3. Species-habitat matrix indicating specific land-cover classes in which individual species are assumed to occur in the Lewis Creek Watershed, Vermont

The species-habitat matrix, linked to the LCLU coverage in a GIS, can easily be used to project a map of the expected distribution of each of the wildlife species in the matrix. For this purpose, a "project" for ArcView GIS that links the species-habitat matrix with the LULC coverage was created.

Figure 4. Example ArcView query showing land-cover classes that may serve as habitat for the Jefferson salamander, Lewis Creek Watershed, Vermont

The entire list of wildlife in the species-habitat matrix may be use to produce maps of species richness. The Gap Analysis Program uses such data to produce maps of "species richness." This involves predicting the distribution of each species in the database, then overlaying all distribution maps and identifying areas where the greatest number of species occurs. This approach may be appropriate for large geographic areas (Gap Analysis is a national program) but is too cumbersome, or even misleading, for conservation planning in a single watershed. Such "hotspots" of species richness for a single watershed would likely feature areas where different land-cover types intersect, and thus might identify a highly fragmented region.

Habitat Indicator Species

Another approach is to select "habitat indicator species." Some wildlife species show narrow preferences for certain habitat conditions; e.g., the indigo bunting is a bird that is found during the breeding season in fields with abundant brush, such as small hardwood trees. In contrast, other species, such as the red fox, survive best in areas where several habitat types converge, providing abundant edge habitats where the fox finds prey species. A suite of species that collectively require a diversity of habitat types comprise the habitat indicators for an entire watershed-planning unit. Habitat indicators should be species that are reasonably abundant and easy to identify and monitor. A subset of 29 wildlife species from the species-habitat matrix that meet theses criteria was designated. No rigorous method was used to identify these species, and certainly others could be just as appropriate.

Figure 5. Possible habitat for the indigo bunting, a habitat indicator species in the Lewis Creek Watershed, Vermont

The project's objective was to promote citizen participation in assessing and monitoring wildlife habitat in the Lewis Creek watershed. The Lewis Creek Association currently has an active program for monitoring a select few mammals through winter tracking. They expand that effort to include more species, in more habitat types, in more seasons of the year. Field activities to locate and monitor selected wildlife species will serve to validate predictions from the species-habitat matrix and to identify best examples of habitats for each of the species monitored.

       Updated: 12 December 2002