5.1 Introduction

As described in the general introduction to this report (see Section 1.2, pg. 1), the primary objective of GAP is to provide information on the distribution and status of several elements of biological diversity. This is accomplished by first producing maps of land cover (see Section 2.2, pg. 13), predicted distributions for selected animal species (see Section 3.2, pg. 27), and land stewardship and management status (see Section 4.1, pg. 52). Intersecting the land stewardship and management map with the distribution of the elements results in tables that summarize the distribution of mapped elements in different categories of land management status. The data are provided in a format that allows users to carry out inquiries about the representation of each element in different landscape circumstances as appropriate to their own management objectives. This forms the basis of GAP’s mission to provide landowners and managers with the information necessary to conduct informed policy development, planning, and management for biodiversity maintenance.

Although GAP “seeks to identify habitat types and species not adequately represented in the current network of biodiversity management areas” (GAP Handbook, Preface, Version 1, pg. I), it is unrealistic to create a standard definition of what constitutes “adequate representation” for either land cover types or individual species (Noss et al. 1995). A practical solution to this problem is to report amounts of the respective elements in biodiversity management areas in a manner that allows the user to determine which are adequately represented and which are not. There are many other factors that should be considered in such determination such as (a) historic loss or gain in distribution, (b) nature of the spatial distribution, (c) immediate versus long-term risk, and (d) degree of local adaptation among populations of the biotic elements that are worthy of individual conservation consideration. Such analyses are beyond the scope of this project, but we encourage their application coupled with field confirmation of the mapped distributions. As a coarse indicator of the status of the elements, one can use three levels of representation (10%, 20%, and 50%) that have been recommended in the literature as necessary amounts of conservation (Noss and Cooperider 1994; Noss 1991; Odum 1972; Specht, Roe and Boughon 1974; Ride 1975; Miller 1994).

The network of Conservation Data Centers (CDCs) and Natural Heritage Programs (NHPs) established cooperatively by The Nature Conservancy and various state agencies maintain detailed databases on the locations of rare elements of biodiversity. GAP cooperatively uses these data to develop predicted distributions of potentially suitable habitat for these elements (see Section 3.3, pg. 28), which may be valuable for identifying research needs and preliminary considerations for restoration or reintroduction. Conservation of such elements, however, is best accomplished through the fine-filter approach of the above organizations and described on pg. 3. It is not the role of GAP to duplicate or disseminate Heritage Program or CDC Element Occurrence Records. Users interested in more specific information about the location, status, and ecology of populations of such species are directed to their state Heritage Program or CDC.

Currently, land cover types and terrestrial vertebrates are the primary focus of GAP’s mapping efforts; however, other components of biodiversity, such as aquatic organisms or selected groups of invertebrates may be incorporated into GAP distributional data sets. Where appropriate, GAP data may also be analyzed to identify the location of a set of areas in which most or all land cover types or species are predicted to be represented. The use of “complementary” analysis, that is, an approach that additively identifies a selection of locations that may represent biodiversity rather than “hot spots of species richness” may prove effective for guiding biodiversity maintenance efforts. Several quantitative techniques have been developed recently that facilitate this process (see Pressey et al. 1993, Williams et al. 1996, Csuti et al., in press, for details). These areas become candidates for field validation and may be incorporated into a system of areas managed for the long-term maintenance of biological diversity.

5.2 Land Cover Analysis

For reasons as described in Chapter 2, the land cover of Pennsylvania was mapped in terms of physiognomy and urbanization, but not in terms of floristics. Tables showing the distribution of land cover by stewardship and management status are given in Appendix 17. The percentages of physiognomic type by level of urbanization are listed in Table 2.2 of Chapter 2 on pg. 21. This table shows Pennsylvania to be 94.5% rural, 4% suburban, and 1.5% urban. Expansion of suburban areas has been determined to be a land-use issue for Pennsylvania by the Governor’s 21st Century Commission on Environment. The distribution and scope of this problem can be appreciated from the map in Figure 2.5 on pg. 21 of Chapter 2. This problem is particularly evident for the Coastal and Lake Plains, the Piedmont, the Pittsburgh Low Plateau, and portions of the Ridge & Valley ecoregions. In these sectors of the state, suburban areas grow outward from more heavily urbanized core zones. The problem takes a different form in the Poconos and adjoining sectors of the glaciated Appalachian Plateaus, where residential developments are spreading throughout otherwise forested areas for reasons of recreation, aesthetics, and related ambiance.

Deciduous forest is the dominant rural land cover in Pennsylvania, accounting for 55.7% of the entire state. Rural deciduous, evergreen and mixed forests combine to encompass 63% of land cover in the Commonwealth. Transitional, herbaceous, and unvegetated areas occupy 30.3% of Pennsylvania’s rural area. As with rural areas, deciduous forest canopy is also the most common land cover in suburban areas. Urban areas are predominantly lacking in vegetative land cover. Water covers a little more than 1% of Pennsylvania’s surface area.

Fragmentation of habitat constitutes a concern at the landscape level for Pennsylvania. Mapping of landscape matrix at a resolution of 100 hectares was performed as described in Chapter 2 to help provide insight on this issue. Comparison of coarse-scale and fine-scale mapping in Figures 2.3 and 2.4 of Chapter 2 reveals that fragmentation has reached advanced stages in Coastal and Lake Plains, the Piedmont, the Great Valley, and most major valleys in the Ridge & Valley ecoregion. Fragmentation is extensive but less advanced in the Pittsburgh Low Plateau and Glaciated Pittsburgh Plateau ecoregions. Pennsylvania’s conservation areas are concentrated in the remaining ecoregions where forested landscape matrix is substantially more intact

5.3 Predicted Animal Species Distributions Analysis

Tabulations of potential habitat for each species by land stewardship and GAP management status are given in Appendices 18-22, with the information being compiled at 30-meter resolution. GAP analysis conventionally takes note from these tables whether a species has 10%, 20%, or 50% of its potential habitat on lands with management status 1 or 2. We follow this convention in the ensuing subsections, but do not attempt to interpret these threshold listings directly. Such interpretation is complicated by the combination of extent and location for conservation lands in Pennsylvania.

Since Pennsylvania has approximately 13% of its total land area in GAP status 1 and 2, a ubiquitous species would have only this percentage of conservation coverage. Common species would therefore be expected to fall mostly in the 10% to 20% proportion of conservation coverage. However, the conservation lands are concentrated in the mountains and the more rugged northern sections of the Appalachian Plateau. Thus, species with northern ranges are favored in terms of conservation coverage. Conservation coverage greater than 13% indicates that the range of the species is to some degree restricted toward the regions of more extensive conservation lands. Since GAP status 3 lands are important to conservation in Pennsylvania, we have also flagged the tables in Appendices 18-22 for species having less than 10% of potential habitat in GAP status 1-3.

For the Pennsylvania situation, it was viewed as being insufficient to provide results primarily in terms of percentages of habitat in the several classes of stewardship using predetermined thresholds of adequacy. It was desired to have a means by which an objective ordination of species would emerge from the modeling that could serve as one index of possible need for conservation attention. It was further desired to have the index provide a direct avenue to focusing attention on landscapes harboring several such biotic elements. Landscapes of this nature not having conservation status of at least GAP level 3 thereby become ‘leading landscapes’ for collaborative conservation.

Using the grid of PA Kilometer-Aggregated Gap Elements (PAKAGE) as described in section 3.4 of Chapter 3, we have formulated an indicator that we call Regional Habitat Insecurity Index (RHII) to serve our intended purpose. The RHII index for a species is determined as follows:

RHII= 100 x (proportion of non-habitat cells in state)
x (proportion of non-habitat cells in GAP status 1, 2, or 3)
x (proportion of non-habitat cells outside GAP status 1, 2, or 3)

The logic of the index is that availability of habitat within current conservation areas confers some security, and that availability of habitat outside current conservation areas provides latitude in establishing new conservation areas. If, however, habitat is scarce regionally and scarce within current conservation areas, and scarce outside current conservation areas, then the species evidently does face circumstances of insecure habitat. In the latter case, the index increases as a cubic function of habitat scarcity.

To provide a rating across a group of elements for a particular cell in the PAKAGE, RHIIs are summed for elements having habitat in that cell. In our analysis, such a composite of RHIIs has been determined separately for mammals, birds, amphibians, turtles, snakes/lizards, and fishes. An empirical threshold on the composite index for a group has been established by interpreting the spatial pattern that emerges from mapping for that group over the entire state. Flagging cells above the threshold that lie outside current conservation areas and purging fragments that lack spatial coherence yields the map of leading landscapes for the group.

A sequence of analytical components is presented here for each of our six taxonomic-ecological groupings. The sequence begins by reference to a tabular appendix showing total habitat cells, number of habitat cells by GAP status, and RHII for each species. A set of maps is then presented. The first is a quartile (quarters of ranked list) map showing RHII totaled across species for cells having GAP stewardship status of 3 or better. The second is a complementary map for areas not having this level of GAP stewardship status. RHII quartiles are determined on a statewide basis for both of these maps. The third is a map of leading landscapes for the group. After the maps comes an ordination table showing the higher ranked species with respect to RHII. The map in Figure 5.1 showing the distribution of stewardship status 1, 2, and 3 by ecoregion is useful for reference throughout the ensuing analysis.

5.3.1 Mammals:

Appendix 18 contains a table for each mammal species showing potential habitat by stewardship and GAP management status. There are no mammals having 50% or more of the potential habitat in status 1 and 2. The following species have 20% or more of potential habitat in status 1 and 2: northern water shrew, long-tailed shrew, pygmy shrew, Indiana myotis, Appalachian cottontail, snowshoe hare, northern flying squirrel, Allegheny woodrat, woodland jumping mouse, common porcupine, fisher, eastern spotted skunk, bobcat, and elk. Species having less than 10% of potential habitat in status 1 and 2 are: eastern mole, evening bat, Norway rat, house mouse, meadow jumping mouse, and least weasel. The remaining species have 10% to 20% of potential habitat in status 1 and 2.

A table showing total (kilometer scale) habitat cells, number of habitat cells by GAP status, and RHII for each species of mammals is given in Appendix 11. Figure 5.2 is a quartile (quarters of ranked list) map of composite (total) mammal RHIIs for cells having GAP stewardship status of 3 or better, with quartiles being determined on a statewide basis. Figure 5.3 is the complementary map for areas not having this level of GAP stewardship status.

The first map looks into the current stewardship areas, whereas the second map looks outside the stewardship areas. Areas open to view and showing the higher RHIIs have relative concentrations of species with scarce or localized habitat. Since the stewardship areas are predominantly in the upper quartile, they are seen to be well located with regard to conservation of mammals. This is supported by the upper quartile pattern outside the stewardship areas, with high values being situated adjacent to and as connectors between the stewardship areas. This is consistent with the capability of most mammals to disperse over time, whereby the more ecologically sensitive species typically find habitat and refuge in large tracts of forest cover where fragmentation is minimal.

Figure 5.4 is a map of “leading landscapes” for mammals, which was obtained through interpretively deciding upon a composite RHII threshold of 250 for areas not having stewardship status of 3 or better by observing whether tentative levels exhibited spatial aggregation or fragmentation. In the case of mammals, these leading landscapes emerge as connectors between existing stewardship areas. Improving conservation status of these leading landscapes would help to maintain connectivity across substantial regions. Table 5.1 contains an ordination of Pennsylvania mammals according to the RHII approach. This table goes one species below the upper quartile with regard to RHII.

The eastern mole is somewhat anomalous with respect to this ordination, being confined to southeastern Pennsylvania by its lack of ability to move beyond hospitable soils. Such an indexed ordination does require professional evaluation, since it would also highlight the localized occurrence of newly introduced exotics.

Table 5.1. Ordination of Pennsylvania mammals relative to RHII, with - - marking the upper quartile.

5.3.2 Birds:

Appendix 19 contains a table for each bird species showing potential habitat by stewardship and GAP management status. There are four species with 50% or more of potential habitat in GAP status 1 and 2: American wigeon, black tern, yellow-bellied flycatcher, and blackpoll warbler. Species having 20% or more of habitat in GAP status 1 and 2 are: northern goshawk, black-necked stilt, northern saw-whet owl, yellow-bellied sapsucker, olive-sided flycatcher, red-breasted nuthatch, winter wren, golden-crowned kinglet, Swainson’s thrush, hermit thrush, blue-headed vireo, yellow-throated vireo, warbling vireo, Nashville warbler, black-throated blue warbler, yellow-rumped warbler, black-throated green warbler, Blackburnian warbler, pine warbler, worm-eating warbler, northern waterthrush, mourning warbler, Canada warbler, rose-breasted grosbeak, white-throated sparrow, dark-eyed junco, and purple finch.

Bird species having less than 10% of potential habitat in GAP status 1 and status 2 are: least bittern, great egret, snowy egret, cattle egret, black-crowned night heron, yellow-crowned night heron, mute swan, Canada goose, mallard, blue-winged teal, northern shoveler, bald eagle, northern harrier, peregrine falcon, ring-necked pheasant, northern bobwhite, king rail, Virginia rail, sora, killdeer, upland sandpiper, common snipe, American woodcock, rock dove, barn owl, short-eared owl, common nighthawk, Chuck Wills’s widow, chimney swift, willow flycatcher, eastern kingbird, horned lark, purple martin, tree swallow, bank swallow, cliff swallow, barn swallow, fish crow, Carolina chickadee, sedge wren, eastern bluebird, loggerhead shrike, European starling, white-eyed vireo, blue-winged warbler, yellow warbler, magnolia warbler, prairie warbler, common yellowthroat, yellow-breasted chat, summer tanager, blue grosbeak, dickcissel, clay-colored sparrow, field sparrow, vesper sparrow, savannah sparrow, grasshopper sparrow, Henslow’s sparrow, song sparrow, bobolink, red-winged blackbird, eastern meadowlark, western meadowlark, common grackle, house finch, house sparrow. The remaining species have 10% to 20% of potential habitat in GAP status 1 and status 2.

A table showing total (kilometer scale) habitat cells, number of habitat cells by GAP status, and RHII for each species of birds is given in Appendix 12. Figure 5.5 is a quartile map of composite (total) bird RHIIs for cells having GAP stewardship status of 3 or better, with quartiles being determined on a statewide basis. Figure 5.6 is the complementary map for areas not having this level of GAP stewardship status.

The picture for birds is not nearly as simple as for mammals. The composite RHII approach tends to focus attention most strongly on areas having wetlands. The existing stewardship lands having GAP status of 3 or better show approximately a proportionate distribution with respect to composite RHII for birds, being neither more nor less strategic that the state as a whole. It is true, however, that the existing stewardship lands favor area-sensitive species because of the landscape matrix being predominantly intact forest habitat.

Figure 5.7 is a map of the “leading landscapes” for birds where composite RHII exceeds 900. This map emphasizes regions containing wetlands, and particularly those around major river systems. Table 5.2 contains an ordination of Pennsylvania bird species according to the RHII. This table goes one species below the upper quartile with regard to RHII. It is notable that the majority of species in the upper quartile have a wetland affiliation of some kind. There are also several species associated with grassland habitats. Thus, it would seem that further conservation focus is warranted for avifauna in these landscape settings. Two species in the ordination should be noted as not being appropriate for emphasis in conservation. One is the black-necked stilt at the top of the ordination, which represents only a single pair known to nest regularly around a sewage treatment facility in southeastern Pennsylvania. The other is the mute swan that is an exotic species established as a breeder.

Table 5.2. Ordination of Pennsylvania birds relative to RHII, with - - marking the upper quartile.


5.3.3 Amphibians:

Appendix 20 contains a table for each amphibian species showing potential habitat by stewardship and GAP management status. The mud salamander is the only species having 50% or more of the potential habitat in GAP status 1 and 2. The valley and ridge salamander along with Wehrle’s salamander are the only species with 20% or more of potential habitat in GAP status 1 and 2. Amphibian species having less than 10% of potential habitat in GAP status 1 and 2 are: hellbender, seal salamander, ravine salamander, mudpuppy salamander, Woodhouse’s toad, northern cricket frog, gray tree frog, mountain chorus frog, western chorus frog, northern leopard frog, and southern leopard frog. The remaining species have from 10% to 20% of potential habitat in status 1 and 2.

A table showing total (kilometer scale) habitat cells, number of habitat cells by GAP status, and RHII for each amphibian species is given in Appendix 13. Figure 5.8 is a quartile map of composite (total) amphibian RHIIs for cells having GAP stewardship status of 3 or better, with quartiles being determined on a statewide basis. Figure 5.9 is the complementary map for areas not having this level of GAP stewardship status.

The major concentration of stewardship lands in the northcentral portion of the state does not fit well with the distribution of crucial amphibian habitats as determined by the RHII approach, since the upper quartile of composite RHII is largely absent from that region. It is evident from Figure 5.9 that the Pittsburgh Low Plateau has special implications for amphibians. This is also an area where human influence has become dominant at a broad landscape scale, but considerable localized naturalistic cover still remains. Since amphibians do not have a capacity for rapid long-distance dispersal, this is a region where collaborative conservation efforts can have an important role. This is also true for several other less expansive sectors in southcentral and southeastern Pennsylvania, as well for an area near Lake Erie and another in the Glaciated Low Plateau region of the northeast. The “leading landscapes” having composite RHII of 325 or more are shown in Figure 5.10. Table 5.3 contains an ordination of amphibian species that are above the median with respect to RHII. These species have major influence in determining the leading landscapes.

Table 5.3. Ordination of Pennsylvania amphibians relative to RHII, with - - marking the upper quartile.

5.3.4 Turtles:

Appendix 21 contains a table for each turtle species showing potential habitat by stewardship and GAP management status. There are no turtle species having 20% or more of the potential habitat in GAP status 1 and 2. The wood turtle and bog turtle have 10% to 20% of potential habitat in status 1 and 2. The other 8 turtle species have less than 10% of potential habitat in status 1 and 2.

A table showing total (kilometer scale) habitat cells, number of habitat cells by GAP status, and RHII for each turtle species is given in Appendix 14. Figure 5.11 is a quartile map of composite (total) turtle RHIIs for cells having GAP stewardship status of 3 or better, with quartiles being determined on a statewide basis. Figure 5.12 is the complementary map for areas not having this level of GAP stewardship status.

Pennsylvania’s conservation geography for turtles is similar to that for amphibians with regard to the main body of stewardship lands in the northcentral area, which have a relatively minor part in the picture. The western part of the state including the Pittsburgh Low Plateau, Glaciated Pittsburgh Plateau, and Erie Lake Plain is important. However, the RHII approach puts major emphasis on southeastern Pennsylvania along with portions of the Ridge & Valley. Northeastern Pennsylvania also has two areas of more limited extent receiving emphasis. Figure 5.13 shows the leading landscapes where composite RHII is 200 or more. Table 5.4 contains an ordination of turtle species that are above the median with respect to RHII. These species have major influence in determining the leading landscapes.

Table 5.4. Ordination of Pennsylvania turtles relative to RHII, with - - marking the upper quartile.

5.3.5 Snakes and Lizards:

Appendix 21 contains a table for each species of snakes and lizards showing potential habitat by stewardship and GAP management status. There are no species with 50% or more of potential habitat in GAP status 1 and 2. Species having 20% or more of potential habitat in status 1 and 2 are: eastern fence lizard, coal skink, five-lined skink, redbelly snake, smooth earth snake, and timber rattlesnake. Species having less than 10% of potential habitat in status 1 and 2 are: broadhead skink, Kirtland’s snake, rough green snake, queen snake, brown snake, copperhead, and massasauga. The remaining species have 10% to 20% of potential habitat in status 1 and 2.

A table showing total (kilometer scale) habitat cells, number of habitat cells by GAP status, and RHII for each species of snakes and lizards is given in Appendix 15. Figure 5.14 is a quartile map of composite (total) RHIIs for cells having GAP stewardship status of 3 or better, with quartiles being determined on a statewide basis. Figure 5.15 is the complementary map for areas not having this level of GAP stewardship status.

Conservation geography for snakes and lizards is different from other groups of terrestrial vertebrates. Large areas of existing stewardship lands in the High Plateau and Deep Valleys regions fall in the upper quartile of composite RHII as determined on a statewide basis. Several existing stewardship areas in southcentral Pennsylvania also have emphasis in terms of RHII. However, major portions of lands having upper quartile RHIIs are not accounted for in stewardship tracts. This situation is well illustrated by “leading landscapes” in Figure 5.16 where total RHII is over 230. Leading landscapes in the more central portion of the state are largely connective to and between existing stewardship areas. However, extensive leading landscapes in the Pittsburgh Low Plateau, Piedmont, and northeastern glaciated plateaus are largely located away from substantial stewardship areas. Table 5.5 contains an upper-quartile ordination of snake and lizard species with respect to RHII.

Table 5.5. Ordination of snakes and lizards relative to RHII, with - - marking the upper quartile.

5.3.6 Fishes:

Appendix 22 contains a table for each fish species showing potential habitat by stewardship and GAP management status. Consistent with the problematic conservation context for fishes in Pennsylvania, the majority of species in this group have less than 10% of the potential habitat in GAP status 1 and 2. Therefore, it is parsimonious to identify species with 10% or more of potential habitat in status 1 and 2. There are no species with 50% or more of habitat in status 1 and 2. Species having 20% of more of habitat in status 1 and 2 are: shortnose sturgeon, brook trout, redside dace, bluespotted sunfish, longear sunfish, and slimy sculpin. Species having 10% to 20% of habitat in status 1 and 2 are: Atlantic sturgeon, American eel, rainbow trout, brown trout, chain pickerel, cutlips minnow, bigeye chub, eastern silvery minnow, hornyhead chub, spotted shiner, silver shiner, ironcolor shiner, southern redbelly dace, blacknose dace, fallfish, satinfin shiner, gravel chub, white sucker, creek chubsucker, northern hog sucker, margined madtom, brown bullhead, green sunfish, pumpkinseed, bluegill, mottled sculpin, and Potomac sculpin.

A table showing total (kilometer scale) habitat cells, number of habitat cells by GAP status, and RHII for each fish species is given in Appendix 16. Figure 5.17 is a quartile map of composite (total) RHIIs for cells having GAP stewardship status of 3 or better, with quartiles being determined on a statewide basis. Figure 5.18 is the complementary map for areas not having this level of GAP stewardship status.

Even more so than for amphibians and turtles, the large body of stewardship lands in northcentral Pennsylvania is not located strategically with respect to fishes that are most in need of conservation attention. Some portions of the Allegheny National Forest are above the median with respect to composite RHII, but more are below. Likewise, most of the stewardship lands in southcentral Pennsylvania lack emphasis in terms of RHII. However, the stewardship lands in the northwestern part of the state are better situated in this regard.

The map in Figure 5.18 shows that the Erie and Ohio River basins along with the eastern part of the Allegheny River basin are important areas with regard to conservation of fishes. Proximal watersheds for other major rivers like the Susquehanna are noteworthy as well. Outstanding areas for fish conservation where composite RHII reaches more than 2500 are mapped in Figure 5.19 as “leading landscapes.” Western Pennsylvania takes precedence over the rest of the state in this regard. However, it comes as no surprise to those involved in fish conservation efforts that the French Creek drainage in northwestern Pennsylvania is a premier area. Since more than a few Pennsylvania fish species are tenuous with respect to conservation, the ordination with respect to RHII in Table 5.6 reaches almost to the middle (median) of the ranks.

Table 5.6. Ordination of fish species relative to RHII, with - - marking the upper quartile.


5.4 PAKAGE Mapping of Potential Habitat Distribution

Pennsylvania Gap Analysis is not meant to end in a report, but to become an active database tool for assisting coordination of conservation efforts across landscapes. The PAKAGE database is our means for accomplishing this purpose. The PAKAGE database is distributed on a Pennsylvania Habitat Explorer CD-ROM produced under the auspices of PASDA (PA Spatial Data Access).

Potential habitat distribution for an individual species at 1-km scale is one of many kinds of information to be extracted from this database. This can be obtained by loading the PAKAGE shapefile into a GIS, accessing the base table of attributes, and then linking the cell table for the taxonomic group of interest. Each species is a column in the table, and each cell containing potential habitat for the species is coded with a 1 in that column. A query of the attribute table will select all cells pertaining to the species. Appearing in the Maps section prior to the appendices are potential habitat distributions obtained in this manner for herp species in their respective upper quartiles of RHII. These maps also have ecoregion boundaries and county boundaries superimposed.

Another application of the PAKAGE database is to determine the number of 1-km cells containing habitat for a species in USEPA’s EMAP hexagons. This can be accomplished by selecting the column for the respective species, and then summarizing by the hex column. Tabulations by county can be obtained in like manner.