Systematic Analysis of Habitat Availability for
 Conservation Planning in Pennsylvania.

JOSEPH BISHOP*, ROBERT BROOKS, WAYNE MYERS, TIMOTHY O’CONNELL,
 DAVID ARGENT, JAY STAUFFER, and ROBERT CARLINE
(The Pennsylvania State University, University Park, PA 16802; Phone:  814-863-3530)

Abstract

Pennsylvania has special characteristics relative to gap analysis that create a need for innovative approaches to interpretation of biological diversity.  During the 20th Century, forest cover rebounded from less than 30% to more than 75%, thus increasing potential animal habitat across the state.  Pennsylvania includes diverse physiographic settings that extend from the southeastern coastal plain, over the Appalachian and Allegheny Mountains, across the Allegheny plateau, and on to the Great Lakes. This geological diversity is reflected in habitat diversity.  GAP stewardship lands account for only 15% of Pennsylvania’s 116,186 km2 (Fig. 1).  Three-quarters of the 470 vertebrate species have less than 20% of their potential habitat contained within GAP stewardship lands.  Despite improved regional forest conditions, there is progressively increasing forest fragmentation.  Impacts of fragmentation and development are particularly severe for aquatic habitats, with approximately 35% of fish species being at risk.

The combination of social and natural influences on the biota of Pennsylvania requires that judgmental aspects of biodiversity analysis be kept to a minimum.  To address this need in an objective manner, the regional habitat importance index (RHII) was devised and calculated for each species.  The index combines scarcity of habitat with lack of provision for conservation.  Those species that have a particular scarcity of habitat and are not well represented in conservation areas have special implications for conservation planning.   RHII values were compiled by taxonomic group for birds, mammals, fish, amphibians, turtles, and snakes / lizards.  A lattice of 1km x 1km cells was created and coded with the composite RHII values for each taxonomic group.  By weighting according to the conservation status of habitat, the resulting data layers complement conventional diversity mapping.

Leading landscapes were determined by setting a threshold on the RHII in each taxonomic group and mapping the cells exceeding that threshold.  Leading landscapes represent the more problematic areas for the respective taxa across Pennsylvania.  Taxonomic groups were then combined to reveal areas of composite interest for conservation planning.  One area of coincidence among five taxonomic groups occurs in northwestern Pennsylvania and several areas encompass leading landscapes for four groups.  Such areas thus constitute objectively identified conservation gaps for Pennsylvania GAP Analysis.  Maps delineating these areas will help direct cooperative conservation initiatives.

GAP results are timely in light of contemporary conservation initiatives underway in Pennsylvania.  The report of Pennsylvania’s 21st Century Environment Commission outlines several recommendations that are directly addressed by GAP products.


Leading Landscapes

GAP analysis conventionally takes note whether a species has 10%, 20%, or 50% of its potential habitat within stewardship lands.  Since Pennsylvania has approximately 13% of its total land area in stewardship lands (Fig. 1), 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.

For Pennsylvania, it was desired to have a means by which an objective group of species would emerge from the modeling that could serve as one index of possible need for conservation attention.  This index would be formulated to analyze more the species diversity alone (Figs. 2 & 3).  It was further desired to have the index provide a direct avenue to focusing attention on landscapes harboring several groups of species.  Landscapes of this nature occurring outside stewardship lands thereby become ‘leading landscapes’ for collaborative conservation.

Using a 1sq-km sampling grid we have formulated an indicator that we call Regional Habitat Importance Index (RHII) to serve our intended purpose.  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 species for a particular grid cell, RHIIs are summed for elements having habitat in that cell (Figs. 2 & 3).  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 yields the map of leading landscapes for the group.


Coincidence Among Leading Landscapes

Mapping the number of groups with leading landscapes in a cell provides an overall indication of conservation importance for vertebrates in the local environment.  This coincidence among leading landscapes constitutes our first-order indicator of conservation relevance for landscapes of Pennsylvania.  In other words, they are the primary gaps for Pennsylvania Gap Analysis.  Areas of leading landscape for multiple groups should receive special consideration with respect to natural diversity.  This map is a coincidence map of leading landscapes with boundaries of ecoregions and counties superimposed (Fig. 4).  It is noteworthy that major coincident areas tend to be situated along ecoregion boundaries where habitat diversity, speciation, and range limitation are likely to occur.

A notable area of multiple leading landscapes occurs in the Western Allegheny Mountain region of the Appalachian Plateau in Westmoreland County (1).  This area also has the ecological advantage of being proximate to existing conservation stewardship lands, thus, presenting an opportunity to help secure landscape integrity for the region.  It consists primarily of lands on or adjacent to a ridge parallel to a more protected ridge to the east.

A pair of similarly advantageous areas having multiple leading landscapes is situated along opposite sides of the Great Valley on the borders of Cumberland County (2).  Each of these areas would serve to extend existing conservation stewardship lands, thereby helping to secure landscape integrity for the region.

Another important case of compound leading landscapes adjacent to existing conservation stewardship area is found in Crawford County on the Glaciated Pittsburgh Plateau (3).  This area is special for its inclusion of relevance to fishes.   Important compound leading landscapes in this regard also occur on the Erie Lake Plain and in Butler and Allegheny Counties on the Pittsburgh Low Plateau.

Still other areas of strong coincidence among leading landscapes occur in Wyoming and Lackawanna Counties on the Glaciated Low Plateau (4), and in Montgomery and Bucks Counties on the Gettysburg-Newark Lowland of the Piedmont (5).