Landscape Indicators and Ecological Condition for Mapped Wetlands in Pennsylvania, USA

Abstract

Although landscape indicators are widely used to assess wetland ecological condition, how they capture the spatial arrangement of land cover is not well addressed. We conducted a Level 1 Landscape Assessment to revise strengths and weaknesses of landscape indicators when links to ecological conditions are strong. Wetland sites mapped by the National Wetlands Inventory were defined as 1-km radius circles around centroid points. Forest fragmentation type, road density, Landscape Development Intensity (LDI) index, and percentage of impervious surface were quantified at each site by integrating land cover and road network information. Based on forest cover, 6% of wetland sites scored in the highest ecological category while 45% fit into the lowest one. Results showed high dispersion of data for the impervious surface indicator in the lowest condition category. When comparing LDI and impervious surface under different landscape compositions and configurations, LDI better described disturbance in agricultural areas where road density was low. Impervious surface better reflected the occurrence of fragmented landscapes at forested areas with high percentage of edge forest cover. In addition, a significant proportion of freshwater wetlands (60%) in the lowest condition category was associated with first-order streams, indicating a wide range of disturbance at some headwater watersheds.