Forest site quality and fledging success of forest interior songbirds: Does topography restrict habitat quality?

摘要

This dissertation evaluated the role of topography as it influences the breeding productivity of forest interior songbirds from the “bottom up.” Based on literature review, I defined the ecological conditions under which spatial variation in food resources should influence breeding productivity of interior songbirds, and suggested that prey resources for interior songbirds are correlated with the same soil characteristics that influence forest productivity. These soil characteristics are related to topographic position within central Appalachian forests. Empirical study evaluated the hypothesis that interior songbird production is significantly correlated with topographic variation in forest productivity, and differs between two physiographic provinces in western Maryland (Appalachian Plateau: AP; Ridge and Valley: RV) that differ in annual precipitation and underlying geology. Site index was chosen as a long-term integrative measure of forest productivity and indicator of soil moisture conditions. Site index measured within older (74–134 year old) mixed-oak stands was evaluated and found to be a reliable indicator of forest productivity relative to other sites of similar stand age. Analysis of covariance indicated that interior songbird density was greater on the AP than in the RV (P = 0.003), and was positively correlated with site index in both provinces (P = 0.007). The higher density of interior species on the AP was attributed primarily to its greater interior species diversity. Relative fledging success of forest interior species and did not differ between physiographic provinces (P > 0.05), and was not significantly related to site index during a severe drought in 1999 (P > 0.05), but was positively related to site index during a typical rain year in 2000 (P 0.001). Results were incorporated into a cartographic model of potential habitat quality for forest interior songbirds using digital elevation model and land cover data and applied to 3000 km2 sections of the AP and RV in and adjacent to western Maryland. Analysis of variance indicated that land use change had a greater impact on interior songbirds than one would expect based on forest pattern alone because development was biased toward more productive topographic positions. This result has important implications for both current and long-term conservation strategies for interior songbirds in the central Appalachians.