Natural and anthropogenic variation in coarse wood among and within lakes

Residential development is often concentrated near aquatic ecosystems and understanding riparian-littoral zone interactions is therefore critical for assessing its ecological effects. Introduction of wood from riparian forests into the littoral zone, where it becomes habitat for aquatic organisms, is an important, but poorly understood, process. We related the density of littoral coarse wood both among and within 45 lakes in Vilas County, Wisconsin, USA, to forest structure, abiotic drivers and land use. Among all lakes and among a subset of low-development lakes, the best predictor of the density of littoral coarse wood was the density of riparian coarse wood. At the within-lake (site) level, two alternative models explain variability in coarse wood abundance: as a function of exposure to wind and amount of riparian coarse wood or as a function of exposure to wind and land-use intensity. Both among and within lakes, areas more modified by humans had a lower density of littoral coarse wood. Conversely, areas with little (current) human impact were tremendously variable; some sites and lakes had abundant wood and others had virtually none. Contrary to previous studies, there was no relationship between living trees and coarse wood density, suggesting that riparian and littoral coarse wood densities may be strongly influenced by past disturbance, both human and natural. This study highlights the importance of cross boundary subsidies in understanding the impact of development on ecosystems. The concentration of residential development at the boundary between terrestrial and aquatic ecosystems appears to reduce the flow of coarse wood from forests to lakes. Loss of this resource may have negative consequences for lake biota and the aquatic food web.