Spatial Distribution of Riparian Zone Coarse Woody Debris in a Managed Northern Temperate Watershed

Coarse woody debris is an important structural component of both terrestrial and aquatic ecosystems. We investigated coarse woody debris size-structure, decay class composition and distribution within the interface between second growth mixed conifer-hardwood forests and perennial streams in a catchment of the Lake Superior watershed on the Keweenaw Peninsula, Michigan. Down dead wood accumulation was nonlinearly distributed along transects perpendicular to streams and reached a peak between 30 and 50 m away from the wetted stream channels. Variability in the abundance of standing snags displayed a significant increase with distance. The coarse wood accumulations we observed were consistent with levels reported for upland, second-growth forests and were low compared to old-growth forest remnants in the region. Large (>40 cm diam) down dead wood will probably be the slowest pool to recover from logging and land clearing activities that occurred in the watershed prior to the turn of the 19th Century. Nevertheless, the large woody debris, especially highly-decayed wood, at the sites we examined was relict white pine (Pinus strobus) stumps, a persistent legacy of those same historic anthropogenic disturbances. Unlike dead wood, we detected no similar spatial distributions of living woody biomass. The small diameter of the existing standing wood suggests there will be a lag in the recruitment of new large dead wood into this ecosystem.