Influence of stream corridor geomorphology on large wood jams and associated fish assemblages in mixed deciduous-conifer forest in upper Michigan

Wood structure and spatial arrangement in rivers reflect hierarchical processes of the stream corridor and valley. Large wood jams (aggregations of 2 or more pieces of wood greater than 10 cm diameter and longer than 1 m; LWJ) often form the focus of stream restoration projects that require knowledge about factors controlling LWJ characteristics and stability. Because geomorphic structure at the stream corridor scale controls stream channel geomorphology and riparian forest structure and dynamics, which have also been shown to control LWJ characteristics, we hypothesized that patches of relatively long sections of similar valley geomorphology create unique LWJ signatures or combinations of LWJ characteristics, and that these signatures should exist in all similar geomorphic patches. We studied characteristics of LWJ in first through third-order streams in the hemlock-hardwood forests of the Porcupine Mountains Wilderness State Park, one of the largest old-growth forest landscapes in the midwestern United States. In the first part of the study we evaluated characteristics of loose large wood (LW) and LWJ compared to riparian forest composition and imminent recruits (dead, leaning, or undercut trees within 10 m of the bankfull channel) in 300 m reaches encompassed by each geomorphic section in one river in old-growth and matching sections in two second-growth streams. We quantified specific relationships between structural characteristics of large wood and 10 geomorphic factors in an effort to develop reference conditions for large wood restoration for streams of the region. In the second part of this study we used linear K-function analysis to quantitatively evaluate spatial patterns of LWJ in repetitions of the four geomorphic settings within 6 rivers (4 in old-growth, two in second-growth). Most LWJ (in 12 of 17 geomorphic sections) and large wood dams (LWJ that spanned more than half of the channel; random in 11 of 14 cases) showed random distribution patterns within geomorphic sections regardless of the scale of evaluation within a geomorphic setting.; During the third part of this study we compared LWJ characteristics (measured at the scale of about 1 km) among geomorphic sections in the same 6 rivers as in part two of the study.; Finally, we surveyed brook trout (Salvelinus fontinalis) and other fish associated with LWJ in October of 2003 and again in June and October of 2004. We did not find a significantly greater abundance of resident brook trout or other fish species at LWJ or in pools with LWJ compared to reference pools without LWJ. (Abstract shortened by UMI.)...