Large woody debris in bull trout (Salvelinus confluentus) spawning streamsof logged and wilderness watersheds in northwest Montana

We measured large woody debris (LWD) in 20 known bull trout (Salvelinus con fluentus) spawning stream reaches from logged and wilderness watersheds in northwestern Montana. Mean bankfull width of stream reaches was 14.1 m rang ing from 3.9 to 36.7 m. Streams were large enough to move LWD and form aggr egates. We determined the characteristics of individual pieces of LWD that were interactive with the stream channel. Large, short pieces of LWD attach ed to the stream bank were the most likely to be positioned perpendicular t o stream flow, while large, long pieces either tended to be parallel to the flow or, when attached, were most apt to extend across the channel thalweg . Observations indicated that the majority of pools were formed as scour po ols by either very large LWD pieces that were perpendicular to the stream o r multipiece LWD aggregates. Among reaches in wilderness watersheds, ratios of large to small LWD, attached to unattached LWD, and with and without ro otwads were relatively consistent. However, among reaches with logging in t he watershed, these ratios varied substantially. These results suggest that logging can alter the complex balance of delivery, storage, and transport of LWD in northern Rocky Mountain streams, and therefore, the likely substa ntive change in stream habitats.