Living trees provide stable large wood in streams

摘要

Large wood exerts strong influences on stream channel morphology and aquatic ecosystems. Previously, in-stream large wood has generally been equated with dead wood. However, in streams in Northern California we found that living wood - trees that entered the channel but remained rooted and living - represented a major portion of the functional in-stream large wood. We hypothesized that living wood will tend to be more stable, due to an attached root wad, and more persistent, due to lack of decay, than similarly sized dead wood. Living wood may provide important in-stream structure in streams with riparian corridors that lack large conifers. We surveyed 20 stream reaches in Northern California with riparian corridors dominated by broadleaved trees and found that a high proportion of wood jams had key pieces that were still living. Living wood was capable of serving as a key piece for a wood jam at a smaller size than dead wood and had a greater influence on channel morphology. We found that only 74% of the jams without living wood persisted over 1-2 years while 98% of those with living key pieces remained in place. Due to living wood, the range of tree species and sizes that provide stable and functional in-stream large wood may be broader than previously described. Copyright (c) 2007 John Wiley & Sons, Ltd.