Aspen Bibliography

Woody debris, forest-stream succession, and catchment geomorphology

E.H. Trotter

Document Type

Article

Journal/Book Title/Conference

Journal of the north american benthological society

Volume

9

Issue

2

First Page

141

Last Page

156

Publication Date

1990

Abstract

The retention potential of forested headwater streams is strongly influenced by forest succession through the input and transport of different amounts and types of wood and the interaction of woody debris with drainage basin geomorphology during forest succession. To evaluate experimentally the effects of changing amounts of wood on the retention potential of streams, ten log dams were added to a 50-m reach on two second-order streams, Aspen 1 and Aspen 2. Both streams lacked woody debris and flowed through a successional aspen forest in the southern Rocky Mountains. All wood >5 cm in diameter was removed from a 50-m reach of a third stream, Conifer, previously choked with wood in an adjacent climax conifer forest. Although both aspen streams were in the same forest type, Aspen 1 appeared to be at an earlier successional stage than Aspen 2. It flooded more frequently, had more erosion in its upper drainage basin, and had an unstable channel compared with Aspen 2. Within each stream, reaches with wood stored twice the organic matter of reaches without wood. Sides of streams stored more than centers (Aspen 1 = 6×, Aspen 2 = 2×, Conifer = 3.5×). Conifer contained 3.5 times and Aspen 2 contained 2 times more stored organic matter than Aspen 1. Average water velocities were lower in reaches with wood than in reaches without wood in Aspen 2 and Conifer, but not in Aspen 1. Velocities decreased and width and depth increased in both aspen reaches with wood. Velocities increased and width and depth decreased in the conifer reach without wood. Dye-measured transit time revealed the greatest difference between Conifer reaches and the smallest differences between Aspen 1 reaches. Experimental releases of uniformly shaped "woodchips" and spray-painted leaves showed that Aspen 1 was least retentive and Conifer was most retentive, but the greatest difference in retention of particles was between the Aspen 1 reaches. When wood is added, streams retain and store organic matter directly by holding back organic matter and indirectly by increasing the physical heterogeneity of the channel and deflecting water movement into eddies and backwaters. Finally, the effects of woody debris vary with channel stability supporting the concept of linkage between stream succession and the geomorphic processes occurring within each catchment as a whole.

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