Dynamics of large woody debris in streams in old-growth Douglas-fir forests

TLDR

Woody debris enters streams sporadically, mainly from single trees rooted away from the streambank. Transfer of large woody debris ranged from 2.0 to 8.8 Mg ha⁻¹ yr⁻¹ over 7–9 year periods, with stream loads of 230–750 Mg ha⁻¹ that were lower in larger channels; wind was the main entry agent and downstream movement was strongly related to piece length, with most moving pieces shorter than bankfull width.

Abstract

Transfer of large woody debris (>10 cm diameter) from old-growth Douglas-fir (Pseudotsugamenziesii (Mirbel) Franco) forests into five first-to fifth-order stream reaches (drainage areas of 0.1 to 60.5 km 2 ) has ranged from 2.0 to 8.8 Mg•ha −1 •year −1 in 7- to 9-year study periods. Amounts of large debris in these streams range from 230 to 750 Mg•ha −1 with generally lower values in larger channels. The addition of woody debris is widely scattered in time and space and comes mainly from single trees rooted away from the streambank. We infer that wind is a major agent for entry of wood into these streams. Downstream movement of debris is strongly related to length of individual pieces; most pieces that moved were shorter than bankfull width.