Potential large woody debris sources in riparian buffers after harvesting in Oregon, USA

Twenty-one riparian buffers on private lands in Oregon were measured after harvest using the 1994 revised Oregon Forest Practices Rules to determine t heir ability to contribute large woody debris (LWD) to streams for fish hab itat. On average, 51% of the trees retained in riparian buffers after harve st currently would be capable of adding debris at least 20 cm diameter and 1.5 m length to the channel. Assuming 30% of trees are windthrown over 10 y ears and that trees fall in random directions, the riparian buffers would b e expected to add an average of 0.6 trees per 100 m (1.9 trees per 1000 ft) of stream as LWD over 10 years. Analysis showed significantly greater LWD inputs (p<0.05) when the likelihood of more frequent windthrow on riparian terraces and of trees tending to fall downhill on steep slopes are consider ed. On the sites investigated and with the information available, consideri ng tree lean did not significantly increase expected LWD delivery. More dat a on windthrow rates and direction are needed to confirm the analyses. Depe nding on longevity, the expected frequency of LWD pieces could remain withi n ranges observed in undisturbed stands. (C) 1998 Published by Elsevier Sci ence B.V. All rights reserved.