Stand mortality in buffer strips and the supply of woody debris to streams in Southeast Alaska

We compared the stand conditions in buffer strips with those in unlogged riparian stands with similar site characteristics using large-scale aerial photography to deduce differences in stand mortality and large woody debris (LWD) recruitment. We found the cumulative stand mortality (CSM) was significantly greater in buffer units compared with reference units and that mortality varied with distance from the stream. In the inner zone (0-10 m from stream), the mean difference in CSM between buffer and reference units was relatively small (22% of unlogged CSM), but the CSM in the buffer units of the outer zone (10-20 m from stream) was more than double (120%) the CSM in the reference units. The greater CSM in the buffer units is primarily the result of a significant increase in mortality by windthrow at a small proportion (11%) of the logged units. We found that logging caused an increase in the proportion of tree recruitment to the stream from the outer zone of buffers and changed the shape of the LWD source distance recruitment curve. Based on our findings, we estimate the future potential supply of LWD is diminished by 10% compared with an unlogged reference stand.