The influence of forest clearcutting patterns on the potential for debris flows and wind damage.

摘要

Models of the topographic influence on debris flow initiation and wind damage are used to assess the influence of forest clearcutting patterns (i.e., location, size, shape and distribution of cut units) on the potential for debris flow initiation and wind damage in Charley Creek watershed, Washington (11.5 km{dollar}sp2{dollar}). Clearcutting patterns consisted of a combination of square or rectangular clearcut units in two sizes distributed either in an aggregated or dispersed pattern under three stream-buffering scenarios. Total area in clearcut units for each cutting pattern was approximately 52 ha. Potentially unstable ground was predicted to be concentrated along steep headwater streams and inner-gorge side-slopes. The location of clearcut units was the most important factor influencing the potential for shallow landsliding while the location, size, shape, and interactions among these three factors were important influences on the potential for wind damage. Manipulation of size and geometric shape of clearcut units are predicted to be more effective for reducing potential wind damage to remaining forest stands adjacent to clearcut units than for shallow landsliding.; A geographic information system (GIS) was used to investigate the spatial coincidence between various buffer widths and extents and potentially unstable ground delineated using a physically-based model for the minimum steady-state rainfall required to cause shallow landsliding in watersheds of Charley and Owl Creeks on the Olympic Peninsula, Washington. The proportion of potentially unstable ground protected by riparian buffer zones is a function of both the width and extent of the channel network being buffered. Buffering all channels with 100 m buffers protected between 75 to 90% of the potentially unstable areas whereas buffering only small headwater channels (Type 9) with 100 m wide leave areas protected 45 to 60% of the potentially unstable areas. The analyses show that (1) riparian buffer zones are not very efficient for protecting potentially unstable ground; (2) wide buffer zones along steep headwater channels can more efficiently protect potentially unstable ground; and (3) no-cut leave areas designed using a physically-based model for the topographic control on shallow landsliding provide a more efficient method to reduce shallow landsliding hazards than extensive buffer zones along stream channels.