Coarse woody debris in streams of the Drift Creek Basin, Oregon

Approved: Robert L. Beschta This study examined the occurrence of coarse woody debris (i.e., pieces greater than 0.15 m in diameter and 2.0 m in length) in firstthrough fifth-order streams located within the Drift Creek Basin of the Oregon Coast Range. Nine reachest were surveyed to determine how three land management treatments (undisturbed, patch clearcut with buffer strip, and entirely clearcut) and/or geomorphology were associated with CWD loadings or piece characteristics. An additional 45 km of thirdto fifth-order channels were surveyed to identify CWD distribution patterns over changing stream size. All surveys recorded channel characteristics and the dimensions and attributes of each CWD piece. Coarse woody debris loadings varied greatly (11 to 62 pieces/lOOm, 0.3 to 4.3 m3/100m2 of inchannel volume) between the tributary reaches, but were not significantly (p > 0.10) related to harvest treatment. However, reaches associated with clearcut treatment contained less hardwood CWD and pieces were significantly shorter, and more decayed than in the other treatments. This suggested that little CWD recruitment had occurred in the 15 to 20 years since harvest. The undisturbed and buffer strip tributaries contained CWD that reflected continued recruitment of both hardwood and conifer trees. Inchannel CWD loadings averaged 0.44 m3/100m2 and decreased significantly (p < 0.01, r2 = 0.68) with drainage area. Coarse woody debris frequency and total loading averaged 10 pieces/lOOm and 14 m3/lOOm, respectively, and were not significantly related to stream size. The percentage of total CWD volume within the channel increased with stream order and decreased with increasing channel gradient. Large debris pieces (i.e., pieces greater than 0.5 m in diameter and 10 m in length) were particularly frequent in the gorge-like reaches of the Drift Creek Wilderness. Over one third of the CWD pieces in larger channels occurred within debris