Plant biomass dynamics following logging, burning, and thinning in Watersheds 6 and 7, Andrews Experimental Forest, 1979 to present

Watersheds 6 (WS06) and 7 (WS07) at the HJ Andrews are part of a three-watershed study initiated in the 1970’s to examine the response of hydrology and forest vegetation to logging. In 1974, Watershed 6 was clearcut logged; Watershed 7 was shelterwood cut, leaving 75-100 overstory trees per hectare (comprising about 40% of the original basal area). A nearby watershed (WS08) serves as an unlogged control. In 1975, all of Watershed 6 and the portion of WS07 below the road were broadcast-burned. In 1976, both watersheds were planted with Douglas-fir seedlings. Natural regeneration of Douglas-fir and western hemlock also established. In 1984, the remnant overstory trees in WS07 were harvested, and in 2001 the young stand in WS07 was thinned to about 550 trees per hectare. The thinning was not planned but provides an interesting twist to the study. The watersheds are located along the northern boundary of the HJA off the 327 and 328 roads, at elevations ranging from 850 to 1,160 m. Initial vegetation measurements were taken in the summer of 2002 in watersheds 6 and 7 for the purpose of characterizing plant succession after thinning in a small, high-elevation watershed. Understory vegetation plots are remeasured at approximately 6 year intervals.