Effects of Two Methods of Timber Harvesting on Microbial Processes in Forest Soil

Abstract

AbstractMicrobial populations and activities in a mature, mixed conifer and hardwood stand were compared with those in similar adjacent stands harvested by conventional (CH) and whole‐tree (WTH) methods. Samples of forest soil (sandy, mixed, frigid Typic Haplorthods) were collected monthly during the first season after harvesting. The NH+4‐N production, measured over the course of 21‐d laboratory incubations, declined in the forest floor of the WTH plot, but increased significantly in mineral soil in both harvested areas. Less than 10% of the NH+4‐N produced was nitrified. Nitrifier and denitrifier populations did not increase during the first year following harvesting, and no significant changes in nitrification activity were noted. Forest floor respiration (measured as CO2 evolved in laboratory incubations) was significantly reduced on both harvested plots relative to the intact stand. Litter bag experiments indicated a reduction in nutrients (N, P, K, Mg) available for decomposer organisms on the WTH plot, and a corresponding reduction in litter decay rates. These effects correspond to reductions in forest floor moisture, water‐holding capacity, and organic matter content after harvesting. In the 0 to 5‐cm mineral soil depth, total bacteria increased on the CH plot but not on the WTH plot. Despite reduced forest floor moisture and nutrient availability, sprouting of trembling aspen (Populus tremuloides Michx.) on the whole tree‐harvested area was vigorous.