No abstract

We investigated the effects of different levels of ground-based skidding traffic intensity on soil disturbance, characterized by resistance to penetration (RP) within the top 15 cm of soil, as well as soil recovery, regeneration, and early growth of quaking aspen (Populus tremuloides Michx.) suckers 3 years after a clearcut with reserves summer harvest. Equipment traffic was confined to a network of skid trails, and a GPS was used to determine the number of skidder passes at each of 30 sampling points that were preestablished along an anticipated disturbance gradient ranging from landings to skid trails to areas off skid trails. Thirty-one percent of the harvest area was affected by skid traffic, and up to 603 passes were recorded for a plot. RP increased nonlinearly with the number of passes and reached highest levels at the soil surface. Three years after harvest, soils showed partial recovery in the upper 10-cm layer, with full recovery of the surface layer (0–5 cm depth) when affected by 4 or fewer passes. The deepest layer (10–15 cm), however, showed little recovery since harvest. Sucker density, height, and basal diameter of all suckers and height, basal diameter, and dbh of the tallest suckers were significantly reduced with increasing traffic intensity but were not related to increases in RP. Predicted reduction of sucker density was approximately one-third after 10 passes; reductions of height, basal diameter, and dbh were between 1.5 and 2.5% at 10 passes and 3.5 and 6.5% at 25 passes. Because skidding traffic affected only a limited portion of the stand, the productivity of the future aspen stand was not severely impaired, at least in the very short term.

We investigated impacts of harvesting on soil disturbance and vegetation in the aspen cover type of northern Minnesota, United States. The soil disturbance (resistance to penetration) and understory vegetation were characterized for 19 sites on five 60-m2 plots placed along a disturbance gradient: landings (high harvesting traffic), skid trails (intermediate harvesting traffic), and areas off skid trails (low to no harvesting traffic). Penetration levels were quite variable, but they still indicated that within-site responses to disturbance patterns created by clear-cut harvesting were not uniform. In general, soil disturbance and understory species composition within landings were similar to those with skid trails. The soil disturbance and vegetation composition of these two levels differed from those of the low-disturbance plots (off skid trails), indicating that removing trees alone did not affect vegetation composition as much as creating an established skid trail, regardless of harvest timing. However, sites with more variable species composition (winter-harvested sites) and lower disturbance levels were less altered than sites with likely lower initial diversity (summer-harvested sites). The results suggest that it is important for recovery of understory plant communities to not only limit the amount and level of disturbances but also consider the spatial layout of harvesting, thus maintaining a spatially connected network of remnant forest patches large enough to contain interior forest species.

No abstract