Mechanical site preparation impacts on soil properties and vegetation communities in the Northwest Territories

Abstract

Greater utilization of hardwood species and societal concerns over maintenance of ecological integrity have provided impetus for forest managers to consider alternative silvicultural practices in boreal mixedwood forests. The objective of this study was to quantify the effects of five mechanical site preparation (MSP) treatments on soil properties and understory vegetation of mixedwood stands in the Northwest Territories (NWT). Soil and understory vegetation conditions in treatments (3 years post-MSP treatment) and adjacent uncut forest controls were sampled. Significant Shearblade – Grizz R-ex and Shearblade treatment soil property effects were consistently found. Increases in bulk density (307%) and decreases for total organic carbon (92%); total nitrogen (86%); cation exchange capacity (74%); and exchangeable calcium (72%), magnesium (67%), and potassium (75%) in the soil surface (0–12.8 cm) were observed. Increases in mineral soil pH (1.0 units), total organic carbon (94%), cation exchange capacity (20%), and exchangeable calcium (35%) and magnesium (56%) were also found. Dissimilarity of the understory community with that of the uncut forest increased as follows: uncut forest < harvested only < Meri–Crusher = Grizz R-ex < Shearblade – Meri-Crusher < Shearblade – Grizz R-ex < Shearblade. This research suggests that winter shearblading should be utilized only where it is necessary to achieve specific management objectives.