Influence of skidder traffic on soil bulk density, aspen regeneration, and vegetation indices following winter harvesting in the Duck Mountain Provincial Park, SK

Abstract

Following a disturbance, extensive aspen (Populus tremuloides) suckering is crucial for ensuring the continued productivity of the future forest. The aim of this study was to assess the suitability of using winter harvesting in a provincial park as a way to mitigate severe soil compaction and ensure sufficient aspen regeneration to rejuvenate the mature forest. Six harvested blocks were selected for this study based on a skidder traffic intensity map, which was generated using GPS data collected throughout the duration of the harvesting event. Soil bulk density, aspen regeneration, and vegetation indices were measured across the different levels of skidder traffic intensity. Soil bulk density increased significantly following as little as 1–5 skidder passes (1.39 g cm−3) compared to the unharvested control (1.29 g cm−3); however, bulk density remained relatively constant as the level of skidder traffic intensity continued to increase. No relationship was found between soil bulk density and the level of aspen regeneration; however, the level of skidder traffic intensity significantly influenced the level of aspen regeneration. Aspen root collar diameter, leaf area index, dry leaf biomass, total N, and total P all decreased as the level of skidder traffic intensity increased; but, these decreases were not significant. Conversely, both aspen sucker density and height decreased significantly as the level of skidder traffic intensity increased, decreasing nearly 50% and 28%, respectively, in areas with 51–100 skidder passes. Multispectral remote sensing using UAV to assess the level of aspen regeneration across an entire harvested block proved ineffective. Although several vegetation indices showed significant relationships with aspen properties, none of these relationships had a coefficient of determination greater than approximately 0.2. Overall, winter harvesting appeared to have mitigated soil compaction concerns as expressed by soil bulk density and. although areas with higher levels of skidder traffic intensity (51–100 passes) experienced a decrease in aspen regeneration vigor, these areas with decreased aspen regeneration only accounted for approximately 1–2% of harvested blocks.