Seedling Regeneration Following Mountain Pine Beetle Infestation And Forest Harvesting

The forests of Colorado and across much of the Mountain West are changing rapidly due to the effects of severe mountain pine beetle infestation. The widespread mortality of many lodgepole pine forests is certain, but the future trajectory of these ecosystems is not. As an initial step in characterizing ecosystem recovery after mountain pine beetle outbreak, this study will compare tree seedling density and herbaceous plant cover between areas that have been harvested to reduce fuel loads and adjacent untreated stands. Our specific objective is to compare various management prescriptions employed by the US Forest Service in response to insect infestations with a no-action alternative. We sampled treated and untreated stands at and near the USFS Fraser Experimental Forest, in central Colorado and compared existing seedling surveys for stands logged during and years prior to the current beetle outbreak. Current treatment units present a range of residual overstory, depth of harvest residue and extent of soil disturbance. Beneath uncut, beetle-killed stands, subalpine fir represented 92% of advanced regeneration below 15cm, and declined in importance with height. Conversely, lodgepole pine represented 44% of seedling above 75cm and the dominance of both lodgepole pine and Engelmann spruce increased in larger seedling classes. In harvested units the density of seedlings established prior to harvest was 18% lower than in untreated stands, the likely result of damage from mechanical operations and burial under harvest residue. On-going work quantifies seedling establishment following overstory mortality and identifies relationships between seedling density and residue depth, soil disturbance and herbaceous cover in post-harvest landscapes