Abstract

Mountain pine beetle (MPB) outbreaks have left millions of hectares of lodgepole pine forest across Alberta with standing dead trees accumulating for nearly two decades. As these snags collapse and surface fuel loads increase, forest managers face decisions about whether to intervene through salvage logging or allow natural recovery. This study assessed whether active management through salvage logging produces different long-term outcomes than natural recovery in terms of stand structure, wildfire risk, understory community composition, and soil nutrient availability. Recovery trajectories were monitored over 16 years after disturbance in a lodgepole pine forest near Robb, Alberta, following simulated MPB attack at two mortality intensities (50% and 100% killed) and salvage logging, compared against an undisturbed control, using linear mixed models, multivariate ordination, and vector fitting analyses.

Salvage logging reset stand structure toward dense lodgepole pine dominance by 2025, while high-intensity beetle mortality led to an 88% decline in lodgepole pine density and left stands in a degraded open-canopy state with no evidence of a replacement tree cohort over the same period. High-intensity beetle mortality also increased large surface fuel loads from ~30 to ~120 Mg/ha through progressive snag collapse, shifting wildfire hazard toward high-intensity surface fire risk. Understory community trajectories diverged across all treatments and were associated with distinct soil nutrient environments, with salvage-logged stands showing elevated base cation availability and beetle-affected stands associated with acidic soil conditions. By 2025, the salvage-logged understory showed signs of recovering toward a composition more typical of mature lodgepole pine forest. These results indicate that salvage logging promotes lodgepole pine regeneration and reduces surface fuel accumulation, while naturally recovering beetle-affected stands may require active fuel management interventions to reduce wildfire risk.