Soil Nitrogen and Carbon Responses to Salvage Harvesting Alternatives In Pine Beetle-Infested, Colorado Forests.

Overstory mortality caused by current mountain pine beetle outbreaks in western North America surpasses both the extent and severity of most forest disturbances experienced by the public or the land management community.  The perceived increase in wildfire risk following beetle-related overstory mortality has prompted management aimed at reducing hazardous fuels on federal, state and private forest land.  This study compares a number of alternatives for treating lodgepole pine-dominated forests that have been severely-impacted by bark beetles.  At 12 sites distributed across northern Colorado, we compared untreated, beetle-infested stands with lop and scatter, whole tree harvest, and whole tree harvest plus mechanical scarification operations.  Managed stands had more than double the extractable soil N in mineral soils as untreated stands.  Logging slash retention as part of the lop and scatter treatment resulted in the highest extractable soil N pools, gravimetric soil moisture and net nitrogen transformations of the management alternatives.  Soil CO₂ efflux did not differ between the dead, untreated and the harvested stands.  It is plausible that these differences in soil N availability and N turnover will influence the rate of forest recovery following pine beetle infestation and associated management.