Soil CO2 efflux in salvage logged versus untreated beetle-kill forests

Background/Question/Methods

The current mountain pine beetle outbreak and subsequent management of beetle-killed forest in the southern Rocky Mountains has impacted millions of hectares of lodgepole pine forest and will influence ecosystem processes for decades. Soil respiration is the largest carbon flux in forest ecosystems and is a product of microbial decomposition of organic debris and vegetative root respiration. Pine beetle induced overstory mortality and forest management options (e.g. salvage logging) will influence organic matter inputs, soil moisture, temperature, and nutrient cycling. Our objective in this study is to compare soil CO₂ efflux in untreated stands with three salvage logging treatments. The initial beetle infestation of FEF began in 2002 with peak infection occurring in 2005 and 2006. Salvage logging treatments occurred in the winters of 2007, 2008 and 2009. Salvage logging plots include replicates of whole tree harvest, scarification and lop and scatter (slash pile). We predicted elevated levels of CO₂ efflux in the salvage logged plots, where we projected higher levels of temperature and moisture associated with the removal of overstory trees. We measured soil CO₂ efflux monthly at four locations in northern Colorado during the summers of 2010 and 2011. Within each plot we quantified soil temperature and moisture at each measurement location. Repeated measures analysis of variance (ANOVA) assessed differences in time and treatment variables.

Results/Conclusions

There was no significant difference in soil CO₂ efflux between uncut and salvage logged stands. Variation of seasonal soil CO₂ efflux was significant with peak flux occurring in July. Soil temperature and moisture were significantly higher in the salvage logged treatments; both are strong regulators of soil CO₂ efflux. Stepwise linear regression indicated soil temperature, vegetation cover and soil moisture account for 38% of the variability in soil CO₂ efflux. Ecosystem processes occur slowly in subalpine forest, so it is possible that changes in the physical and biological factors controlling soil respiration will lead to treatment differences in the future. Early results suggest salvage treatments of infested forest will not significantly cause a rapid increase in soil respiration when compared to non-treated forest.