Short-term resistance of ecosystem properties and processes to simulated mountain pine beetle attack in a novel region

Natural forest disturbance regimes are changing, as evidenced by expansion of the mountain pine beetle (MPB) north and east from British Columbia into pine forests east of the Canadian Rockies. Thus, research that examines potential impacts of shifting disturbance regimes on ecosystem properties and processes in these forests is needed. We examined short-term effects (up to one year after treatment) of three treatments that emulated MPB attack and associated forest management disturbance (i.e., moderate and high intensity simulated MPB attack, salvage harvest) on above-and below-ground properties and processes of mature lodgepole pine forests in MPB's recently expanded range east of the Rockies. While the salvage logging treatment showed dramatic effects on the understory plant community and downed woody material with several less dramatic below-ground responses, there were no effects of the moderate MPB attack, and only limited below-ground responses to the high intensity attack. The salvage logged stands showed decreases in species richness and understory plant cover, increases in small downed wood, litter cover, forest floor pH, and plant available Ca, Mg, and P, and differences in multiple microbial properties compared with the other treatments. The high intensity simulated MPB attack showed increased respiration rates of several carbon substrates compared with the salvage treatment. There was considerable variation among years for many below-ground variables (e.g., multiple soil nutrients, microbial respiration rates and phospholipid fatty acids), and these were unrelated to treatments. For the majority of below-ground response variables, differences among study years rather than differences due to the MPB treatments suggest that inter-annual variability exerts a stronger influence than does disturbance effects of MPB red attack. The lack of potential response to MPB attack in the short-term suggests these forests are resistant to change early after attack, and/or have high ecological inertia. In contrast, salvage logging had immediate and dramatic effects. We don't yet know how these pine forests will develop under this modified disturbance regime of partial canopy disturbance, but it appears likely that salvage logging will push these stands in a potentially very different direction than the modified natural disturbance regime due to MPB will.