Short-term resistance of ecosystem properties and processes to simulated mountain pine beetle attack in a novel region
McIntosh, A. C. S. and S. E.Macdonald. 2013. Ecosphere
Abstract
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.
Key Words
bove-ground interactions; below-ground interactions; climate change; Dendroctonus ponderosae; disturbance regime; ecosystem change; lodgepole pine; Pinus contorta; range expansion; red attack; salvage logging.
