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2013 - Mountain Pine Beetle Ecology Program Research – Practitioner Information Exchange Forum April 24, 25, 2013

Transformation of Alberta forests by mountain pine beetle René Alfaro1, Brad Hawkes1, Lara vanAkker1 and Jodi Axelson2 1

Canadian Forest Service, Victoria, BC BC Ministry of Forests, Williams Lake, BC


Abstract As the mountain pine beetle infestation threat in Alberta increases, there is a need to understand future ecosystem responses to this outbreak. We report a study of the dynamics of forests impacted by the 1980’s outbreak in Waterton National Park, Alberta. Using historical ecology approaches (dendrochronology) and stand mensuration data, we compared stand structures before and after beetle outbreaks and determined the role that beetle disturbance plays on the ecology of lodgepole pine in Southern Alberta. Severe infestations remove the old, dominant canopy, creating large timber losses as the merchantable canopy is killed by the beetle. However, our studies indicate that mountain pine beetle can be regarded as an agent of forest transformation, and in the long term, impacted stands display remarkable resiliency. We also surveyed stands in the Grand Prairie area of Alberta, in sites where beetle has not been known to occur at outbreak levels in recent history (last 100 years?). We projected that, depending on the intensity of beetle disturbance, these stands will follow the same trajectories as similar stands in BC and Southern Alberta. These trajectories can be described as follows: • •

Stand replacing fires initiate even-aged lodgepole pine stands; Multiple MPB disturbances create openings providing opportunities for natural regeneration to occur (a regeneration delay my take place) and for fast growth release in the existing advance regeneration. Frequency and severity of MPB outbreaks determine the structure and composition of the residual stand. Intense outbreaks lead to regeneration by shade intolerant species. Low intensity outbreaks would favour regeneration with shade tolerant species The result is stands that have variable canopy and cohort structure

In the absence of fire disturbance MPB will play a dominant role in directing stand dynamics and structure in the Alberta. We speculate that beetle impacted Jack pine stands will sustain similar transformations, leading to stands of complex structure. Notes:

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