USING LAKE SEDIMENT CORES TO INVESTIGATE PAST MOUNTAIN PINE BEETLE OUTBREAKS

Current mountain pine beetle (MPB) outbreaks are threatening many pine communities in the western United States. It is believed that the increased severity of mountain pine beetle outbreaks is a response to climate change. Warming climate allows for faster reproduction of MPB and can also contribute to a forests susceptibility to MPB outbreaks through increased drought stress. There is little context for these current outbreaks as there is little known about past bark beetle outbreaks and the environmental conditions surrounding them. While early work suggested that beetle elytra from lake sediments may provide long-term outbreak histories, it has been shown that very specific conditions are associated with these types of records. New studies in spruce forest have used pollen composition changes to demonstrate past outbreaks, however it has been unclear if this would work in pine dominated systems where a decline in one taxa is closely associated with the release of another. A historical (last ~500 years) record of disturbance, including fire and MPB outbreaks from a high elevation lodgepole pine forest in the Sawtooth Mountains, Idaho has been developed using pollen, plant macrofossils and charcoal. This study demonstrates that pollen ratios can be used to identify past MPB outbreaks in a pine dominated forest. A baseline for the frequency and severity of past disturbances (specifically bark beetle outbreaks) and climate conditions is needed to understand the current outbreaks. The data provided by this project will help researchers and land managers understand how climate has affected outbreaks in the past which will be useful for understanding and trying to mitigate present and future outbreaks, especially as climate continues to change.