A Holocene Record of Vegetation Change and Mountain Pine Beetle Outbreaks at Lake of the Woods, Montana, USA

Recent mountain pine beetle (Dendroctonus ponderosae) outbreaks have been characterized as unprecedented largely in the absence of information about their occurrence prior to historical documentation. The ability to reconstruct presettlement outbreaks from sediment cores requires the identification and validation of appropriate proxies. In this paper, we provide a Holocene record of vegetation change indicating putative mountain pine beetle outbreaks in a lodgepole pine (Pinus contorta)/mixed-conifer forest at Lake of the Woods, Montana. Using a normalized difference pollen index, we positively identified postsettlement mountain pine beetle outbreaks, which served as cali-bration points for identifying other outbreaks through the Holocene. The Lake of the Woods record indicates that vegetation change was being driven primarily by precipitation and that the multiple reconstructed contemporary and presettlement mountain pine beetle outbreaks occurred during periods when the forest composition was dominated primarily by Pinus spp. The occurrence of one of these outbreaks at similar to 8200 cal yr BP is coincident with 2 other records from the Northern Rockies, suggesting a large regional outbreak at this time.