Pine Beetles Respond to Cooler Climate
New research finds evidence that bark beetles have a long history of responding vigourously to climate change.
Records of beetle activity going back thousands of years come from lakes, rather than trees. During epidemics, mountain pine beetles become so numerous that many adults end up trapped in water.
Scientists have extracted ancient beetle remains from lake sediments in Montana and Idaho to reveal chronicles of beetle epidemics.
The bottom of Baker Lake in Montana contains traces of a large mountain pine beetle infestation occurring during the 1920s and 1930s. Fossilized beetles also document a spate of epidemics spanning several centuries around 8000 years earlier.
At Baker Lake, the beetles were abundant about 8590, 8470 and 8390 years ago. Then near Hoodoo Lake in Idaho, bark beetle epidemics occurred an estimated 8220 and 8010 years ago.
Those dates correspond with a period of rapid change in climate to cooler and wetter weather. In this region of the northern US Rocky Mountains, the beetles would have infested high-elevation forests dominated by whitebark pine.
Climate change is also a driver behind the latest mountain pine beetle epidemic in British Columbia. In the last decade, unusually warm winters in central BC have produced a massive population boom of mountain pine beetles that are killing lodgepole pines.
Andrea Brunelle, Gerald E. Rehfeldt, Barbara Bentz and A. Steven Munson. 2008. Holocene records of Dendroctonus bark beetles in high elevation pine forests of Idaho and Montana, USA. Forest Ecology and Management. 255(3-4): 836-846.