Long thought to produce only one generation of tree-killing offspring annually, some populations of mountain pine beetles now produce two generations per year, dramatically increasing the potential for the bugs.
Because of the extra annual generation of beetles, there could be up to 60 times as many beetles attacking trees in any given year, their study found. And in response to warmer temperatures at high elevations, pine beetles also are better able to survive and attack trees that haven’t previously developed defenses.
That’s from the University of Colorado, Boulder news release for a new study in in The American Naturalist.
We’ve known that climate change favors invasive species, but the mountain pine beetle infestation is far worse than anyone had imagined even a decade ago. This this new study, “Mountain Pine Beetle Develops an Unprecedented Summer Generation in Response to Climate Warming,” spells out the grim facts:
The current MPB epidemic is the largest in history, extending from the Yukon Territory, Canada, to southern California and New Mexico…. To date, more than 13 million ha [hectares] of trees have been killed in British Columbia. The MPB-killed trees in British Columbia alone will release 990 million tons of CO2 into the atmosphere, an amount equal to five times the annual emissions from all forms of transportation in the country. Forests affected by bark beetles also have altered hydrology and biogeochemical cycles. Thus, extensive beetle kill is altering forest ecology and tipping conifer forests from regional carbon sinks to carbon sources, thereby creating positive feedback for climate-change factors.
For more on the amplifying feedback, see “Nature: Beetle tree kill releases more carbon than fires.”
It turns out that there has been an “exponential increase in the beetle population.” Why has infestation been nonlinear? The study’s abstract explains:
The mountain pine beetle (MPB; Dendroctonus ponderosae) is native to western North America, attacks most trees of the genus Pinus, and periodically erupts in epidemics. The current epidemic of the MPB is an order of magnitude larger than any previously recorded, reaching trees at higher elevation and latitude than ever before. Here we show that after 2 decades of air-temperature increases in the Colorado Front Range, the MPB flight season begins more than 1 month earlier than and is approximately twice as long as the historically reported season. We also report, for the first time, that the life cycle in some broods has increased from one to two generations per year. Because MPBs do not diapause and their development is controlled by temperature, they are responding to climate change through faster development. The expansion of the MPB into previously inhospitable environments, combined with the measured ability to increase reproductive output in such locations, indicates that the MPB is tracking climate change, exacerbating the current epidemic.
[Read about diapause here. I welcome a simpler explanation from any biologist reading this.]
For more background on the study, here is an extended excerpt from the news release: