By Michelle Werts

A lodgepole pine displaying pitch tubes
A lodgepole pine displaying pitch tubes, where mountain pine beetles begin their tunneling. Credit: Steven Katovich, USDA Forest Service,

You know when you have an itch, but scratching it only seems to make it worse, and you’re stuck in a perpetual cycle of misery? Well, nature experiences similar phenomena: feedback loops. In technical terms, a feedback loop is when an output from a past event influences the same event, creating a cyclical pattern that’s difficult to break. And in a new book, a biologist claims that one of these vicious cycles is currently at play in our western forests thanks to those pesky mountain pine beetles.

Mountain pine beetles have been coexisting, relatively peaceably, with our pine forests for centuries. They can be found from Canada to Mexico and from sea level to 11,000 feet. Adult mountain pine beetles emerge each July and feast on our forests through September when the species then overwinters as eggs and young larvae before emerging again. Hard winters with cold temperatures used to kill many of the eggs and larvae, but with warmer winters over the last decade or so, more beetles are surviving, which means more mouths are feasting and more trees are being damaged.

As biologist Reese Halter discusses in The Insatiable Bark Beetle, warming temperatures and more frequent droughts have allowed beetles to occupy new climate zones and, thus, destroy huge expanses of pines. This destruction is systematically eliminating thousands of acres of natural carbon sinks, as trees absorb much more carbon than they emit — except when they die. According to Halter’s book, “Over the next decade, the beetle-killed forests will emit 250 million metric tons of CO2 — the equivalent of five years of car and light-truck emissions in Canada.” So, climate change causes beetles to spread, allowing them to kill our pine forests, which in turn causes more carbon to be released into the atmosphere than before. Which means more climate change. Which means more beetles survive each winter and can climb to now-milder, higher elevations. And kill more trees. Feedback loop indeed.