Friday, September 22, 2017

Small Pests, Big Problems:  The Global Spread of Bark Beetles

Warming temperatures are fueling the expansion of pine and spruce beetle outbreaks across North America, Europe, and Siberia, ravaging tens of thousands of square miles of woodlands.  Scientists warn that some forest ecosystems may never recover. 

Dead trees in a California forest in August 2016. (Credit: U.S. Forest Service) Click to Enlarge.
First, mountain pine beetles devastated lodgepole and ponderosa pine trees across western North America. Then came spruce beetles, which have targeted high-elevation Engelmann spruce, spreading from New Mexico into Colorado and beyond.  Altogether, with their advance fueled by climate change, bark beetles have ravaged 85,000 square miles of forest in the western United States — an area the size of Utah — since 2000.  Pine beetles also have killed trees across roughly 65,000 square miles of forest in British Columbia, and in the southeastern U.S., they have caused millions of dollars of damage to the timber industry in states such as Alabama and Mississippi.

The beetles are now advancing up the Atlantic coast, reaching New York’s Long Island in 2014 and Connecticut the following year.  A new study projects they could begin moving into the twisting pitch pines of New England and the stately red pines of Canada’s Maritime provinces by decade’s end.  Warming winters could push the beetles north into Canada’s boreal forest within 60 years, climate scientists say.

And from Europe to Siberia, bark beetle outbreaks are erupting with increasing frequency in woodlands weakened by rising heat and drought.  Switzerland is preparing for the eventual loss of spruce, its most important tree, as warmer weather fans conditions that will make it nearly impossible for all but those high in the Alps to survive.  The Czech Republic, Poland, Germany, and Slovakia are all experiencing intense beetle attacks on their Norway spruce.  In Siberia, a related spruce beetle has helped another insect pest, the Siberian silk moth, damage more than 1,100 square miles of Siberian fir, pine, and spruce since 2014.  That infestation is now spreading northward into historically outbreak-free boreal taiga stands.

“The amount of conifer mortality that we’re seeing both here and in Europe is unprecedented historically,” says Jesse Morris, a geographer with the University of Utah in Salt Lake City. Morris and other scientists are trying to determine the potential impacts, such as more intense wildfires, disrupted watersheds, destroyed habitats, and reduced carbon storage, as climate change spurs increasingly widespread and severe beetle outbreaks.

Bark beetles are a natural part of the conifer forest life cycle, regularly flaring and fading like fireworks.  But the scope and intensity in the past two decades is anything but normal, scientists say, in large part because rising temperatures are preventing the widespread winter die-off of beetle larvae, while also enhancing the beetles’ killing power.  Not only are the insects expanding into new territory, they’re also hatching earlier and reproducing more frequently.  New infestations become full-blown with astonishing speed, and the sheer numbers of beetles exceeds anything forest experts have seen before.  Morris says he’s seen spruce beetle epidemics in Utah so intense that when the insects had killed all the trees, they began attacking telephone poles. 

Perhaps even more concerning is that beetles are beginning to target novel species, such as the jack pine — found across wide swaths of Canada — that had escaped assault until now. 

Read more at Small Pests, Big Problems:  The Global Spread of Bark Beetles

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