"Nature on stunning new climate feedback: Beetle tree kill releases more carbon than fires"
“He that troubleth his own house shall inherit the wind.” A Biblical proverb for our times, it turns out….
The bark beetle is devastating North American trees (see “Climate-Driven Pest Devours N. American Forests“).
Global warming has created a perfect climate for these beetles — Milder winters since 1994 have reduced the winter death rate of beetle larvae in Wyoming from 80% per year to under 10%, and hotter, drier summers have made trees weaker, less able to fight off beetles. [Picture shows forests turned red by beetle.]
New reseach published in the journal Nature, “Mountain pine beetle and forest carbon feedback to climate change,” (subs. req’d, abstract reprinted below), quantifies the current and future impact just from the beetle’s warming-driven devastation in British Columbia:
… the cumulative impact of the beetle outbreak in the affected region during 2000–2020 will be 270 megatonnes (Mt) carbon (or 36 g carbon m-2 yr-1 on average over 374,000 km2 of forest). This impact converted the forest from a small net carbon sink to a large net carbon source.
No wonder the carbon sinks are saturating faster than we thought (see here) — unmodeled impacts of climate change are destroying them:
Insect outbreaks such as this represent an important mechanism by which climate change may undermine the ability of northern forests to take up and store atmospheric carbon, and such impacts should be accounted for in large-scale modelling analyses.
Any “good news” here? Only if you like very dark irony. The accompanying news story (here, subs. req’d) notes:
Even if climate change brings further warm winters to the region, however, experts think this infestation has probably peaked. Mountain pine beetles can only reproduce in the largest trees, which were abundant thanks to a growth spurt after wildfires raged across western North America 80 to 140 years ago. Soon 80 to 90% of those large trees will be gone, Kurz says. “The beetle will eat itself out of house and home, and the population will eventually collapse.”
Hmm. “Eat itself out of house and home.“ Does the bark beetle sound like any other species we know? Finally, the species formerly known as homo sapiens sapiens is no longer alone in its self-destructive quest to destroy its habitat. Inhert the wind, indeed.
“The pine beetle infestation is the first major climate change crisis in Canada” notes Doug McArthur, a professor at Simon Fraser University in Vancouver. “We’re seeing changes in [mountain pine beetle] activity from Canada to Mexico,” said Forest Service researcher Jesse Logan in July 2004 (here), “and the common thing is warming temperatures.” In a May 2006 speech on climate change, Senator Lisa Murkowski of Alaska pointed out that the tremendous recent warming had opened the door to the “voracious spruce bark beetle,” which devastated over three million acres in Alaska, “providing dry fuel for outbreaks of enormous wild fires.”
A 2005 study, led by the University of Arizona, with Los Alamos National Laboratory and the U.S. Geological Survey, “Regional vegetation die-off in response to global-change-type drought,” examined a huge three-million acre die-off of vegetation in 2002-2003 “in response to drought and associated bark beetle infestations” in the Four Corners area (Arizona, New Mexico, Colorado, and Utah). This drought was not quite as dry as the one in that region in the 1950s, but it was much warmer, hence it was a global-warming-type drought. The recent drought had “nearly complete tree mortality across many size and age classes” whereas “most of the patchy mortality in the 1950s was associated with trees [greater than] 100 years old.”
Most of this tree death was caused by bark beetle infestation, and “such outbreaks are tightly tied to drought-induced water stress.” Healthy trees defend themselves by drowning the tiny pine beetles in resin. Without water, weakened, parched trees are easy meals for bugs.
One final note: This catastrophic climate change impact and its carbon-cycle feedback were not foreseen even a decade ago — which suggests future climate impacts will bring other equally unpleasant surprises, especially if we don’t reverse our emissions path immediately.
Here is the full Nature abstract:
The mountain pine beetle (Dendroctonus ponderosae Hopkins, Coleoptera: Curculionidae, Scolytinae) is a native insect of the pine forests of western North America, and its populations periodically erupt into large-scale outbreaks. During outbreaks, the resulting widespread tree mortality reduces forest carbon uptake and increases future emissions from the decay of killed trees. The impacts of insects on forest carbon dynamics, however, are generally ignored in large-scale modelling analyses. The current outbreak in British Columbia, Canada, is an order of magnitude larger in area and severity than all previous recorded outbreaks. Here we estimate that the cumulative impact of the beetle outbreak in the affected region during 2000–2020 will be 270 megatonnes (Mt) carbon (or 36 g carbon m-2 yr-1 on average over 374,000 km2 of forest). This impact converted the forest from a small net carbon sink to a large net carbon source both during and immediately after the outbreak. In the worst year, the impacts resulting from the beetle outbreak in British Columbia were equivalent to 75% of the average annual direct forest fire emissions from all of Canada during 1959–1999. The resulting reduction in net primary production was of similar magnitude to increases observed during the 1980s and 1990s as a result of global change. Climate change has contributed to the unprecedented extent and severity of this outbreak. Insect outbreaks such as this represent an important mechanism by which climate change may undermine the ability of northern forests to take up and store atmospheric carbon, and such impacts should be accounted for in large-scale modelling analyses.