Climate and the Beetle
This is the second in a series of blogs on the pine beetle, western forests in the U.S. and Canada, and their relation to climate change. There have been many discussions on the relationship of the pine beetle infestation and climate change. The analysis of the relationship of infestations of this type to climate change is very difficult. I give a set of links to primary references below. Logan and Powell (2001)
describe a model that represents the population of the pine beetle. There are many environmental parameters that affect the population, but in the end, temperature is one of the most important. They point out that within the “normal” range of variability the population is relatively stable. However, outside of this normal range, warmer or cooler, the population is very sensitive. What is normal? Perhaps, in this case it is the temperature range to which the pine beetle has adapted. When it gets very cold, about – 40 C, there is 100% mortality.
Logan and Powell estimated the expansion of the pine beetle, and they found that extension of the range 7 degrees of latitude northward was likely. This projection used climate predictions models were available in 2000 and investigate the impact of an average temperature rise. Both observations and predictions show that the northern high latitudes temperature increases are higher than the global average. Therefore, as far as temperature is concerned, Logan and Powell have likely underestimated the increase in latitudinal range of the pine beetle.
The recent changes in the pine beetle range and death of pine trees is consistent with the signal of global warming – extension northward and to higher altitudes. There is history, however, of infestations in the past. In fact, during the 1930s there was a documented infestation. The 1930s is a period, where readers of this blog know, when it was warm. The history of infestations and remissions and the sensitivity to parameters other than temperature make it difficult to directly attribute the current infestation to global warming.
While it might be a challenge to attribute the current outbreak of pine beetles to global warming, it is less challenging to document the impact on global warming of the pine beetle. As the forests are killed, they change from removing carbon dioxide from the atmosphere to releasing carbon dioxide to the atmosphere. In a 2008 paper in Nature, Kurz and co-authors
document the carbon release from a study area that covers the now-historic pine beetle outbreak in British Columbia. This release is found to be 75% of the 1959-1999 average release of carbon dioxide from all Canadian forest fires. This rapid, large release stands in contrast to the slow, steady take up of carbon dioxide by a growing forest. Because the uptake of carbon dioxide by trees is relatively slow, any recovery of the infested forest will take many years.
This weekend I was watching a candle burn. It was a tall, conical candle with its point at the top. As the wick burned into the widening candle it built a pool of wax. This pool threatened to put out the flame. As the flame approached extinction, there was a breach in the wall of solid wax that held the pool. The liquid wax poured down the side of the candle. The wick was exposed to air and burned rapidly. The breach was such that all the new wax that melted flowed down the side. The wick continued to burn rapidly. It is this sort of change, one caused by rapid transitions that the pine beetle infestation represents. Forests are not wholly represented by slow, steady changes and gradual adaptation to a new environment. In fact, episodic, rapid proesses are often the mechanism of irreversible change.
Damage from the Mountain Pine Beetle, Boreas Pass Road, Colorado, 2009. (R. Rood)
Primary References:Kurz et al., Nature, 2008Logan and Powell, American Entomologist, 2001 Climate Change and Forest Disturbances: Dale et al. 2001 class readings Effects of Climate Change on Range of Pine Beetles: Carrol et al. 2003 Pine Beetle Symposium 2003 Mountain Pine Beetle: US Forest Service, Amman et al. 1990
Previous Pine Beetle Blogs: Beetles and the Climate
Previous Blogs on Phenology and Ranges of Trees Series of Blogs in 2008 of Spring Coming Earlier Trees Moving North