In reference to the Lynch study, “correlation” is really the wrong word (even though they used it in their abstract). What they did is match a model of the burn to the observed burn pattern, and found that their model predicted correctly 87% of the pixels on a map that actually burned. Based on this model, areas with beetles were 11% more likely to burn. Drought was actually the most important factor predicting burn, as one would expect. But from what I could tell they included drought and beetles as separate factors, when we know that they are not independent – beetles are more successful during droughts. But what that means is that a beetle x drought interaction term is key. (Drought may or not be affected by climate change; it is most conservative to say not necessarily, because recent tree-ring data (as you probably know) shows that the west of the past few hundred years has been very dry, and the period of intense settlement actually coincided with an unusually wet period: see http://bioblog.biotunes.org/bioblog/2007/03/16/the-definition-of-drought/)

Still, it is certainly more complicated than I presented in this brief column – as Lynch et al state in their discussion:

“…we concur with Bigler and others (2005), who also concluded that the more important effect of beetle activity on fire risk is through a change in stand structure and composition, as opposed to an increase in fuels.”

Even if some lodgepole stands burn over a larger interval of 150-200 years, then suppressing fire in stands getting close to those ages, which haven’t yet burned, has increased the interval unnaturally until the next burn, so it doesn’t really matter. That said, I had a really interesting discussion recently with a fire specialist from our local FS office, which enlightened me more about the history of fire suppression, which shows it to have been a lot more complicated than just policy positions. I am planning to do a follow-up on this post soon.

Finally though, you state that entomologists you know don’t think that climate change is a major cause of the spread of MPB. Could you please elaborate? Given that they are spreading into areas that until recently were regularly cold enough to kill them off, it seems as though climate change is a pretty strong contender. Do your colleagues believe that this is just a natural cycle unrelated to a longer term trend? Or do they think that the spread into historically too-cold areas is unimportant? The former is certainly a possibility; one of the challenges in climate change work is separating natural, shorter cycles from the overall global trends. We may not definitively be able to determine the truth until a hundred years from now.

But, I’m one entomologist who believes that the evidence, although circumstantial, suggests that climate change is a big player in MPB demographics. Whether the changes we will see will really amount to an “ecological disaster” is a more open question to me, despite my hyperbole, because long-term ecological change (on a scale beyond human lifetimes) itself is indeed a natural process. We humans just tend to think of changes that happen during our lifetimes as subjectively bad.

Could you please give me a more complete reference for the paper you cite? I certainly am interested in what the latest thinking on this is – I’m sure it has evolved since I wrote this three years ago.

Cheers.

In addition many lodgepole pine fire return intervals are on the order of 150-200 years, much longer then the fire suppression era. Also, the 1910 fires created a landscape of similar aged lodgepole pine that has contributed to the food source availability for MPB, and is another non-climate, non-human related reason for some of the current large-scale epidemics. I do believe that climate change has a role in all of this, but I don’t think it’s the major cause, and many of my entomology colleagues agree.