Fule et al. 2012

Post date: Sep 20, 2012 8:26:29 PM

Here's an idea: climate is a fundamental control over fire regimes, and, all other things being equal, widespread fire should occur in years that are drier or warmer than usual. (Biondi et al. (2011) first proposed this idea as a testable hypothesis, and it's actually a little more complicated. It could be that fires occur in dry years, or in somewhat dry years following extremely wet years.) While this is probably true, it could also be true that human activity could decouple this "pyroclimatic" relationship. But how would one test this? Well, Peter Fule and his buddies (2012) had an awesome idea: find two places that have pretty much the same vegetation and climate historically, but experienced a change in land use activity at a known point in the past. He found a place just like this, in the mountains of southeast Arizona and northern Mexico. While frequent fires continued in Mexico, organized fire suppression and livestock grazing in Arizona resulted in no fires after 1892. Climate predicted that fire regimes would essentially continue unchanged in both locations. Thus, the pyroclimatic hypothesis is supported for the Mexican study sites, but is rejected for the Arizonan study sites, where human activity decoupled fire activity from climate.

This is one of the big questions that the WildFIRE PIRE project is trying to address, but over a much longer time scale, and for a much larger spatial extent. The best scientific guess right now is that places like New Zealand and Tasmania had their fire regimes decoupled from climate when humans arrived (about 600 and 6000 years ago, respectively), whereas places in the western United States didn't have their fire regimes decoupled from climate until the arrival of Euro-American settlers. (Although I would suggest that there are some places in the western US, like the Willamette Valley, where humans decoupled fire from climate thousands of years ago.) Our plan right now is to use simulation modeling in Tasmania to test how different pattern of land use under historic climate affect vegetation and fire dynamics. It essentially the same "natural experimental" approach that Fule et al. used, except that we'll be using the exact same landscape, and simulating two different human activity regimes, rather comparing historical observation for two similar landscapes.