Wednesday, July 31, 2013

Fire Ecology: East vs. West

Note: This program first aired on July 20, 2013.

I recently had the good fortune to travel to the Rocky Mountains, specifically the greater Yellowstone ecosystem. For people like many of my friends and me, East coast kids that we are, the mountainous west has long held an almost mythic standing in our minds. Besides the fact that it lacks an ocean, on its face the west seems to have everything an outdoorsy girl could want: bottomless powder skiing, endless trail running, essentially perfect weather all the time, no biting insects, wide open spaces, and more truly high mountains than you could climb in a lifetime. At the end of a solid two weeks of downpours and fog, or when the blizzard ends in rain, sometimes Maine doesn’t quite stack up.

There’s something Maine has though, that the West doesn’t, and it influences the biological community we find here, and minimizes our exposure to one of the more unpredictable, and frankly terrifying natural phenomena out here. I’m referring of course to water, we’ve got it, in spades, and to wild fires, which are pretty rare here in the Pine Tree State, but oh so common out west.

Fire ecology is a complicated topic; it includes factors like climate, weather, forest type and age, tree species, fuel load, and human management. All of these factors can change from year to year, and day to day, and some, like human management decisions, have had repercussions that are felt for decades. So bear with me when I simplify these factors in an attempt to get to some ground truths. Maine is a forested state, and the reason we have so much forest is that we have so much water, specifically, precipitation. Remove human interference and given enough time essentially the entire state would be forested (with a few odd and extremely localized exceptions). The west is different. It gets much less precipitation, and much of what it does get is in the form of snow fall. At certain elevations that is enough precipitation to support forest, but above and below those elevations, temperatures combine with water stress to yield treeless landscapes.

The first lesson you learn in fire fighting school is about the fire triangle, the three components required for a fire to burn. The first is oxygen, chemically a fire is the exothermic reaction that occurs when the carbons and hydrogens that are combined in any kind of carbohydrate molecule recombine with oxygen. No oxygen, no fire. The second leg of the fire triangle is an ignition source. Something has to ignite the fire, lightening and human carelessness are common sparks. The third leg is fuel, which brings us back to our two forests, east and west. Forests anywhere are nothing if not fuel for fires. The frequency and intensity of fires that occur, and they will occur, depends on the volume and flammability of the fuel; just how dry is it? Here in Maine we carry a potentially high fuel load, but it seems our flammability must be fairly low, as the average presettlement rate of fire return was something well over 1000 years. The disturbances to the forests here tend to be small scale (even the fires). The transitional “Acadian” forest that covers much of Maine is not particularly fire adapted as a result, though it is sandwiched between the much more fire adapted boreal forest to the north and oak forests to the south. Western forest and woody shrub communities tend to have much shorter rates of return for fire frequency, a few hundred years for high intensity stand killing fires, and just decades for lower intensity ground fires. The trees in these forests are adapted to high fire frequency, to the point where some of the species are actually dependent on fire at some point in their life cycle. Looking beyond the fact for a moment that as a result of climate change, summers are supposed to get hotter, winters warmer, droughts worse, and precipitation events heavier but less consistent, all of which will potentially lead to more fuel, we have to look at the other way human choices are impacting the effects of wild fires.

It is scarcely two weeks since 19 firefighters were killed in the line of duty in the Yarnell fire north of Phoenix, Arizona. They were working just beyond what is called the Wilderness Urban Interface*, the zone where housing butts up to forest vegetation. This is the big topic of conversation in western fire management circles, as housing development pushes further and further into naturally fire prone dry forest and shrub areas. And it is easy to sit here in Maine and shake our heads at those silly folks building houses in burnable canyons in Colorado and Arizona, but when I look out my window, you know what I see? Trees, and only trees. It turns out that I live in the wilderness urban interface too, though it is a stretch to call West Sedgwick urban. There is actually more housing in the WUI on the East coast than anywhere out west. The problem is that many western ecosystems are so much more fire adapted, they are supposed to burn. And as anyone who has argued with Mother Nature knows, its hard to stop her when she is doing what she is supposed to. So when the humidity is so high it is hard to breath, or the fog so persistent that things start to mildew, or the rain so torrential you can’t see across the yard, I thank my lucky stars I live in Maine, and although I know wild fire could certainly happen here, I don’t have to treat it as inevitable, as I think I would if I were living the western dream, enjoying that fluffy Rocky Mountain snow and hiking all those 14,000 footers. It was fun to visit, but I’ll take our vibrant, almost decadent temperate lushness here anytime.

*The Wilderness Urban Interface is also known by its acronym WUI, pronounced “woo-eee”, but that was just too silly to say on the air.


The Yarnell fire outside Prescott AZ is just one example of the complicated intersection of climate change, human fire management, and unpredictability in nature

Precipitation info for Yellowstone:

A good radio piece on the Wilderness Urban Interface (WUI) from Colorado College: