Plants could override climate change effects on wildfires
A wildfire burns in the boreal
forests of Alaska's Yukon Flats in summer of 2006. (Photo courtesy of Philip
Higuera)
Scientists predict that global climate change will make many regions
around the world warmer and drier, a factor which, taken by itself, would
seem to increase the risk of wildfires.
But a new study led by a Montana State University researcher shows that
changes in the types of vegetation covering an area play a major role in
determining how often that area is burned by fires and could even counteract
the effects of changes in temperature and moisture.
In the study, MSU earth sciences post-doctoral researcher Philip Higuera and
his colleagues show that the risk of wildfires can be either reduced or
increased by changes in the distribution and abundance of plants. The study
will be published in the May issue of the journal Ecological Monographs.
"Climate affects vegetation, vegetation affects fire and both fire and
vegetation respond to climate change," Higuera said. "Our work emphasizes
the need to consider the multiple drivers of fire regimes when we anticipate
how they will respond to climate change."
Higuera and his colleagues studied fire history in northern Alaska by
analyzing sediments at the bottom of lakes, some dating as far back as
15,000 years. In the samples from the lakes, the scientists measured the
abundance of different preserved plant parts, such as pollen, to determine
what types of vegetation dominated the region in the past. Like rings in a
tree, different sediment layers represent different times in the past.
The scientists then looked at charcoal deposits in the sediments to
determine how often wildfires had burned over those soils. They compared
that to the kinds of vegetation that were dominant at the time and finally
looked at what is known about historical climate changes in northern Alaska.
The scientists discovered that, in many cases, changes in climate were less
important than changes in vegetation when it came to affecting the frequency
of wildfires.
For example, 10,500 years ago, the climate in northern Alaska went from cool
and dry to warm and dry. The scientists found that the vegetation changed
along with the climate, from flammable shrubs to more fire-resistant
deciduous trees. As a result, there was a sharp decline in the frequency of
fires.
Contrast that to about 5,000 years ago, when the area became cooler and
wetter again. Considered alone, that would seem to decrease the risk of
wildfire, yet the scientists found evidence of more frequent fires, a
pattern they attributed to the development of high flammability spruce
forests in the region.
"Climate is only one control on fire regimes," Higuera said. "If you only
considered climate when predicting fire under climate-change scenarios, you
would have a good chance of being wrong. You wouldn't be wrong if vegetation
didn't change, but the greater the probability that vegetation will change,
the more important it becomes when predicting future fire regimes."
Higuera hopes his findings will help predict modern changes in large-scale
wildfire patterns as the world's climate changes. While his work mostly
deals with boreal forests, it still shows scientists that the effects of
vegetation on wildfire is an important area for future study, he said.
"With global climate change, we're going into a period where things aren't
going to be the same as what we know," he said. "By looking into the past,
we see a larger set of possibilities that will help us prepare for the
future."
Higuera's research stems from a work funded by a four-year, $742,000 grant
from the National Science Foundation, which was awarded to the University of
Washington in 2001.
Higuera's co-authors on the study include Linda Brubaker and Patricia
Anderson from the University of Washington, Thomas Brown from Lawrence
Livermore National Laboratory and Feng Sheng Hu from the University of
Illinois.
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