Plants could override climate change effects on wildfires

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."

Source: Montana State University