Chile had some of the worst wildfires in its nation's history in 2017, but policymakers and communities should expect larger and more frequent wildfires in the years to come, according to a new study co-authored by a Portland State University professor.
In the study, published online Aug. 22 in the journal PLOS ONE, researchers from the U.S. and Chile examined the large-scale trends and drivers behind fire activity in central and south-central Chile over a period from 2001 to 2017. During the 2016-17 season alone, a series of fast-spreading fires destroyed more than 1.4 million acres (580,000 hectares) of land.
The study builds on previous research that found that the combination of changing climatic conditions, land cover and land use will continue to result in more fires across south-central Chile.
Vegetation type, elevation and slope, mean population density and climatic conditions such as precipitation were found to have the greatest influence on the probability of fire occurrence and the amount of area burned for any given year.
Andrés Holz, a geography professor in PSU's College of Liberal Arts and Sciences and a co-author of the study, said that through the years, vast swaths of native forests across Chile have been cut down and replanted with pine and eucalyptus trees, both of which are highly flammable. That shift to more homogenous crop-like tree plantations has allowed fires to spread much more quickly.
"There needs to be a more concerted effort to increase the structural diversity of tree planting so if there are new fires — and there will be — that the fires at least have trouble moving along," said Holz, who also serves as a faculty fellow in PSU's Institute for Sustainable Solutions.
The study also raised concerns that some prescribed burns set on pasture and agricultural lands escape control and spread into neighboring forests. That, combined with a warming and drying climate, are expected to result in larger fires. When extended periods of warm and dry conditions coincide with strong winds, small wildfires can quickly grow into ones that are out of control.
The study suggests that efforts be made to re-establish native forests that are more heterogeneous to help reduce overall landscape flammability.
"Fires preferentially burned in areas that were most conducive for burning — the homogenous vegetation types like tree plantations and pasture lands," Holz said.
The study also recommends that policymakers and officials consider the role that prescribed burns play in the spread of wildfires. Holz suggests that during heat waves and prolonged droughts, post-harvest burns be monitored more closely or banned altogether.
The study's other authors are David McWethy, Julian Stahl and Bryce Currey from Montana State University, Thomas Veblen from the University of Colorado, Boulder, Aníbal Pauchard from the Universidad de Concepción in Chile, Rafael García from the Instituto de Ecología y Biodiversidad in Chile and Mauro González from the Universidad Austral de Chile.