How Fire Could Change the Face of the West
The vast wildfires of this summer and last represent a new normal for the western United States. They may signal a radical landscape transformation, one that will make the 21st century West an ecological frontier.
Unlike fires that have occurred regularly for thousands of years, these fires are so big and so intense as to create discontinuities in natural cycles. In the aftermath, existing forests may not return. New ecosystems will take their place.
“These transitions could be massive. They represent the convergence of several different forces,” said Donald Falk, a fire ecologist at the University of Arizona. “There is a tremendous amount of energy on the landscape that historically would not have been there. These are nuclear amounts of energy.”
Falk’s specialty is fire dynamics in the American Southwest, a region where record fires have become routine. Fueling the infernos is a combination of fire suppression, livestock grazing and logging.
Because small, low-intensity blazes are usually prevented from spreading, dead wood has accumulated, especially in arid and semi-arid regions where decomposition occurs slowly. Without these fires, dense shrubs and small trees proliferate, as they also do in gaps opened by harvesting of large trees. Grazing removes grasses that traditionally carried small fires and causes erosion that reduces soil’s ability to hold water.
Much of the West is now a giant tinderbox, literally ready to combust. Yet thanks to fire suppression, the consequences have been postponed for decades.
“When you look at the long record, you see fire and climate moving together over decades, over centuries, over thousands of years,” said pyrogeographer Jennifer Marlon of Yale University, who earlier this year co-authored a study of long-term fire patterns in the American West.
“Then, when you look at the last century, you see the climate getting warmer and drier, but until the last couple decades the amount of fire was really low. We’ve pushed fire in the opposite direction you’d expect from climate,” Marlon said.
The fire debt is finally coming due. In the Southwest, fires are reaching historically exceptional sizes and temperatures. “The fuel structure is ready to support massive, severe fires that the trees have not evolved to cope with,” said forest ecologist Dan Binkley of Colorado State University. “When the extent of the areas burned becomes large, there are no remaining sources of seeds for the next generation.”
Filling the newly open space will be grasses, shrubs and aspen, said Binkley. The forests will be gone. Something similar may also happen in California’s high-elevation Ponderosa forests, though different plant species will take their place than in the Southwest.