“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.