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Wildfires in southern Arizona high-elevation forests: More severe but not larger

Date: April 15, 2015


A specimen from the Pinaleño Mountains with seven fire scars between 1785 and 1863, but no scars from 1864 until the tree was killed by bark beetles in 1995. (Photo: C.D. O’Connor)
A specimen from the Pinaleño Mountains with seven fire scars between 1785 and 1863, but no scars from 1864 until the tree was killed by bark beetles in 1995. (Photo: C.D. O’Connor)

Background

Scientists with the USDA Forest Service Rocky Mountain Research Station and the University of Arizona established the Pinaleño Demography project. The primary goal of the project is to determine how forest vegetation, wildfire, insect outbreaks, humans, and climate interact by using tree-ring analysis to provide a historical context for modern wildfire events.

The project area is located in the Pinaleño Mountains in southeast Arizona. The substantial elevational gradient and southern location of the Pinaleño Mountains make them an ideal location for studying disturbance interactions, serving as a “canary in the coal mine” for the effects of changing climate on the extensive conifer forests further north.

Research

The Pinaleño Demography project began with scientists looking at two base questions: Are size and severity of wildfires and insect outbreaks increasing in high elevation forests in the American Southwest? and, Are changes in disturbance regimes attributable to natural variation, past forest management, or climate change?

C.D. O’Connor samples a fire scar from a dead ponderosa pine in the Pinaleño Mountains in July 2009.
C.D. O’Connor samples a fire scar from a dead ponderosa pine in the Pinaleño Mountains in July 2009.
They found that historically, fires were often quite large, burning 50 percent or more of the landscape in single years. Prior to 1880, about 70 percent of the landscape burned every 20 years, or more frequently. However, since 1880, 70 percent of the landscape has not burned at all. Modern wildfires are more severe than historical fires -- compared to pre-1880 wildfires the proportion of high-severity area in burned areas is four times greater. Modern changes in fire spread and severity are attributed to accumulation of fine- and large-sized fuels over the landscape.

Differences in fire severity and spread before and after 1880 are primarily attributable to human-caused changes in forest structure and fuels. Managers can reverse these trends by reducing stand densities and fuel connectivity, particularly in the mixed-conifer. If left untreated, managers should expect large severe fires during moderate as well as severe drought conditions.

 

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Principal Investigators: 
Forest Service Partners: 
Coronado National Forest
External Partners: 
University of Arizona, U.S. Fish and Wildlife Service