Fire Regime

Oak trees with burned grass and wood on ground.
Before widespread settlement in southern Arizona, low-intensity lightning-strike fires occurred every five or so years. These fires cleared the undergrowth and usually did not kill mature trees.

NPS/M. Regan

Imagine arriving in southern Arizona around 1750. Large open valleys teem with Sonoran pronghorn, grazing on grasses and cholla cactus. One startles and flees, and the other pronghorn follow, even though you are more than a mile away. You turn your horse towards a small river, coming out of the nearby mountains, and trace it into a spacious woodland. Large boulders are interspersed with a wide variety of oak trees, junipers, and manzanitas. It seems as though a fire had burned here recently, within the last five years, since there is very little undergrowth. Most of the big, mature oak trees are alive, although one or two succumbed to the fire, you notice. Woodpeckers bore holes in the dead trees, to shelter their eggs.

Prior to widespread European settlement, this part of Arizona experienced frequent, low-intensity fires. The pattern often was wet years when grasses and shrubs grew, providing fire fuel for the following dry years, when lightning could easily ignite wildfires. Scientists look at tree ring records, and can tell that across the southwest, dry years had more fires than wet years, and these fire patterns were cyclical.

Now flash forward to 1888, and you are an early homesteader, settling in Bonita Canyon with your family. You graze cattle on your own homestead, as well as all the unclaimed forest and canyon land around you. Your small herd of cattle, along with thousands of others foraging across the southwest, reduce grass and shrubs wherever they go. Cattle are creatures of habit, and follow the same trails year after year, essentially creating firebreaks across the terrain.

Although the United States Forest Service was established in 1905, fire suppression policies did not begin in earnest until 1935 with the so-called “10 am policy.” This policy's goal was to completely suppress any fire before 10 am the next day. From 1935 through 1978, fire suppression was a priority for land management. For decades, managers of forests thought eliminating fires would help increase timber production, and ignored the fuel buildup and increased danger of people living in fire-suppressed, forested landscapes (now called the Wildland-Urban Interface).

 
smoke billowing up from rugged mountains
An aerial view of the Horseshoe Two Fire, which burned over 222,000 acres.

NPS/ E. Hutchins

It wasn’t until 1978 that the US Forest Service acknowledged the ecological importance of fire, and lifted its policy to always put out every single fire that started on public lands. Still, fire suppression continued, especially in southern Arizona, until 1994, when the Rattlesnake Fire burned more than 25,000 acres in the Chiricahua Mountains. Very dry conditions and almost a century of fuel buildup, due to fire suppression, propelled the fire across the landscape, and it grew quickly. Much of the Chiricahua Mountains is managed by the US Forest Service, while Chiricahua National Monument is managed by the National Park Service, which has its own fire policies.

For some scientists, the Rattlesnake Fire is the first in a new era of fires—the intensification era. In June 2011, after more years of drought, another massive wildfire roared across the Chiricahua Mountains. This one consumed over 222,000 acres, destroyed 23 structures, and cost more than $50 million dollars to fight. In its wake, the Horseshoe Two Fire left a ravaged landscape of burned trees and barren mountainsides. When the summer monsoon rains arrived, they beat the bare ground, and caused massive flash floods and wide-scale erosion.

The landscape you see now at Chiricahua National Monument is a result of these three fire eras, but the most visible aspects are from the more recent Fire Intensification Era. Across the western United States, wildfires are getting larger, destroying more homes, and impacting the local and national economy. How should US forests be managed today? What role does climate change play in fires? Will wildfires continue to intensify, be larger, and more devastating? How will that impact the plants, animals, and humans that call this area home now, and in the future?

 

Explore in-depth fire ecology of the Chiricahua Mountains with this article.


See how the Chiricahua Mountains have recovered after the Horseshoe Two Fire with an interactive story map from Northern Arizona University/Southwest Fire Science Consortium.

Discover how other national park sites deal with both structural fires and wildfires.

Billowing black, grey, and orange smoke over canyon filled with rock pinnacles.
The Horseshoe Two Fire burned for about a month, before entering Chiricahua National Monument.

NPS/K. Flanery

 
View from Sugarloaf Mountain in 1934 and 2000
Black and white photo of a rocky mountain range black and white photo of a rocky mountain range with lots of vegetation on lower slopes
View from Sugarloaf Mountain in 1934, prior to fire suppression. NPS
View from Sugarloaf Mountain (looking toward Cochise Head) during the fire suppression era, in 2000. A. Taylor



 
Rocky mountain behind rock pinnacles and spires, interspersed with trees.
The view from Sugarloaf Mountain six years after the Horseshoe II Fire swept through the Chiricahua Mountains.

W. McGurdy

 
three photos: sparse vegetation in canyon; canyon full of vegetation; canyon still mostly full of vegetation
Three views of Bonita Canyon, showing the changes in vegetation during and after fire suppression. The first view is in the 1920s, the second in 2000 (before the Horseshoe II Fire), and the third is in 2017 (six years after the Horseshoe II Fire). Sugarloaf Mountain is marked to help orient the images.

Image 1: NPS --Image 2: A. Taylor --Image 3: W. McGurdy

 

Last updated: December 1, 2018

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