On November 8th, 2012, the Southwest Fire Science Consortium hosted a field trip to the Chiricahua National Monument in southeastern Arizona. The Southwest Fire Science Consortium comprises scientists, land managers and policy makers who interact and share science in one of the regions most dominated by fire in the United States. Representatives from the University of Arizona, Northwest Fire District, Tecnológico de Monterrey, Arizona State Forestry Division, Arizona Game and Fish Department, Cochise County LEPC/RACES/Search & Rescue, Arizona Game and Fish, ACME Services, US Forest Service, Rocky Mountain Research Station, Coronado National Forest, Arizona Geological Survey, National Parks Service - Southeast Arizona Group, National Park Service, Student Conservation Association, Bureau of Land Management, Gila National Forest, Prescott National Forest, and Sky Island Alliance attended and discussed the implications of the Horseshoe 2 Fire on debris flows, bark beetle distribution, and ecosystems in the Chiricahua Mountains (Figure 1). The consortium also discussed how to handle and prevent future wildfires in the Southwestern U.S. in the face of a decade-long drought.
The Horseshoe 2 Fire
On May 8th, 2011, at 11:00 a.m. the Horseshoe 2 Fire, one of the largest wildfires in Arizona history, started in the Coronado National Forest near the Chiricahua Mountains of southeastern Arizona (Figure 2). The Horseshoe 2 Fire originated in Horseshoe Canyon. 
The human-caused fire scorched about 222,954 acres of land and destroyed 23 structures (Table 1). By the time it was 100% contained on June 25th, 2011, it was the fourth largest wildfire in Arizona history. Over 1,379 personnel aided in containing the fire, including 38 crews, 66 engines, 36 water tenders, 4 dozers, 9 helicopters, 3 heavy airtankers and 3 heavy helitankers. The total cost of suppressing the fire topped $50 million.
At the onset fire crews thought the fire would consume no more than 35,000 acres due to informed estimates from the Horseshoe 1 Fire of 2010. The first sign that the Horseshoe 2 Fire proposed a major challenge occurred when the fire raced down a canyon in 12 hours as opposed to the anticipated 18 hours. Kristy Lund from the Coronado National Forest recalls asking the question, “Really, it’s going to come down hill nine miles?” (Watch Kristy Lund from the Coronado National forest recalls the adverse variability of the Horseshoe 2 Fire at the Southwest Fire Science Consortium field trip held on November 8, 2012 in the Chiricahua Mountains.) The fire reached the bottom of the canyon and the town of Portal, Arizona, was evacuated. After the fire was 100% contained the U.S. Forest Service Burned Area Emergency Response (BAER) team assembled to quickly assess the situation and help develop plans to address where post-wildfire impacts, such as hill slope erosion and flooding, posed immediate and significant threats to human life and property.
| 2011 Horseshoe 2 Fire At-A-Glance | ||
|---|---|---|
| Dates: 8 May to 25 June, 2011 | Cause: Human | |
| Location: Near Portal, AZ in the Chiricahua Mountains. | ||
| Total Size: 222,954 acres. Acres by ownership: Private 13,934; State 2,874; USFS 192,647; BLM 1,336; NPS 12, 163 | ||
| Vegetation types: Mixed conifer, oak brush, pinyon, juniper, ponderosa pine and grasses | ||
| Burn Severity | Acres | % of Area |
| High | 27,730 | 12.4% |
| Moderate | 66,226 | 29.7% |
| Low | 84,852 | 38.0% |
| Unchanged | 44,146 | 19.8% |
Table 1. 2011 Horseshoe 2 Fire statistics (Southwest Fire Consortium)
Why was the Fire so Severe?
High intensity wildfires increased in the last century due to suppression of fires and lack of active forest management. Research shows frequent, low temperature fires are important to a forests health by maintaining natural plant conditions and reducing the buildup of fuels. During the last century fire suppression caused forests to become extremely dense in the West. The combination of increased fuel and droughts make forests in the West susceptible to severe wildfires.
Direct causes for the severity of the Horseshoe 2 Fire included a “100 years freeze,” which occurred in February 2010. A multitude of trees, and low desert vegetation including cacti were killed. The large amount of available fuel resulting from the heavy freeze and low moisture content fed the intensity and unpredictable behavior of the fire and producing a soil burn severity pattern that was large and complex (Figure 3).
Fire Impacts on Land and Ecosystems
Joel McMillan from Northern Arizona University describing the behavior of certain species of bark beetles noted that the Douglas-fir beetle infested fire-damaged trees while other species show no preference between a fire-damaged tree and a tree not damaged by fire. Douglas-fir trees are habitat for the Mexican spotted owl and further post-fire tree mortality by the Douglas-fir beetle could threaten its habitat. Currently, the Arizona Zone of Forest Health Protection is monitoring populations of Douglas-fir beetles in the Chiricahua Mountains. In the future they may recommend using a species-offensive pheromone as a “No Vacancy” signal to protect stands of trees.
Pre- and post-fire observations by ecologist Jim Malusa from the University of Arizona in Pinery Canyon at elevations of 5,700 and 6,050 feet show rapid recovery of vegetation in the scorched areas. Even areas where soil burn severity was high to moderate, notably the 6,050 feet level near Methodist Road, show signs of recovery among woodland stands of Chihuahuan pine and oaks.
One of the last presentations of the field trip involved Ann Youberg, research geologist at the Arizona Geological Survey, discussing post-fire debris flows in the Upper Pine Canyon gully. Ann showed how the canyon went from being gully-free in May 2011 to a hosting a visible gully in August 2011, following substantial rainfall. The newly formed gully’s measured 4.5m to 8m wide. Rates of soil regeneration are lower in post fire environments with rates decreasing with increasing slopes.
How to Manage Future Wildfires
Preparing for wildfires is a difficult and chancy business. To ensure the best possible outcome it is essential to document the progression and impacts of wildfires; how rapidly they grow, their geographic pathways and distribution, and the impact or severity on vegetation and soil.
As the Southwestern US climate becomes warmer and more arid the frequency and size of wildfires may increase. The potential rise in wildfires could produce devastating impacts both locally and nationally. Forests, grasslands and other ecosystems in the West are essential to sequestering over 100 million tons of carbon each year, counterbalancing anthropogenic emissions. With the advent of more frequent large fires and climate change, ecosystems of western U.S. may not serve to sequester CO2 as they have in the past
The Southwest Fire Science Consortium fieldtrip offered food for thought concerning wildfires and their impact in the Southwestern U.S. As Kristy Lund from the Coronado National Forest stated, “I think the field trip re-emphasized to me that we often have a skewed perspective of a wildfire while it’s occurring, and in the short term. We often perceive that higher fire intensities are very destructive, and that the damage is so great that the ecosystem recovery will take many years. The reality is that our ecosystems are inherently resilient and begin to recover more quickly than we expect.” Lund’s comments show how much we still have to learn and share about wildfire processes and their intrinsic role in the health and well-being of forests of the arid SW. Wildfires serve, in part, to rejuvenate forests and it is due largely to human suppression coupled with drought that voracious mega-wildfires have become the new normal in the arid Western U.S .
*To learn more about the Horseshoe 2 Fire or the Southwest Fire Science Consortium feel free to visit their website at http://swfireconsortium.org
References & Resources
Kuyumjian, G., 2004, BAER Team: Responding to Post-Fire Threats. Southwest Hydrology, p. 14-16. (http://www.swhydro.arizona.edu/archive/V3_N5/feature1.pdf)
U.S. Dept. of the Interior, 12/05/2012, Interior Releases Study of Carbon Storage and Sequestration in Western Ecosystems as Part of National Assessment. Press Release - http://www.doi.gov/news/pressreleases/interior-releases-study-of-carbon-storage-and-sequestration-in-western-ecosystems-as-part-of-national-assessment.cfm?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+UsgsNewsroom+%28Newsroom+-+National+Releases%29
InciWeb, 6/27/2010, Final Horseshoe Fire Update. http://www.inciweb.org/incident/article/1966/10071/
InciWeb, 2011, BAER Soil Burn Severity Map – Horseshoe 2. http://www.inciweb.org/incident/map/2225/0/
NASA Earth Observatory, 5/21/2011, Horseshoe 2 Fire, Arizona. http://earthobservatory.nasa.gov/IOTD/view.php?id=50676
Southwest Fire Science Consortium. http://swfireconsortium.org
U.S. Forest Service, 2002, Healthy Forests: An Initiative for Wildfire Prevention and Stronger Communities, 22 p. http://www.fs.fed.us/projects/documents/HealthyForests_Pres_Policy%20A6_v2.pdf
VIDEO: Kristy Lund from the Coronado National forest recalls the adverse variability of the Horseshoe 2 Fire at the Southwest Fire Science Consortium field trip held on November 8, 2012 in the Chiricahua Mountains (Arechederra-Romero 2012).
