Forest Fire Histories of La Frontera: Fire-Scar Reconstructions of Fire Regimes in the United States/Mexico Borderlands

Fire is a dominant ecological process in almost all landscapes of La Frontera. Fire histories from throughout the region on the United States side of the border show that, before circa 1900, extensive surface fires occurred within pine-dominant forests at about the same frequency as wet-dry cycles related to the El Niño-Southern Oscillation, i.e., 2 to 7 year intervals (Swetnam and Betancourt 1990, 1998; Swetnam and Baisan 1996a, 1996b). Regionally synchronous fire events occurred at the rate of about 10 per century and often coincided with the most extreme wet-dry cycles.

Invasive Plants in the Sonoran Desert

By Garry Rogers

(First in series on Sonoran Desert invasive plants.)

Introduction to Invasive Plants in Deserts

Invasive species, like storm troopers leading the surging ruin of global warming, are demolishing Earth's ecosystems.

A diversity impaired firescape.Photograph: Once diverse landscape of small trees and tall Saguaro cactus was converted to impoverished shrubland after invasion by fire-prone plants.

Once they began crossing the oceans, Humans introduced thousands of plant species to new regions.  Freed of the diseases and competitors of their homeland, some of the introduced species began spreading into native habitats.  For instance, Cheatgrass (Bromus tectorum), introduced to the interior of the western U. S. during the 1800s began spreading, and now dominates many millions of acres.  Such invasions produce vegetation with low structural diversity and biotic communities with low genetic diversity (Tellman 2002).  In 2007, the U. S. Bureau of Land Management (BLM) had this to say about the state of the invasion of the western U.S.

Wildfires Raging near Rancho Pan Duro

Pan Duro fires, SonoraWe just returned from Rancho Pan Duro on the spine of the Sierra Madre. It is located south of Los Ojos, 50 miles or so southeast of Agua Prieta/Douglas. Mexico doesn't have fire suppression infrastructure in place as does the US. Also the forests are more heavily used so consequently there is not so much fuel loading. Nevertheless, monsoons bring thunderstorms and lightning; and much fire. Ruben's vaqueros went to the rancho, and with the air heavy with smoke they scraped a fireline to protect the main house, the vaqueros bunkhouse, and some outbuildings. Some hilltops were really decimated, and some of the thick manzanita overgrowth was obliterated, but the ranchhouse survived. The corral between some of the houses didn't fare so well. Good job, vaqueros. Muy valiente. Now there will be quite a lot of work to prevent erosion.


Analysis of fire-related Vegetation Patterns in the Huachuca Mountains, Arizona, USA, and Sierra los Ajos, Sonora, Mexico

There is general interest among fire ecologists to integrate observed fire regimes into long term fire management. The United States-Mexico borderlands provide unique research opportunities to study effects of contrasting forest management activities on forest structure and pattern. To increase understanding of the range of forest stand conditions in borderland ecosystems, we compared tree crown patterns from two forests near the US- Mexico border that are managed under contrasting fire policies and have contrasting fire histories.

Fire on the Mountain

Pines and view in the Sierra PinitoIn June I trekked with a friend to the top of the Sierra El Pinito, a good-sized range just Southeast of Nogales. The Sierra El Pinito nudge their way into the pine forest community at 2230 meters, high enough to compete for serious Sky Island status in Sonora. They are just South of the border from the Santa Ritas and Patagonias on the US side, but because of the the political boundary they are a world away when it comes to fire suppression and natural fire regimes.

To drive the point home the Sierra Azul, just to the south, was actively burning. The fire had burned a significant percentage of the range by the time we laid eyes on it. By the time we left the area it had burned itself out naturally. Little is done to combat wildfires and indeed, in contrast to U.S. fire policy, people don't treat every wildfire as an utterly dire situation.

In my 15 years of experiences in Sonora I’ve seen people with a very different attitude toward fire than I am used to. Little is done to suppress wildfires in Mexico. Fires often burn mountains, grasslands, and even buffelgrass sided freeways, just to burn themselves out without much attention from authorities or locals. Combined with the lack of resources to fight wildfire in Mexico, this has created vegetation communities with a substantially different fire regime than similar communities on the U.S. side of the border.

Some conditions that affect the spread of natural wildfire are unfortunately still present in Sonora, such as cattle grazing and logging. Luckily a few rugged and/or remote locations have even been spared these effects.

This dramatic difference in fire management bisecting the Sky Islands offers an opportunity to study the differences as well as the massive problems associated with fire suppression in Arizona and the West in general.

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