The fierce start of the 2012 fire season last weekend offers a frightening portent of things to come in Rim Country, according to mounting evidence.
Researchers say that the tree-ring and fossil records stretching back for thousands of years show little sign of the sort of recent “mega fires” that have sterilized soils and reduced whole forests to a moonscape of ash with increasing frequency in the Southwest.
“Mega fires are huge, landscape-scale fires in excess of 100,000 acres. We’re seeing this throughout the West, but Arizona is on the leading edge,” said forest ecologist and Northern Arizona University Regent’s Professor Wally Covington.
Covington noted that unbroken stretches of forest cluttered with thickets of small, parched trees guarantee that Mogollon Rim will see at least three more mega fires, similar to the last summer’s Wallow Fire and the Rodeo-Chediski Fire, which each totaled more than 500,000 acres.
He said these crown fires will likely spread from treetop to treetop and inflict wrenching ecological change and catastrophic damage, overwhelming the defenses of a ponderosa pine forest once perfectly adapted to frequent, low-intensity ground fires.
Such racing crown fires can throw flaming embers out three miles ahead of the fire line, menacing even distant communities.
“There’s the Payson to Winslow corridor, the Sedona to Flagstaff corridor and the Prescott corridor. If we don’t get out in front of these and do restoration treatments, it’s just going to be a matter of time before we have three more major landscapes burn up.”
As it happens, the U.S. Forest Service sent out a notice that this morning in Flagstaff it will award the biggest tree-thinning and harvesting contract in Arizona history, part of the long-awaited 4-Forests Restoration Initiative.
Forest managers hope that timber companies will invest millions in new mills and bio-fuel plants if guaranteed a steady supply for decades to come of the small-diameter trees that now choke millions of acres between the Grand Canyon and New Mexico.
The award of the contract has been delayed for months as the Forest Service has negotiated with potential bidders, but comes now at the early onset of a scary fire season.
Historically, Rim Country doesn’t face such severe fire danger until June, after rising temperatures dry out fuels moistened by spring rains. This year, May brought dangerous conditions after the spring rains failed. Computer models predicting the impact of a projected rise in average temperatures in the coming decades suggest that not only will Rim Country spring rains falter, but the region could even lose the life-saving summer monsoons.
So far, the 14,465-acre Sunflower Fire or the 2,000-acre Bull Flat Fire that have blanketed Rim Country in smoke this week, don’t hold a candle to last summer’s 600,000-acre Wallow Fire in the White Mountains or the nearly 500,000-acre Rodeo-Chediski Fire, which in 2002 forced the evacuation of Show Low, Pinetop-Lakeside, Heber, Overgaard and Pinedale.
Although Rim Country has for centuries sometimes suffered dry, hot droughts lasting for decades, such massive fires are a terrifying new phenomenon, according to a tree-ring study of fire patterns in the Southwest in the past 1,500 years published this month in the journal Holocene.
The researchers from the University of Arizona and Southern Methodist University analyzed the fire scars on thousands of ponderosa pines from 100 different locations in the Southwest, according to the study funded by the International Arid Lands Consortium.
The study showed that the old growth trees survived frequent, low-intensity ground fire, usually once every five to 10 years. In rare cases, the big trees grew for 40 or 50 years without a fire.
However, most trees in the Southwest now haven’t faced a fire in the past 140 years.
As a result, thickets of trees and tons of downed wood plague almost every acre, concluded U of A’s Thomas Swetnam, one of the leading experts on using tree ring patterns to reconstruct past climate, rainfall and fire patterns.
Changes in forest management largely account for that abrupt change in fire patterns. Starting about 100 years ago, the Forest Service issued permits for cattle grazing across millions of acres. The cattle consumed the swales of grass that once filled the forest and carried the frequent, low-intensity ground fires.
The arriving settlers also confined most Indian tribes to reservations, preventing them from setting grass fires to clear and rejuvenate the land, a practice that stretches back thousands of years.
Then in the early 20th century, the Forest Service dedicated itself to snuffing out wildfires whenever possible.
The study found no sign of mega crown fires even during extended drought that have taken hold from time to time in the past 1,000 years.
Previous studies have focused a lot on a cool, wet period between 1600 and the mid 1800s known as the Little Ice Age. The lack of mega fires in that period posed little surprise, given the abundant rainfall.
However, this study also included on the Medieval Warm Period between 800 and A.D. 1300, a period of rising temperatures and below-average rainfall. But even during this warm period, the study revealed no sign of mega fires like the Wallow or the Rodeo-Chediski.
Unfortunately, other studies suggest that rising average temperatures and deeper, longer droughts will only accelerate the increase in mega fires throughout the Southwest.
We just went through the warmest March since the federal government began keeping records in 1895. The month set 15,000 highest temperature records, with an average temperature of 51.1 degrees — a full 8.6 degrees above the March average in the 20th century, according to the Monthly Climate Report issued by the National Oceanographic and Atmospheric Administration.
Moreover, since the 1970s the total number of wildfires in the American West has increased four-fold and the number of acres burned has increased six-fold, according to a study published in the Journal of Biogeography.
Finally, the American West has experienced weather extremes and fire behaviors unmatched in the past 3,000 years, according to a study of charcoal buried in lakebottom sediments published in the Proceedings of the National Academy of Science.
The report concluded that the beginning of the 20th century enjoyed the fewest fires in the past 1,000 years. However, by the end of that century, the fire frequency had increased to the highest average in 1,000 years.
“In other words, humans caused fires to shift from their 1,000-year minimum to their 1,000-year maximum in less than 100 years,” said study co-author David Gavin, a geography professor at the University of Oregon.