Study reveals a forest of startling complexity

Study reveals a forest of startling complexity

6 December 2009

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Australia — The key to managing forests via landscape-scale fires is knowing what’s in them.

For the Catalina-Rincon FireScape program, the Coronado National Forest contracted with University of Arizona scientists to compile a picture of a forest that is far more complex and detailed than our common understanding of the handful of life zones in the Sky Island ranges.

Biologist Jim Malusa has spent the past year poring over maps and then hiking into the forest to verify the information compiled in them. He said our view of the forest is shaped by the road up Mount Lemmon, which spends a third of its 30-mile traverse in a ponderosa pine forest that accounts for less than 1 percent of the area shown on the map.

That basin full of ponderosa just happens to be the preferred route for road builders, Malusa said.

Likewise, we might think giant cedars are a regular feature of the Catalinas when, in fact, they grow only at Bear Wallow.

Much of the forest is actually desert. The largest component of the Rincons and Catalinas is the Sonoran and Chihuahuan deserts at the base of those mountains — 310,000 of the 775,000 acres of Forest Service, national park, state and private land mapped here.

Each of the 11 zones shown on the map is divided into many subregions, more than 300 in all, in recognition that the slope, orientation and geology of the sites influence the way the plants grow, and how they might burn.

Land-form mapping, paired with geology, is more precise than anything the Forest Service has previously used, said Randall Smith, forest-restoration officer for the Coronado.

It’s getting even better. Tyson Swetnam, the son of fire historian Tom Swetnam and a graduate student in the school of natural resources, is compiling LiDAR data — a Light Detection and Ranging technology previously used for hydrology reports — to measure the size, shape and even the number of trees and shrubs.

The detailed inventory will help land managers determine when not to fight fires and where to set them.

The UA is also offering the services of Steve Yool, a professor of geography who describes himself as a “pyrogeographer.” Yool has developed a method for using infrared satellite data to predict the moisture content of vegetation six months in advance.

And the UA is refining its measurements of historic fire intervals in the Catalinas to provide information on how often fires should occur in various vegetative types.

“You’re getting a base set of data that is unparalleled and analysis that is unparalleled,” said Chris French, deputy executive officer of TEAMS, a U.S. Forest Service group of 138 environmental planners hired to help implement the plan.

There is another benefit to bringing in the scientists, Malusa joked: “If it goes wrong, you can just blame it on the eggheads at the university.”

The coolest forest, holding not only big pine but also massive Douglas and white fir. On the north slopes of the tiptop of Mount Lemmon, there are scattered corkbark fir, a cousin of Colorado’s pointy subalpine fir. This forest rarely burns and is often choked with underbrush and dead trees. This is the forest you see when you head up the Catalina Highway. It occupies a broad basin that highway engineers also love, which makes it seem a much bigger part of the forest. Because the terrain here is not terribly steep, relatively low-intensity fires can eliminate the smaller trees and leave the magnificent parks that are perfect for camping. Typically steep canyonlands, where ponderosa pine and Douglas fir huddle on cool north slopes. The southern exposures are home to thickets of silverleaf and netleaf oak, along with an occasional twisted madrone tree, with bark the color of cinnamon. Fire is, or at least was, common and voracious on the south slopes. Dense vegetation broken by enormous outcrops of granite and gneiss, which makes for spectacular landscapes yet often subdued fires. Rock doesn’t burn. But fire is capricious, and much of the Windy Point ridge looks as if it exploded during the 2003 Aspen Fire. Small, unruly trees that live where others cannot, atop the bands of limestone that built Marble Peak on the old road to Oracle. Mesquite is king wherever the soils are deep. Oaks take root where the land is rocky, as in much of Redington Pass. Much of this landscape was mostly grasslands a century ago, and it’s believed the return of regular fires might restore the fields of grama and plains lovegrass. Emory and Arizona oaks are the hallmark trees, scattered among grasses on south-facing slopes and clustered in woodlands on cooler north-facing slopes. They’re fire-adapted, quickly resprouting from the ashes. Between the desert and the woodland, saguaros persist on sunny slopes, and rosewood, hopbush and desert cotton take over the shady spots. In flatter terrain you’re likely to find plenty of creosote bush and chain-fruit cholla, but on rocky slopes this is the frost-sensitive but picture-perfect desert of ferocious teddy-bear cholla and whimsical saguaro rising among palo verde and the early-blooming samota. The fire-adapted buffelgrass, however, is colonizing these lands. Saguaros may like warmth, but fire means death. This is one ecological unit that should be spared the flame. Mostly dry but occasionally very wet, the watercourses once supported cottonwood and willow in lower reaches, and sycamore farther upstream. They thrived on hidden waters, but Tucson’s thirst has eliminated many, leaving only the mesquite that naturally prefers the terraces just above the main channel. Too dry for trees and too cold for saguaros, the Chihuahuan Desert is mostly well east of Tucson, extending into north-central Mexico. But there is no better term for the land on the east side of the Rincons, where white-thorn acacia lives among stiff clumps of mariola and sandpaper bush.

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