Once the Fire's Out

Courtesy of Robert FaustWildfires destroyed more than 3,600 homes and 750,000 acres of southern California's chaparral forests in 2003. Although these ecosystems are adapted to frequent, low-intensity burns, many ecologists say that fuel-load buildup due to years of fire suppression has led to catastrophic blazes. Brent Roath, a soil scientist stationed at the Sierra National Forest, says that once a fire is extinguished, assessing the damage and implementing necessary treatments "can take weeks, if it's a big incident like the southern California fires."These infernos leave behind a charred, barren landscape, susceptible to erosion by wind and rain. Soil structure normally retains water, but soil hydrophobicity, caused by the distillation of volatile oils and aromatics from burning trees, prohibits absorption. Soil-dwelling invertebrates, bacteria, and fungi recycle essential nutrients such as carbon, nitrogen, and phosphorus, but increases in temperature and pH disrupt natural cycling. Fast-moving, low-intensity burns increase nutrient availability, whereas high-intensity wildfires make these elements susceptible to erosion, leaching, and volatilization.Additionally, lands scorched by fire and drought can be hit with heavy rains, resulting in mud-slides such as those near southern California's San Bernardino Mountains in December 2003. Plants stabilize the soil, but revegetation cannot occur when nutrient-rich earth is washing down the mountainsides.Some people work to halt this destructive cycle. US Forest Service (USFS) Burn Area Emergency Reclamation (BAER) teams comprise ecologists, hydrologists, and geologists interested in rehabilitating fire-damaged land. Besides the immediate effects, such as road blockages and watershed contamination, they address long-term recovery. According to Roath, BAER team coordinator, mulching can stabilize soil structure and provide a seed bed to encourage revegetation. Helicopters apply hydromulch, a moist, fibrous compound containing cellulose, straw, and possibly grass seeds; dump trucks deliver dry mulch.Fast-moving wildfires affect the uppermost ground layers, so micro-organisms deeper in the soil remain relatively unharmed. "Unless you lost considerable amounts of topsoil, the bacterial populations will come back on their own," says Roath.Other ecosystems plagued by fire aren't so lucky. Mary Stromberger, soil microbiologist at Colorado State University (CSU) in Fort Collins, is examining the recovery of land destroyed by the 2001 Hayman Fire, which consumed 138,000 acres in central Colorado. "Soils were burned down several centimeters," says Stromberger. "They were basically sterile." A year later, the microbial community was beginning to recover, but DNA patterns seen in soil extracts were less diverse than those from unburned sites.1 Especially susceptible to fire are the mycorrhizal fungi that colonize plant roots and mineralize phosphorus, allowing plants to absorb it. "There is no sign of these fungi even up to a year after the fire," says Stromberger.Ken Barbarick, CSU soil scientist, monitored revegetation in areas damaged by the 11,900-acre Buffalo Creek Fire near Denver in 1996. Barbarick and his colleagues treated some plots with biosolids – the dry, composted sludge taken from sewage treatment facilities and mixed with USFS-recommended grass species. In-press research suggests that treated plots recovered more quickly than untreated ones. Even five years later, says Barbarick, noticeable differences in revegetation confirm biosolids' positive effects.Sequoia Pacific Research in Draper, Utah, takes a different approach to soil stabilization with its hydromulch, SoilSET, which the company markets as a nanotech soil binder. Designed to bind natural silicates in the soil, the product improves water retention. While heavy rains can wash away other mulches, SoilSET can remain on 70-degree slopes for 6–12 months, says Paul Clayson, Sequoia Pacific's chief operating officer.Used on 200- to 400-acre plots in the Mendocino National Forest following the 2001 Trough Fire, SoilSET curbed erosion but prevented some lighter plant species from breaking through its crust, says David Isle, a forest botanist in the Mendocino National Forest. While ground cover returned 40% in untreated areas, only 10% to 20% broke through the soil binder. "It was not a total blitz, but it was selective," says Isle. In September 2003 the Bureau of Indian Affairs announced that it would use SoilSET on burn sites on the Taos Indian Encebado Mountain in New Mexico. Isle says that it is also being used on sites in southern California. A price tag topping $600 per acre, not including application costs, may make the product unrealistic for widespread use. Biosolids, which are natural waste by-products, may be less cost-prohibitive and more readily available, according to Barbarick. Better, long-term management, including prescribed burns, could reduce the problem. These ecosystems are adapted to natural fire cycles, says Dan Neary, at the Rocky Mountain Research Station in Flagstaff, Ariz. "Aggravating the problem is that man comes along and builds houses in those areas."Maria W. Anderson can be contacted at manderson@thescientist.com.

Once the Fire's Out

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