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Evaluating New Tools for Habitat Management and Biodiversity


Sacha Heath

Fire in a wild landscape, though sometimes feared by people, is often vital for habitat health. Indeed, biodiversity--and the ecosystem services required for healthy wildlife and human communities--may depend upon fire.

Fire, and methods such as tree thinning to mimic fire's effects, are now in use as tools for maintaining healthy ecosystems. But well-intentioned management plans are often implemented--fires lit or suppressed, or trees removed to simulate fire--before important bird and habitat questions have been answered.

To help ensure that fire-related management efforts meet their conservation goals, PRBO is addressing the need for a better understanding of fire ecology. In studies throughout the West, we provide land managers with science-based recommendations to sharpen this ecological tool so that target bird populations and habitats truly benefit.

The issues, naturally, are complex. The behavior and effects of wildfire depend upon a great many factors: fire's frequency; the season and climate; the site's vegetation community, fuel loads, elevation and orientation; and past and current management practices (to name but a few). Time is also a factor: fire can transform one habitat into another, setting back the successional clock or spurring it in a new direction. The human dimension--how wildland fire affects nearby communities, for example--adds another layer of complexity.

Also complex are birds' relationships to their fire-shaped landscapes. Human manipulation of fire, through either suppression or prescribed burning, can lead to the favoring of one species' preferred habitat over another's. Management planning for birds often entails a balancing act. In the Sierra Nevada, one might prioritize contiguous old-growth conifer forests for Northern Goshawks, but post-fire shrub fields for Fox Sparrows, or meadow openings for Great-Gray Owls. In the Great Basin, sagebrush is crucial for Brewer's Sparrows, pinyon-juniper groves for Black-throated Gray Warblers, grasslands for Western Meadowlarks.

Given the complexities surrounding fire as an ecological tool, how can it best be used? Under what circumstances? When fire is not an option, are there suitable management alternatives? Ultimately, will employing these tools achieve stated bird and habitat conservation objectives? In several studies aimed at answering such questions, PRBO has evaluated bird populations' responses--to fire suppression, to free-burning wildfire, and to mechanical methods intended to mimic or manage fire's effects.
Dusky Flycatcher. Photo © Peter LaTourrette

Fire Suppression's Effects. In the northern Sierra, more than a century of fire suppression has created a sea of conifers at the expense of other habitats such as aspen, black-oak and chaparral. The loss of forest diversity may spell disaster for the full complement of Sierran birds (Observer 132, Spring 2003). Many fire-adapted, open-forest bird species, such as Olive-sided Flycatcher, Warbling Vireo, Chipping Sparrow, Red-breasted Sapsucker and Black-backed Woodpecker, are in decline; several are exceedingly rare. In the eastern Sierra, likewise, PRBO's studies in aspen habitats found that sites with higher-percent conifer cover supported fewer aspen-breeding birds and species, and that Dusky Flycatchers were less likely to occur there.

The USDA Forest Service has incorporated our results into a synthesis of the ecology, management and restoration of aspen habitats for the Sierra Nevada. In ongoing work in the region, PRBO is helping evaluate the use of mechanical treatments, intended to mimic the effects of fire, to restore aspen, oak and chaparral habitats for birds and other wildlife.
Song Sparrow. Photo © Peter LaTourrette.

Wildfire: Let it Burn? In coastal northern California, PRBO has investigated the effects on breeding bird populations of a 12,000-acre wildfire (Observer 108, Fall 1996). The 1995 Mount Vision fire at Point Reyes National Seashore transformed streamside forests, the following spring, into lush, low-growing thickets of shrubs and herbs with diminished tree cover. These new habitats, compared to unburned riparian sites, held more low-nesting species (Song Sparrows, Allen's Hummingbirds, Orange-crowned Warblers and Bewick's Wrens) but fewer tree nesters (Pacific-slope Flycatchers and Chestnut-backed Chickadees). Moreover, reproductive success for Song Sparrows was higher at burned sites, suggesting that the benefits of the fire went beyond changes in numbers alone.

In the Mount Vision fire, many variables lined up to benefit bird populations, but this is not alway the case. PRBO's work in a third region of the West demonstrates the wide range of uses for--and outcomes of--fire.

Fire Management. Severely degraded and reduced in extent, sagebrush ecosystems still cover large expanses of western North America. They are crucially important to biodiversity. Fire plays a central role in these landscapes, and conservation of sagebrush-breeding birds and other wildlife depends on understanding fire's effects--which are multiple.

Complex, compromised and vulnerable, these ecosystems yield no simple answers. Here are a few cases in point from PRBO's work with partners in Oregon, Nevada and eastern California.

Wildfire Detrimental? In certain sagebrush habitats, wildfire has quite different results for birds than the positive ones at Point Reyes. At low elevations, where cheatgrass and other non-native annual plants have become established, fires are now more frequent and burn more uniformly across the landscape. The outcome is conversion of sagebrush stands to exotic grasslands, from which restoration is difficult--often impossible. Negative effects ensue for some sagebrush-dependent birds.
Loggerhead Shrike. Photo © Peter LaTourrette.

At the Boardman Bombing Range in northeastern Oregon (Observer 118, Fall 1999), PRBO found that the number of Loggerhead Shrike territories fell by about half in the years following a lightning-induced wildfire. In nearby Malheur County, we found that sagebrush-obligate Brewer's Sparrows decreased in number as the percentage of area burned increased.

Encroaching Trees. Another threat to sagebrush ecosystems is woodland expansion. The combination of overgrazing, fire suppression, and climate change has led to the rapid expansion of pinyon and juniper woodlands in sagebrush ecosystems. Historically, fire helped restrict trees to rocky ridges and other relatively fire-safe areas, but in the absence of fire, woodlands readily encroach upon the shrublands.

Fire as a management tool can limit woodland expansion by killing trees and maintaining open ground for sagebrush or herbaceous cover. Prescribed burns can be timed to minimize negative effects on soils and native grasses.

Alternatives to Fire. Sometimes, even fire-adapted habitats are not suited to management using fire. Some woodlands have grown so dense that large, high-intensity wildfires would completely replace woodlands and sagebrush with relatively poor habitats dominated by annual grasslands. Elsewhere, ground fuels are so reduced that a fire won't burn or spread.

In such cases, mechanical or manual thinning methods can be used as "fire surrogates." Cut trees can be left on site with branches spread on the ground to encourage new growth of desired plants (sagebrush, herbaceous growth). A prescribed fire may follow, to limit the trees' return and further encourage herbaceous growth.

How might birds respond to such treatments? In the Steens Mountains of southeastern Oregon, controlled burns and mechanical fire-surrogate methods both have been tested in juniper-sagebrush habitats. There we have found that Vesper Sparrows, at home in grasslands with sparse shrub cover, evidently do not benefit from woodland reduction alone: they also need the herbaceous growth that is best stimulated by fire. In contrast, species that rely on shrubs (Brewer's Sparrow, Green-tailed Towhee) appear to benefit from mechanical clearing but did not use recently burned areas, where their preferred shrub habitat was lacking.

The story of birds in sagebrush habitats affected by fire is complex, and our work to gain more scientific understanding continues. A new study in the pinyon woodlands of eastern California's Mono Lake Basin will enable PRBO to compare results across varied landscapes, better informing our partners about the uses for fire and fire-surrogate techniques.

Looking Ahead. Ecological processes are complex and vary through time; the effects of fire on habitats and birds are no exception. Much of the information presented here is the result of data gathered within the first few years following a fire or a fire surrogate treatment. As these studies continue, we may find, for example, that Song Sparrow nest success in coastal riparian habitat will decrease as habitat succession continues in the wake of the Mount Vision fire.

This possibility illuminates the need for long-term bird and habitat monitoring studies--and, in some cases, for the ongoing use of fire or fire surrogates as ecological management tools. After all, fires occur naturally: in most habitats a given site will burn sooner or later. While it may prove difficult to mimic the irregular and unpredictable nature of fire, managers appear up to this stewardship challenge. PRBO's role will be to provide measures of the success of fire management in improving bird habitat, and to make recommendations that managers can use to achieve wildlife and habitat goals.