PRBO Conservation Science
Quarterly Journal of PRBO Conservation Science, Number 132, Spring 2003: Assessing Forest Management

Our special single-focus spring Observer this year surveys PRBO's Northern Sierra Project.


Monitoring songbirds in the Northern Sierra Nevada

Assessing Forest Management

Ryan Burnett

Northern Sierra Nevada

Olive-sided Flycatcher. ©Peter LaTourrette
The first rays of sunlight pierce the canopy of towering firs and pines that flank us on all sides. As the sun rises higher its rays glisten off the icy slopes of majestic Mount Lassen, across the valley ten miles to our north. The "quick three beers" song of the Olive-sided Flycatcher can be heard coming from atop a large snag, while ten feet below, a White-headed Woodpecker probes the bark for a morning snack. Fox Sparrows, Green-tailed Towhees, Dusky Flycatchers, and MacGillivray's Warblers are busy building nests in the ceanothus, chinquapin, and manzanita shrubs that dominate this 300-meter radius opening in the forest.

It is late May in the Northern Sierra, and we are conducting a census on songbirds in one of the many habitat types where PRBO has been conducting field research since 1997. Using songbirds as indicators of habitat conditions, PRBO is providing the National Forests and Lassen National Park with science-based recommendations to help guide ecosystem management.

White-headed Woodpeckers. ©Peter LaTourrette

With its great diversity of habitats, the Sierra Nevada Range is remarkably rich in flora and fauna, harboring half of all the native plant species found in California and at least 230 species of birds. While most think of the Sierra as simply a coniferous forest, in fact there is a great range of habitats, which the diverse assemblage of Sierran songbirds has evolved to exploit.

The Sierra Nevada ecosystem was historically dependent upon frequent fire. Many of the plant species rely on fire to propagate their seeds and release nutrients back into the soil. Fire created complexity across the landscape by opening forests for shrub communities and creating snags, logs, and a varied-age plant structure-all critical features that support diverse and abundant wildlife.

California and its burgeoning population have become exceedingly dependent on the Sierra for water, timber, power, and recreation. These taxing demands over the past 150 years have placed an enormous strain on the system, making the value of effective ecosystem-based management in the region ever greater.

Overgrazing, damming, and water diversion have resulted in degraded meadow ecosystems, causing declines of bird species such as Willow Flycatcher and Great Gray Owl, both now on the state endangered species list. Timber harvest of too-short rotations, combined with fire suppression, have resulted in less complex forests made up of dense stands of shade-tolerant species, mainly white fir.

To exacerbate these issues, unlike much of the Central and Southern Sierra, the northern third of the range has a gentler topography (few peaks exceed 8,000 feet), which has led to easier access and a greater intensity of resource extraction.

In the last 15 years great debate has grown over the most appropriate course of action to take for restoring degraded forests in the Northern Sierra, to prevent loss of species and support the historic diversity of wildlife and plant life. The U.S. Forest Service (USFS), the largest landowner in the Sierra, is responsible for managing nearly 43% of the land base and therefore has the greatest influence on management of the system.

In 1996, the Sierra Nevada Ecosystem Project (SNEP), a massive scientific study commissioned by Congress to evaluate the state of the Sierra Nevada system, was completed. This groundbreaking effort identified key concerns and gaps in the information needed to properly manage the Sierra employing an ecosystem approach.

Following the findings of SNEP, several plans enacted by Congress have mandated changes in Sierran national forest management. These include:

* the Herger-Feinstein Quincy Library Group Forest Recovery Act (Quincy Library Group Act) in 1999, and

* the Sierra Nevada Forest Plan Amendment Act (Sierra Forest Plan Act) in 2001.

The stated goals of both the Quincy Library Group Act and the Sierra Forest Plan Act are similar: to reduce the risk of catastrophic fire and promote forest ecosystem health. However, they call for different strategies to achieve these goals.

In general, the Sierra Forest Plan Act emphasizes greater use of controlled burning and light mechanical thinning to restore the natural successional patterns of these forests over time. The Quincy Library Group Act legislates more intensive treatment, emphasizing immediate reduction of hazardous fuel conditions through timber harvest and shrub removal.

There is no question that treatment is needed in some form. Fire suppression and excessive harvesting over the past 150 years have resulted in unhealthy and hazardous forest conditions. With an ever- increasing human population in the Northern Sierra, allowing forests to return to a natural fire regime is not possible. Most agree that it will take active management to return these systems to healthier, structurally complex, pre-European conditions. The challenge is to determine the appropriate types and intensities of treatments, and how much timber harvest, livestock grazing, and other resource use can and should be allowed.

Currently, the scientific basis for choosing one plan over the other is lacking. There is a great need for more scientific research and an adaptive management feedback loop to guide the best course of action to sustain healthy forests.

In the past year, the USFS executed a review of Sierran forest management policies. The review recommendations call for a more aggressive thinning program, allowing for the cutting of more and larger trees, and relaxing livestock grazing restrictions. It has spurred new debate as to how best to manage these lands.

Getting at the Answers

The need for ecological feedback to guide management has never been greater. PRBO is well equipped to provide just that through the study of bird populations.

Northern Sierran areas now under long-term study to assess forest management strategies. Click on map for larger view..

In 2002, PRBO, along with researchers from the USFS and the Universities of California at Davis and Berkeley, initiated an ambitious research project to evaluate the success of different forest management strategies in reducing threats of catastrophic fire while promoting forest health and sustaining local economies in the Northern Sierra Nevada.

We will assess the ability of management approaches to create healthy ecosystems by measuring five key forest ecosystem components: fire behavior, vegetation, Spotted Owls, small mammals, and songbirds. This unprecedented study aims to compare the results of various treatments across a large northern Sierran landscape over at least 20 years. An experiment at this scale and time frame has never before been attempted.

Specifically, PRBO's study is looking at how different intensities of firebreaks, group selection (removing all of the trees under a designated size from a 1-2 acre area), and forest thinning will impact songbird populations. The working hypothesis is that within a large, dynamic landscape, subject to natural processes of vegetation growth and mortality as well as forest management treatments, songbird populations remain stable.

Our work in the region over the past six years has demonstrated the value of different habitat types and varying structure within habitats for maintaining diverse avian communities. Some examples: Olive-sided Flycatcher favors open forest with snags and scattered trees and has been declining over the past 30 years, due in part to the loss of this Sierran habitat. Species such as Fox Sparrow and Dusky Flycatcher rely on montane scrub. Brown Creeper and Pileated Woodpecker rely on older forests with large-diameter trees. Black-backed Woodpecker is dependent on burned forest. Willow Flycatcher and Lincoln Sparrow require willow- and alder-filled meadows.

The new study addresses how specific management approaches might support healthier forest ecosystems and, therefore, the birds and other wildlife dependent upon them.

Using PRBO's multi-species, ecosystem-based approach, songbird monitoring will be an excellent tool for assessing changes in, and management treatments for, overall ecosystem health across a broad range of habitats.

This is an exciting and important time for science and management in the Northern Sierra, providing a significant opportunity to study the long-term impacts of forest management practices at a landscape level. Using birds as indicators of ecosystem health, and employing an adaptive management feedback approach, PRBO will provide the USFS and other land managers with some of the vital information they need to manage for a healthy, dynamic, and sustainable Sierra Nevada ecosystem.

Through this long-term commitment to research in the Northern Sierra, PRBO and our partners are helping inform forest management strategies for decades to come-and helping ensure that the sweet springtime music of diverse and abundant songbird populations will continue to be heard in the meadows, shrub fields, old-growth forests, and other habitats that make up this splendid ecosystem.

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