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Northern Sierran Birds: Indicators for Ecosystem-Based Management

Ryan Burnett

Managing forest ecosystems (aspen and conifer forests) calls for multi-species avian monitoring. PRBO photo by Ryan Burnett.

Managers of our national forests in the Sierra Nevada have a formidable charge—to protect and enhance wildlife populations on over 11 million acres of land while providing for many other uses and ecosystem services (e.g., recreation, water, timber products). In order to improve the chance of success, decision-makers must have information on how management actions, or inaction, affect the system. Single-species approaches to the management of such a large-scale, complex, diverse and dynamic ecosystem are unlikely to provide information that will result in the needs of the majority of species being met. Monitoring even a fraction of the ecological variables that may be influenced by management is unfeasible.

Multi-species avian monitoring—using a carefully chosen suite of species that have diverse ecological needs—can provide an indication of the state of the ecosystem as a whole. When properly integrated with management and policy, multi-species studies can guide a more holistic approach, ensuring the persistence of a range of ecological conditions and the species that depend on them.

In the northern Sierra Nevada, PRBO has been using such an approach to help inform national forest management. Our multi-species monitoring has been used at the landscape scale to provide insight into important habitat types and features that may be at risk and need management attention. At the local scale, it has been used to help guide and evaluate aspen, black oak, and riparian restoration projects.

The Aspen Example. Aspen habitat restoration is a new practice in the Sierra Nevada, and monitoring to inform management actions thus is a key to success. Aspen in the northern Sierra are generally in bad health, due primarily to two practices that have tipped the balance against this relatively short and shade-intolerant tree. One is overgrazing—cattle eat aspens; the other, fire suppression—rapidly growing conifers shade out aspens. Thus, restoration treatments involve removal of most of the conifers in aspen stands and fencing to exclude livestock.
Red-breasted Sapsuckers, a focal species. Photo by Tom Grey

In order to help guide and evaluate these restoration projects, we chose 12 focal bird species, all of which showed affinities for aspen and that, as a suite, represented a range of ecological conditions found in this habitat. For example, we chose Red-breasted Sapsucker because it reaches its greatest abundance in aspen and excavates nest cavities that are subsequently used by other species. We chose Chipping Sparrow because it is declining in the Sierra, nests in the understory, and forages on and near the ground in herbaceous vegetation that abounds in aspen groves.

We have been able to provide a broad yet detailed view of the response of these and other focal species to restoration efforts. We have also identified key habitat attributes for which to manage, that otherwise may have been overlooked.

For example, aspen habitats support a diverse array of cavity-nesting species, leading to a recommendation to manage for old and large-diameter aspen and aspen snags. Species such as Mountain Bluebird, Chipping Sparrow, and Red-breasted Sapsucker were significantly more abundant in recently treated aspen stands, revealing that open-canopy, young aspen growth is not just a necessary transitional restoration phase but an important condition for managers to promote. Warbling Vireo abundance increased as aspen cover increased. The number of focal species at a site increased with the number of aspen stems in the understory.

The multi-species study approach has allowed us to understand the importance of increasing aspen stand size and total aspen cover but—importantly—also to manage for disturbance in the future. This will result in continued aspen regeneration, which supports a unique set of aspen-associated species.

Managers pursuing an ecosystem approach recognize the value of using multi-species avian monitoring. Many of our results are now influencing management across an array of habitats, and the U.S. Forest Service has proposed adopting a suite of birds as their primary indicators for all Sierra Nevada forests.