This report was commissioned by the USDA Forest Service Lake Tahoe Basin Management Unit to synthesize existing information on the ecology and management of aspen (Populus tremuloides) in the Sierra Nevada of California and surrounding environs. It summarizes available information on aspen throughout North America from published literature, internal government agency reports, and experienced scientists and managers. The historic distribution, abundance, and ecologic role of aspen in the Sierra Nevada are discussed, along with the reproductive physiology of aspen. Issues that affect aspen health and vigor in the Sierra Nevada and elsewhere are covered, along with methodology for assessing the condition of aspen and monitoring the effects of management activities to restore and maintain aspen. Descriptions of the types of aspen that occur in the Sierra Nevada are presented along with alternative techniques to manage and restore aspen that are applicable wherever aspen is found.

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Quaking or trembling aspen (Populus tremuloides Michx.) forests occur in highly diverse settings across North America. However, management of distinct communities has long relied on a single aspento-conifer successional model. We examine a variety of aspen dominated stand types in the western portion of its range as ecological systems; avoiding an exclusive focus on seral dynamics or single species management. We build a case for a large-scale functional aspen typology based on existing literature. Aspen functional types are defined as aspen communities that differ markedly in their physical and biological processes. The framework presented here describes two "functional types" and seven embedded "subtypes": Seral (boreal, montane), Stable (parkland, Colorado Plateau, elevation and aspect limited, terrain isolated), and a Crossover Seral-Stable subtype (riparian). The assessment hinges on a matrix comparing proposed functional types across a suite of environmental characteristics. Differences among functional groups based on physiological and climatic conditions, stand structures and dynamics, and disturbance types and periodicity are described herein. We further examine management implications and challenges, such as human alterations, ungulate herbivory, and climate futures, that impact the functionality of these aspen systems. The functional framework lends itself well to stewardship and research that seeks to understand and emulate ecological processes rather than combat them. We see advantages of applying this approach to other widespread forest communities that engender diverse functional adaptations.

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