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.

No abstract

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.

No abstract

No abstract

Question Aspen forests in the northern hemisphere provide richer biodiversity compared to surrounding vegetation types. In both North America and Europe, however, aspen stands are threatened by a variety of human impacts: clear felling, land development, water diversion, fire suppression and both wild and domestic ungulate herbivory. We conducted a landscape assessment of quaking aspen (Populus tremuloides) for the purpose of identifying key components of resilience. Specifically, we tested novel measures linking plant–animal interactions, compared crucial functional differences in aspen types and made restorative recommendations based on the outcome of these assessments. Location Book Cliffs region, eastern Utah and western Colorado, USA. Methods Seventy‐seven 1‐ha plots were sampled for forest structure, composition, regeneration and recruitment, landscape elements, browse level and herbivore use. Use was determined by counting the number of pellet groups from ungulate species at each sample location. We tested the efficacy of a visual stand condition rating system when compared to objective metrics. A series of non‐parametric analyses were used to compare functional aspen types and stand condition groups by key variables. Non‐metric multidimensional scaling (NMS) allowed us to explore all our data to find the most critical measures of aspen stand conditions for the purpose of better informing future aspen monitoring. Results Plots differed significantly in seral or stable aspen functional types, stand condition rating and browse species use. Ordination analysis revealed that regeneration level and herbivore use were the strongest objective indicators of aspen stand conditions, while stand condition rating proved a valuable subjective index of forest status. While ungulate herbivory of aspen is problematic internationally, our results show acute impacts where moderate slopes, relatively low water availability and intense browsing predominate. Conclusions Appropriate measures for aspen communities, informed by crucial functional divisions, allowed us to gain a clear understanding of conditions across this large landscape. Overall, aspen in our study landscape is highly vulnerable to collapse due to narrow physiographic and climate limitations and browse levels. Without herbivory reduction, future conservation in such areas will be strained and widespread system failure may occur.

Long-term qualitative observations suggest a marked decline in quaking aspen (Populus tremuloides Michx.) primarily due to advancing succession and fire suppression. This study presents an ecoregional coarse-grid analysis of the current aspen situation using Forest Health Monitoring (FHM) data from Idaho, Wyoming, and Colorado.A unique feature of aspen forests in western North America is regeneration primarily by asexual ''suckering'' although rare seeding events do occur. The dominant clonal process provides the basis for this analysis. In essence, the remaining aspen stems of previously large clones provide a window to the past and possibly a view of the future. The author uses baseline observations of aspen and associated tree species regeneration, forest size and structure components, stand age, tree damage, and recent disturbance to assess regional aspen conditions. Analysis of stands where aspen is dominant (aspen forest type) and where aspen merely occurs (aspen present) are presented. Basic groupings within the aspen forest type plots were obtained by cluster analysis of 10 FHM variables derived from tree-and plot-level measurements. Stable and unstable aspen forest types were verified using principal component analysis. A further criterion of at least 25% conifer species present was placed on the unstable group to render a more conservative population estimate of instability.The unstable aspen forest types, along with the plots having only the presence of aspen, comprise the dynamic portion of the aspen community in this area. These results support the hypothesis of an aspen decline within the past 100 years. However, additional regional plots and long-term remeasurements should provide a clearer picture of the decline's extent. Altering current and future management practices may significantly affect the rate of change. Published by Elsevier Science B.V.

No abstract