Exploring A Stable Aspen Niche Within Aspen-Conifer Forests of Utah

Quaking aspen (Populus tremuloides Michx.) is the most widespread broadleaf tree species of North America. Increasing evidence shows that aspen has diverging ecological roles across its range as both “seral” and “stable” aspen community types. This leads us to believe that the successional pathway of aspen may not always lead to a climax conifer sere, but may in some cases consist of persisting stands of pure aspen. This study is an attempt to understand the relationship of aspen community types to climatic, physical, and biophysical variables by modeling patterns of aspen and conifer distribution using remote sensing and GIS technology. Study methodologies and results were specifically designed to aid land managers in identifying extent and status of aspen populations as well as prioritizing aspen restoration projects. Four study sites were chosen in order to capture the geographic and climatic range of aspen. Photointerpretation of NAIP color infrared imagery and linear unmixing of Landsat Thematic Mapper imagery were used to classify dominant forest cover. A Kappa analysis indicates photointerpretation methods to be more accurate (Khat=92.07%, N=85) than linear unmixing (Khat=51.05%, N=85). At each plot, variables were calculated and derived from DAYMET data, digital elevation models, and soil surveys, then assessed for precision and ability to model aspen and conifer distributions. A generalized linear model and discriminant analysis were used to assess habitat overlap between aspen and conifer and to predict areas where “stable” aspen communities are likely to occur. Results do not provide definitive evidence for a “stable” aspen niche. However, the model indicates 60 to 90 cm of total annual precipitation and topographic positions receiving greater than 4,500 Wh m‐2 d‐1 of solar radiation have a higher potential for “stable” aspen communities. Model predictions were depicted spatially within GIS as probability of conifer encroachment. In addition, prediction‐conditioned fallout rates and receiver operating characteristic curves were used to partition the continuous model output. Categorical maps were then produced for each study site delineating potential “stable” and “seral” aspen community types using an overlay analysis with landcover maps of aspen‐conifer forests

Herbivory strains resilience in drought-prone aspen landscapes of the western United States

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

Exploring succession within aspen communities using a habitat-based modeling approach

Quaking aspen (Populus tremuloides Michx.) forest communities play a crucial ecological role across western North America. However, there is increasing evidence that these communities have diverging ecological roles across aspen\u27s expansive range. Previous studies show evidence for both “seral” and “stable” aspen functional types. This leads us to believe that the pathway of these systems may not always lead to a climax conifer sere, but in many cases results in a stable community dominated by aspen. This study is an attempt to use a static model, based on large-scale environmental variables, to account for successional dynamics within aspen–conifer systems and predict distributions of aspen functional types across large landscapes. Environmental factors influencing aspen–conifer succession have been observed in past research but not fully explored. Our study methodologies and application of model results were specifically designed to aid land managers in identifying extent and function of aspen forest communities in order to plan restoration projects. Four study sites were chosen within Utah in order to capture the widest geographic variance. Photointerpretation of National Agriculture Imagery Program (NAIP) color infrared imagery was used to classify dominant forest cover at approximately 250 plots within each site. At each plot, variables were calculated and derived from DAYMET data, digital elevation models, and soil surveys and assessed for precision and ability to model forest type distributions. A generalized linear model was used to assess habitat overlap between aspen and conifer in order to explore successional dynamics and predict areas where stable aspen communities are likely to occur. Model results indicate an interaction between topographic position and moisture influence the probability of conifer encroachment but do not preclude conifers entirely. The highest probability for stable aspen communities occurs between 60 and 90 cm of total annual precipitation on topographic positions receiving greater than 4500 W h/m2/d of solar radiation. Prediction-conditioned fallout-rates were used to partition the continuous model output into a “hard” classification. These results were applied in an overlay analysis with Southwest Regional Gap landcover data, indicating 19% of aspen forests across Utah are potentially stable functional types, whereas the remaining 81% are vulnerable to conifer encroachment