TitleWillow abundance and condition mapping in Rocky Mountain National Park
Publication TypeReport
Year of Publication2023
AuthorsNielsen E
Series TitleInstitute for Natural Resources, Portland, Oregon
Date Published05/2023
InstitutionInstitute for Natural Resources - Portland

Riparian and wetland willow species have undergone serious declines in Rocky Mountain National Park as a consequence of a variety of environmental changes and, most recently, damage resulting from moose overpopulation. To address concerns about the long-term status of willows in the park, we developed remote sensing-based raster maps of riparian and wetland willow species presence, canopy cover percentage, canopy height, and leaf area index. All outputs were produced at 3-meter resolution, and represent willows as they existed in 2021. The mapping was performed via random forests classification and regression models trained on several hundred vegetation plots from a variety of sampling efforts, and making use of predictive layers derived from aerial and satellite imagery, topographic and climatic data. The maps allowed comparison of willow abundance across spatial subsets of the park, including an assessment of areas within ungulate exclosures. Riparian and wetland willow species were mapped as present on 5.45% of the park’s total area. Across these areas, most of which likely represent vegetation types where willow is not dominant but only a component, the mean mapped willow leaf area index was 0.694. Accuracy assessment relied on cross-validated model error estimates. The habitat and imagery-based presence classification models with which the willow presence map was created had error rates of 12% and 19% respectively. The regression models for prediction of canopy cover, canopy height, and leaf area index explained 50%, 56%, and 52% of the variance in the dependent variables. The maps will be used to support assessments of willow habitat in the park and (through allometric conversion of leaf area index to leaf biomass production estimates) the determination of summer seasonal moose carrying capacity.


View PDF.