PS 19-55 - Modeling the impacts of fuel treatment on future forest diversity in the Lake Tahoe basin

Tuesday, August 8, 2017
Exhibit Hall, Oregon Convention Center
Zachary James Robbins, Alec M. Kretchun and Robert M. Scheller, Department of Environmental Science and Management, Portland State University, Portland, OR

Greater biodiversity has been shown to enhance an ecosystem’s ability to remain within a functional state, increasing resilience in the face of unknown climate conditions. Climate change will put increasing abiotic pressures upon many temperate forested ecosystems through rising temperatures and altered disturbance regimes. This increase in the importance of diverse forest systems should be consideration when determining management practices. The Lake Tahoe Basin is a highly managed coniferous forested system in the Sierra Nevada Mountains, with a hundred year history of aggressive fire suppression. Recent wildfires and property losses within the wildland-urban interface have warranted greater fuel treatments throughout the area. The removal of ladder fuel species alters the successional process of the forest through preferential selection of targeted tree species. Given that management choices alter species composition, the long term impacts on biodiversity are not yet known. We looked at the intersection of these management decisions and its effect on long term diversity within the Lake Tahoe Basin. To study how diversity would be impacted by these decisions over the next 100 years, we modeled species composition for two differing fuel treatment scenarios (‘business-as-usual’ and ‘no management’) using the LANDIS-II model.


Overall, though species composition changed with the presence of fuel treatments, diversity remained relatively constant. Furthermore, species evenness decreased as a function of time across both one hundred year management scenarios. Statistical comparison showed no difference in diversity measures between models run with active fuel reductions and those without. Fuel reduction had the biggest impact in the areas that were most diverse, resulting in as much as a 5% decrease in species evenness across models. The species that increased most from management activities were Jeffrey Pine (Pinus Jeffreyi) and Quaking Aspen(Populus tremuloides). Quaking Aspen had an increase in mean share of total biomass of 155%, while Jeffrey Pine had a increase of 84%. Our results show, though fuel treatment in Lake Tahoe has the ability select for the presence of certain tree species, the overall diversity of the area will not likely be negatively impacted.