Buffelgrass invasion impacts native plant diversity and carbon storage

Emily Fusco and Bethany A. Bradley, Environmental Conservation, University of Massachusetts, Amherst, Amherst, MA, Jennifer K. Balch, Adam L. Mahood and R. Chelsea Nagy, CIRES, University of Colorado Boulder, Boulder, CO, Kimberly A. Franklin, Arizona-Sonora Desert Museum, Tucson, AZ, R. Chelsea Nagy, Earth Lab, University of Colorado Boulder, Boulder, CO

Background/Question/Methods
Buffelgrass (Pennisetum ciliare) is an invasive perennial bunchgrass in the southwestern United States. Originally introduced as a forage crop, buffelgrass is now known to have pronounced negative ecological impacts. While some work suggests that buffelgrass has negative impacts on biodiversity, it remains unclear how biodiversity is impacted at various levels of buffelgrass cover. In addition to biodiversity, buffelgrass impacts on ecosystem carbon storage are not well understood. Therefore, we investigated buffelgrass impacts on plant diversity, aboveground carbon, and soil carbon across a gradient of buffelgrass invasion. We established 13 20 x 20 m plots across two sites in the Arizona Sonoran Desert and identified all plants to calculate biodiversity. To determine carbon stored as aboveground herbaceous biomass, we harvested herbaceous cover from subplots within each plot. Finally, we collected soil cores (0-10cm) under native vegetation, buffelgrass, and on bare ground to determine total soil carbon under each cover type. We used generalized least squares models to predict Shannon diversity and herbaceous carbon as a function of buffelgrass cover, using site as an interaction term. To analyze total soil carbon below cover types, we used an ANOVA test and estimated marginal means (post hoc).
Results/Conclusions
Buffelgrass cover ranged from 0-68% (mean 24%) across plots. Species richness ranged from 21-46 across plots, and a total of 103 unique species were identified. Preliminary results suggest Shannon diversity significantly decreased with buffelgrass cover (p<0.01). Because this relationship followed a linear trend, management strategies that reduce buffelgrass cover may still have positive ecological impacts even if total eradication cannot be achieved. Not surprisingly, herbaceous biomass carbon significantly increased with buffelgrass cover (p<0.01), however it is unclear whether buffelgrass would have a positive relationship with total aboveground carbon because high buffelgrass cover likely leads to a reduction in woody and cacti biomass. Preliminary results also suggest that total soil carbon was below buffelgrass and bare ground compared to native vegetation. Because total soil carbon levels below buffelgrass cover and bare ground are similar, replacement of native woody and cacti biomass by buffelgrass is likely to lead to substantial declines in belowground carbon storage. Carbon and biodiversity losses are a particular concern because buffelgrass is associated with the human-grass-fire cycle, promoting more frequent fires and subsequent invasion by buffelgrass. Our results suggest that conversion to buffelgrass grassland would lead to considerable declines in biodiversity and carbon storage.