University of Arizona Tucson, Arizona, United States
Background/Question/Methods
Understanding drivers of population dynamics of invasive species is vital for explaining patterns of expansion and identifying areas at risk of novel invasions. Environmental factors such as climate are known to affect plant demography over large scales, but the effects of small-scale variation in environmental factors on plant demography are less well studied. Small-scale variation in topography influences microclimate conditions, which can in turn affect the demographic rates of plants. We investigated how the demography of the invasive perennial bunchgrass buffelgrass (Pennisetum ciliare) varies as a function of local scale topography, buffelgrass density, and native plant cover.
We established 33 plots on north-, south-, east-, and west-facing hillsides in Sonoran Desert scrub habitat in Tucson, AZ. In each plot, we tracked the growth, reproductive output, and survival of ten buffelgrass individuals during the monsoon seasons of 2020 and 2021 (n=330). We modeled the effects of physical topographic characteristics (slope aspect and grade), buffelgrass density, and native plant cover on buffelgrass demographic rates.
Results/Conclusions
We found that local scale topography had significant effects on buffelgrass demography. Buffelgrass plants were largest and produced the most reproductive culms on south-facing slopes and were smallest and produced the fewest reproductive culms on north-facing slopes. Grade amplified the effects of slope aspect, with plants on steeper north-facing slopes producing fewer reproductive culms than plants on shallower north-facing slopes. Buffelgrass plants on east-facing slopes suffered the highest mortality rates.
The observed effects of local-scale topography on buffelgrass demography help explain large-scale patterns of buffelgrass distribution in Sonoran Desert scrub habitat. Buffelgrass invasion poses a risk to native Sonoran Desert scrub plant communities via competition and increasing the risk of wildfire. Our results indicate that local scale topography may be a powerful predictor in distribution and spread of buffelgrass and can help identify suitable habitats at risk of invasion by buffelgrass.
