COS 64-5 - Impact of Priority Effects and Native Plant Diversity on Performance of Buffelgrass (Pennisetum ciliare), an Invasive C4 Perennial Bunchgrass in the Southwestern United States

Abstract: Buffelgrass (Pennisetum ciliare) is an invasive C4 perennial bunchgrass in the Sonoran Desert. Bufflegrass threatens natural areas in aridlands by outcompeting native plants and increasing wildfire frequency and spatial extent. Removing buffelgrass is key to reducing wildfire risk, but its seedbank persists in the soil for multiple years, promoting reinvasion. The Biotic Resistance Hypothesis suggests that increasing native species diversity can limit invasion of a community by non-native species by reducing available niche space. One strategy to limit reinvasion by buffelgrass is restoring the native plant community to a pre-invasion state by adding seeds of native plant species to limit encroaching invasive grasses. However, restoration of invaded areas via adding native plant seeds frequently fails, in part because buffelgrass germinates and emerges quickly, enabling it to preempt limited resources such as soil moisture, nutrients, and space (priority effects). Our aim was to determine how both native plant diversity and priority effects (seedling emergence time) influence buffelgrass and native plant performance.

We performed a fully factorial greenhouse experiment in which we manipulated native species diversity and seedling emergence time in experimental plant communities. The experimental treatments were native species richness (one, two, or three native species) and seedling emergence time (buffelgrass first, native plants first, and same emergence time). The native species used were Digitaria californica, Bothriochloa barbinodis, and Festuca microstachys. Plants were grown in climate controlled a greenhouse in Tucson, AZ from September to December in 2022.

Preliminary analyses indicate that priority effects had a greater influence on buffelgrass and native plant performance than native community diversity. In treatments where buffelgrass emerged first buffelgrass plants had high biomass regardless of native species diversity. In treatments where native plants emerged first, native plants had higher biomass than in treatments where buffelgrass emerged first or where native plants and buffelgrass had the same emergence time. This suggests that priority effects may have a greater influence on plant performance than community diversity alone. Furthermore, in order to successfully reduce reinvasion by buffelgrass and enhance native plant performance practitioners should try to reduce germination and emergence time of native plants via seed enhancement technologies such as priming seeds prior to seeding for restoration.