Invasive annual grasses destabilize plant communities in a northern mixed-grass prairie

Authors: FROST, MORGAN - University Of North Carolina Greensboro; Porensky, Lauren; Reinhart, Kurt; KOERNER, SALLY - University Of North Carolina Greensboro

Submitted to: Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plant community stability through time can support the reliable production of ecosystem services such as livestock forage and wildlife habitat. Invasive species can reduce temporal plant community stability, and the extent of community destabilization may depend on invader abundance. Using an observational field study conducted over three years in northeast Wyoming, we assessed which metrics of plant community stability were altered by invasion. We also asked whether invasive species affected stability indirectly by altering two environmental variables (light and soil moisture). Bromus arvensis and B. tectorum are two invasive annual weeds found across United States rangelands, including in the northern mixed-grass prairies of Wyoming. We established plots along natural invasion gradients of B. arvensis and B. tectorum abundance and collected plant species composition data over three growing seasons. We tested associations between nine different metrics of plant community stability and invasion by B. arvensis and B. tectorum. We found that plant species turnover increased with invasion by both species, while the stability of forb cover, C4 grass cover, and C3 grass cover decreased with invasion. All results supported the hypothesis of a destabilizing effect of invasion on the native plant community. Further, we found that in some cases, invasive species impacted the stability of light and soil moisture, which in turn reduced plant community stability. Overall, our results suggest that invasive annual bromes can reduce native plant stability, with important implications for forage production, and thus, food security.

Technical Abstract: Temporal community stability, here defined as temporal mean divided by temporal standard deviation, plays an important role in predicting certain ecosystem services. However, temporal stability can change with invasion, with greater abundances of invasive species potentially having greater impacts on native community stability. The exact consequences of invasion for temporal stability are unclear, and in part depends on the particular metric of stability measured. In rangeland ecosystems, predictable forage is important for livestock production but can be threatened by invasion. Therefore, using an observational field study conducted over three years in Wyoming, we assessed which metrics of plant community stability were altered by invasion and whether those effects were mediated by two environmental variables (light and soil moisture). Bromus arvensis and B. tectorum are two invasive annual weeds found across United States rangelands, including in the northern mixed-grass prairies of Wyoming. We established plots along natural invasion gradients of B. arvensis and B. tectorum abundance and collected plant species composition data over three growing seasons. We tested associations between nine different metrics of plant community stability and invasion by B. arvensis and B. tectorum. We found that species turnover increases with invasion by both species, while stability of forb (both brome species), C4 grass (B. arvensis only), and C3 grass (B. tectorum only) cover decreases with invasion. All metrics of stability associated with invasion supported the hypothesis of a destabilizing effect of invasion on the native plant community. Further, we found that these light and soil moisture did mediate some associations between stability and invasion. Overall, our results align with previous work suggesting that invasive annual bromes can lead to decreased native plant stability, which has important implications for forage production, and thus, food security.