Executive Director Southeastern Grasslands Institute, United States
Abstract: Much of the plant biodiversity in the continental United States is found in grasslands. An estimated 100 million hectares of a grassland-dominant matrix once covered the southeastern US providing vital habitat to plants and animals, yet over 90% of these grasslands have been lost over the last several hundred years. Success of restoration efforts of these lost grasslands are threatened by multiple global change drivers like invasive species and climate change. Climate change is hypothesized to favor invasive over native species because invasives have broader thermal niches and higher adaptability potential to future climates. These invasive species may be at an advantage under future climates, potentially altering the long-term success of grassland restoration efforts. We examine how community dynamics on a restoration prairie in Tennessee are impacted by two global change drivers. We used a fully factorial design of simulated future climates (1-1.5°C mean warming and altered precipitation) and the presence of a detrimental invasive grass (Sorghum halepense) to track success of grassland restoration. Our three treatments were: a control (S. halepense absent, ambient climate conditions); S. halepense present (ambient climate); and climate x invasive (S. halepense present, climate change manipulation). Each treatment was replicated eight times. Open-top chambers (OTCs) were used to warm plots in the climate x invasive plots, simulating climate warming (~1-1.5°C mean annual temperature above ambient). In combination with these OTCs, we installed rainout shelters during the growing season (March-October), collected and stored precipitation, and applied it to OTC plots at two-week intervals, allowing us to better match predicted precipitation pulses for our region. While plant communities across treatments were similar at the start of the experiment (May 2022 NMDS: p = 0.31; stress = 0.22), communities in control plots diverge from climate x invasive plots towards the end of the growing season (September NMDS: p < 0.001; stress = 0.242). The change in community composition is largely driven by an increase in invasive plant coverage. In both invasive and climate x invasive plots, invasive plant cover decreased native plant cover compared to control plots (p < 0.001 linear regression). Furthermore, invasive plant coverage was higher in the climate x invasive plots than the invasive only plots, suggesting that climate change may promote additional invasive species growth, causing further reductions in native plant coverage. A coordinated approach to invasive species and climate change management is thus critical to maintaining biodiversity in restored grasslands.
