The longleaf pine (LLP) savanna ecosystem is among the most biologically diverse habitats in the world due to the high density of understory plant species. Once spanning ~92 million acres throughout the southeastern U.S. only a fraction of the ecosystem remains today. This loss is attributed to anthropogenic influences, such as fire suppression, that left ground layer communities in poor condition throughout much of the LLP range. Practical tools for restoration are undeveloped, and these restoration tools are key for meeting United States Department of Agriculture (USDA) agency goals and objectives, particularly in this rapidly changing world. Several recent studies have found an increased risk of more intense, longer lasting and more frequent heatwaves in a future climate, with specific warning for the southeast U.S. To explore the effect of heatwaves on the restoration process of LLP savanna, one of the dominant understory bunchgrass species, Sorghastrum nutans, was potted (n=240) and a heatwave event (high temperature, low humidity and no water) was simulated in a greenhouse. As part of a Course-Based Undergraduate Research Experience (CURE), ~150 undergraduate students took weekly measurements of control and heatwave treatment grasses to address how heatwaves may influence growth rates and survival.
Results/Conclusions
Immediately following a simulated 10-day heatwave event, S. nutans individuals had, on average, a significantly lower maximum plant height (12.45% shorter) and stem number (16.75% fewer stems) than control individuals. Additionally, in the weeks following the heatwave event, the experimental individuals did not recover from the stress induced by the heatwave. Upon completion of the greenhouse experiment, heatwave grasses were 21.19% shorter, had 21.73% fewer stems, had 37.26% less live aboveground biomass, and had a 59.9% smaller leaf area index than control grasses. This CURE greenhouse experiment provides insight into the challenges that face restoration of LLP savannas in the face of climate change factors such as heatwaves. Bunchgrasses are ecosystem engineers in NC LLP savannas as they facilitate the spread of fire through the understory, which is essential for survival and growth of numerous understory plant species. Due to its important role in LLP savanna understory structure and function, S. nutans is an important component to understory restoration efficacy. With the increased occurrence of heatwaves, LLP savanna restoration may face new challenges as this dominant grass species may be more difficult to restore than in the climate of recent past.