The combined effects of an extreme heatwave and wildfire on tallgrass prairie vegetation

Abstract

Questions: Climate extremes are predicted to become more common in many ecosystems. Climate extremes can promote and interact with disturbances, but the combined effects of climate extremes and disturbances have not been quantified in many ecosystems. In this study, we ask whether the dual impact of a climate extreme and concomitant disturbance (wildfire) has a greater affect than a climate extreme alone. Location: Tallgrass prairie in the Konza Prairie Biological Station, northeasternKansas, USA. Methods:We quantified the response of a tallgrass prairie plant community to a 2year climate extreme of low growing-season precipitation and high temperatures. In the first year of the climate extreme, a subset of plots was burned by a growing-season wildfire. This natural experiment allowed us to compare community responses to a climate extreme with and without wildfire.Results: In plots exposed to the climate extreme but not wildfire, community structure, diversity, and composition showed minor to insignificant changes, such as a 20% reduction in grass cover and a slight increase in species diversity. Plots exposed to both the climate extreme and wildfire underwent larger changes, including an 80% reduction in grass cover, 50% increase in forb cover, and increased plant diversity. Two years after the climate extreme, structural shifts in burned plots showed little sign of recovery, indicating a potentially lasting shift in plant community structure. Conclusions:Our results suggest that community responses to climate extremes need to account for climate-related disturbances -in this case, high temperatures, drought and wildfire. This response diverged from our expectation that heat, drought, and an additional fire would favor grasses. Although growing-season wildfires in tallgrass prairie have been rare in recent decades, they will likely become more common with climate change, potentially leading to changes in grassland structure. K E Y W O R D Sclimate change, climate extremes, drought, fire, pulses, regime shifts, resilience 688 | Journal of Vegetation Science RATAJCZAK eT Al.

Rapid recovery of ecosystem function following extreme drought in a South African savanna grassland

“…In a frequently burned mesic C 4 ‐dominated grassland (tallgrass prairie in Kansas, USA), experimentally imposed extreme drought resulted in a loss of forbs with rapid recovery of aboveground net primary productivity (ANPP) postdrought because of increased abundance of grasses (Hoover et al ). However, in the same C 4 ‐dominated grassland, wildfire during a naturally occurring extreme drought increased forb abundance postdrought (Ratajczak et al ). Furthermore, Koerner and Collins () showed that shifts in grass and forb relative cover were minimal in both mesic grasslands in North America and South Africa under short‐term experimental drought across different fire regimes.…”

Extreme drought has limited effects on soil seed bank composition in desert grasslands

“…Many grasslands experience a complex disturbance regime that includes grazing, fire and periodic drought (Collins et al, 1998;Smith et al, 2016;Ratajczak et al, 2019). This complex disturbance regime partly determines the persistence of soil seed banks (Fenner & Thompson, 2005), and grassland species exhibit a wide spectrum of seed longevity.…”

Resilience to Large, “Catastrophic” Wildfires in North America's Grassland Biome

“…It is important to note that currently available data do not allow us to track the potential for within functional group transitions, such as shifts from a native to invasive annual grass. In a local field‐based study, Ratajczak et al (2019) noted a shift in the dominance of grasses versus forbs following wildfire during drought, which we could not assess. Continued advancements in data products will allow us to better unravel these complexities.…”

“…A more nuanced assessment of the relationships between variability in drought, vegetation, and wildfire is needed in the Great Plains to fully gauge the outcomes of large wildfires. Numerous small‐scale studies have documented the complex interactions between drought, fire, and vegetation composition (e.g., Fuhlendorf & Smeins, 1997; Ratajczak et al, 2019; Taylor et al, 2012; Twidwell et al, 2016). Wildfire characteristics like intensity and size are strongly influenced by drought (Krueger et al, 2015; Twidwell et al, 2016); however, the impacts of drought on fire are spatially and temporally heterogeneous.…”