Cheatgrass (Bromus tectorum), a non-native invasive grass, is prevalent across the Great Basin region of the U.S. The species has been well studied due to its link to increased fire frequency, with many studies assessing the consequences of invasion or invasion and fire on carbon pools. However, these plot-level studies have never been synthesized to quantify the overall impact of invasion and fire on carbon (C) stocks across the Great Basin. We performed a systematic literature review to identify all studies assessing the consequences of invasion or invasion and fire on one or more of five C pools (aboveground biomass (AGB), litter, belowground biomass (BGB), and organic and total soil). We compiled data from 24 articles containing unique C studies, based on location, current and native vegetation, C pool, and soil depth (if applicable), to assess C storage in uninvaded/unburned, invaded/unburned (sagecheat), and invaded/burned sites. We hypothesized that cheatgrass invasion (in the absence of fire) would marginally increase aboveground and belowground C stocks compared to those with only native vegetation. However, we predicted that cheatgrass dominance after fire would substantially decrease C stocks (particularly AGB, BGB, and total soil) compared to univaded, unburned sagebrush.
Results/Conclusions
AGB C was significantly higher in sagecheat than sagebrush and was significantly higher in sagebrush than cheatgrass. BGB C was significantly lower in sagecheat and cheatgrass than sagebrush. Litter C was not significantly different in cheatgrass compared to sagebrush. Organic C in surface soils (0-10 cm) was significantly higher in cheatgrass than sagebrush or sagecheat, but this trend was not significant at 10-20 cm depth. Total C in surface soils (0-10 cm) was not significantly different in cheatgrass and sagecheat. Our meta-analysis indicated non-significant effect sizes of vegetation type for organic soil C and total soil C at 0-10 cm between paired sites, suggesting that changes in soil C pools are small or more nuanced. We lack a complete picture of the combined effects of cheatgrass invasion and fire on C storage in the region. Notable gaps include 1) litter quantification in sagecheat systems and comparisons with sagebrush; and 2) total soil carbon measurements in surface soils (sagebrush) and deeper soils (sagebrush vs. sagecheat vs. cheatgrass). A better understanding of the link between cheatgrass, fire, and carbon storage advances our understanding of how human activities alter fundamental environmental processes and can inform the management and control of fire-prone invasive grasses.