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Photographs of representative sites, the primary microsites comprising each site, and generalized predictions for relative differences in carbon stock above ground and by depth in the soil for each microsite Over all soil depths, the relative ranking of carbon stock by microsite was predicted to be Shrub>PBG > EAG > BS, where PBG is perennial bunchgrass, EAG is an exotic annual grass, and BS is bare soil. Photo credit: Toby Maxwell.
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Ecological disturbance can affect carbon storage and stability and is a key consideration for managing lands to preserve or increase ecosystem carbon to ameliorate the global greenhouse gas problem. Dryland soils are massive carbon reservoirs that are increasingly impacted by species invasions and altered fire regimes, including the exotic-grass-fi...
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Citations
... Drylands make up 41% of the earth's ice-free land area and despite their relatively low productivity, they store 32% of global SOC due to their vast extent (Prăvălie 2016, Plaza et al 2018. Disturbances such as fire, species invasion, and human-driven land management can significantly change the quantity of SOC stored in drylands with consequences for atmospheric CO 2 concentrations and for the provision of dryland ecosystem services (Maxwell et al 2024, Shrestha & Stahl 2008, Nichols et al 2021, Pellegrini et al 2022. Yet, despite its important role, there is a dearth of information about the consequences of large-scale disturbances on the potential for long-term C sequestration in drylands. ...
... Biomass of cheatgrass is 0.16 kg ha −1 for cover values ranging from 51 to 82, compared to 21.1 Mg ha −1 and 41 to 51 for sagebrush. Litter production for the same cover values is 0.23 kg ha −1 for cheatgrass and 0.49 kg ha −1 for sagebrush (Maxwell et al 2024). Soil moisture usage is higher under sagebrush than under cheatgrass because of the extensive roots of sagebrush (Wilcox et al 2012). ...
... Studies of cheatgrass effects on SOC have varied in their conclusions on its impacts, with some suggesting that that both exotic annual grass invasion and wildfire can independently reduce SOC by almost 50%, yet other research has shown possible increased SOC stocks with cheatgrass invasion (reviewed in Germino et al 2016, Nagy et al 2021, Maxwell et al 2024. The variability in findings about cheatgrass effects on soil C could relate to (1) confusion of cause-and-effect relationships (Germino et al 2016, Maxwell andGermino 2022), (2) background climate and edaphic factors that modulate cheatgrass effects (Belnap et al 2016), (3) dissimilarity in soil depth and microsite type of sampling (e.g. ...
Soil organic carbon (‘SOC’) in drylands comprises nearly a third of the global SOC pool and has relatively rapid turnover and thus is a key driver of variability in the global carbon cycle. SOC is also a sensitive indicator of longer-term directional change and disturbance-responses of ecosystem C storage. Biome-scale disruption of the dryland carbon cycle by exotic annual grass invasions (mainly Bromus tectorum, ‘Cheatgrass’) threatens carbon storage and corresponding benefits to soil hydrology and nutrient retention. Past studies on cheatgrass impacts mainly focused on total C, and of the few that evaluated SOC, none compared the very different fractions of SOC, such as relatively unstable particulate organic carbon (POC) or relatively stable, mineral-associated organic carbon (MAOC). We measured SOC and its POC and MAOC constituents in the surface soils of sites that had sagebrush canopies but differed in whether their understories had been invaded by cheatgrass or not, in both warm and relatively colder ecoregions of the western USA. MAOC stocks were 36.1% less in the 0–10 cm depth and 46.1% less in the 10–20 cm depth in the cheatgrass-invaded stands compared to the uninvaded stands of the warmer Colorado Plateau, but not in the cooler and more carbon-rich Wyoming Basin ecoregion. In plots where cheatgrass increased SOC, it was via unstable POC. These findings indicate that cheatgrass effects on the distribution of soil carbon among POC and MAOC fractions may vary among ecoregions, and that cheatgrass can reduce forms of carbon that are otherwise considered stable and ‘secure’, i.e. sequestered.
