Resolving the Dust Bowl paradox of grassland responses to extreme drought

Abstract

During the 1930s Dust Bowl drought in the central United States, species with the C3 photosynthetic pathway expanded throughout C4-dominated grasslands. This widespread increase in C3 grasses during a decade of low rainfall and high temperatures is inconsistent with well-known traits of C3 vs. C4 pathways. Indeed, water use efficiency is generally lower, and photosynthesis is more sensitive to high temperatures in C3 than C4 species, consistent with the predominant distribution of C3 grasslands in cooler environments and at higher latitudes globally. We experimentally imposed extreme drought for 4 y in mixed C3/C4 grasslands in Kansas and Wyoming and, similar to Dust Bowl observations, also documented three- to fivefold increases in C3/C4 biomass ratios. To explain these paradoxical responses, we first analyzed long-term climate records to show that under nominal conditions in the central United States, C4 grasses dominate where precipitation and air temperature are strongly related (warmest months are wettest months). In contrast, C3 grasses flourish where precipitation inputs are less strongly coupled to warm temperatures. We then show that during extreme drought years, precipitation–temperature relationships weaken, and the proportion of precipitation falling during cooler months increases. This shift in precipitation seasonality provides a mechanism for C3 grasses to respond positively to multiyear drought, resolving the Dust Bowl paradox. Grasslands are globally important biomes and increasingly vulnerable to direct effects of climate extremes. Our findings highlight how extreme drought can indirectly alter precipitation seasonality and shift ecosystem phenology, affecting function in ways not predictable from key traits of C3 and C4 species.

Precipitation–productivity relationships and the duration of precipitation anomalies: An underappreciated dimension of climate change

“…For example, mega‐droughts are common in the paleo record and are expected for the future (Clark et al, 2002; Cook et al, 2014). A famous historical example over the last century is the Dust Bowl drought of the 1930s (Knapp et al, 2020; Weaver & Albertson, 1940). Prominent contemporary examples include Australia's ~1997 to 2010 Millennium (Herberger, 2012) and 2017–2019 ‘Big Dry’ Droughts (De Kauwe et al, 2020), the California drought from ~2011 to 2015 (Goulden & Bales, 2019), and the ongoing megadrought in southwestern North America since the turn of the 21st century which, intriguingly, was preceded by the wettest 19‐year period in the last millennia for that region (Williams et al, 2020).…”

“…Theory of temporal dynamics suggests lag effects as one potential driver of nonlinear dynamics through time (Ryo et al, 2019), and a hierarchical progression of mechanisms from changes in plant physiology to re‐ordering of species abundances may also produce nonlinear NPP responses to PPT anomalies through time (García‐Valdés et al, 2020; Smith, 2011; Smith et al, 2009). Natural events such as the Dust Bowl drought (Weaver & Albertson, 1940) and multi‐year drought experiments in forests (Brando et al, 2008, Liu et al, 2020), grasslands (Griffin‐Nolan et al, 2019; Knapp et al, 2020), and deserts (Winkler et al, 2020) provide empirical examples of the progressive effects on plant communities.…”

“…Conducting these experiments in ecosystem with existing long‐term PPT–NPP datasets can yield additional insights (Felton et al, 2020; Knapp et al, 2018). Long‐term data adds historical context about past responses (Knapp et al, 2020) and are all‐inclusive in terms of drivers of NPP. Increasing understanding of the historical relationships between duration and magnitude of PPT anomalies (Figure 5) can also help guide and contextualize experimental design.…”

Optimizing livestock carrying capacity for wild ungulate-livestock coexistence in a Qinghai-Tibet Plateau grassland

“…Third, our NDVI-based forage production estimation neglects the potential difference in edible forages of different plant communities or grasslands with different health conditions. This fixed average forage ratio has been widely used in previous studies 39,40 but could still be problematic, especially when the plant community shifts under climate change, e.g., from C 4 -dominant grasslands to C 3 -dominant grasslands with extreme drought 41 . Extensive field surveys of grazing preferences and edible proportions of different grassland plant communities, together with high-resolution remote sensing that can distinguish these different plant communities, are needed to improve our forage production estimation.…”

The Ecology Underground coalition: building a collaborative future of belowground ecology and ecologists

“…Temporal scaling of microorganisms also seems to be more complex than originally estimated (Kivlin et al ., 2020) and it requires studies which will examine responses in relation to climatic history and current variation. For instance, precipitation variation on decadal time frames can influence drought responses in plants and microbes (Knapp et al ., 2020; Veach & Zeglin, 2020). Understanding how previous environmental conditions influence ecosystem responses to disturbance is critical in the design of experiments over relevant time scales to accurately predict future ecosystem responses to climate change.…”