Drought Cycles and Landscape Responses to Past Aridity on Prairies of the Northern Great Plains, Usa

Abstract

Widespread drought is among the most likely and devastating consequences of future global change. Assessment of drought impacts forecast by atmospheric models requires an understanding of natural drought variability, especially under conditions more arid than today. Using high‐resolution lake‐sediment records from the northern Great Plains, we show pronounced 100‐ to 130‐yr drought cycles during the arid middle Holocene (8000 calendar yr BP). During drought phases, grass productivity declined, erosion and forbs increased, and fuel limitation reduced fire importance. Intervening humid decades saw grass production rise, with stabilization of soils and renewed fire as fuels became abundant. Although both C3 and C4 grasses declined during droughts, a lasting shift to C3 dominance occurred during a single drought ∼8200 calendar yr BP. During the more humid Late Holocene (2800 calendar yr BP), climate was less variable and without evident drought cyclicity. Consequently, drought severity during past, and possibly future, arid phases cannot be anticipated from the attenuated climate variability evident during contemporary humid phases. Our study demonstrates that agriculturally important grassland ecosystems respond sensitively to drought variability, uncertainty in which has profound implications for the future of these ecosystems.

Response of C 3 and C 4 plants to middle-Holocene climatic variation near the prairie–forest ecotone of Minnesota

“…Our data, together with other recent results (1,25), demonstrate the complex responses of vegetation to climatic change in this region. Our results confirm that C 4 plants appear to be adapted to warm and arid environments.…”

“…During the late MH, the cooler and wetter climatic conditions resulted in increased productivity and C 4 grasses, which enhanced biomass accumulation and changed the vegetation structure at WOL, as inferred from our pollen and charcoal ␦ 13 C data. Thus, fire was a direct consequence of changes in fuel conditions in response to climatic variation; the warmest and driest conditions of the early MH did not result in maximum burning because of biomass limitation (1,25). Unlike those at WOL, MH fires at SL were likely never biomass-limited, and the fire regime did not show a large response to increased effective moisture from the early to late MH.…”

“…P ervasive drought, expected to be associated with climatic change in continental interiors, will have profound ecological, economic, and societal repercussions (1)(2)(3)(4). Drought conditions are likely to alter ecosystem function by changing the relative abundance of plant functional groups (e.g., C 3 vs. C 4 ) in natural systems (5)(6)(7).…”

“…(19), the midwestern United States experienced higher summer temperatures and lower annual precipitation than during the early or late Holocene (20,21), with episodes of pronounced drought (1). Retrospective studies of this period provide an opportunity to examine vegetational dynamics in response to climatic change.…”

Fire cycles in North American interior grasslands and their relation to prairie drought

“…An annual deficit of precipitation minus evaporation also characterizes the region (15), making it highly sensitive to changes in the moisture regime. Previous paleoclimatic investigations have documented oscillations in several disparate climate proxies, revealing a high degree of past climatic variability on the plains (13,(16)(17)(18)(19)(20)(21)(22), especially in precipitation. Such variability has been linked to solar cycles (21) and to Pacific Decadal and Atlantic Multidecadal Oscillations (23,24).…”