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 C 3 and C 4 grasses declined during droughts, a lasting shift to C 3 dominance occurred during a single drought ϳ8200 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.

Stable Carbon Isotope Record of Holocene Environmental Change in the Central Great Plains

“…Following the drought, perennials (mostly C 4 shortgrass species, e.g., buffalo grass and blue grama) quickly regained their dominance at the expense of weedy annuals, marking the shift to more stable conditions (Weaver and Flory, 1934;Albertson and Weaver, 1946). These historical observations and the findings of Clark et al (2002) support our interpretation of increased C 3 vegetation during periods of drought and Bignell Loess deposition throughout the Holocene.…”

“…Pollen evidence from the Great Plains indicates that episodic drought was common during the Holocene, signaled by increased pollen from disturbance indicators, e.g., Chenopodeaceae-Amarathanceae (Cheno Am) or Ambrosia type pollen, and fluctuating water levels (Watts and Wright, 1966;Grüger, 1973;Fredlund, 1995;Loope and Swinehart, 2000;Grimm, 2001;Clark et al, 2002). Arbogast and Johnson (1998) analyzed faunal and floral remains gathered in south-central Kansas and concluded that the late-Wisconsin environment was cooler and more moist than the Holocene.…”

“…The presence of C 3 vegetation, as indicated by 13 C values, may be attributed to high levels of disturbance, whereby C 3 annuals, drought tolerant C 3 grasses (e.g., western wheatgrass), and some shrubs were more suited to the dry and harsh conditions typical of loess deposition. Specifically, the stronger C 3 signal present in Bignell Loess indicates an ecosystem affected by high rates of disturbance, possibly dominated by herbaceous pioneer annuals such as ragweed (Ambrosia) and shrubs or forb species of Artemisia, which were possible early successors on bare or highly disturbed ground (Keen and Shane, 1990;Clark et al, 2002). Working in the northern Great Plains, Clark et al (2002) noted a decrease in grasses (Poaceae) and an increase in weedy species (Ambrosia type) during dry intervals with aeolian sedimentation, with the carbon isotope ratio of lake sediment generally becoming more C 3 during drought.…”

“…Specifically, the stronger C 3 signal present in Bignell Loess indicates an ecosystem affected by high rates of disturbance, possibly dominated by herbaceous pioneer annuals such as ragweed (Ambrosia) and shrubs or forb species of Artemisia, which were possible early successors on bare or highly disturbed ground (Keen and Shane, 1990;Clark et al, 2002). Working in the northern Great Plains, Clark et al (2002) noted a decrease in grasses (Poaceae) and an increase in weedy species (Ambrosia type) during dry intervals with aeolian sedimentation, with the carbon isotope ratio of lake sediment generally becoming more C 3 during drought. Conversely, the percentage of C 4 plants is higher during episodes of soil formation, indicative of species that are better adapted to landscape stability as a result of greater annual precipitation.…”

Projections of aridity and its regional variability over China in the mid‐21st century

“…Enhancement ET o may have negative implications on ecosystem and agriculture, like crop growth in the Haihe River Basin which is an important grain production base in eastern China (Wang et al, 2011). Moreover, increased aridity has the potential impact on grassland composition and productivity (Clark et al, 2002), and the forest growth would decline and mortality rates may increase substantially response to rising aridity (Williams et al, 2010). Therefore, ecosystem across the eastern China would be affected adversely by future warming and increasing aridity.…”