Species Interactions Reverse Grassland Responses to Changing Climate

Department of Integrative Biology, University of California, Berkeley, CA 94720, USA.
Science (Impact Factor: 33.61). 03/2007; 315(5812):640-2. DOI: 10.1126/science.1136401
Source: PubMed


Predictions of ecological response to climate change are based largely on direct climatic effects on species. We show that,
in a California grassland, species interactions strongly influence responses to changing climate, overturning direct climatic
effects within 5 years. We manipulated the seasonality and intensity of rainfall over large, replicate plots in accordance
with projections of leading climate models and examined responses across several trophic levels. Changes in seasonal water
availability had pronounced effects on individual species, but as precipitation regimes were sustained across years, feedbacks
and species interactions overrode autecological responses to water and reversed community trajectories. Conditions that sharply
increased production and diversity through 2 years caused simplification of the food web and deep reductions in consumer abundance
after 5 years. Changes in these natural grassland communities suggest a prominent role for species interactions in ecosystem
response to climate change.

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    • "Accurately predicting how invasion risk will change as the climate changes is important for effective management and restoration strategies (Dukes and Mooney 1999; Bradley et al. 2009). Additionally, climate change will affect entire communities, not single species living in isolation, and research needs to address how changes in climate will affect interactions between biotic elements in an ecosystem to understand how any one species will be affected (Suttle et al. 2007; Adler et al. 2012). In this study we sought to examine how precipitation change associated with climate change may impact the invasive grass Bromus tectorum, one of the most ubiquitous non-native species in the Intermountain West, using a unique combination of empirical studies and demographic analyses. "
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    ABSTRACT: Shifting precipitation patterns resulting from global climate change will influence the success of invasive plant species. In the Front Range of Colorado, Bromus tectorum (cheatgrass) and other non-native winter annuals have invaded grassland communities and are becoming more abundant. As the global climate warms, more precipitation may fall as rain rather than snow in winter, and an increase in winter rain could benefit early-growing winter annuals, such as B. tectorum, to the detriment of native species. In this study we measured the effects of simulated changes in seasonal precipitation and presence of other plant species on population growth of B. tectorum in a grassland ecosystem near Boulder, Colorado, USA. We also performed elasticity analyses to identify life transitions that were most sensitive to precipitation differences. In both study years, population growth rates were highest for B. tectorum growing in treatments receiving supplemental winter precipitation and lowest for those receiving the summer drought treatment. Survival of seedlings to flowering and seed production contributed most to population growth in all treatments. Biomass of neighboring native plants was positively correlated with reduced population growth rates of B. tectorum. However, exotic plant biomass had no effect on population growth rates. This study demonstrates how interacting effects of climate change and presence of native plants can influence the population growth of an invasive species. Overall, our results suggest that B. tectorum will become more invasive in grasslands if the seasonality of precipitation shifts towards wetter winters and allows B. tectorum to grow when competition from native species is low.
    Oecologia 07/2015; 179(3). DOI:10.1007/s00442-015-3398-z · 3.09 Impact Factor
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    • "spring precipitation in a California grassland, forbs decreased due to an increase in competition with introduced annual grasses, which in turn altered higher trophic levels (Suttle et al., 2007). "
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    ABSTRACT: Projected changes in climate are expected to have widespread effects on plant community composition and diversity in coming decades. However, multi-site, multi-factor climate manipulation studies that have examined whether observed responses are regionally consistent and whether multiple climate perturbations are interdependent are rare. Using such an experiment, we quantified how warming and increased precipitation intensity affects the relative dominance of plant functional groups and diversity across a broad climate gradient of Mediterranean prairies. We implemented a fully factorial climate manipulation of warming (+2.5-3.0°C) and increased wet-season precipitation (+20%) at three sites across a 520-km latitudinal gradient in the Pacific Northwest, USA. After seeding with a nearly identical mix of native species at all sites, we measured plant community composition (i.e., cover, richness and diversity), temperature, and soil moisture for three years. Warming and the resultant drying of soils altered plant community composition, decreased native diversity, and increased total cover, with warmed northern communities becoming more similar to communities further south. In particular, after two full years of warming, annual cover increased and forb cover decreased at all sites mirroring the natural biogeographic pattern. This suggests that the extant climate gradient of increasing heat and drought severity is responsible for a large part of the observed biogeographic pattern of increasing annual invasion in U.S. West Coast prairies as one moves further south. Additional precipitation during the rainy season did little to relieve drought stress and had minimal effects on plant community composition. Our results suggest that the projected increase in drought severity (i.e, hotter, drier summers) in Pacific Northwest prairies may lead to increased invasion by annuals and a loss of forbs, similar to what has been observed in central and southern California, resulting in novel species assemblages and shifts in functional composition, which in turn may alter ecosystem functions. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Global Change Biology 07/2015; DOI:10.1111/gcb.13052 · 8.04 Impact Factor
    • "This amount mimicked a moderate storm event, and the total precipitation increase per year was roughly 18 % over mean annual rainfall (see Suttle et al., 2007 for a similar treatment level). In general, we based our watering treatment on previous work in Californian grasslands, which found water addition has strong effects in spring when rainfall has largely ceased and soils are drying rapidly, but little effect during the rainy winter (Suttle et al., 2007; see also Dukes et al., 2005, 2011). Some climate models have projected wetter springs for northern California (National Assessment Synthesis Team, 2000), although most recent models predict slightly to moderately drier springs (Cayan et al., 2012). "
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    ABSTRACT: The environmental and biotic context within which plants grow have a great potential to modify responses to climatic changes, yet few studies have addressed both the direct effects of climate and the modulating roles played by variation in the biotic (e.g. competitors) and abiotic (e.g. soils) environment. In a grassland with highly heterogeneous soils and community composition, small seedlings of two native plants, Lasthenia californica and Calycadenia pauciflora, were transplanted into factorially watered and fertilized plots. Measurements were made to test how the effect of climatic variability (mimicked by the watering treatment) on the survival, growth and seed production of these species was modulated by above-ground competition and by edaphic variables. Increased competition outweighed the direct positive impacts of enhanced rainfall on most fitness measures for both species, resulting in no net effect of enhanced rainfall. Both species benefitted from enhanced rainfall when the absence of competitors was accompanied by high soil water retention capacity. Fertilization did not amplify the watering effects; rather, plants benefitted from enhanced rainfall or competitor removal only in ambient nutrient conditions with high soil water retention capacity. The findings show that the direct effects of climatic variability on plant fitness may be reversed or neutralized by competition and, in addition, may be strongly modulated by soil variation. Specifically, coarse soil texture was identified as a factor that may limit plant responsiveness to altered water availability. These results highlight the importance of considering the abiotic as well as biotic context when making future climate change forecasts. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email:
    Annals of Botany 07/2015; 116(6). DOI:10.1093/aob/mcv109 · 3.65 Impact Factor
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