Invited Synthesis
Climate Change and North American Rangelands: Trends, Projections, and Implications

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Abstract

The amplified “greenhouse effect” associated with increasing concentrations of greenhouse gases has increased atmospheric temperature by 1°C since industrialization (around 1750), and it is anticipated to cause an additional 2°C increase by mid-century. Increased biospheric warming is also projected to modify the amount and distribution of annual precipitation and increase the occurrence of both drought and heat waves. The ecological consequences of climate change will vary substantially among ecoregions because of regional differences in antecedent environmental conditions; the rate and magnitude of change in the primary climate change drivers, including elevated carbon dioxide (CO2), warming and precipitation modification; and nonadditive effects among climate drivers. Elevated atmospheric CO2 will directly stimulate plant growth and reduce negative effects of drying in a warmer climate by increasing plant water use efficiency; however, the CO2 effect is mediated by environmental conditions, especially soil water availability. Warming and drying are anticipated to reduce soil water availability, net primary productivity, and other ecosystem processes in the southern Great Plains, the Southwest, and northern Mexico, but warmer and generally wetter conditions will likely enhance these processes in the northern Plains and southern Canada. The Northwest will warm considerably, but annual precipitation is projected to change little despite a large decrease in summer precipitation. Reduced winter snowpack and earlier snowmelt will affect hydrology and riparian systems in the Northwest. Specific consequences of climate change will be numerous and varied and include modifications to forage quantity and quality and livestock production systems, soil C content, fire regimes, livestock metabolism, and plant community composition and species distributions, including range contraction and expansion of invasive species. Recent trends and model projections indicate continued directional change and increasing variability in climate that will substantially affect the provision of ecosystem services on North American rangelands.

Section snippets

INTRODUCTION

Climate change science predicts warming and greater climatic variability for the foreseeable future, including more frequent and severe droughts and storms, as a consequence of increasing atmospheric concentrations of greenhouse gases (GHGs). A climate change footprint has become evident in the form of atmospheric warming, rapid glacial retreat, accelerated plant phenology, modified precipitation patterns, and increasing wildfires (Parmesan and Yohe 2003; IPCC 2007). These changes to the Earth

Recent Climatic Trends

Climate change refers to a significant and lasting change in the statistical distribution of meteorological conditions and variations. The Earth’s climate has changed throughout geological history in response to natural events, including orbital variation of the planet’s axis and volcanic eruptions that altered the amount of solar energy reaching Earth. However, the Earth has now entered an era in which human impacts on the fluxes of radiative energy through the Earth system have demonstrable

ECOLOGICAL IMPLICATIONS OF CLIMATE CHANGE

The drivers of climate change, coupled with greater frequency and intensity of extreme weather events, will collectively affect soil water availability to influence many aspects of ecosystem structure and function, even though these drivers have unique and potentially counteracting effects (Luo 2007; Knapp et al. 2008; Morgan et al. 2011). Climate change impacts will vary regionally because the magnitude, decadal timing, or seasonal patterns of warming and precipitation modification will be

REGIONAL SCENARIOS

The ecological consequences of climate change will vary substantially among geographic regions in response to antecedent environmental conditions and nonadditive interactions among major climate change drivers (Fig. 5). Climate change models project unique climatic scenarios for the southwestern United States and northern Mexico, the southern Plains, the northern Plains and south-central Canada, and the northwestern United States and southwestern Canada (IPCC 2007). Therefore, the ecological

SYNOPSIS OF ECOLOGICAL IMPLICATIONS

  • The three major drivers of climate change—rising atmospheric CO2 concentration, atmospheric warming, and modified amounts and temporal patterns of precipitation—collectively affect soil water availability to influence many aspects of rangeland systems.

  • The ecological consequences of climate change will vary substantially among biogeographic regions in response to antecedent environmental conditions and the differing expression of warming and precipitation modification among regions. Ecosystem

KNOWLEDGE GAPS

  • Precise projections of mean climatic trends, especially at regional levels, and of the intensity, frequency, and ecological consequences of extreme climatic events (Diffenbaugh et al. 2005; Reyer et al. 2013).

  • Sufficient insight into interactive effects among climate change drivers on soil water and NPP in major rangeland ecoregions (Fay et al. 2008; Knapp et al. 2008; Heisler-White et al. 2009).

  • Extent of species and community shifts that may occur in response to climate change, including range

MANAGEMENT IMPLICATIONS

A compelling footprint of climate change has been emerging since the mid-20th century that lends tremendous credibility to model projections of increased deviation from mean climatic trends and greater climatic variability. Uncertainties regarding climate projections and the specific consequences of these changes are to be expected given the unprecedented rate and scale of this phenomenon. However, it would be irresponsible to ignore the cumulative evidence for climate change and its current

ACKNOWLEDGMENTS

Matt Reeves and Rebecca Sherry provided helpful reviews of the manuscript prior to submission. The associate editor, Jeanne Chambers, and an anonymous reviewer provided valuable guidance for manuscript organization and presentation. Jon Eischeid prepared the temperature and precipitation graphics.

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This article was commissioned by the board of directors of the Society for Range Management in support of the society’s position on climate change.

The alternate editor-in-chief, M. K. Owens, was responsible for the editorial handling of this manuscript.

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