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Shrub encroachment in North American grasslands: shifts in growth form dominance rapidly alters control of ecosystem carbon inputs

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Shrub encroachment into grass-dominated biomes is occurring globally due to a variety of anthropogenic activities, but the consequences for carbon (C) inputs, storage and cycling remain unclear. We studied eight North American graminoid-dominated ecosystems invaded by shrubs, from arctic tundra to Atlantic coastal dunes, to quantify patterns and controls of C inputs via aboveground net primary production (ANPP). Across a fourfold range in mean annual precipitation (MAP), a key regulator of ecosystem C input at the continental scale, shrub invasion decreased ANPP in xeric sites, but dramatically increased ANPP (>1000 g m−2) at high MAP, where shrub patches maintained extraordinarily high leaf area. Concurrently, the relationship between MAP and ANPP shifted from being nonlinear in grasslands to linear in shrublands. Thus, relatively abrupt (<50 years) shifts in growth form dominance, without changes in resource quantity, can fundamentally alter continental-scale pattern of C inputs and their control by MAP in ways that exceed the direct effects of climate change alone.

Keywords: LAI; MAP; aboveground net primary production; carbon; climate change; grasslands; growth form; shrublands

Document Type: Research Article


Affiliations: 1: Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523-1878, USA, 2: School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA, 3: Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA, 4: School of Natural Resources, University of Arizona, Tucson, AZ 85721, USA, 5: Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA, 6: Department of Botany, University of Wyoming, Laramie, WY 82071, USA, 7: USDA, ARS, Jornada Experimental Range, New Mexico State University, Las Cruces, NM 88003, USA, 8: Department of Biology, Virginia Commonwealth University, Richmond, VA 23284, USA, 9: Marine Biological Laboratory, The Ecosystems Center, Woods Hole, MA 02543, USA

Publication date: March 1, 2008


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