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United States Department of Agriculture

Agricultural Research Service

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

Authors
item Knapp, Alan - COLORADO STATE UNIV
item Briggs, John - ARIZONA STATE UNIV
item Collins, Scott - UNIV OF NEW MEXICO
item Archer, Steve - UNIV OF ARIZONA
item Bret-Harte, M. Syndonia - UNIV OF ALASKA, FAIRBANKS
item Ewers, Brent - UNIV OF WYOMING
item Peters, Debra
item Young, Donald - VIRGINIA COMMONWEALTH UNI
item Shaver, Gaius - WOODS HOLE MARINE BIO LAB
item Cleary, Meagan - UNIV OF WYOMING

Submitted to: Global Change Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 18, 2007
Publication Date: January 30, 2008
Citation: Knapp, A.K., Briggs, J.M., Collins, S.L., Archer, S.R., Bret-Harte, M., Ewers, B., Peters, D.C., Young, D., Shaver, G., Cleary, M.B. 2008. Shrub encroachment in North American grasslands: Shifts in growth form dominance rapidly alters control of ecosystem carbon inputs. Global Change Biology. 14:615-623.

Interpretive Summary: We compared aboveground net primary production (ANPP) for eight North American grasslands that have been invaded by shrubs. Grassland types ranged from arctic tundra to deserts to Atlantic coastal dunes. Across a 4-fold range in mean annual precipitation (MAP), shrub invasion decreased ANPP in dry sites, but dramatically increased ANPP (>1000 g/m2) in wet sites, where shrub patches maintained extraordinarily high leaf area. Concurrently, the relationship between MAP and ANPP shifted from non-linear in grasslands to linear in shrublands. Thus, relatively abrupt (<50 yrs) shifts from grasslands to shrublands without changes in resource quantity can alter continental-scale patterns of ANPP as controled by rainfall in ways that exceed the direct effects of climate change alone.

Technical Abstract: 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 4-fold 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/m2) at high MAP, where shrub patches maintained extraordinarily high leaf area. Concurrently, the relationship between MAP and ANPP shifted from being non-linear in grasslands to linear in shrublands. Thus, relatively abrupt (<50 yrs) shifts in growth form dominance, without changes in resource quantity, can fundamentally alter continental-scale pattern of C inputs and control by MAP in ways that exceed the direct effects of climate change alone.

Last Modified: 4/20/2014