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

• Published in: Global Change Biology
• Main Authors: Knapp, Alan K., Briggs, John M., Collins, Scott L., Archer, Steven R., Bret-Harte, M. S., Ewers, Brent E., Peters, Debra P., Young, Donald R., Shaver, Gaius R., Pendall, Elise (R17757), Cleary, Meagan B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: U.K., Wiley-Blackwell 2008
• Subjects: XXXXXX - Unknown; Arctic; Climate change; Tundra
• Online Access: http://handle.uws.edu.au:8081/1959.7/546485; https://doi.org/10.1111/j.1365-2486.2007.01512.x

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 gm-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.