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Regional NPP and Carbon Stocks in Southwestern USA Rangelands: Land-use Impacts on the Grassland-Woodland Balance

C.A. Wessman¹, S.R. Archer², G.P. Asner³,
C.A. Bateson¹ T.W. Boutton⁴, M. McClaran^2
1University of Colorado
²University of of Arizona
³Carnegie Institute of Washington-Stanford
⁴Texas A&M University

Historical changes in grazing and fire regimes have resulted in an increase in woody plant abundance in the world's drylands. Rates and dynamics of these increases are poorly understood, but are known to vary with soils and topography. This change in land cover has been the impetus for brush management practices (chemical/ mechanical treatments, prescribed burning). As a result, ongoing increases in woody plant cover on some landscapes have been offset by decreases in woody plant cover on others. Regional tracking of plant carbon pools thus requires quantification of carbon losses associated with management-induced reductions in woody plant biomass and carbon gains associated with woody plant encroachment and regeneration. We are studying the dynamics of patch structure associated with major changes in shrub/grass due to grazing, fire, and management practices. Our sites capture the range in potential vegetation production and carbon storage throughout the region as constrained by the strong gradient in Southwestern precipitation.