Cooperative Institute for Research in Environmental Sciences

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Bryan Brandel

bryan.brandel@colorado.edu

Woody Plant Encroachment

Woody plant encroachment has occurred in arid and semiarid grasslands worldwide, including the grasslands of the southwestern United States. The mechanisms and consequences of woody plant encroachment are uncertain and complex. However, given the current uncertainty in estimates of carbon (C) sequestration associated with woody plant encroachment, research directed at assessing the consequences of this conversion is necessary. The encroachment of creosotebush (Larrea tridentata), in particular, is not well understood, and yet it is the most broadly distributed shrub in the semiarid regions of the Southwest. Research will be performed at the Sevilleta Long-Term Ecological Research site in central New Mexico, USA, where creosotebush has invaded adjacent Bouteloua sp. grasslands. The boundary between the shrubland and grassland forms a distinct transition zone that serves as a temporal gradient of woody plant ingress. This research will address the impact of resource islands on the formation of creosotebush patches, the distribution of C and nitrogen (N) resources across the ecotone, and the effects ecotone structure has on resource distributions and aboveground biomass. Preliminary results suggest ecosystem processes are influenced by location across the ecotone and cover type (shrub, grass, or bare ground). Field measurements will serve as the basis for scaling aboveground biomass and soil organic C across the ecotone gradient to larger spatial scales using remote sensing analysis. AVIRIS and Landsat ETM+ imagery will be used to estimate the contribution of woody plant encroachment to C sequestration at the landscape and regional scales. This research will improve our management decisions and estimates of C stocks following woody plant encroachment in the semiarid grasslands of the southwestern U.S. It will also demonstrate the significance of gradation in landscape structure and whether spatially explicit research is necessary for accurate assessments of landscape and regional ecosystem processes.