U.S.-Argentina Cooperative Research on Grass/Shrub Interactions in Two Temperate Semiarid Regions

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This award supports cooperative research between Prof. William K. Laurenroth of Colorado State University and Prof. O. E. Sala of the University of Buenos Aires on grass/shrub interactions in semiarid regions. The vegetation of arid and semiarid regions is dominated by one of two life-forms of plants: grasses or shrubs/low trees. The replacement of grasses and grasslands by shrubs and shrublands is a serious worldwide problem in semiarid regions. Associated with this problem of brush encroachment is a collection of theoretical problems concerned with resource partitioning between these two dominant forms. Other problems arise from the study of the geographical distribution of grasslands and shrublands. Models that emulate the interaction between grasses and shrubs have been quite successful in predicting that interaction in tropical savannas. These models often make the simplifying--and limiting with regards to resource allocation--assumption that differentials in soil water use by coexisting grasses and woody plants is due to access to different soil layers (two-layer hypothesis). The investigators plan to study the question of the applicability of such models to temperate regions. Additionally, the investigators plan to explore the potential for a biogeographic model, based upon current theoretical models of resource partitioning, that may be used to better predict the distribution of grasslands and shrublands. The North American site for this project is in the Central Crossland Region in Colorado and is part of a nationwide network for long-term ecological research (LTER) funded by NSF. Comparison of results coming from the Argentinian site, will not only serve to continue a long standing collaboration and aid our theoretical understanding of woody plant/grass interactions, but will also aid in judging the management potential of sites and in the decision making about alternate land uses.