Despite the importance of water in arid and semi-arid environments and the numerous amount of work centered around competition and resource gradients, no studies have been made to separate out the effects of root and shoot competition along a soil water gradient. This information is critical if we are going to understand the ecology of wood seedlings establishment in grassland communities. This research will examine the establishment of woody seedlings in arid and semi-arid environments. A large multi-factor field experiment will be undertaken at the Cedar Creek LTER site in which water input, nitrogen input and competition from grasses will be manipulated. This experiment will permit the quantification of root, shoot and whole plant competition by grasses along the water-nitrogen gradient. It will also allow an independent quantification of root and shoot competition intensity between the tree seedlings (Quercus macrocarpa and Q. ellipsoidalis) in each of the above combinations. This research should provide important new information on the effect of resource supply on competitive interactions between grasses and trees. Although implemented at a single site, the research should have broad implications for competition theory as it relates to water and nutrients and for predicting plant response to natural and human-caused disturbance. Findings from this proposed research should help in understanding how global and regional changes in the environment involving increased levels of nitrogen deposition, changes in precipitation, and replacement of native by exotic grasses my be affecting woody seedling establishment in grassland communities.
