LTREB: Competition and Plant Community Structure Along Experimental Gradients of Disturbance and Nitrogen

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In spite of a general concensus that nutrients, disturbance and competition are the most important factors controlling plant community structure, there is considerable controversy over the relative importance and the modes of action of these factors. This controversy can only be resolved through experiments that simultaneously manipulate all these variables. This has never been done. The objectives of this work are 1) to examine the effects of nutrients and disturbance on plant community structure in a full factorial experiment that will allow both their interactive and independent effects to be examined; and 2) to investigate the role of both above and below ground competition in shaping community structure in a range of nutrient and disturbance regimes. A factorial nutrient and disturbance experiment will be constructed in a well-studied old field at Cedar Creek Natural History Area in Minnesota. The limiting nutrient (nitrogen) and the most important disturbance (gopher mounds) in this field will be applied for five years to allow the communities to approach equilibrium under the experimental treatments. The effects of treatments on soil, light and the plant community will be measured annually. After the communities have had three years to equilibrate, we will transplant four "target" species into the gradients and use removal experiments to test whether competitive hierarchies and competition intensity vary with nutrients and disturbance. The results of this experiment will allow explicit tests of current, divergent hypotheses about the interactions of nutrients, disturbance and competition in shaping community structure.