Tests of the Equiv#aence of Competitors and Asymmetry of Competition Hypotheses in Multispecies Woody Communities

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Despite the central importance of competition in ecological theory, field tests of hypotheses about plant competition are rare. Two current major hypotheses are the Competitive Equivalence Hypothesis and the Asymmetrical Competition Hypothesis. No attempts have been made to apply these hypotheses to woody plant communities. The P.I.s propose experiments that will test both the Competitive Equivalence Hypothesis and the Asymmetrical Competition Hypothesis using individuals of Betula alleghaniensis and Fagus grandifolia. The proposed research is based on three working hypotheses: 1) Aboveground competition for light is of equal or greater importance to the growth and survival of seedlings than belowground competition for soil resources. This is an underlying assumption of the remaining two hypotheses. 2) Target seedlings will respond equally to equal densities of similar-sized neighbors of different species. This is the Competitive Equivalence Hypothesis. 3) Target seedlings will show reductions in growth directly proportional to the sizes of equal densities of different-sized neighbors. This is the null form of the Asymmetrical Competition Hypothesis. The investigators will create replicated neighborhoods around central target individuals by thinning existing high-density areas to leave neighbors of the desired density, species, and size. Response of target seedlings will be measured as growth in height and stem diameter, and analyzed as relative growth rate. Responses will be measured over two years from the time of treatment. Results will determine whether the above hypotheses accurately describe the competitive interactions among these woody species and how the species differ in their competitive effects on one another.