COEXISTENCE AND COMMUNITY STRUCTURE OF TROPICAL TREES IN A HAWAIIAN MONTANE RAIN-FOREST

We measured che diameter at breast height of all trees and shrubs grea ter than or equal to 5 meters in height, including standing dead trees , on 68 0.04-hectare study plots in a montane, subtropical rain forest on Mauna Loa, Hawai'i. The canopy species consisted of 88 percent Met rosideros polymorpha (ohia) and 12 percent Acacia koa (koa). Negative associations were found between the densities of koa and ohia, the den sity of koa and the total basal area of ohia, and the total basal area s of koa and ohia. The two-species lottery competition model, a stocha stic model in which the coexistence of two species in a space-limited community results from temporal variation in recruitment and death rat es, predicts a quadratic-beta distribution for the proportion of space occupied by each species. A discrete version of the quadratic-beta di stribution, the quadratic-beta binomial distribution, was fit to the l ive koa and ohia densities and assessed with goodness-of-fit tests. Li kelihood ratio tests provided evidence that the mean adult death races of the two species were equal but that the relative competitive abili ties of che two species favored ohia. These tests were corroborated by a contingency table analysis of death rates based on standing dead tr ees and growth rate studies which report that koa grows much faster th an ohia. The lottery model predicts a positive covariance between deat h rates and ohia recruitment when mean death rates are equal and koa h as a higher growth race than ohia. We argue that the competitive advan tage of ohia is due to its superior dispersal ability into large gaps, which would yield the positive covariance described above, and ic is this positive covariance term chat skews the occupation of space in fa vor of ohia.