JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecological Monographs. Abstract. One general hypothesis to explain how forest tree diversity is maintained is that rarer species are favored over commoner species in their reproduction, growth, and/or mortality. Mechanisms acting in this way would continually compensate for the tendency of some species to increase at the expense of others, and would reduce the chance of local extinction of rare species. Two hypotheses concerning such compensatory mechanisms were tested in subtropical and tropical evergreen rain forests in Queensland, Australia.Hypothesis 1: on the scale of 1 -2 ha, commoner species have lower rates of recruitment and growth and higher rates of mortality than do rarer ones. This hypothesis was tested using abundances either of adults or of members of the same size-class, and was rejected for growth and mortality and for recruitment of over-story species, but not rejected for recruitment in subcanopy and understory species in either forest.Hypothesis 2: the close proximity of other individuals is more deleterious (i.e., causes slower growth or higher mortality) if they are the same species than if they are different species. This hypothesis was accepted for growth or survival of nearest neighbors in several of the seedling size-classes in both forests. In contrast, increased densities of the same species in quadrats had no more deleterious effect on growth and survival than did increased densities of different species. At the scale of proximity to adults, hypothesis 2 predicts that young trees have higher mortality nearer conspecific adults than farther away. In both forests, 90% of the species tested showed no such pattern of mortality of seedlings or saplings, nor was the strength or direction of the deviation from equal mortality correlated with the abundance of adults of that species. Field experiments gave the same results.In summary, tests of both hypotheses showed that some compensatory trends occurred and that these were very similar in the two forests. The mechanisms producing these compensatory trends may be attacks by natural enemies (grazers, pathogenic fungi, etc.), interference, or, less likely, competition for resources.This assumption contrasts with another commonly held one that each species has an equilibrium population size toward which it returns if perturbed away. Under this latter assumption, common species remain common, fluctuating around a high equilibrium population size, while rare species do the same around a lower population level. In this framework, compensatory mechanisms are density-dependent changes in reproduction, mortality, etc., ...

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In the first comprehensive floristic classification of Australian rainforests and monsoon forests, fresh insights made possible by the use of floristic as distinct from structural data are outlined. A set of 561 individual communities, on sites ranging from North Queensland westwards to the Kimberley region and southwards to Tasmania, is defined by the presence or absence of 1316 tree species, or 406 genera. The data have been subjected to numerical classification, first with respect to species, then to genera.The species classification first divides into three 'ecofloristic regions': A, temperate (microtherm) and subtropical (mesotherm) humid evergreen rainforests; B, tropical (megatherm) humid evergreen grading into highly seasonal raingreen (monsoon) forests; and C, subtropical {mesotherm} moderately seasonal humidisubhumid raingreen forests. The sites are further divided into eight' ecofloristic provinces', for each of which a core area is identified and the ten most common diagnostic tree species listed for selected floristic elements, whose ecological relationships are briefly described.Gradients of quantitative thermal-moisture indices are added to standard climatic typology to provide a more ffexible identification of local climates that characterize community-types of each

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