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The physiognomic—structural features used to classify Australian rain forest vegetation into 20 structural types vary along different gradients. The high correlation demonstrated between the structural types and the climatic and edaphic factors enables the identificatin of habitat types which are defined by limits of mean annual temperature and rainfall, and soil mineral status and soil drainage. The physiognomic—structural features are arranged in a hierarchical table. The primary division into vine, fern, and moss forests corresponds with tropical—subtropical, warm temperate (submontane), and cool temperate (montane) thermal regions, respectively. The temperate forms are strictly evergreen. Further subdivision of the vine forests into evergreen (including associated sclerophyll forests) and raingreen (more of less deciduous) types is correlated with differences in soil mineral status as inferred from topography, depth of soil, and parent materials. The tropical forms are differentiated from the sub—tropical forms by a higher proportion of mesophyll than notophyll leaf sizes. Further differentiation of vine forests with complex, mixed, and simple structure is correlated with inferred soil nutrient status defined as eutrophic, mesotrophic, and enriched obligotrophic. Obligotrophic soils do not support rain forest vegetation. Climatic and topographic factors tend to outweigh soil nutrient availibility at the climate extremes of the monsoonal and cool temperate regions. The structure types are finally differentiated by differences in height of canopy closure, nature of emergents, or proportion of deciduous species, and are further correlated with variations in soil moisture availability and drainage, or local exposure in montane situations. A field key to the habitat types associated with the different structural types is given. The inter—relationships thus established enable the prediction of either the type of vegetation, climate, or soil once any two of these are known. Deviations from the inferred distribution of rain forest are related to the past influence of wildfires which favor the regeneration of eucalypts and other scle sclerophylls after the destruction of the mostly fire—sensitive rain forest species. Destruction by surface fires in the tropical—subtropical region, or by running—crown fires of the mass—ignition type in the temperate regiion results respectively in abrupt ecotones, or diffuse ecotones and the virtual absence of climax rain forest vegetation. The practical implications of the ecological relationships established are briefly discussed in relation to land use and conservation.

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., ...

The influence of cyclones on the structural and floristm composition of tropical lowland and foothill rain-forest in north Queensland is briefly described. Local topographic effects, as well as the general frequency and intensity of cyclones, are important. The local intensification of wind velocities, probably exceeding 100 m.p.h., which occur regularly in parts of the coastal corridor south of Cairns, produces "cyclone scrubs". Because of extensive windthrows, these have a low uneven canopy with scattered emergents densely draped by vines. In more sheltered areas, with cyclonic winds averaging 60–80 m.p.h. not locally accelerated by turbulence, upper canopy defoliation and occasional windthrows have resulted in a dense understorey of the shade-intolerant lawyer vine (Calamus australis (Mart.) Beccari) under a relatively even canopy averaging 90–110 ft high. On exposed spurs of the rugged coastal ranges, Acacia aulacocarpa A. Cunn. is a common emergent of vine forests. Fire following "dry" cyclone damage may further modify vine forests adjacent to fire-paths in sclerophyll or grassy forest. The principal effects of fire are the absence of the fire-sensitive Calamus spp., and the presence of numerous sclerophyllous species in addition to A. aulacocarpa. The reactions of Queensland tropical rain-forest to cyclones are compared with those described for west Africa, Malaya, and the West Indies. The catastrophic effect of cyclones on rain-forests overrides the usual ecological factors, and in such areas, even without human interference, a stable forest climax is not attained. The frequency of cyclonic damage means that exposed sites of the tropical lowlands and adjacent foothills of north Queensland have an uncertain silvicultural future.

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