Diversity of Eucalyptus species predicted by a multi-variable environmental gradient.

Changes in species diversity are examined in relation to a multidimensional environmental gradient using Eucalyptus species in south-eastern Australia. By fitting a generalized linear model, the response of the community parameter, species diversity, is shown to be related to three environmental variables, mean annual rainfall, mean annual temperature and a relative measure of solar radiation. The effects of rainfall and temperature were both statistically significant and large, solar radiation was significant but small. However, the influence of the two major variables was not independent but interacted in a complex way that prevents adequate description of species diversity as a function of either variable alone. Possible biological explanations of the complexity are discussed in terms of limiting conditions at low temperatures, and competition between guilds of species at high temperatures and medium to high rainfall.