Fern species diversity in relation to spatial scale and structure

Species with different requirements can coexist if the environment varies in space; we therefore expect a positive relationship between species diversity and environmental heterogeneity. In this thesis I examine the influence of environmental structure on patterns of fern diversity in one hectare of old-growth forest and compare these patterns to other surveys covering a broad range of scales. The nineteen species recorded in the hectare had non-random spatial distributions and differed in their soil preferences. Diversity was positively related to soil moisture and negatively related to soil fertility, but there was no relationship with environmental variance. The counteracting influence of dispersal may predominate over selection processes at the hectare scale. Both species-area curves and the decreasing correlation of species composition with distance had very similar slopes over quadrat sizes ranging from 1 x 1 m to 50 x 50 km, suggesting that some diversity patterns may be independent of scale