Environmental heterogeneity and the spatial structure of fern species diversity in one hectare of old-growth forest

The precise relationship between species diversity and spatial heterogeneit y has not often been investigated using quantitative and repeatable measure s of environmental variation. In this study, we map the metre-level distrib ution of fern species in one hectare of old-growth forest and test for a re lationship between diversity and heterogeneity of physical features and soi l conditions. The nineteen species recorded in the hectare were non-randoml y distributed and varied greatly in abundance and spatial aggregation. Diff erent species distributions were not independent of one another; three grou ps were formed with species which occurred together significantly more ofte n than random expectation. Physical and soil conditions were highly variabl e and spatially autocorrelated from the 5 m scale up to the extent of the w hole hectare. Based on the sites where they grew, species differed in their preferences for soil moisture, fertility and pH. Fern diversity was highes t at sites with high soil moisture and low soil fertility; however, there w as no relationship between diversity and the environmental variance within quadrats. Unpredictable spatial distribution patterns produced by processes of dispersal and immigration may obscure any relationship between diversit y and spatial heterogeneity at this fine scale.