Relationships of some environmental variables to the aggregation patterns of soil microarthropod populations in forests

Soil Collembola populations exhibit a non-random distribution pattern, which has been associated with a number of environmental variables. The purpose of this study is a) to investigate the patterns of aggregation and the relationship of the population density of selected soil Collembola species to environmental variables and b) to test whether numerical abundance and biomass as measures of population density lead to consistent results regarding these aspects of their ecology. A gradient of soil organic matter content and a gradient of soil pH, both occurring within limited space, were studied in two different sites. Taylor's b was used as an aggregation index. Two multiple regression models were estimated for each dominant species in each study site linking numerical abundance or biomass to environmental variables. The species studied exhibited different degrees of aggregation. These differences matched closely the differences in the strength of the association between population density and soil organic matter or pH, depending on the site. The regression models estimated for the biomass of species for which accurate methods of biomass estimation are available, exhibited a better fit than the models estimated for the numerical abundance of the same population.