Spatial variability of earthworm populations in a permanent polder grassland

We studied the earthworm distribution in a permanent polder grassland by making two detailed surveys in 1983 and in 1990. Geostatistical procedures were used to investigate the changes in species composition and to determine the dispersal rate. Attention was focused on two soil survey variables closely related to earth-worm distribution, the thickness of the A_h horizon and the number of burrows. The dispersal rate between the two survey dates was 13 m year^-1 compared with 10 m year^-1 before 1983. The difference was attributed either to the development of new population centres due to dispersal by cow's feet or tractor wheels, this altering the spatial dynamics, or to a lag phase in population development in the years following inoculation.