Earthworm succession in abandoned fields - a comparison of deductive and sequential approaches to study

Earthworms were studied in abandoned arable fields in South Bohemia, Czech Republic, over the years 1986-1997. Four experimental plots representing di fferent stages of succession were chosen and the earthworm fauna was regula rly analysed: (a) a field - under arable use until 1990 and then abandoned, (b) young fallow - uncultivated from the beginning of the study (1986), (c )old fallow - abandoned since 1976 and (d) subclimax forest - a field not u sed as arable land since 1926. Comparison of the earthworm communities in i ndividual plots based on the results of an initial two-year study (deductiv e approach) had led to the conclusions that during the course of succession the density of earthworms and their proportions in upper soil layers incre ased, and earthworms community structure changed markedly without any incre ase in species numbers. The following 10 year study carried out at the same plots (sequential approach) verified some of these conclusions and showed that the dynamics of successional changes in earthworm communities is depen dent on the cropping system used before the cessation of field cultivation, that the earthworm populations in the early stages of succession are signi ficantly influenced by the development of shrub vegetation, and that anthro pogeic interference (i.e. the use of fallow for haymaking) may affect the c ourse of succession substantially. Moreover, significant changes were obser ved even in the earthworm community of the subclimax forest resulting from the natural oscillation of both biotic and abiotic conditions.