Long-term changes in collembolan communities in grazed and non-grazed abandoned arable fields in Denmark

摘要

In order to explore long-term changes in microarthropod communities after introduction of livestock grazing in abandoned fields with herb-grass vegetation at Mols, E. Jutland, Denmark, soil and litter samples were collected from 7 pairs (blocks) of grazed and non-grazed plots over a period of 14 years. Sampling began just before fencing and initiation of cattle and sheep grazing in the spring of 1985. The total material included 76 collembolan species; 65 and 68 species were recorded in the grazed and non-grazed plots, respectively. The number of species recorded at individual sampling dates fluctuated considerably through the period. In the vegetation/litter layer the mean number of species per plot was significantly higher in the non-grazed than in the grazed plots at several sampling dates while in the soil no significant differences were observed. Grazing significantly reduced the abundance of total Collembola, three composite species groups and 12 species at one or more sampling dates. Only three species or species groups (excluding some accidental occurrences) showed significant population increment in response to grazing at one or more sampling dates, most pronounced towards the end of the study period. No species changed from being significantly highest in grazed plots to being significantly highest in the non-grazed plots or vice versa during the study period. Significant relationships between grazing pressure and grazing effect on population density were only found in the vegetation/litter layer and the combined vegetation/litter/soil strata but not in the soil. The three regularly occurring taxa that had highest population densities in the grazed plots were positively correlated with grazing intensity while this was not the case for the majority of those taxa which were most abundant in the non-grazed plots. Canonical correspondence analysis based on species composition suggests separate successional trends for grazed and non-grazed plots. Grazing pressure accumulated through the whole period from start of grazing andprecipitation accumulated over one year preceding the sampling date were the most important environmental variables correlated with species composition. According to a permutation test based on a split-plot design water content of the soil measured at each sampling was not significantly correlated with the community development.