Colonization of industrial reclamation sites by Acari, Collembola and other invertebrates.
The soil fauna colonizing four reclaimed coal pit heap sites at different stages of reclamation in Northumberland, England, were sampled monthly for 2 yr. The population density of mites was low initially, but rose rapidly to a maximum of 131 X 103 m-2 after reclamation was complete. The pioneer mites on the younger sites were Astigmata and the prostigmatid families Tarsonemidae, Pyemotidae and Nanorchestidae. Even on the older sites, Mesostigmata were never abundant and few Cryptostigmata were found. Seasonal fluctuations of density occurred on the older sites with maxima in the late autumn and winter and minima in the summer or early autumn. Some negative associations between groups of mites had developed on the older sites. 33 species of arthropleone Collembola were recorded, 18 of which occurred on all four sites. Their population densities were low initially (0.3 X 103 m-2) but rose rapidly, probably due to the low density of predators. By the end of the survey, a very high density had been attained on the younger woodland site (152 X 103 m-2 in December). On the two older sites, seasonal fluctuations of density were detected with maxima in spring and autumn or winter, and minima in summer. The species able to live in bare shale were quickly superseded by a fauna more typical of agricultural soils as the vegetation cover developed. Populations were dominated by either Tullbergia krausbaueri or Isotoma notabilis and only on one older site were more than one species dominant. In the second year of the survey, Isotomidae (mainly Isotoma viridis and I. notabilis) made up much of the total biomass. Other arthropods (symphypleone Collembola, Hemiptera, Araneida, Thysanura, Diptera larvae and Coleoptera) occurred irregularly in low numbers; earthworms had not penetrated the sites by the end of the survey.