Spider colonization of former brown coal mining areas — time or structure dependent?

Colonization of former mining areas by a highly mobile arthropod group, spiders (Arachnida), is studied based on a comparative analysis of four mining areas of different age and habitat structure including adjacent undisturbed areas. Species number was lowest in sparsely vegetated sites, and highest in dense vegetation regardless of age. Species number may exceed that of undisturbed adjacent sites after 70 years. Similarity among the sites ranges from 26 to 75% (Sörensen index). A DCA ordination of sites revealed a grouping into three relatively distinct clusters, one including the vegetation free sites, the second the sparsely vegetated short grass sites, and the third both the plant species rich, mature, short grass sites and the tall grass stands. Environmental variables were related to the species composition by means of CCA. However, most of these relations proved to be spurious being either not significant or if so, showing a low contribution to variance explanation. The influence of scale parameters such as area size and distance (when analysing all data, data from mining areas only, or data from one mining area separately) becomes visible in all analyses. A detailed analysis including age as an independent variable shows that age has some influence on the structure of the whole data set including undisturbed sites, but not within the subset of the mining areas. Using data from one mining area only it is shown that the influence of age and spatial autocorrelation effects cannot be properly distinguished on the larger scales. A more detailed account on the known autecology of the species encountered showed that biological spectra of the communities remain similar in the course of development. Initial colonization occurs very rapidly during the first years after dumping. The most decisive aspect of population establishment is the structure of the vegetation, as expressed by height or volume amenable for colonization. Despite some developmental trends such as increase in species number clearly separated successional stages cannot be distinguished.