Predatory mite instars (Acari, Mesostigmata) and decomposing tree leaves in mixed and monoculture stands growing on a spoil heap and surrounding forests

In the past, ecological research mainly omitted the sexual and developmental variability of mite communities, and therefore could not fully reflect the actual state and function of mite communities in the ecosystems studied. The aim here was to analyze how habitat conditions (mixed vs. monoculture stands) and single-species litter of 14 tree species (in mixed stands) affect the sex and developmental stages of Mesostigmata mites living on the decomposing litter. The research was conducted in 2011-2016, at the Bełchatów Lignite Mine external spoil heap (Central Poland) in mixed stands growing on the spoil heap, as well as in pine and birch monoculture stands growing on the spoil heap and an adjacent forest area. We found significant influences of habitat on females, males and juveniles. Additionally, we found that soil mean temperature had a significant effect on males and juveniles, but not on females. Moreover, despite the insignificant influence of litter species on mite communities, we found that percentage litter mass loss significantly affected female and juvenile mites. Taking into account habitat type, the percentage litter mass loss significantly affected female and male mites, but not juveniles. The mite abundance calculated per dry litter mass usually gradually increased during decomposition. Interestingly, the highest mean female, male and juvenile abundances were recorded in birch stands growing on the adjacent forest area; however, juvenile mites were also very numerous in mixed stands on spoil heap. Therefore, our results confirm that mixed stands on post-mining areas are a potentially better habitat for development of mesostigmatid communities compared to monocultures, among others by relatively higher humidity and lower temperatures.