Oribatid mite diversity and community dynamics in a spruce chronosequence

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A comparative study on oribatid mite communities was carried out at four sites forming a chronosequence of spruce forest stands (stand age: 5, 25, 45 and 95-years; Tharandter Wald, Germany). A total of 70 species was found. The moderate decline of oribatid species richness at the 5-years-old stand together with a strong deviation from the log-series model indicate that the community had not recovered from initial disturbance after 5 years. Close community similarity between the 5 and the 95-years-old stands nevertheless suggests a delayed response of the oribatid fauna to strong changes in environmental conditions. Species richness significantly increased from 5 to 25-years-old stand. This was accompanied by a strong increase of oribatid abundance that was largely due to the increase of only two species: Oppiella nova and Tectocepheus velatus. Particularly strong deviation from the log-series model at this site suggests that community disturbance becomes most intense at intermediate stages of forest development. Further analyses revealed an alteration of the feeding structure as well as a stimulation of species that either prefer or are at least able to colonize deeper layers of the soil profile in the 25-years-old stand. This indicates marked changes in both nutritional conditions and microclimate in the uppermost horizons 25 years after clear-cutting. A very high C mineralization rate measured in the 5-years-old stand confirms the important contribution of decomposition processes to net ecosystem production in young stands. However, no strong correlation between oribatid mite community variance and environmental conditions could be established by means of a canonical correspondence analysis. It is concluded that oribatid mite communities are a fairly conservative element of the decomposer fauna in temperate spruce forests and might thus be an important component in the decomposer systems buffering mechanisms against strong environmental change. Our data indicate a multifaceted reaction of the oribatid community to long lasting changes in site conditions rather than a straightforward response to certain environmental factors.