Combining pitfall traps and soil samples to collect Collembola for site scale biodiversity assessments

Collembola are rarely included in landscape-level biodiversity assessments, large-scale surveys and monitoring projects because huge numbers of specimens would accumulate even in moderately sized programmes. Budgets are always limited, so sampling methods and identification need to be optimized. As no single sampling method collects all collembolan species equally well, we tested the efficiency of a combination of six pitfall traps and five soil subsamples in 30 oil seed rape fields in Eastern Austria. Work effort in man hours for sampling, sorting and identification was quantified for each method and related to the species richness of the collected fauna. Total identification effort was four times higher for the soil subsamples than the pitfall traps, however, soil samples also yielded more species (53 and 34, respectively). Out of the 70 species collected in total, an average of thirteen species per site was found in the pitfall samples, seventeen in the soil subsamples and 25 when combining the two methods. Using more than six pitfall samples alone would not have collected considerably more species. For the soil subsamples, still more species can be expected with the processing of more than five subsamples, but this would also result in higher costs. When including Collembola in large scale biodiversity assessments, surveys or monitoring projects, we therefore recommend combining the two methods. In combination, the identification of the catch from only two pitfalls and two soil subsamples already collected more than the average number of species in five soil subsamples or six pitfalls, respectively. Thus, combining the methods yielded a more complete picture of the collembolan community of a site than either method alone.