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Abstract

Because arthropods dominate terrestrial ecosystems in species number and
biomass, they can potentially play a major role as environmental indicators in applied
ecology and nature conservation. We tested the suitability of arthropods as indicators for
particular forest types based on a comprehensive standardized sampling of various taxa by
different trap types in 93 mature temperate forest sites in three regions of Germany. We
tested whether indicator species (1) can be derived for different forest types across regions,
(2) are more widespread and more abundant than non-indicator ones, (3) belong to a
particular taxon or trophic guild, and (4) are consistent between regions and years. Among
2041 sampled arthropod species, only four were significant indicator species for the same
forest type in all region, and no single taxon or guild performed better than other groups.
Indicators were generally more abundant and more widespread than non-indicators, but
both abundance and distribution varied widely between species. When the analysis was repeated using data from the next year, indicator values of species significantly correlated
between years, but the identity of more than 50 % of significant indicators changed,
suggesting high among-year variability. We conclude that overall, arthropods did not turn
out to be reliable indicators, at least at the scale of Germany. If anything, arthropod
indicator species should be defined at the regional scale. Furthermore, indicators should be
selected across taxa and trophic levels. Future evaluation of indicator species among
arthropods should be conducted over several years based on standardized sampling protocols
to develop a reliable definition of indicator species despite the high fluctuations in
abundance of species among arthropods, which might either mask or overestimate the indicator value of particular species.