Long-term restoration success of insect herbivore communities in seminatural grasslands: a functional approach

A slow-fast trait continuum at the whole community level in relation to land-use intensification

Organismal functional strategies form a continuum from slow- to fast-growing organisms, in response to common drivers such as resource availability and disturbance. However, whether there is synchronisation of these strategies at the entire community level is unclear. Here, we combine trait data for >2800 above- and belowground taxa from 14 trophic guilds spanning a disturbance and resource availability gradient in German grasslands. The results indicate that most guilds consistently respond to these drivers through both direct and trophically mediated effects, resulting in a 'slow-fast' axis at the level of the entire community. Using 15 indicators of carbon and nutrient fluxes, biomass production and decomposition, we also show that fast trait communities are associated with faster rates of ecosystem functioning. These findings demonstrate that 'slow' and 'fast' strategies can be manifested at the level of whole communities, opening new avenues of ecosystem-level functional classification.

Evaluating long-term success in grassland restoration: an ecosystem multifunctionality approach

It is generally assumed that restoring biodiversity will enhance diversity and ecosystem functioning. However, to date, it has rarely been evaluated whether and how restoration efforts manage to rebuild biodiversity and multiple ecosystem functions (ecosystem multifunctionality) simultaneously. Here, we quantified how three restoration methods of increasing intervention intensity (harvest only < topsoil removal < topsoil removal + propagule addition) affected grassland ecosystem multifunctionality 22 yr after the restoration event. We compared restored with intensively managed and targeted seminatural grasslands based on 13 biotic and abiotic, above- and belowground properties. We found that all three restoration methods improved ecosystem multifunctionality compared to intensively managed grasslands and developed toward the targeted seminatural grasslands. However, whereas higher levels of intervention intensity reached ecosystem multifunctionality of targeted seminatural grasslands after 22 yr, lower intervention missed this target. Moreover, we found that topsoil removal with and without seed addition accelerated the recovery of biotic and aboveground properties, and we found no negative long-term effects on abiotic or belowground properties despite removing the top layer of the soil. We also evaluated which ecosystem properties were the best indicators for restoration success in terms of accuracy and cost efficiency. Overall, we demonstrated that low-cost measures explained relatively more variation of ecosystem multifunctionality compared to high-cost measures. Plant species richness was the most accurate individual property in describing ecosystem multifunctionality, as it accounted for 54% of ecosystem multifunctionality at only 4% of the costs of our comprehensive multifunctionality approach. Plant species richness is the property that typically is used in restoration monitoring by conservation agencies. Vegetation structure, soil carbon storage and water-holding capacity together explained 70% of ecosystem multifunctionality at only twice the costs (8%) of plant species richness, which is, in our opinion, worth considering in future restoration monitoring projects. Hence, our findings provide a guideline for land managers how they could obtain an accurate estimate of aboveground-belowground ecosystem multifunctionality and restoration success in a highly cost-efficient way.