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

Abstract

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.

Long‐term recovery of above‐ and below‐ground interactions in restored grasslands after topsoil removal and seed addition

“…Such an approach is not necessarily much more costly compared to the assessment of plant species richness that is typically used in restoration monitoring. Specific combinations of low‐cost measures of above‐ and below‐ground properties might even be better indicators for restoration success (Resch, Schütz, Buchmann, et al, 2021). Furthermore, our study also indicates that topsoil removal is a successful method that helps to restore intensively used agricultural areas of low ecological value entering into a new trajectory.…”

“…PCRs were run in triplicates, pooled and sent to the Genome Quebec Innovation Centre (Montreal, QC, Canada) for barcoding using the Fluidigm Access Array technology (Fluidigm) and paired‐end sequencing on the Illumina MiSeq v3 platform (Illumina Inc., San Diego, CA, USA). Quality filtering, clustering into operational taxonomic units (OTUs, 97% similarity cut‐offs) and taxonomic assignment were performed as previously described (Resch, Schütz, Buchmann, et al, 2021).…”

“…We randomly collected one undisturbed soil core (5 cm diameter, 12 cm depth) per 4‐m 2 subplot using a steel cylinder that fit into the soil corer. The cylinders were capped to avoid disturbance during transport and used to measure field capacity, rock content and fine earth density as previously described (Resch, Schütz, Buchmann, et al, 2021). We randomly collected another three soil cores (5 cm diameter, 12 cm depths) in each 4‐m 2 subplot to determine soil chemical properties.…”

“…Kiehl & Wagner, 2006 [study period: 9 years]; Wubs et al, 2016 [6 years]; Resch et al, 2019 [22 years]; Neff et al, 2020 [22 years]). Below‐ground recovery lagged, however, behind the above‐ground development and did not reach target levels, not even 20 years after restoration (Frouz et al, 2009; Geissen et al, 2013; Resch, Schütz, Buchmann, et al, 2021). Thus, it has been argued that topsoil removal and seed addition create a mismatch between above‐ground and below‐ground properties (Kardol et al, 2009).…”

Ecosystem coupling: A unifying framework to understand the functioning and recovery of ecosystems

“…100 ll restoration practices such as topsoil removal that deliberately disrupt ecological connections allowing the reassembly of networks and biogeochemical processes, initiating a transition toward a potentially more ecologically coupled, and thus energetically efficient, target state. 126,127 Here the key concept would be adaptation through relaxation. In other words, some couplings within the system are relaxed by topsoil removal, and that allows the self-reconfiguration of the system toward the desired configuration, which may involve the favoring of preferential energy pathways.…”