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

Abstract

Seminatural grasslands are important biodiversity hotspots, but they are increasingly degraded by intensive agriculture. Grassland restoration is considered to be promising in halting the ongoing loss of biodiversity, but this evaluation is mostly based on plant communities. Insect herbivores contribute substantially to grassland biodiversity and to the provisioning of a variety of ecosystem functions. However, it is unclear how they respond to different measures that are commonly used to restore seminatural grasslands from intensively used agricultural land. We studied the long‐term success of different restoration techniques, which were originally targeted at reestablishing seminatural grassland plant communities, for herbivorous insect communities on taxonomic as well as functional level. Therefore, we sampled insect communities 22 yr after the establishment of restoration measures. These measures ranged from harvest and removal of biomass to removal of the topsoil layer and subsequent seeding of plant propagules. We found that insect communities in restored grasslands had higher taxonomic and functional diversity compared to intensively managed agricultural grasslands and were more similar in composition to target grasslands. Restoration measures including topsoil removal proved to be more effective, in particular in restoring species characterized by functional traits susceptible to intensive agriculture (e.g., large‐bodied species). Our study shows that long‐term success in the restoration of herbivorous insect communities of seminatural grasslands can be achieved by different restoration measures and that more invasive approaches that involve the removal of the topsoil layer are more effective. We attribute these restoration successes to accompanying changes in the plant community, resulting in bottom‐up control of the herbivore community. Our results are of critical importance for management decisions aiming to restore multi‐trophic communities, their functional composition and consequently the proliferation of ecosystem functions.

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

“…In Target grasslands, biomass is harvested once a year in late summer or early autumn. Eleven 5 × 5 m (25 m 2 ) plots were randomly established in each of the five treatments (in total 55 plots; for a detailed map see Neff et al 2020). An additional 2 × 2 m (4 m 2 ) subplot was randomly established at least 2 m away from each 25‐m 2 plot for destructive sampling.…”

“…Aboveground arthropods.-Aboveground arthropods were sampled at two locations in each 25-m 2 plot in early July 2017 (see also Neff et al 2020). Briefly, two cylindrical baskets (50 cm diameter, 67 cm height; woven fabric) were thrown simultaneously from outside the plot into two opposite corners.…”

“…Yet, to evaluate restoration success, usually only a few aboveground biotic properties, typically plant community composition, sometimes the presence/absence of selected insect species or taxa (e.g., grasshoppers, beetles) are used (e.g., Patzelt et al 2001, Kardol et al 2005, Kiehl and Wagner 2006, Kiehl and Pfadenhauer 2007, Klimkowska et al 2007, Verhagen et al 2008, Neff et al 2020). More exhaustive evaluations are lacking and only few studies assessed belowground community composition and soil properties to determine restoration success (e.g., Frouz et al 2009, Kardol et al 2009 b , Wubs et al 2016, Resch et al 2019).…”

Coppicing and topsoil removal promote diversity of dung‐inhabiting beetles (Coleoptera: Scarabaeidae, Geotrupidae, Staphylinidae) in forests

“…Nitrogen accumulation can be reduced by prescribed burning (Hubbard et al ., 2004), grazing, mowing (Jones et al ., 2017), litter harvesting (Sayer, 2006), removal of tree‐biomass and logging residues (Lundborg, 1997) or humus and topsoil removal (Prietzel & Kaiser, 2005; Tarvainen et al ., 2011). However, such measures might only have a short‐term effect, given the continuous atmospheric nitrogen deposition, yet topsoil removal is one of the most efficient and long‐lasting measures (Jones et al ., 2017; Neff et al ., 2020). Topsoil removal was implemented to restore plant communities (Hölzel & Otte, 2003; Kiehl et al ., 2010), support the re‐establishment of light‐demanding herb species (Emsens et al ., 2015), restore communities of herbivorous insects (Neff et al ., 2020) and support thermophilic and epigeic arthropods, such as many carabids and spiders (Borchard et al ., 2014).…”

“…However, such measures might only have a short‐term effect, given the continuous atmospheric nitrogen deposition, yet topsoil removal is one of the most efficient and long‐lasting measures (Jones et al ., 2017; Neff et al ., 2020). Topsoil removal was implemented to restore plant communities (Hölzel & Otte, 2003; Kiehl et al ., 2010), support the re‐establishment of light‐demanding herb species (Emsens et al ., 2015), restore communities of herbivorous insects (Neff et al ., 2020) and support thermophilic and epigeic arthropods, such as many carabids and spiders (Borchard et al ., 2014). So far, topsoil removal has been barely applied in forest ecosystems (but see Ewald & Pyttel, 2016; Soto & Puettmann, 2018).…”