2.1 Active restoration of invertebrates
The return of invertebrates to revegetated areas is crucial for
restoration goals as they are critical components of functioning
ecosystems. Invertebrates may fail to actively recolonise due to
inadequate habitat within the restoration site or characteristics that
limit dispersal, such as a lack of wings (Haase and Pilotto, 2019).
Regardless of the cause, proactive solutions are rarely implemented when
monitoring reveals that important trophic groups have failed to
recolonise revegetated sites. As such, there are few examples of active
rewilding of invertebrates. The limited examples centre on rewilding
earthworms (usually a single species) into degraded areas to improve
decomposition rates (Snyder and Hendrix, 2008). Jouquet, Blanchart and
Capowiez, (2014) reviewed the role of earthworms (and termites) in
restoration so far and highlighted their limited use (only three field
studies from 1999 - 2014) and how projects could be expanded e.g., using
earthworms to alter reduce erosion. Further, although the practice of
rewilding to improve ecosystem function and biodiversity may be informed
by the much larger literature on invertebrate translocations, the
intention of this practice is very different. Species translocations are
usually conducted for species conservation and the functional role of
the species is rarely considered, let alone assessed (Bellis et
al. , 2019). Invertebrates targeted for translocations are often large,
charismatic endangered species (such as Wetas and butterflies), with
smaller, functionally important, taxa ignored.
Similarly, there are emerging
studies noting the effect of trophic rewilding on invertebrates and
microbes which differ from the points raised in this review (Andriuzzi
and Wall, 2018; van Klink and WallisDeVries, 2018; Gibb et al. ,
2021). These studies examine the effect of rewilding other biota on
invertebrate and microbe communities, rather than directly manipulating
invertebrates and microbes via rewilding.
Entire communities of invertebrates have been reintroduced in multiple
studies, although the practice is in its infancy. Topsoil inoculum
contains whole communities of invertebrates (and microbes), potentially
offering an avenue for community restoration. Several studies test the
impacts of inoculating restoration sites with soil taken from target
areas (Brown and Bedford, 1997; Wubs et al. , 2016; Lance et
al. , 2019). Although the focus is often on changes in ecosystem
function, the process of soil transplantation is in effect rewilding the
whole soil invertebrate community. Yet, quantification of soil
invertebrate responses to these treatments is rare, with only 29% of
studies monitoring post-transplant changes in invertebrate communities
(Table 1). Those studies that have quantified invertebrate responses
have shown that transplants of whole soil communities can improve the
biodiversity and density of mites and springtails (Wubs et al. ,
2016; van der Bij et al. , 2018), soil nematode abundance
(Benetková et al. , 2020), and soil macrofauna abundance (Moradiet al. , 2018).
The paucity of invertebrate rewilding projects demonstrates that there
are significant knowledge gaps regarding if, how and when invertebrates
should be used to restore ecosystem function. However, the diversity of
ecosystem functions provisioned by invertebrates may be matched by an
equally diverse range of situations which call for active rewilding
efforts.
Table 1. We found 21 published examples where whole communities
of invertebrates and microbes were reintroduced during restoration
projects (ignoring mesocosm and glasshouse experiments). This is
excluding single species reintroductions of earthworms and termites
(which are reviewed in Jouquet, Blanchart and Capowiez, (2014)), single
species reintroduction of Arbuscular Mycorrhizal Fungi (which are
reviewed in Asmelash, Bekele and Birhane, (2016)), and single species
reintroductions of cyanobacteria (which are reviewed in Rossi et
al. , (2017)).