2.3 When is rewilding invertebrates and microbes necessary?
Whether or not a practitioner chooses to rewild invertebrates or
microbes is highly dependent on the first critical step in restoration:
setting goals and targets (Prach et al. , 2019) (Figure 2). For
example, practitioners that accept a novel ecosystem may let a
post-disturbance community form from whichever biota are best adapted to
the novel abiotic conditions, regardless of their status as native to
the area or their functional role, thereby avoiding active intervention
(Hobbs, Higgs and Harris, 2009). Other approaches aim to restore an area
to a “natural” predefined target state in terms of species composition
or ecosystem function. This is a common goal in ecological restoration
and is the first of six key concepts underpinning best practice in
ecological restoration as defined by the international Society for
Ecological Restoration (Mcdonald et al. , 2016). These target
states are often based on the species, trait, and/or functional
diversity of one or more nearby remnant sites, or if no remnant sites
exist, literature that describes the community pre-disturbance (Prachet al. , 2019). This paradigm is inherently interventionist as it
can take significant effort and resources to push a degraded ecosystem
towards its pre-disturbance state. As such, practitioners may be more
inclined to rewild fauna from remnant sites when there is a desired
remnant target state (Figure 2).
Restoration success or failure can often depend on the ability of
dispersal-limited species to reach and recolonise restoration sites and
how this factor interacts with temporal changes in habitat conditions
(Baur, 2014). The amelioration of microclimatic and biotic conditions
over time will no doubt influence the colonisation rate of restored
areas. However, empirical tests of metacommunity theory demonstrate that
dispersal constraints can often outweigh the importance of environmental
conditions for invertebrate community structuring post-restoration.
For example, Kitto et al. ,
(2015) used metacommunity analysis to evaluate the importance of
dispersal constraints versus amelioration of environmental conditions
for the restoration of benthic invertebrate communities in restored
streams. They found that although some environmental variables
structured communities, this was independent of the effect of stream
location across a landscape and the proximity to remnant source
populations. Chen et al. ,
(2020) found analogous relationships in soil microbial restoration,
noting that dispersal limitation was a stronger determinant than
environmental filtering for the reconstruction of archaeal, bacterial,
and fungal communities post-disturbance. This demonstrates that, where
restoration sites are geographically isolated from remnant sites, or
where target fauna are dispersal constrained, rewilding can play an
important role in achieving restoration goals. It is also crucially
important that abiotic and biotic conditions of restoration sites are
monitored pre-rewilding. This is not only to establish that abiotic
conditions will be receptive to transplantees, but to confirm the
restoration site has reduced efficiencies of an ecosystem function
and/or biologically depauperate communities, thus justifying active
rewilding efforts. This can be extended beyond simple monitoring
methods. For example, Thierry and Rogers, (2020) proposed a conceptual
framework that identified priority rewilding sites based on habitat
suitability, areas with inefficient ecosystem functions, and societal
factors.