3.2 How can we rewild whole communities?
Successful whole-of-community rewilding, and indeed any form of
reintroduction, depends on the suitability of habitat to which the
transplantees are moved. For whole-of-community rewilding, the
transplants of whole habitat would ideally come from nearby remnant
areas of similar original state as they are most likely to contain
species appropriate to the environment of the revegetated area (Wubset al. , 2016; Jourdan et al. , 2019; Dumeier, Lorenz and
Kiel, 2020). This both increases the likelihood of successful
establishment and ensures that communities with appropriate functional
and life history traits are used during restoration. Using nearby
remnant target sites is the more common method for setting restoration
goals (Mcdonald et al. , 2016) and is how most documented cases of
whole-of-community rewilding choose their source of rewilded populations
(86%) (Table 1). Further, it is vital that environmental conditions of
the restoration site have been appropriately ameliorated and are
receptive to transplantees. For
example, Haase and Pilotto, (2019) assessed and required 21 abiotic
variables of restored streams (physiochemical variables,
hydromorphology, and land use) to be within specific thresholds of that
of intact streams before choosing to rewild entire benthic communities
of invertebrates.
Successful establishment also hinges on transferring communities at
appropriate times and in appropriate quantities. This will undoubtedly
vary according to the target
communities. For example, when
transferring whole communities of stream invertebrates, Haase and
Pilotto, (2019) suggest using a modified version of sampling (German EU
Water Framework Directive) that adequately samples all microhabitats in
a stream and to repeat this every second month for a year to capture all
life stages. Similar protocols would need to be developed when
transporting other elements of the community. Once transferred,
successful establishment of communities depends on translocating a
Minimum Viable Population (MVP) of each species that can overcome
mortality rates and inbreeding depressions. This would ideally be
factored into pre-translocation thinking, with targeted monitoring of
source populations to determine the amount of habitat that contains
enough species and individuals to establish a new community. Although
there have been attempts to develop a general MVP regardless of taxon
(Flather et al. , 2011), the amount of habitat collected to obtain
an MVP will undoubtedly vary according to taxon, the environment from
which they are sampled, and the size of the area into which they are
transplanted. For example, there is great variation in the amount of
transplanted habitat needed to achieve successful whole-of-community
rewilding, which can range from 0.16 l /m2 (Emam,
2016) to 2.5 l/m2 (Wubs et al. , 2016) of soil
(Table 1). There would be a considerable amount of effort needed to move
larger amounts of habitat, yet smaller amounts could be preferred given
that transplantees successfully spread throughout the restoration site.
Dispersal of transplanted individuals is highly dependent on the
surrounding environmental conditions. For example, Moradi et al. ,
(2018) found that although soil transplants lead to greater abundances
of soil macrofauna, areas adjacent to transplant sites were devoid of
soil macrofauna due to physical and chemical limitations of the
surrounding soil.
There are clear advantages that invertebrate and microbial rewilding has
over traditional (vertebrate-focussed) projects. Because invertebrates
and microbes are miniscule, whole communities can be easily transported
within small transplants of habitat containing a multitude of species,
individuals, and propagules – bypassing the slow species-by-species
reintroductions seen in current restoration practices (Corlett, 2016).
This is inherently advantageous as the purpose of restoration is the
complete return of biota and function, not just some specific species.
Unlike traditional rewilding projects, whole-of-community rewilding also
does not discriminate based on “likeability” of a species, meaning
that overlooked, yet functionally important species, can be incorporated
into restoration more frequently (Jourdan et al. , 2019). These
benefits may be why the whole-of-community reintroduction paradigm is
ingrained in soil restoration and starting to gain traction in stream
restoration (Haase and Pilotto, 2019; Dumeier, Lorenz and Kiel, 2020).
This is not to say that single species rewilding has no place in future
projects. For instance, single species reintroductions of butterflies
and bumblebees in the United Kingdom were the most feasible way to
reconstruct historic pollinator communities and improve pollination
across the landscape (Steele et al. , 2019).