3.1 Future possibilities for invertebrate and microbial
rewilding
Stepwise restoration of communities by adding individual species is
becoming increasingly unattainable, unrealistic, and ineffective in our
rapidly changing and dynamic world. This has no doubt influenced the
trajectory of restoration and rewilding projects, which have
increasingly focussed on reinstating ecosystem function and
self-organising communities, rather than compiling set groups of species
(Harris, 2014; Perino et al. , 2019). This changing paradigm suits
the unique characteristics of invertebrates and microbes, further
encouraging their use in future rewilding projects. For example, the
astounding diversity of invertebrates and microbes, the lack of
knowledge of their functional roles, and their high spatial turn-over
rates means that in any given community we are often unsure of which
species are functionally critical (Setälä, Berg and Jones, 2005). Thus,
targeted rewilding of single species may not lead to desired changes in
ecosystem function efficiency. However, invertebrates and microbes are
miniscule and thus easily manipulated, meaning we can readily move whole
communities, and the functions they provision, from one place to another
(given the habitat is appropriate and enough species establish). This is
already how a majority of invertebrate and microbial rewilding projects
operate. For instance, soil inoculation is a common form of invertebrate
and microbial rewilding which consists of moving soil from target sites
(with invertebrate and microbe communities in situ ) into
restoration sites (Wubs et al. , 2016). We term this practice
“whole-of-community” rewilding and although it is evident within soil
inoculation studies, it is highly under-researched outside of soil
transplants and thus rarely considered during restoration (Table 1).
Whole-of-community rewilding consists of transporting small subsets of
whole habitats, complete with invertebrate and microbe communities, from
desired sites into restoration areas. The desired sites are at the
practitioner’s discretion; thus, they can tailor the constructed
community based on whichever site they choose. However, a summary of
whole-of-community rewilding for restoration purposes highlights that
nearby remnant sites are most frequently chosen (86% of projects),
which conforms to mainstream restoration paradigms (i.e., choosing a
nearby “intact” site as the desired endpoint community) (Table 1)
(Mcdonald et al. , 2016).
Even within the limited examples of whole-of-community rewilding, there
are clear knowledge gaps and missed opportunities. For example, very few
studies monitor invertebrate and microbe communities post-inoculation
(Table 1), making it difficult to quantify the efficacy of
whole-of-community rewilding and its effect on community dynamics.
Post-reintroduction changes were only recorded in 24% of transplant
projects for invertebrates and 29% of projects for microbes,
highlighting that monitoring post-reintroduction is crucial for greater
understanding of the successes and failures of this holistic form of
rewilding. Changes in ecosystem function post-reintroduction were
recorded more frequently (67% of projects), but it is difficult to link
the effect of rewilded invertebrates and microbes to changes in function
when they are not monitored. Further, invertebrates and microbes are
ubiquitous, meaning there may be many more instances outside of those
documented (Table 1) where whole-of-community rewilding may be applied.
For example, litter communities are critical for efficient nutrient
cycling and can be easily transported within their habitat (Silvaet al. , 2020). However, litter transplants with the purpose of
improving decomposition rates during restoration have not been attempted
before (Box 1).
Although the direct mechanisms by which whole-of-community rewilding
improves ecosystem function is likely highly contextual, this practice
can influence a broad range of functions, including; nutrient dynamics
(Lance et al. , 2019), plant growth (Emam, 2016), and community
trajectories (Wubs et al. , 2016). One possible link between
ecosystem function and this rewilding practice is the associated rapid
increase in biodiversity. This relationship is known as the Biodiversity
– Ecosystem Function (BEF) hypothesis and posits that increases in
biological diversity (number of species, genotype varieties etc.) will
see similar increases in the efficiency of ecosystem functions
(Srivastava and Vellend, 2005). Although debate surrounds the generality
of patterns between biodiversity and ecosystem function (e.g., how the
effect varies over spatial scales (Thompson et al. , 2018)) it may
be of particular use to restorationists as post-disturbance communities
are biologically depauperate and their diversity can be easily and
directly manipulated through practices such as rewilding (Srivastava and
Vellend, 2005).