4.2 Biotic barriers need to be considered
Invertebrate and microbial rewilding projects also need to consider the
impact of biotic barriers and the challenges these barriers pose to
successful establishment. For example, soil microbe rewilding projects
have historically ignored the benefits of reinstating indigenous
whole-communities and instead focused on using single commercial species
for restoration purposes (Asmelash, Bekele and Birhane, 2016). These
commercial species are often non-native and encounter competition with
indigenous microbiota that have superior adaptions to local abiotic
conditions. The potential impact of the biotic barrier is demonstrated
by recent studies that compare singular non-native AMF inoculation with
indigenous whole-of-community rewilding. They found that introduced AMF
were scarce as compared to indigenous AMF, indicating the former were
ineffective at establishing and proliferating within the in situsoil community (Emam, 2016; Lance et al. , 2019). This was
expressed as increased soil function in revegetated areas inoculated
with indigenous soil whole-communities, resulting in greater soil
Phosphorous concentration (Lance et al. , 2019) and increased
plant biomass (Emam, 2016). Conversely, the ecological consequences of
commercial AMF outcompeting native species are unknown but could pose a
threat for native soil biodiversity and ecosystem function (Hartet al. , 2018).
Although there are limited examples of invertebrate rewilding, we can
learn much from the success and failures of these projects. Reducing
competition between in situ communities and rewilded communities
by removing the former can have significant effects on the establishment
of rewilded invertebrates and microbes. For example, a topsoil
inoculation study looked at the difference in restoration success
between areas where the topsoil and its resident soil community had been
removed as compared to areas where the resident soil community was
unaltered (Wubs et al. , 2016). They found that when rewilded,
whole soil communities were more likely to establish in areas where
topsoil had been stripped and the competitive effects of resident soil
communities removed, which manifested as a more successful restoration
effort. Whether this is a general pattern, or dependant on the habitat
in question, is not known. Benetková et al. , (2020) speculated
that it may be more appropriate to strip the resident community in
forests as opposed to grasslands as soil formation is much faster under
forests. They posit that other soil restoration projects (Moradiet al. , 2018; van der Bij et al. , 2018) were more
successful than theirs due to their different rewilding methodology
((Benetková et al., (2020) transplanted soil on top of the
resident community as opposed to removing the resident community prior
to the transplants). Further, literature on invertebrate translocations
revealed that predation from species in the established community was a
significant barrier to the establishment of reintroduced invertebrates
(Bellis et al. , 2019). This should also be a consideration for
invertebrate and microbial rewilding.