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.