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.