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).