Figure 2. Conceptual framework of trajectories and restoration options for degraded communities modified from Bradshaw, (1996) and Hobbs and Norton, (1996) (A) . Each step of restoration is associated with key questions practitioners need to answer to justify active interventions or to evaluate restoration goals (B) . Following these stages, the degraded community (S1) is replanted with vegetation (S2). Fauna from the reference remnant community (S5) then passively recolonise the new restoration habitat. Where biodiversity and function are exceedingly slow or unlikely to reach remnant levels, active intervention via rewilding (S3) may push the restoration community closer to the reference community. Over time, biodiversity and function in the restoration community may sit within the natural variation (wavy lines) of the target reference community (S4).
Given a practitioner has chosen to rewild, the next critical question is: when is it appropriate to intervene? One of the main advantages of choosing a desired target community endpoint is that you can track the trajectory of post-disturbance communities towards that of the target. The difficulty with this approach is that realistic timelines need to be set as to when these targets should be met. Some restored wetlands are over 50 years old and have only recovered 53% of their biogeochemical function as compared to remnant states (Moreno-Mateos et al. , 2012). Ecosystem recovery can take much longer than 50 years (100s – 1000s years), however restoration projects are often under pressure to demonstrate success through attainment of predefined goals (Wortley, Hero and Howes, 2013). Whether or not a project is failing, or just exceedingly slow to reach its goals, is a key question for restoration ecologists. Addressing this question, Parkyn and Smith, (2011) hypothesised when intervention is needed and how this interacts with the dispersal capabilities of target fauna. They estimated that well connected restored streams in New Zealand would often reach their desired invertebrate community reference state in between 10 – 50 years whereas poorly connected streams may never reach this state, regardless of improving environmental conditions. The latter scenario might be common in highly disturbed systems and may have stimulated emerging studies that examine the feasibility of rewilding whole communities of invertebrates into streams undergoing restoration (Haase and Pilotto, 2019; Dumeier, Lorenz and Kiel, 2020).