We know very little about wild nature. What might happen if we step back and let nature ‘do its thing’ in a given area? Not sure. We can state expectations, based on current understanding of ecosystem assembly, compositional changes through time, structure, function, etc.
We’ve been able to observe some of the consequences of defaunation, particularly changes arising from the loss of larger-bodied species from a landscape. That’s the science of ‘trophic cascades’.
We know that larger-bodied species can have large and disproportionate effects on ecosystem structure and function.
But, as yet, we’ve been unable to observed what happens as larger-bodied species recover and come to re-occupy landscapes from which they have been extirpated, except in a few instances and with few species.
That makes it difficult to set targets. But it’s easier to state expectations. I.e., given what we know, this is what we might expect. I think it’s OK to set a few specific targets for rewilding and natural recovery projects – say ‘we aim to subject X,000 ha to rewilding by XXXX’, but that we should accompany these explicit targets with stated expectations – or hypotheses. Then we set the scientists the task of watching what happens, so we can build an evidence base for the future.