So what is resilience? In their words resilience is the
measure of the amount of change or disruption that is required to transform a system from being maintained by one set of mutually reinforcing processes and structures to a different set of processes and structures.which is a definition that I like, but is hard to operationalize. If you can write down a system of equations describing the evolution of a system, this definition is equivalent to the "robustness" of an equilibrium point, which is a quantity that can be mathematically defined and calculated, so that is typically how I think of it. Of course, writing down the system of equations isn't so easy ... They go on to state that "...[f]or a system to be resilient implies that it maintains certain key properties ..." where a key property is one that is central to its identity. This is much more difficult - what is the identity of an ecosystem? How can you tell if an ecosystem has changed its key properties? The paradigmatic examples involve pretty obvious shifts, like woody plants invading a grassland, algae taking over a coral reef, and the classic clear/turbid lake example. Tough luck if you're managing a woodland park with lots of birds and understory plants.
One of the things that continues to bug me about ER AM is that a series of normative goals (all of which I happen to agree with) are deemed to be necessary because they contribute to resilience, which in turn contributes to those goals. For example
We expect that managing for resilience will sustain diversity, permit natural perturbations, facilitate the action of natural processes and integrate both social and ecological dimensions of sustainability.But earlier they state "[c]omplex systems theory suggests that the conservation of function is strongly dependent on diversity ...". But this is completely circular - having diversity increases resilience and resilience sustains diversity. So it appears to me that resilience is an attempt to attach some kind of scientific objectivity to the normative goal of maintaining diversity, whether it is diversity of functions or species.
I like the idea of resilience as stated in the first definition, but I think it faces an uphill battle for implementation. This article doesn't advance the cause very much, because it falls into the trap of using resilience as support for a normative goal. Until we can calculate resilience, and predict, credibly, the effects of loss of resilience in a range of systems I don't think we'll have much success convincing the rest of humanity to forego maximizing production.