Arks in reference to Noah and the ark from jewish mythology, arks as in something with the purpose of carrying life through a crisis. Now I'm going into this with the assumption that climate and such will undergo radical changes, leading to the death of countless species in the aftermath of civilization.
What I'm thinking is groups of rewilders in valley's, islands and generally remote locations who deliberatly build up ecosystems around them to the maximum sustainable population of species, to maximum diversity, not just living there and doing what they need to do in order to eat. For instance introducing species of plants not necessarily native to that exact location, but native to the bioregion. Keeping an eye on each population of plants so imported ones don't outcompete native ones, just generally helping every species get through the changes so they can be reintroduced once things stabilize. Same of course with animals, insects, mushrooms, whatever. Imagine a valley with thousands of species, all tended carefully to maintain harmony. And from these valleys the species can spread to the surrounding land as they see fit. Like in England, there are no large predators left, no wolfes or bears or lynxes. Deer populations and such will explode if a lot of humans disappered. Guess rewilded dogs could possibly fill that niche though, but would be better in my eyes to reintroduce wolves and bear and lynxes...
This again would require carefull consideration on the rewilders part, and a finely tuned relationship with the land and it's inhabitants, thus making it a kind of accelerated learning course in the skills needed to survive everywhere else. These groups would also, because of the need to mindfully observe nature, build sustainable cultures and invisible technologies much more rapidly than otherwise. I think it could vastly accelerate the process of returning Earth and humans to something beautiful. Also, I think Gaia likes her genepool;-)