In the Emma Marris video linked below, there appears to be an abandoned railway roadbed in the background. Such spaces almost automatically return to nature, left to themselves for a few years, but if the rails haven't been removed they are ideal testbeds for robotic equipment designed to guide, elaborate, and accelerate that process.
Besides the usual gardening techniques, such machines could move some soil and gravel from the rail-bed around to create microclimates with various shading/exposure, slope, drainage, water collection and/or even distribution across a flat bottom. They could weave vines together to create sheltered spaces for small birds, train high branches of trees from both sides of the rail-bed to arch overhead, creating deep shade by tying them together, position art objects intended to provide habitat for mice, birds, and bats and anchor them with soil and gravel. These machines could also assist other species in the creation of their preferred shelters, for instance by digging a bit of a hollow at the bases of trees with roots that spread abruptly just under the surface, or providing platforms in the forks of tree branches, just big enough to support proper nests, constructed of sticks and twine.
Emphasis on avian habitat would mean faster accumulation of a diversity of plant species, because birds frequently pass the seeds of berries they've eaten through, undigested. And, because the seeds of berries preferred by birds predominate, the result is a positive feedback loop.
Such machines could also provide damage-free access to the resulting space through inclusion of observation decks on top of the robotic rail platforms. If several such machines are to be spread along a single rail-bed, they should be designed so that they are able to approach each other closely enough that their observation decks come together, allowing riders to step across from one to another.