Just having farmland be fields is not very good for the land or the eco system. Breaking up farmland with hedges, woods, wetlands or whatever nature decides it should be is often a good idea. Next best thing is to manually plant trees.
Edit: add planting trees
> Breaking up farmland
One thing I have wondered was the relative benefits of a concentrated wilderness versus distributed habitat.
The common agricultural policy set-aside distributes payments for the wilderness across many farms (for equity, one supposes), whereas a concentrated wilderness would benefit few (and probably only the landowners).
For a short period I looked into carbon stuff and while forests were good, wetlands were deemed much bigger sinks.
It feels like wetlands is a huge ignored area. If what I read at the time holds (I think it was like 6-12x sequestration rate in some regions), a simple thing like rising sea levels would have a huge impact.
And anthropogenic destruction of wetlands is also a huge issue and one that is relatively easy to reverse in a lot cases (dams, rerouted rivers). And in some cases, water can just be rerouted occasionally to create temperarly wetlands that are good ecosystems as well. Mossy Earth I think is doing some of these.
Strangely enough I have been seeing wetland creation coming up on my radar recently. Hinkley Point C nuclear power station has been proposing these as alternative to acoustic fish deterrent, but the locals who might be affected are not happy.
https://www.bbc.co.uk/news/articles/ckgzwrgv71no
It would transform the biodiverse habitat into barren, species-poor salt marsh and tidal mud.
I do a lot of volunteering work with the Woodland Trust in the UK, negotiating with people who want to donate their land to restoration purposes. Britain is a land of fields and hedgerows (distributed). Many people fail to understand that most "wilderness" that we want to bring back is reliant on density (or concentration). I know many land owners who want to rewild parts of theirs, but are expecting temperate rainforest on a plot of land a couple acres across. It doesn't work like that.
The only way to bring back these lost or dying ecosystems is across large stretches of land, hundreds if not thousands of acres across. We have tiny pockets left in Cornwall, Wales and Scotland, but for the most part the country is ecologically baren in comparison to that a couple of thousand years ago.
Vast and continuous National Parks are one of the few viable ways to maintain or bring back our species rich ecosystems. Distributed "wilderness" between city blocks or cattle grazing land is duct tape on a leaky bucket.