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Accomplish really nothing more than everyone dedicating some part of garden/land they own or just guerilla-stake out a square in a forest and keep looking after the fence. It is up to nature to use the land as it sees fit, insects, flowers, dry decay... etc.

I would like to add one thing to the earlier comment: It will of course serve as a resource for biodiversity, allowing microorganisms, insects and smaller animals to do their work. It would be interesting to see what would happen if for example every balcony in a city had a small patch of grass or similar.