[Schroedingersat]

In concept the answer is simple (although avoiding loopholes is difficult).

If it's your only residence then you get to cap the tax on one unit of housing worth of land at max(x% of income, y% of net wealth excluding that particular unit of land).

In your scenario the poor locals must subdivide and sell or commercialise some of their land, but get to continue benefiting from the commons they have built even if they have 0 income and survive purely off of that commons.