Lima, Peru has some rather unusual suburbs. Rural villagers who move into the capital often end up living on the outskirts of town — steep hillsides that envelop the city. The land is cheap, but it comes with risks and downsides, namely landslides and a lack of water.

In order to help remedy both problems, the government has set up a sort of homesteader’s law. If new residents squat on unclaimed land, after a time, they’re allowed to obtain the land’s title by planting trees uphill, an insurance policy against landslides. More trees also help re-establish the area’s natural water cycle, returning the precipitation that they don’t absorb themselves back into the groundwater.

The only problem is there’s not much water around for irrigation, or anything else for that matter.