I wondered before if the solution to retain humidity in dry climates comes from plant density, but what you described is what happened to me.

Instead, I find the best solution was to combine plants that grow at different heights, as the larger ones give shade and the lower ones with shallow roots keep the land humidity from evaporating.

(That's with some tricks mixed in for water conservation on dirt mixture, using a layer of porous rocks, using ditches of thatch, ceramic pearls, etc..)