How do trees help with water?

Trees are a water machine. Their crowns catch fog and dew and slow the rain, so it soaks in instead of running off; leaf litter and roots make the soil a sponge that holds water for weeks; leaves breathe moisture back into the air, and forests help make the next rain. Bare land swings from drought to flood. On your plot: keep the soil covered (mulch, green manures), plant trees, shrubs or a hedge along the top of a slope and across it, not down it, and dig shallow ditches with a bank along the contour so rain stays where it falls. On a steep spot a stone laid across the runoff holds back water and soil: plant a tree just above it. In dry lands people dig half-moons with the bank downhill and small pits filled with compost: they gather the rain. Stones on the south side of a plant act as a heat trap.