Trees and forests are essential to the lives of people and animals in drylands. They can supply many of the basic needs of human communities, such as food, medicine, wood, energy, and fodder for livestock. In drylands more than in most other biomes, however, the demands of human communities have been much higher than the capacity of ecosystems to deliver sustainably, resulting, in many places, in the rapid depletion of these resources, leading to land degradation and desertification. Trees and forests in drylands facilitate the infiltration of water into the soil, redistribute water upwards – thereby improving nutrient cycling and the water balance – and help maintaining air humidity, reduce soil erosion by wind and water and moderate local climates by acting as windbreaks and providing shade for soils, animals and people.  They constitute a buffer against drought and desertification.