Science & Nature - Earth's forests: massive biomes that regulate regional rainfall

Forests are Earth's largest terrestrial ecosystems, covering over four billion hectares, or about thirty-one percent of global land. Beyond holding eighty percent of the planet's plant biomass, they generate three-quarters of the biosphere's gross primary production. In the Amazon, trees alter regional rainfall by releasing water from leaves, triggering the wet season two to three months early. However, deforestation and anthropogenic climate change hold the potential to disrupt this process, causing forests to pass a threshold into savanna.

Source: Wikipedia