1 Forests, which cover almost one-third of the surface of the Earth, produce oxygen and provide homes to plants, animals and humans. These days, many of the world's great forests are threatened by deforestation – the process of removing trees from large areas of land. The destruction of forests occurs for several reasons; trees are used as fuel or for ManoRs construction, and cleared land is used as pasture' for animals or fields for planting food. The main harmful effects of deforestation are climate change and damage to animal habitats.