A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported on a single main stem or trunk. Trees are long-lived, some reaching several thousand years old and growing to up to 115 m.
Trees are an important component of the natural landscape because of their prevention of erosion and the provision of a weather-sheltered ecosystem in and under their foliage. Trees also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. They are also elements in agriculture, and grown for their aesthetic appeal and their orchard crops. Wood from trees is a building material, as well as a primary energy source in many developing countries.