n.
Woody perennial plant.
Most trees have a single self-supporting trunk containing woody tissues, and in most species the trunk produces secondary limbs called branches. Trees provide many valuable products, especially wood , one of the world's chief building materials, and wood pulp, used in papermaking. Wood is also a major fuel source. Trees supply edible fruit s and nut s. In addition, trees take in carbon dioxide and release oxygen during photosynthesis . Their root systems help retain water and soil, preventing floods and erosion. Trees and forests provide habitats for a wide variety of animals, and they beautify both natural and altered landscapes. Growth ring s in the trunk indicate the age of most trees. The tallest trees are the Pacific coast redwood s; the oldest are the bristlecone pines, some of which are over 4,000 years old. See also conifer ; deciduous tree ; evergreen ; forest ; shrub ; softwood .