Trees
A tree is a perennial plant with an elongated woody stem, or trunk, supporting branches and leaves. Most definitions of a tree require a single stem reaching a minimum height at maturity—commonly 3 to 5 metres. Trees are not a taxonomic group, but rather a form found in many different orders and families of plants, from towering conifers to flowering broadleaves.
Trees cover approximately 30 percent of Earth's land surface and are home to approximately 80 percent of the world's terrestrial biodiversity. They play a critical role in the global carbon cycle, absorbing an estimated 2.6 billion tonnes of carbon dioxide per year.
Taxonomy and Classification
Trees span multiple unrelated groups within the plant kingdom. The two primary structural categories are gymnosperms (cone-bearing trees such as pines, firs, and spruces) and angiosperms (flowering trees including oaks, maples, and cherries). The oldest-known tree lineages, such as the cycads, predate the dinosaurs.
Wood, the defining material of trees, is composed primarily of cellulose and lignin. Lignin provides structural rigidity and resistance to decay, while cellulose forms the fibrous skeleton of the cell walls. The annual growth rings visible in cross-section record variations in seasonal growing conditions and allow dendrochronologists to date wood samples and reconstruct historical climates.
Featured Species
The following articles cover ten of the most widely distributed, ecologically significant, or culturally important tree species found across the globe. Click any entry to read the full encyclopaedia article.
Oak
Quercus robur
Oak trees are among the most iconic and ecologically important trees in the temperate forest biome. Known for their dist…
Read article →Maple
Acer saccharum
Maples are celebrated for their brilliant autumn foliage and the sweet sap used to produce maple syrup. The sugar maple …
Read article →Pine
Pinus sylvestris
Pine trees are evergreen conifers found on every continent except Antarctica. They are characterised by bundles of needl…
Read article →Birch
Betula pendula
Birch trees are known for their distinctive white, papery bark that peels in thin layers. Fast-growing and cold-hardy, b…
Read article →Cedar
Cedrus libani
True cedars are majestic conifers native to the mountains of the western Himalayas and the Mediterranean. Their aromatic…
Read article →Willow
Salix babylonica
Willows are graceful trees most commonly found near water. Their long, weeping branches and narrow leaves create a disti…
Read article →Elm
Ulmus minor
Elm trees once dominated the hedgerows and landscapes of temperate Europe and North America. Their vase-shaped canopy cr…
Read article →Walnut
Juglans regia
Walnut trees are prized for both their delicious nuts and their exceptionally fine-grained, dark timber. Native to Centr…
Read article →Cherry
Prunus avium
Wild cherry trees are celebrated for their spectacular spring blossoms and sweet fruits. In Japan, the tradition of hana…
Read article →Redwood
Sequoia sempervirens
Coast redwoods are the tallest trees on Earth, with some individuals exceeding 115 metres in height. Found only in a nar…
Read article →Distribution by Region
Trees are found on every continent except Antarctica and at every altitude from sea level to the treeline, which occurs at roughly 3,500 metres in the Alps and up to 4,900 metres in the tropical Andes. Tropical rainforests in South America, Central Africa, and Southeast Asia contain the greatest diversity of tree species, with a single hectare of Amazonian rainforest hosting up to 300 species.
Boreal forests, also known as taiga, form the world's largest terrestrial biome, stretching in an almost unbroken belt across northern Russia, Canada, and Scandinavia. They are dominated by cold-tolerant conifers including spruce, fir, and pine, as well as deciduous species such as larch and birch.
Conservation
Deforestation remains one of the most pressing environmental issues of the 21st century. According to Global Forest Watch, the world lost approximately 4.1 million hectares of primary tropical forest in 2022 alone. The leading causes are agricultural expansion, illegal logging, and infrastructure development.
Conservation efforts range from international agreements such as the Kunming-Montreal Global Biodiversity Framework, which aims to protect 30 percent of the planet's land area by 2030, to grassroots tree-planting programmes like the Trillion Trees initiative. Many countries have enacted legislation designating ancient and veteran trees as protected heritage specimens.