A tree grows in two ways. Primary growth happens at the tips of roots and stems and makes them taller or longer. The vascular cambium is a thin layer of cells that makes new xylem and phloem, and xylem cells account for most of the diameter growth in a tree each year. Xylem carries water and minerals up from the roots to the leaves, while phloem carries food made in the leaves to the branches, trunk and roots.

Inside the trunk, sapwood is the tree's pipeline for water moving up to the leaves. As new rings of sapwood form, the inner cells of older sapwood turn into heartwood, which is the central, supporting pillar of the tree. A heartwood post only 12 inches long and 1 by 2 inches across can hold up twenty tons.

A trunk cut across shows a pattern of rings, and the number of rings shows how old a tree or limb is. In spring, when a tree is growing fast, its xylem cells are large with thin walls. The width of a tree's ring changes with the weather and other conditions of that year. Drought makes narrow rings and plenty of rain makes wider rings.

The science of studying the past by looking at tree rings is called dendrochronology. Scientists learn about past weather patterns and forest fires by studying the annual rings of trees. Some living bristlecone pines are more than 4,000 years old.

Roots take in water and food from the soil for the tree. Most tree roots are in the top three feet of soil, and a tree's roots often spread out much wider than its crown. Coast redwoods have root systems only 6 to 12 feet deep. Tree roots give fungi food the tree has made, and the fungi give back water and minerals. Mycorrhizae are partnerships between fungi and roots. Plants lose most of the water their roots take in to the air through their leaves, a process called transpiration.

Leaves make food for the tree, and they get their green color from a pigment called chlorophyll. As nights get longer in autumn, trees get a signal that the growing season is ending, and the green chlorophyll fades. Shortening day length is the most dependable seasonal signal for autumn leaf color, more than chilly mornings. Yellow and orange colors in leaves come from carotenoids, which are in the leaf all summer.

Evergreen trees stay green all year, and a pine tree is an evergreen tree. Most evergreen trees have needle-shaped leaves. Pine trees and other conifers carry their seeds in cones. Squirrels hide acorns by burying them, and that moves oak seeds around.

Coast redwoods are the tallest trees in the world, as of November 2026, and the tallest known coast redwood is about 380 feet tall, as of November 2026. Redwood forests grow naturally in a narrow band along the Pacific Coast, from central California to southern Oregon. Coast redwood bark is thick and protects the tree from fire. The General Sherman Tree stands 275 feet tall and is more than 100 feet around, as of November 2026. It is the largest tree in the world by trunk volume, at 52,508 cubic feet, as of November 2026. It is thought to be between 2,200 and 2,700 years old, as of November 2026. Fire is part of the life cycle of giant sequoias.

Words to know

• cambium: growing layer
• xylem: water pipeline
• dendrochronology: tree-ring dating
• mycorrhizae: root-fungus partnerships
• carotenoids: yellow-orange pigments