Tree

A tree is a perennial plant characterized by an elongated stem, often called a trunk. This trunk usually supports branches and leaves at a distance from the ground.

While there is no single universal definition, trees are often identified by their height or their woody structure. Some broad definitions include tall herbaceous plants like bananas, palms, or bamboos. Narrower definitions focus on plants with secondary growth. This means the trunk thickens each year as it grows outward.

Trees are essential to Earth's ecosystems because they moderate the climate and reduce soil erosion.

The biological mechanism of a tree relies on a complex vascular system. This system interconnects all living cells to distribute water, nutrients, and chemicals.

Roots grow beneath the ground to anchor the plant and extract moisture from the soil. Water travels from the roots up through the stem via the xylem. This process happens through capillary action as water evaporates from the leaves during transpiration.

To grow wider, many trees use a vascular cambium. This tissue allows for the expansion of vascular tissue, creating woody growth. Because this growth can rupture the outer epidermis, a cork cambium also develops. The cork cambium produces thickened cork cells that protect the surface and reduce water loss.

Trees can be categorized into several distinct biological groups. The majority of tree species are angiosperms, which are flowering plants. These plants typically produce seeds enclosed within fruits. Other trees are gymnosperms, often referred to as softwoods. Gymnosperms carry their seeds in open structures, such as the cones found on conifers.

Trees also differ in how they manage their foliage. Evergreen trees keep their green leaves throughout the entire year. Deciduous trees shed their leaves at the end of a growing season. Some species, like certain cypresses, undergo cladoptosis, where they shed small leafy shoots annually.

The history of trees is a story of parallel evolution. Trees are not a single taxonomic group. Instead, many unrelated plant species evolved trunks and branches independently. This happened so they could tower above other plants to compete for sunlight.

The earliest trees began to evolve approximately 400 million years ago. Today, scientists estimate there are roughly 3.04 trillion mature trees on Earth.

This massive number was calculated based on tree densities measured across over 400,000 plots. This estimate is significantly higher than previous scientific calculations.

Trees are distributed across the globe in various important biomes. The taiga, or boreal forest, is the world's largest land biome. It covers 29 percent of the world's forest cover and is dominated by conifers.

In tropical regions, rainforests provide some of the most biodiverse habitats on the planet.

South America holds the highest biodiversity with 43 percent of all tree species. Eurasia follows with 22 percent, while Africa holds 16 percent.

In many areas, forests are shrinking. This happens as land is cleared for agriculture. In the last 12,000 years, the global tree population has decreased by 46 percent.

Humans find many ways to use trees for survival and industry. Trees provide timber, which is wood used for construction and furniture.

They also provide fuel for cooking and heating.

Some trees offer food in the form of fruit.

Beyond physical resources, trees have deep cultural significance. Many cultures have revered trees as sacred. They appear frequently in the mythologies of many different people around the world.

Trees are also vital for regulating the Earth's atmosphere. They play a major role in the carbon cycle by removing carbon dioxide from the air. The trees then store large quantities of carbon within their own tissues. This process helps to moderate the global climate. By forming a dense canopy, trees also create unique environments for countless other species.

This canopy layer is a critical part of the forest structure, acting as a ceiling for the life below.