A tree is a perennial woody plant with three basic characteristics that distinguish it from all other plants.

1. Size: In maturity it is much bigger than all other plants.
2. Form: A typical tree has a single stem which bears branches at a distance above the ground.
3. Way of life: Under natural conditions trees grow in stands (forests) which dominate their area of land.

By the wood of their trunks, their fruits, and the special kind of environment they create, trees influence life on earth more than any other kind of plant.

—1001 Questions Answered about Trees by Rutherford Platt; Dodd, Mead & Company; New York; 1959.

The zones or levels in the highest areas of forests.

• The highest level of an acrodendrocola is known as the emergent layer where the large birds of prey can scan the lower treetops for potential quarry or take off high flights.
• Two examples of birds that live in the emergent layer of an acrodendrocola are Monkey-eating Eagles in Asia and the Harpy Eagles of South America.
• Emergent layer in an acrodendrocola refers to a scattering of trees that project much higher than the other trees.
• This "attic" of the forests in the acrodendrocola has the most variable conditions of any other area of a forest because it is more exposed to the elements in that it gets the full force of the sun, wind, and rain.
• Beneath the emergent area of an acrodendrocola is the canopy layer which has colorful flowers and fruits, which are said to be delicately plucked and eaten by certain birds with very large and light bills; such as, the great hornbills in Africa and the toco toucans of South America and sloths usually spend most of their lives hanging upside down from branches in the forest canopy where they depend on the camouflage to keep from being attacked.
• The ringtailed possums have special tails that help them climb along high branches to reach flowers and fruit in the acrodendrocolas.
• Koalas normally live in the forest canopy of an acrodendrocola and they also walk across the ground to reach isolated clumps of trees.
• The golden-crowned kinglet bird is one of several small insect eaters which eat and nest high above the ground in the canopies of acrodendrocolas while the great horned owl flies at night from the canopies hunting small mammals and birds that live in the forests.
—Source: Smithsonian Animal Encyclopedia, pages 48 & 49.
• The forest canopy is a third layer in a rain forest, below the canopy layer, consisting of a thick layer of branches, leaves, etc. providing acrodendrocolas for many animals.
—Source: Smithsonian Animals, page 16.

Growing on bark.

1. A genealogical diagram of the ancestry of a related set of individuals: Harriet's cousin is very interested in creating a family tree to identify all her family ancestors.
2. The antecedents and descendants of a unit of related people: The family tree, or genealogical tree, identified all of the related ancestors going back about six generations.