Shirley Byrd, age 12, of Lamar, S.C., for her question:
HOW MANY TYPES OF TREES ARE THERE?
A tree's wood is made of about 50 percent water. A large tree in full leaf may absorb 95 gallons of water from the soil daily, and on a hot summer day, water will be moving up through the trunk at the rate of about three feet every minute. Sunshine, air and lots of water are needed by every tree to carry out its development and growth.
Trees are the largest and oldest of all the world's plants. We couldn't live very well without them since they provide us with food, fiber and medicine. Wood from trees gives us many of our building materials. And the living tree conserves our natural resources and supplies oxygen for us from the carbon dioxide it absorbs from the air.
There are more than 20,000 different kinds of trees on earth. More than 7,000 grow in North America. The largest variety grow in wet, tropical regions.
Six different classifications divide the main groups of trees. They are the broadleaf trees, needleleaf trees, palms, cycad trees, fern trees and ginko trees.
Largest grouping of trees are in the broadleaf class. As the name implies, they have flat, broad leaves and for the most part they are deciduous that is, they lose their leaves in the fall and grow new ones each spring. Among the exceptions are the evergreen live oaks and the holly trees.
Broadleaf trees have flowers which develop into fruit. The fruit, in turn, completely surrounds the seeds. For the most part, trees in this group have hard, tough wood.
More than 500 species of needle leaf trees can be found. For the most part, the trees are evergreen although they do produce new needles each year. Most of the needle leaf trees are classified as softwood. Most of the trees produce seeds in cones.
There are about 2,500 varieties of the palm trees on earth. Most have no branches and are made up of feather¬ shaped or fan shaped leaves at the crown of the trunk.
Cycad trees look much like palms but are more closely related to pines. They grow mostly in Africa, Asia and Central America and have crowns of long, feathery leaves.
Fern trees, which like the tropics or mild climates, reproduce by tiny bodies called spores. They do not form flowers, fruit or seeds.
The ginko tree, in a class by itself, has fan shaped leaves and can trace its history back millions of years. It is often called the maidenhair tree.
A tree differs from other plants in a number of ways. First, it has a woody stem called a trunk. It can grow to be at least 15 to 20 feet tall. While shrubs have woody stems also, they do not have one that grows thicker than the rest and can stand alone..
Trees need at least 15 to 20 inches of rain each year. They'll grow in almost any type of soil with the broadleaf trees preferring fertile ground and the needleleafs enjoying poor, sandy soil.