INTRODUCTION:

A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to 6 m; some authors set a minimum of 10 cm trunk diameter (30 cm girth). Woody plants that do not meet these definitions by having multiple stems and/or small size, are called shrubs. Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (379 ft) high.

Trees are an important component of the natural landscape because of their prevention of erosion and the provision of a weather-sheltered ecosystem in and under their foliage. They also play an important role in producing oxygen and reducing carbon dioxide in the atmosphere, as well as moderating ground temperatures. They are also elements in landscaping and agriculture, both for their aesthetic appeal and their orchard crops (such as apples). Wood from trees is a building material, as well as a primary energy source in many developing countries. Trees also play a role in many of the world's mythologies .

A tree is a living thing which has leaves, branches, a trunk that is wooden and roots. Some trees have fruits or flowers and are tall in height.

Trees are classified according to their features and characteristics. They can be classified as green and non green depending on the leaves. Some trees have leaves that are ever green while others are green and dry up in some seasons.

Here is a list of different types of trees:

Deciduous trees: this one looses its green colour at a certain time in season. They include; black oak and cherry, plane tree, pawpaw among others.

Evergreen trees: where its leaves are always green despite the climatic condition of the season. They include; pine, cedar and the spruce trees.

A conifer tree: which leaves are needle like and are evergreen but bear cones. The examples are; bald cypress, pine, spruce and cedar. They have been in existence for more than 290 million years and are grown all over the world. They lead in producing renewable resources.

Flowering trees: produce flowers which create a pleasing scenery from the different colours of flowers. They include; pawpaw, cheery, mimosa tree among others.

Oak trees: are hard wood trees and have clustered flowers. They are mostly identified by the fruit they bear called acorn. They grow in wet or high low lands on mountain slopes. The flowers grow during spring shedding big quantities of pollen to the wind.

Christmas trees: originates from as early as the 17th century. It is believed that they were discovered by Martin Luther as he was walking in the forest. also in England, in 1841 Prince Albert gave queen Victoria a Christmas tree as a gift which later spread all over the world. They add beauty to the season since people add lots of decorations around them.

Ash trees: consist of seventy different types of species and are mostly valued for timber and appear in early spring. They produce single fruits called samaras and have long petals and produce sweet gum. Scientists have failed to get a permanent solution to a disease that kills the trees in a period of ten years.

Big trees: are those that grow up to a height of forty feet and provide shelter or protection. They include; sweet gum, oak among others.

Willow trees: grow in moist areas like river banks and grow very fast. Their leaves provide food for wild animals while others are used in making ornaments. Its wood is also used for different purposes. They have male and female flowers which lack sepals and petals.

Shade trees: are commonly known to provide shade and protection from direct sunlight. They have big leaves and many branches that are close to each other which enable the trees provide a good shade.

Olive trees: are known for their sweet fruits and wood. They have white flowers and have a small green fruit that turns blue or purple when ripe. However before the fruit can be eaten it is recommended that it is prepared well because it contains acid. The fruit is also used as a fat since oil is extracted from it.

EVER GREEN TREES:

Evergreen trees are trees which retain their foliage year-round, rather than losing their leaves annually like deciduous trees do. There are a number of different types of evergreen trees, and some distinct advantages to being evergreen as opposed to deciduous. Many tropical trees are evergreens, and evergreens are also very common in temperate climates. In colder regions of the world, evergreens are more rare, but still present.

From the tree's perspective, being evergreen requires less work. Deciduous trees require a lot of energy and nutrients in the spring, when they put out new leaves. Evergreen trees, on the other hand, conserve energy and nutrients by slowly growing new foliage year-round, which can be an advantage in regions where nutrients are tight, as an evergreen can endure a rough season, while a deciduous tree might fail. The leaves also provide insulation for the tree, preventing sun and frost damage on the branches and trunk. Evergreen trees also fertilize themselves, thanks to their nutrient-rich leaf litter, which also acts as mulch to protect the roots.

Some evergreen trees grow new foliage constantly, with older foliage dropping off as it is displaced. Others have slower rates of growth, losing leaves only periodically. In all cases, the foliage remains green and crisp year-round, with paler growth being newer. In spring, for example, new growth can appear almost yellow next to the more mature foliage.

Most evergreens have needle-shaped leaves, to conserve water, and many evergreens have slightly waxy foliage, which also helps to prevent evaporation through the leaves.
Conifers such as cypress, pine, and fir trees are all evergreens, as are hollies, some oaks, eucalyptus, and rhododendrons, among others. As you can see from these diverse examples, evergreen trees come in an assortment of shapes and sizes, and they can be found all over the world, from the harsh outback of Australia to the lush forests of South America.

Evergreen trees are popular as ornamentals because they retain their foliage year-round, rather than dropping their leaves in the fall and creating an unsightly mess. Deciduous trees can also create a very stark landscape in the winter when they lose their leaves, while evergreen trees keep the garden looking green and alive, even in snowy climates.

Many cultures also include evergreen trees in their folklore. These trees are associated with constancy, faithfulness, and other enduring traits, thanks to their persistent foliage. The practice of cutting evergreen boughs to use as decorations in the winter is also very common, especially in Northern climates, where the sight of green foliage is rare in the winter.

THE IMPORTANCE OF TREES:

Trees are the largest and longest living organisms on earth. To grow tall the tree has become a miracle of engineering and a complex chemical factory. It is able to take water and salts out of the earth and lift them up to the leaves, sometimes over 400 ft above. By means of photosynthesis the leaves combine the water and salts with carbon dioxide from the air to produce the nutrients which feed the tree. In this process, as well as wood, trees create many chemicals, seeds and fruit of great utility to man. Trees also remove carbon dioxide, the main greenhouse gas, from the air.

Trees are of continued importance to the environment. Tropical rain forests have of particular significance; although they now occupy less than 6 per cent of the land surface of the earth they probable sustain more than half of the biological species on the planet.

Notwithstanding the debt we owe to trees, their emotive power, and their importance to other forms of life, the forested area of the earth is steadily being depleted. This is leading to the degradation of the environment and the extinction of many species. There is now a real danger that in the not very distant future man will destroy a large proportion of the present population of species on earth, create an uninhabitable environment, and then die out himself. If this happens it will not be the first time that a large proportion of the species on the earth have been extinguished.