Trees are an essential component of life as they provide us with various products and services that include timber for furniture and construction purposes, pulp, paper, handicrafts, fuel-wood, fruits, forage for animals, shade and even act as windbreaks. They are an integral part of our eco-system and habitat, and also support wildlife. They help in regulating humidity and temperature,thus moderating climate. Furthermore,trees help in reducing, soil erosion, binding and conserving soils, regulating fresh water supplies and reducing noise pollution.

Forests are being felled at a tremendous rate without being rehabilitated. Approximately 20 ha of forests that is an area equal to 20 football fields is being deforested per minute. If this situation continues most of the world's forests will be destroyed in 60 - 70 years . Usually, importance is not given to the fact that trees take many years to grow and that they are more valuable to us while they are growing than when they are felled.

Trees are woody-plants. Their height at maturity is 6 meters or more. Some of them grow even higher than 25 meters. A tree consists of a root system, a stem (single main trunk), branches and leaves. The tree is anchored to the ground by roots which also provide water and nutrients to the tree. The shape of the leaves and the crown is such that it ensures optimum nourishment to the tree. Flowers or cones are their reproductive organs. Some also reproduce through root suckers, coppice and other vegetative growth methods.

Trees are of two types i.e.

• Coniferous trees and
• Broad-leaved trees

Coniferous Trees:

The coniferous trees produce cones instead of flowers. They are generally evergreen and have needle-like leaves. They are straight and tall. Their branches are slender, usually growing at right angles and have thick barks. They are found in mountainous areas at high altitudes and in comparatively cold regions.

The coniferous trees found in Pakistan include the following;

• Cheer pine (3 needle pine)
• Blue pine or kail (5 needle pine)
• Persian pine (2 needle pine)
• Edible or Chalghoza pine
• Cedar or Deodar
• Fir
• Spruce
• Juniper

Broad-leaved Trees:

As the name suggests, they have broad leaves and produce flowers for reproduction. Their branches are thick that usually grow upward and outward to form the crown, which may be broadly round or oval. The broad-leaved trees usually shed their leaves in autumn and early winter. The branches contain terminal and lateral buds during winter that have flowers and immature leaves.

Some of the common broad-leaved trees found in Pakistan are;

• Mango or Aam
• Neem
• Peepal Ficus religiosa
• Cotton wood or Simal (Salmalia malibaricum)
• Scarlet cordia (lasoora)
• Babul or kikar (Accacia nilotica)
• Rose wood or Shisham (Dalbergia sisso)
• Obhan (Populus euphratica)
• Eucalyptus
• Poplar
• Mulberry (Toot)
• Banyan (Barh)

Food for the Tree:

Trees get water and nutrients from the soil through the roots and carbon-dioxide and sunlight from the atmosphere through the leaves for PHOTOSYNTHESIS. A leaf has a thin stalk and a blade which contains chlorophyll and provides surface area of contact with the air. The organic compounds prepared by leaves provide nourishment to the tree. This process is known as ‘PHOTOSYNTHESIS’. Besides meeting the food requirement of trees, photosynthesis also provides oxygen which is essential for all life forms and reduces the quantum of carbon-dioxide which is harmful in higher concentrations. The leaves of trees are spread out advantageously to make use of sun’s energy. The surface of the leaves are dotted with microscopic pores called ‘stomata’. The stomata absorbs carbon-dioxide for photosynthesis and help in the process of ‘transpiration’. i.e. the release of extra water taken up by the tree back into the atmosphere.

Parts of a Tree:

Leaves:

Trees contain leaves which vary greatly in shape, size and colour. The broad-leaved trees have either simple leaves with a single blade or compound leaves (several small blades or leaflets from the same stalk). Deciduous trees shed all their leaves almost simultaneously during autumn or early winter every year so that their branches are leafless in winter. The absence of leaves reduces loss of water from the tree during harsh winter months. Evergreen trees lose and replenish their leaves throughout the year. Their stomata may close during winter months to prevent loss of water from the tree.

Root System:

The roots anchor the tree to the ground and also absorb water and nutrients from the soil and serve as storage for reserve food supplies. The intake of water and mineral elements is through the root hairs, which are filamentous outgrowths near the tip of each rootlet. The rate of water absorption is governed by osmotic function of roots and by the rate of transpiration in the leaves.

Flowers:

The flowers are the reproductive organs of the trees. They possess stamens, which produce pollens, and stigma. The flowers are pollinated in different ways, either by self pollination or by insects, air or water or by other means . The size, colour, and structure of flowers are important in the process of pollination.

Fruits and seeds:

After the process of fertilisation , the ovary of the flower develops into fruit, which contains seeds. There is a variation in the type of fruits produced by trees. Some are fleshy fruits, others produce nuts, pods, winged fruits and so on.