The tree is one of the categories of plants. Plants are classified into 3 categories i.e., herbs, shrubs, and trees.
- Herbs: Herb is a plant whose height is not more than 1 meter and always green and tender. Herbs are classified as annuals, biennials, and perennials.
- Shrubs: Shrub is the category of plant, who have a woody stem but short stature and its branching start from the base. A shrub plant doesn’t grow more than 6 meters in height.
- Tree: It is woody perennial. It has a single well-defined stem (bole or trunk) and a more or less definite crown. The height of the tree is usually more than 6 meters in height.
Parts of Tree
The crown is the upper branchy part of a tree above the bole. It is formed of foliage of the branches springing from the bole.
Shape and size of Crown
The shape and size of the crowns of trees vary with species and the conditions in which they grow. Phoenix, Cocos, and Borassus have crowns of large leaves at the tops of cylindrical unbranched stems. This characteristic distinguishes them from other forest trees which are generally much branched.
In Chir, Deodar and some other conifers, the lower branches are longer while the upper branches are gradually shorter, giving the crown a conical shape. On the other hand, the crowns of Mangifera indica, Azadirachta indica, Tamarindus indica, Madhuca indica, etc., are spherical in shape.
In Albizzia stipulata the crown is broad and flat-topped, while in Abies pindrow it is moer or less cylindrical. Except for the palms, the crowns of other trees are affected by the situation in which they grow.
Normally, the trees grew in open have large branches and big crowns, while those in dense forests have smaller branches and smaller crows because the branches on the lower part of the bole die out gradually due to shade and the crowns are limited to the upper part of the bole the tree. The size of the crown depends upon crown development which is “the expansion of crown measured as crown length and crown length”.
Mode of branching (Tree)
The mode of branching varies with species and sometimes, it is characteristic of the genus or the family. In most of the species, it is absolutely unsystematic. In species with opposite leaves, the branches are also in opposite pairs, though sometimes, this is visible only in the upper branches. Some species, e.g., Bombex ceiba and Pinus wallichiana, with alternate leaves sometimes develop branches in whorls.
The angle that the branches make with the stem, is also specific character. Though in most cases, the branches make an angle of 60° to 70° with the stem, yet in some species. e.g., Populus nigra, cuppressus sempervirens, they make angles upto 20° to 30°. In quite a few species, e.g., old deodar and Duabanga sonneratiodes, the branches are almost horizontal and form terraces of foliage, while in other, e.g., Anogeissus pendula, Terminalia myriocarpa, leading shoot of young deodar and branchlets and twigs of spruce, they are drooping downwards.
The size and the number of branches also varies with species. While in some species branches are thin and twiggy in other they are thick. Some species have large number of branches while others have only a few. The larger the number of branches and thicker the branches, the more the wood is knotty; this is considered as a defect in timber for several purposes.
Leaf color, size, and texture
Normally the mature leaves are green. The shade of color of two surfacce of leaf is often different, the lower being often paler than the upper. In addition to the difference in shade, the lower surfacce of the leaf is sometimes covered with white (e.g., in Quercus incana) or rusty brown tomentum (e.g., in Quercus semicarpifolia). Some species have characteristic attractive color in their young leaves. For example, young leaves of Quercus incana are pinkish or purplish, those of Acer caesium, Schleichera oleosa bright red, those of mango brown and those of Cassia fistula dark red-brown.
In some species, leaves undergo a striking change in color before falling from the tree; such color are called ‘autumn tints‘ and help the forester in recognizing the species form a distance. For example, before falling the leaves of Lannea coromandelica turn yellow, those of Anogeissus latifolia dark red or bronze, and sapium sebiferum beautiful red, purple and orange. But quite a few species, e.g., Elaeocarpus, Bischoffia are charcterized by the presence of a few conspicuous red leaves in almost all seasons.
Size of leaf depends upon rainfall and the species. As a rule, the leaves in low rainfall areas are small while they are generally bigger in heavy rainfall areas. In some species, e.g., teak, Dillenia, the leaves are bigger than the usual size of most leaves. Leaves of most conifers are needle shaped and that is why they are called needles.
While the texture of leaves of some species is soft and membranous, it is hard and coriaceous in others. The membranous and soft leaves of species, e.g., Grewia, Ougeinia, Anogeissus, etc., on falling not only decompose rapidly and get mixed up with the soil but hasten the decomposition of the hard and coriaceous leaves of species, e.g., sal and conifers, which otherwise, decompose very slowly and create problem for natural regeneration.
All trees shed their old leaves regularly and produce new leaves. On the basis of the presence or absence of old green leaves at the time when the new leaves are produced, the trees and other plants are classified into Deciduous and Evergreen.
Deciduous: A tree or plant which remains leafless for some time during the years. It produces the new flush of leaves after all the old leaves shed and it has remained leafless for some time. The leafless period varies with species and situation. For eg., Sal is leafless for about a week or ten days while Hymenodictyon excelsum remain leafless for about six months. Even in the same species, different trees remain leafless for the different period because of their situation.
Evergreen: A perennial plant which is never entirely without green foliage, the old leaves persisting until a new set has appeared. The persistence of the old green leaves after the new leaves have been produced. It depends upon species and in the same species upon the environment. For e.g., in a chair, the old leaves persist from one year five months to two or three years but in deodar, they persist for five or six years. On lower altitudes, due to higher temperature, chir, which is normally evergreen, become deciduous.
Tree Stem or Tree trunk
The stem is defined as the “the principal axis of plant from which buds and shoots are developed; in trees, stem, bole, and trunk are synonymous’ but bole is ‘sometimes used to refer’ to only lower part of the stem upto a point where the main branches are given off i.e., as a synonymous for clear or clean bole. The clear or clean bole is defined as the part of the bole that is free of branches.
Shape and length of Stem (Tree)
The shape and length of the stem vary with species and the situation in which the tree grows. Some species have long and straight stem with relatively few branches, while others have the stem which is crooked and /or much branched. Normally the stem is thicker at the base and thinner in the upper portion of the tree.
The decrease in diameter of the stem of a tree or of a log from the base upwards, is known as a taper.
This due to the pressure of wind which is centered in the lower one third of the crown and is conveyed to the lower parts of the stem, increasing with increasing length. To counteract this pressure, which may snap the tree at the base, the tree reinforces itself towards the base.
The situation in which tree grows affects the shape and length of the stem. Threes in plains and on ridges in hills have shorter and conspicuously tapering stem. This tapering is due to the wind pressure. On the other hand, the trees growing in the dense forest have relatively longer and more or less cylindrical stem. The production of a long cylindrical bole is a desirable quality in trees because that increases their timber volume.
In earlier stages, thin branches cover the entire stem but as the sapling grows into poles and trees. The lower branches fall off resulting in a clean bole. But even in later life, sometimes, due to some adverse factors, the clean bole again develops small branches known as epicormic branches. Which is defined as ‘branches originating in clusters from dormant or adventitious buds on the trunk of a tree or on an older branch when exposed to adverse influence such as excessive light, fire or suppression.” They are also caused by drought and that is why they are generally found on stag-headed trees.
Buttress: It is outgrowth formed usually vertically above the lateral roots and thus connects the base of the stem with roots. It is formed in Acroccarpus fraxinifolius, Bombax ceiba, Pterocarpus dalbergiodes, Terminalia myriocarpa.
Fluting: It is an irregular involution and swelling on the bole just above the basal swell. It is generally in present in teak. As fluting decreases the basal volume considerably, it is considered to be a serious defect. It is attributed to epicormic branches, insect attack, unsuitable site or faulty thinnings.
The Root of Tree
The root is that portion of the plant which develops inside the soil. It is away from the light. Unlike stem it does not produce leaves, flowers or fruits. The roots of trees support them firmly to the ground, absorb soil moisture containing mineral salts and sent it to stem for onward transmission to the leaves. They, generally, comprise of two kinds of roots, viz., The taproot and the lateral roots.
Taproot is the primary descending root formed by the direct prolongation of the radicle of the embryo. In trees, it is the main axis of the large root system. It descends vertically below the stem. The primary root is conical in shape develops towards the permanent moisture in the soil and sometimes, attains considerable length.
Lateral roots are the roots that arise from the taproot and spread laterally to support the tree. As the taproot grows, it develops lateral roots which are branched and re-branched and ultimately form rootlets. The ends of the rootlets are covered with fine hairs, called the root hairs.
All the above-given information about tree is important for tree improvement