Parts of Trees : The Crown

The crown of a tree  is defined as the part of tree formed by branch part of a tree above the bole. It is formed by the leaves and branches springing from the bole.

Shape and Size

The shape and size of the crowns of trees vary from species to species and depend on the conditions they grow. Some species such as Cocos, Borassus and Phoenix have crowns of large leaves at the tops & cylindrical unbranched stems. This characteristic distinguishes
them from other forest trees which are generally much branched. In air, 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 more or less cylindrical.

Except the Palms, the crowns of other trees are affected by the situation in which they grow. Normally, the trees growing in the open have large branches and big crowns, while those growing in dense forests have smaller branches and smaller crowns, 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 of the tree. The size of the crown depends upon crown development. Crown development is defined as the expansion of crown measured as crown length and crown width.

Mode of branching—

The mode of branching varies with species to species and sometimes, it can also be 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., Bombax ceiba and Pines wallichiana, with alternate leaves sometimes develop branches in whorls. The angle that the branches make with the stem is also a specific character of the species. Though in most cases, the branches make an angle of 60° to 70° with the stem, yet in some species, e g., Populus nigra„ Cupressus sempervirens, they make angles upto 20° to 30°. In quite a few species, e.g., old deodar and Duabanga sonneratioides, the branches are almost horizontal and form terraces of foliage, while in some other, e.g., Terminalia myriocarpa Anogeissus pendula, leading shoot of young deodar and branchlets and twigs of spruce: they droop downwards.

The number of branches and size in a tree also varies with species. While in some species branches are twiggy and thin in others they are thick. Some species have large number of branches while others have only a few. More the number of branches and thicker the branches, the more the wood is knotty. Presence of knots in wood is considered as a defect in timber for several purposes.

 

Leaf Colour, Size and Texture—

Normally the mature leaves are green. The shade of the two surfaces of leaf is often different, the lower being often paler than the upper surface . In addition to the difference in shade, the lower surface 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 colour in their young leaves. For example, young leaves of Acer caesium, Schleichera oleosa bright red, those of Quercus incana are pinkish or purplish, those of, those of Cassia fistula dark red brown and those of mango are brown.

In some species, leaves undergo a striking change in colour before falling from the tree; such colours are called `autumn tints'. This change in colour help the forester is recognizing the species from a distance. For example, before falling the leaves of Anogeissus latifolia dark red or bronze, those of Lannea coromandelica turn yellow, and Sapium sebiferum beautiful red, purple and orange. But very few species such as Bischoffia, Elaeocarpus are characterized by the presence of a few conspicuous red leaves in almost all seasons.

Size of leaf depends upon rainfall and the species. As a thumb rule, the leaves in low rainfall areas are small while they are generally bigger in heavy rainfall areas. In some species such as Teak, Dillenia, the leaves are bigger than the usual size of leaves of most other trees. Leaves of most conifers are needle shaped and that is why they are called needles.

While the texture of leaves of some species is membranous and soft, it is coarse and hard in others. The membranous and soft leaves of species, e.g., Grewia, Anogeissus, Ougeinia, , etc., on falling not only decompose rapidly and get mixed up with the soil but hasten the decomposition of the hard and coarse  leaves of species, e.g., Sal and conifers, which otherwise, decompose very slowly and inhibits  natural regeneration.

Leaf shedding—

Trees shed their old leaves regularly and produce new one. New leaves may be produced on the trees while the old leaves are still present on the tree or after they have fallen down. On the basis of the presence/absence of old green leaves at the time when the new leaves are produced, the trees can be classified into deciduous and evergreen.

A deciduous tree generally remains leafless for sometime during a year. It means that it produces new flush of leaves after all the old leaves have been shed and it has remained leafless for some time. The leafless period varies with species and situation. For instance, Sal is leafless for about 7-10 days while Hymenodictyon excelsum remains leafless for about 6 months. Even in the same species different remain leafless for different periods due to their situation. Such as , in drier areas, Teak remains leafless for about 6 months while in areas with  abundant and well-distributed rainfall, teak becomes nearly evergreen. Santalum album is exception to the above general rules; it becomes deciduous or evergreen according to the habit of its host plant.

An evergreen is 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, depends upon species, and in the same species upon the environment. In Chir (Pinus roxburgii), for example,  the old leaves persist from one year five months to 2-3 years However, in other species such as  in Deodar, they persist for 5-6 years. On lower altitudes, due to higher temperature, chir, which is normally evergreen, become deciduous. Some common examples of deciduous and evergreen trees:

Deciduous: Adina cordifolia, Acacia catechu, Ailanthus excelsa; Bombax ceiba, Holoptelia integrifolia, Garuga pinnata, Melia azedarach Lannea coromandelica, Terminalia tomentosa, Schleichera oleosa

Evergreen: Cedrus deodara, Abies pindrow, Hopea parviflora, Cupressus torulosa,, Mangifera indica, Mallotus philippinensis, Michelia champaca, Pinus wallichiana, Picea smithiana, Pterospermum acerifolium.

 

 

Author’s Note: Try to identify more and more trees in your locality on the basis of the features you study ,every day. Gradually ,you will have your own list trees that you will be able to identify easily.