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Trees are a fundamental component of terrestrial ecosystems. They have different shapes and sizes but all have a similar basic structure. Each tree has a column on which it is structured: its trunk. This trunk is covered with a bark, and is both the origin and where the branches that make up the treetop are supported. From the branches grow leaves and flowers. The degree of development of the trunk and its crown differentiates a tree from a shrub.
All trees are anchored in the ground by their roots, which extend underground in a proportion of the foliage that rises above the ground. A developed tree is composed mostly of dead or inactive cells, which make up the wood of the tree. A tree’s tissues grow in very few places in its body: at the ends of branches and roots, and in a thin layer that unfolds beneath the bark. In temperate forests where there are marked seasonal differences, trees can be found in which the living layer of the trunk is incorporated into the wood and forms growth rings for each year of development. The reproductive structures of the trees are associated with the flowers and in some cases also with their roots.
From the observation of the basic components of a tree, information can be obtained that allows it to be quickly identified. These components are the leaves, the bark, the branches and their flowers and fruits.
The shape of the leaves of the trees
The leaves are the food factories of the tree. The leaves capture the sun’s energy using chlorophyll, the element that gives them their characteristic green hue. Through photosynthesis leaves produce carbohydrates together with carbon dioxide from the air. In this process the leaves produce oxygen, which in turn is released into the air. All this gas exchange, the tree’s respiration, occurs in its leaves. The leaves of a tree have characteristic shapes and sizes of each species that transform them into indicators; therefore, in most cases the species of a tree can be determined only by looking at its leaves.
The leaves of the trees can be characterized by observing their base, their edges, their grooves and their tip or vertex. There are star-shaped leaves, which are totally different from a heart-shaped leaf. The shape of each leaf has a name that is associated with an identification process.
The structure of a sheet can be defined as simple when it does not have additional folios, or compound when it has three or more folios. The structure of the leaf is important for its characterization and the subsequent identification of the tree species. In a simple leaf, each folio is attached directly through a stem to the main branch, while in a compound leaf all the folios are attached to a single stem or rachis.
There are many variants of compound leaves. The main characteristics can be distinguished in the palmate leaves, which are those in which the folios or lobes grow from the stem with a configuration similar to a hand, as well as in the pinnate leaves, in which the folios grow on opposite sides. from a stalk, as in a feather. There are also leaves whose structure is doubly compound, that is, composed of two different shapes.
The flowers and their fruits
In addition to branches, roots and leaves, in a developed tree other structures of great importance are generated: flowers and strobila, also called cones or cones. Flowers and strobili are the reproductive structures of trees, from which seeds are produced.
Seed pods, strobilus types, and fruits are characteristic of each tree species and also allow their identification. However, it is not as reliable an element as the characterization of the leaf, since in many cases they are only found at certain times of the year. It is always possible to find leaves from a tree, even in the case of deciduous species; if you search the ground adjacent to the tree you will surely find one. The acorn of an oak is a completely different seed than the samara of a maple. In turn, the different shapes and colors of the oak acorn or the maple samara also make it possible to determine the variety of each of the two species.
The branches
The species of a tree can also be identified through the characterization of its branches, particularly in the case of its small branches. This can be important in deciduous trees, as it makes identification possible during the winter; This method is not used in the other seasons of the year.
Small tree branches have structures called papillae, which are leaf scars and scar bundles that vary between species. Among the many possible distinguishing characteristics of the branches is the presence of spines, which can be used for identification.
the bark
The bark is the protection of the tree trunk against external threats. It also has other functions such as eliminating waste from the body, which it does by encapsulating the waste in the dead cells of the trunk, in its wood, or eliminating it through the resins.
The xylem in the bark transports water, salts and other nutrients from the roots to the leaves of the trees. Meanwhile, the phloem of the bark redistributes the inorganic and organic nutrients, mainly the carbohydrates that are generated in the leaves (where photosynthesis occurs) and go to all parts of the tree. The cambium is a layer a few cells thick that is located under the cortex; there originates the secondary xylem (which grows towards the interior zone of the tree) and the secondary phloem (which grows towards the exterior zone).
The texture of the bark is usually quite uniform along the trunk, and is characteristic of each tree species, which allows its identification. The texture of the tree trunk can be classified into at least 18 types, from the smooth texture of a beech ( Fagus sylvatic ) to the prickly texture of a drunken tree ( Ceiba speciosa ). The classification of the bark according to its texture is bounded, therefore a precise classification cannot be achieved characterizing only the bark of a tree.
the shape of the tree
Although the shape of a tree cannot technically be considered a component or part of its structure, it is a distinctive feature that can help determine its species. Depending on the species, a juvenile tree may have a very different shape from a mature specimen, making it difficult to use the shape of a tree for identification.
The shape of the tree may also depend on how it developed. For example, an artificially cultivated forest will produce tall, slender specimens, while a specimen of the same species grown in a natural forest may have a totally different shape, and in turn also be different from a specimen grown in the open. Therefore, even when there is a general classification of the shape of the trees associated with its species, it is not possible to conclusively identify it without having another element for its characterization.
Sources
- The secret of the trees . Scientific Culture Unit of the University of Zaragoza – Spanish Foundation of Science and Technology, 2018.
- Gola, G., Negri, G., Cappeletti, C. Treatise on Botany . 2nd edition. Editorial Labor SA, Barcelona, 1965.
- Borrás, C. Identify trees from the leaves . Green ecology.
- Tree Identification: The Key to Determination . Klorane Botanical Foundation.
