Tree

A tree is a Plante able to develop in height thanks to a structure forming a trunk with possibly ramifications called Branche S. It is a perennial plant which generally saw many years.

With the botanical direction, the trees are plants with genuine Bois. This one, also called secondary Xylème, is produced by a cellular line, the vascular Cambium, located under the bark.

The genesis of wood is a repetitive process which deposits a new layer on the preceding ones. The result is often visible in the shape of rings of increase. One does not find plants with genuine wood, and thus of trees in a strict sense, that at the Gymnospermes and the Dicotylédone S.

There exist other types of plants with genuine wood, but the trees are characterized some by more important dimensions (compared with those of the Arbuste S) or by the formation from a clearly individualized trunk (that do not have the Arbrisseau X) and carrier (whereas the woody liana S must find a support to rise).

According to the fertility of the ground and at the end of their vertical growth, the trees can reach a certain height, which is more important than that of the shrubs. No universal definition fixes absolute value, but institutions as FAO consider that a tree is a species able under good conditions of growth pushing at least up to 5 m height. Others as IFN fix the threshold of definition at 7 Mr.

The statute of tree is given by the potential of the species and not by the dimension of an individual to one moment or a given place. Thus a Chêne three years of 1.50 m only is a young tree and not a shrub. In the same way an old man pine rabougri fixed on the skeletal ground of a peak beaten by the winds is a nanifié tree and not a shrub.

In ecology, one compares to the trees various arborescent plants, like the palm tree S, the dragonnier S, etc having developed a hard trunk, ramified or not, but which is not composed of genuine wood. A sheet of Raphia reaches up to 25 m by 4 Mr.

The records greatest heights reached by trees are held by sequoias with sheets of yew ( Sequoia sempervirens ) in California. The most individual measures 115.55 m, it was baptized Hyperion .

The development in height and the ramification of the branches make it possible the trees to increase their capacity of exploitation of the airspace. The position of the sheets on several levels makes it possible the tree to multiply the heat-transferring surface for the Photosynthèse.

The first trees appeared on Earth approximately 375 million years ago, with the Dévonien. It acted, the such Archaeopteris , ancestors of current conifers.

The vegetable formations dominated by trees pushing the ones beside the others are Forêt S, but the trees can also grow in a way more or less isolated out of the forests.

The trees play an important role in terrestrial ecological operation, because of their capacity to store the Carbone, to take an active share in the Cycle of water and a general way to constitute the ecosystem S complexes which are the forests, sources and refuges of Biodiversité.

They also constitute for the human society a considerable material resource (mainly of wood), food products (in particular of the food fruits) and multiple services. They occupy in almost all the cultures of the world a real place and important symbolic system.

Morphology

A tree is generally composed of root S, one or more principal trunks and ramifications called branches.

The trunk is normally single but it arrives sometimes, following an accident of growth, which it duplicates or which he is fourchu. Sylviculture in coppice, which consists in cutting the trees and to let the stocks bud gives in particular called multiple trunks “cépées”.
The basal part of the trunk which is dismantled branches forms the barrel.

The whole of the branches trains the houppier.

The majority of the trees have sheets charged to ensure photosynthesis and the main part of the gazeux.
exchanges Some species have however, in the place of the sheets, other bodies which can resemble to them and which provide the same functions: some Acacia S carry Phyllode S which are transformed petioles, some arborescent euphorbiums have chlorophyllian naked branches, the needles of the pines are pseudophylles (false sheets of secondary formation) and the filaos have ends resembling stems of Prêle S. On the other hand, the needles of the fir trees are true sheets… in the shape of needles.

On the surface of the trunks sometimes also “appear epicormic S”: buds, cluster, epicormic growths (hairs, greedy and greedy branches), barbs, sphéroblastes and broussins; those appear starting from stimuli (light, wounds, infections, tensions, etc) and evolve/move with the age of the tree and according to the gasoline considered.

Anatomy

Wood is mainly made up of vessels.

Physiology

The Feuille S of the tree make it possible to produce, by Photosynthèse, Cellulose, Hémicellulose and Lignine.

In 2007, a team of biologists of the University Blaise Pascal studied the rectification of the trees by providing those with innumerable sensors and thus placed them in a magnetic field. The researchers thus could follow in 3D the evolution of the growth of their trees planted in skew. Cells were identified like having a role of spirit level, this thanks to the use of aggregates of Glycogène like level gauges.

Evolution and classification

The invention of the conducting vessel of saps during the evolution of the vegetable kingdom made it possible certain groups of plants to take height… Thus, gradually, one passed from the foam S (without vessels) to the plants Herbacée S then of thousands in thousands of years initially to conifers (gymnospermes) then to the trees angiospermes. The first trees to colonize the grounds were thus conifers, groups plants considered like less advanced compared to the trees of the group of the plants with flowers. The size of the tree is allowed by the vascularization of its air and underground bodies.

Gymnospermes

They are oldest. This group develops a Sexualité thanks to naked Ovule S simply protected by scale S. the Pollinisation is done thanks to the wind and not with the insects. Not very powerful system since it requires an enormous quantity of Pollen to ensure a correct Fécondation ovules.

Commonly, these trees are called " Coniferous s" because the majority produce fruits in form of cone, also called pine cones or pives; these trees are also called " résineux" because the majority produce resin, chemical substance complex which allows the tree the cicatrization wounds, to even fight against certain attacks of parasites.

This group is in the process of regression within the meaning of the evolution.

See also: Gymnospermes

Angiospermes

Appeared more recently, this group of trees is regarded as more advanced. In their mode of sexuality, the angiospermes developed a different and more economic strategy in pollen, therefore in energy. An Co-evolution with the insects allows more reasoned pollination.

The plants protect the ovules by membranes, the unit forming the Fruit. This one can be a bay, a Drupe, a Akène…

Commonly, these trees are called the " Leafy s".

This group is in full expansion within the meaning of the evolution.

See also: Angiospermes

Uses

The tree gets raw materials for a great number of industries (paper, second transformation of wood, chemical…) ; he plays an important economic part.

Here some examples of its exploitation:

  • for its Wood

    • firewood
    • sawlog (frame, naval construction…)
    • wood joinery
    • Cellulose (Pulp paper)
    • charcoal
    • Tannin S (barrels of Wine in oak,…)
  • for its bark (suber)
  • for its sheets
  • for its fruits
    • fresh fruits, dry fruits, tropical fruits…
    • oleaginous matters: Coconut, olive-tree, Palm tree with oil…
    • fibers: Kapokier
  • for its inflorescences
  • for its sap
    • resin of the pine, sap of the maple, Hévéa (natural rubber)
  • for approval
    • trees ornamental, shade
    • trees of alignment: Plane tree…
    • for the images that it gives us Vie of the trees
  • for its ecological functions
    • draining of the marshes (Eucalyptus)
    • curtain windshield
    • fight against the erosion
    • fixing of the Carbonic gas (“Puits of carbon”)
    • refuge for many species, it is essential to preserve the Biodiversité.

In beam, many species are used in Phytothérapie.

Certain species of trees as the Moringa will oleifera, the Margousier or the Moabi cumulate many economic advantages and cultural; they are currently studied to be produced with large scales.

Categories by fields of interest

the botanists classify the trees in autochtones, introduced, or acclimatized. They botaniquement are botaniquement classified by kind, species and family, with if necessary of the subspecies. The trees are also classified in communities or vegetable groupings described by the Phytosociologie, and type of forest where the tree can be classified according to the layer which it occupies, its character dominating, etc

The foresters classify the trees in “gasolines” (Feuillu S, Résineux), alive in places answering a typology of the forest stations or according to their forestry utility (gasoline-objective) or of accompaniment and also according to their diameter (small, average and large wood or very large wood). The criteria of classification vary according to the countries, the times and the actors.

In France , for example IFN class in " large bois" the trees whose diameter (measured to 1,30 m height) exceeds 47,5 cm. But some CRPF classify the trees from 40 to 60 cm like " large wood " , and beyond like " very large wood ". The IFN notes that the trees of these diameters (which would be regarded as very average in a primary Forêt moderate normal) are more numerous with being " capitalisés" in the public forests, in Corsica (50% of timberings) and in the areas where the functions aménitaires of the forest are important (Brittany, Aquitaine, Champagne-Ardenne, Picardy). These trees however are very often cut before reaching the stage " very large bois" or deadwood, which limits their interest for the organizations saproxylic. In Poland, it is interdict to cut down the Tilleul S whose diameter exceeds 2,20 m, for their ecological interest (10% of the trees remain in this way upright around the forest of Bialowieza.

Symbolic system

The tree symbolizes sometimes the forces of the Life like the Arbre of life, sometimes the man, sometimes a family: family tree. In the Scandinavian traditions Yggdrasil is a tree which symbolizes the World. In Islam, it is also refers, in certain spiritual writings, with the Tree of the World.

At the time of the seasonal cycles, the " mort" supposed and the " renaissance" annual of the tree to the Printemps made it adopt like symbol of fruitfulness, of return to the life. Witnesses traditions of Tree of May and Christmas tree.

Certain trees have a clean symbolic system: the olive-tree ( Olea europea ) represents peace, serenity (it is also a symbol of the Christ), the Chêne ( Quercus sp.) represent the robustness, longevity.

One finds this representation in certain personality tests ( Test of the tree ): the roots represent the anchoring of the person in her own life, in reality, the trunk its posture, the branches and the sheets its blooming.

The olive-tree is one of the symbols of the ancient Athens: it would have been offered to the city by the Athéna goddess at the time of a contest with the god of the sea Poséidon. The olive-tree is also symbol of Paix.

Trees emblems: the sheet of maple to sugar ( Acer saccharum ) is the emblem of the Canada, the Cèdre ( Cedrus libani ) that of the Lebanon. The Pernambouc ( Caesalpinia echinata ) is the national tree of the Brésil (see also the list of the plant-emblems ).

With the Japan, Hanami, the period of flowering of the cherry trees, the Sakura, ( Prunus sp.) at the end of the winter and Momijigari, the period of passage to the colors of autumn of the Japanese maple ( Acer japonicum ) is events celebrated in all the country.

to also see: Forêt#Fonctions social, symbolic systems and cultural

Proverbs

  • One should not put the finger between the tree and the bark.

  • the fruit does not fall far from the tree.
  • the tree which hiding place the forest.
  • a tree does not have more chance than two trees.
  • the trees do not go up to the sky.
  • One recognizes the tree with his fruits.

References

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