As regards growth in diameter the case is somewhat different. In all woody plants it takes place throughout the period of vegetation, from the time the tree comes into leaf until the leaves fall in the autumn, and the extent is influenced by the weather of the current year.
Trees grown for their wood are cultivated in forests. Unlike other raw materials where the supplies are exhausted after a time, if felling is wisely planned, the supply of wood in a forest remains constant and the felled wood is replaced by new wood in the form of new growth.
In the mild climate of central and western Europe, the annual increment per hectare, depending on the site, type of soil and prevailing species, averages from three to ten cubic metres of wood that can be cut without decreasing the supply and production of further wood. With systematic care and fertilization this increment can be increased even further, as is shown by the plantations of cultivated hybrid poplars with an annual increment of fifteen to twenty- live cubic metres of merchantable wood.
The proportion of wood processed by chemical means is growing rapidly. The papermills of the developed countries, for example, consume large areas of forest every month. Other raw materials yielded by trees are essential oils, rosin and turpentine. These are obtained from live trees by boring holes in the outer layer of wood or bark, and catching the oils in containers placed beneath them.
The best species of trees for this purpose are various pines, larches, and, in sub-tropical regions, members of the genera Agathis, Shorea and Canarium. Similar methods are used in the case of certain tropical, broad- leaved trees to obtain caoutchouc and latex, which are of importance in the rubber, textile and food industries - trees of the genera Hevea, Castilloa, Mimusops, Achras, etc.
In the furniture industry, it is mainly the wood of broad-leaved trees such as oak, elm, walnut, ash, beech, cherry arid certain tropical exotics that is used to make the finer, more delicate pieces. In recent decades, only thin layers, called veneers, of these costly woods are being used; they are main structure made of soft wood, thus making the final product not only lighter but also less expensive.
Trees grown for their wood are cultivated in forests. Unlike other raw materials where the supplies are exhausted after a time, if felling is wisely planned, the supply of wood in a forest remains constant and the felled wood is replaced by new wood in the form of new growth.
In the mild climate of central and western Europe, the annual increment per hectare, depending on the site, type of soil and prevailing species, averages from three to ten cubic metres of wood that can be cut without decreasing the supply and production of further wood. With systematic care and fertilization this increment can be increased even further, as is shown by the plantations of cultivated hybrid poplars with an annual increment of fifteen to twenty- live cubic metres of merchantable wood.
The proportion of wood processed by chemical means is growing rapidly. The papermills of the developed countries, for example, consume large areas of forest every month. Other raw materials yielded by trees are essential oils, rosin and turpentine. These are obtained from live trees by boring holes in the outer layer of wood or bark, and catching the oils in containers placed beneath them.
The best species of trees for this purpose are various pines, larches, and, in sub-tropical regions, members of the genera Agathis, Shorea and Canarium. Similar methods are used in the case of certain tropical, broad- leaved trees to obtain caoutchouc and latex, which are of importance in the rubber, textile and food industries - trees of the genera Hevea, Castilloa, Mimusops, Achras, etc.
In the furniture industry, it is mainly the wood of broad-leaved trees such as oak, elm, walnut, ash, beech, cherry arid certain tropical exotics that is used to make the finer, more delicate pieces. In recent decades, only thin layers, called veneers, of these costly woods are being used; they are main structure made of soft wood, thus making the final product not only lighter but also less expensive.
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Garden planning for the urban front garden often has to provide parking space. While it is difficult totally to hide parked cars, sensible planting can offer partial screening.
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