The principal raw material yielded by trees is wood, which can he used in many ways and for many purposes and which, along with coal - the product of trees of earlier geological periods - made possible the smelting of ores and the development of all branches of industry.

In some trees it equals two to three centimetres in a favourable year. Of the European trees great thickness is attained by the plane, chestnut, oak, lime and sycamore, and of the conifers by the fir and to somewhat lesser degree by the spruce. The “big trees” The attainable thickness of the trunk goes naturally hand in hand with the tree’s attainable age.

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 aspen, goat willow, birch and mountain ash may attain 100-150 years. Twice that age, from 200 to 300 years, is reached by the eastern cottonwood, hornbeam, alder, pine and larch; about 500 years by the beech and sycamore; and 700 years by the spruce and fir.

The favoured wood of the building industry is that of conifers: spruce, pine, fir and larch. It is long, light, well suited for beams, columns, sawn wood, doors, window-boxes and in building ships and transport vehicles.

The leather industry could not function without tannins, another product of many woody plants. In some trees, these are obtained from the bark (spruce, oak), in others from the wood and bark (chestnut, false acacia), and in still others from the leaves (staghorn sumach) or fruits (sapan). Before the day of synthetic dyes, trees were also an important source of natural dyes.