Forestry

Forestry, the science and art of the management of forests. It is sometimes divided into arboriculture (q.v.), which treats of plantations, and sylviculture (q.v.), which deals with natural forests. It studies the conditions best adapted to tree growth and the climatic results of such growth; the protection of forests from injuries; their exploitation or realisation at the period of maturity; their renewal, whether by seeding or planting; their restoration after periods of neglect; the utilisation of their products; and the legitimate increase in the revenue derived from them. The study depends, therefore, largely upon vegetable physiology, but borrows also from systematic and structural botany, meteorology and political economy, and, to some extent, from chemistry, geology, and entomology. The chief direct effects of forests upon climate are (1) screening the soil from the sun's rays; (2) exposing an immense leaf surface for the cooling process of radiation; and

(3) giving off moisture in evaporation. Indirectly, these actions secure greater equability of temperature, humidity, and rainfall, and so regulate the flow of rivers, prevent floods, and maintain springs. In Europe at the present time Russia has 40 per cent. of its area under forest; Norway and Sweden, 34; Austria, 29; Germany, 26; Italy and the Balkan peninsula, 22; Switzerland, 18; France, 17; Spain, Belgium, Holland, and Great Britain, 4; and Denmark, 3. Even in Russia the plentiful supply of timber is only in the north, and in Norweey and Sweden the supply shows itself to be by no means inexhaustible. The wasteful destruction of forests in the United States, Canada, India, and many other countries has not only threatened in many cases the future supply of timber, but in some countries has seriously affected the water-supply.

Forests supply timber, fuel, material for paper, and a variety of valuable substances such as cork, bark for tanning, gums, dyes, drugs, and articles of food. For both climatic and economic reasons, therefore, it has been urged that forests should be preserved by valuation-surveys and working-plans, by the prohibition of cutting immature trees, by the replacement of mature trees by seedlings, and by the establishment of nurseries for this purpose. The increase in value of maturing timber may be gauged from the consideration that annual rings of wood, if assumed to be of equal width, vary in sectional area in the series 1, 4, 9, 16, 25, etc., giving an annual gain of 3, 5, 7, 9, etc., whilst at the same time the trees are gaining in height and the timber is increasing in quality and, from its size, in value per cubic foot. In Britain trees are generally felled by selection, so that several ages are left upon one area; or coppice (q.v.) with selected "standards" is adopted; or the whole wood when mature is felled and replanted. On the Continent it is the rule to fell by rotation of area, all the trees in each area being of one age; and natural seeding or reproduction is generally relied on to replace the crop. The reafforestation (reboisement) of districts denuded of forests is often, as in the case of Ireland, a matter of national importance. On steep slopes it may have a great effect in checking the removal of the surface-soil by rain, and the landward march of the sand-dunes of the Landes of Bordeaux has. been checked by planting the maritime pine. The prevention of forrest fires and the checking the ravages of the various fungoid and insect enemies of forest trees are special subjects of the forester's study. On many estates in Scotland the woodlands are under a responsible keeper or forester, but in England their maintenance is in the hands of land-agents. England, not suffering from deficient rainfall and supplied with cheap foreign timber, bas neglected the study of forestry more than alt other European countries.