Page:A primer of forestry, with illustrations of the principal forest trees of Western Australia.djvu/35

29 CHAPTER VIII.

SYLVICULTURE.

Sylviculture literally means the culture of forests. Although business management and the utilisation of timber occupy a great deal of the forester's time, his real work is growing trees. Sylviculture is the science of growing trees in such a manner that they shall most economically realise the desires of the owner of the forest land.

The owner may be a private individual or a Government, and it remains with the owner to indicate to the forester the purposes which he desires the forest to serve. The forester adopts these proposals as his "objects of management." The following list serves to show that the treatment of a forest must depend largely on the "objects of management" which govern it.

A forest may be managed with the object of providing—


 * (1) the largest possible annual income; or


 * (2) the largest possible yield of timber each year; or


 * (3) a special class of forest-produce such as turpentine; or


 * (4) shelter for man and beast and beautifying the landscape; or


 * (5) protection against excessive floods, droughts, and extremes of temperature.

As soon as the objects of management are fixed the forester must decide upon the species of tree and the method of growing it which will give the best results. To decide upon the species of tree to be grown a close study of the "factors of the locality" is necessary. The next consideration is the "method of regeneration" to be adopted, and linked with it the "sylvicultural system" under which the forest is to be managed.

The factors of the Locality which influence tress are numerous, and interact to such an extent that it is impossible in many cases to discover why one species of tree should flourish in a certain position, and other specimens of the same species show poor development on apparently similar soil in the same neighbourhood.

The factors in the locality may be divided into factors dependent on climate and factors dependent on soil and subsoil.

The climate of a given locality depends on its geographical position, and it is no use trying to introduce trees from Canada, England, or Scandinavia into Western Australia on a large scale. In order that trees may grow here with any degree of success they must be either indigenous or brought from some country, such as certain land bordering the Mediterranean Sea, which has a similar climate to Western Australia. Within Western Australia itself the main climatic factor is rainfall. It is not sufficient to refer to the average rainfall; the minimum rainfall and its distribution throughout the year are of vital importance. Certain parts of England have less rainfall than many parts of this country, but it is evenly distributed over the twelve months of the year, whereas in Western Australia trees have to withstand nearly six months' drought each year.

Soil and Subsoil.—In countries where rainfall is distributed more or less evenly throughout the year the soil is of greater importance than the subsoil, for the roots of a tree flourish and continue to flourish in the top soil layers.

In southern Australia, however, most trees are forced to go to the subsoil for the necessary moisture, especially during the summer months, and consequently the subsoil is there of major importance.