Page:A primer of forestry, with illustrations of the principal forest trees of Western Australia.djvu/30

24 was ringbarked, with the result that some small streams that used to carry water all the year round now run only during a portion of the year. In some parts of the world, and more especially in France, inquiries have been conducted into the question whether forests influence the amount of the rainfall. The evidence adduced by these French experiments showed that within a forest the rainfall is appreciably greater than in outside bare country. More than a century ago in a forested region in France vast forests were cut down for war purposes. The result was disastrous. In the absence of the trees the heavy rains, which fall at certain seasons, washed away much of the soil on hill sides and caused floods in the rivers that did much damage. The position was so serious that the inhabitants of the district petitioned the Government to have the forests replanted, and this was done. New forests in time occupied the place of the old ones, and the flooding and damage ceased.

Forests also influence the temperature of the soil at varying depths. Forest soil is warmer in winter and cooler in summer than bare land. The effect of this is that the degree of humidity within a forest is always greater than outside.

Growth of Forests as influenced bit Soil and Climate.—It is the very general rule that such crops as are grown by farmers give better results on good soil than on poor soil. With the trees the rule is not quite so general. Some trees demand a really good class of land to exhibit their best results: marri (redgum) may be quoted as an instance. Others prefer a second or third class soil: banksia is an example of this class. It may be stated here, that the trees of which Western Australia possesses the largest number and the trees upon which her reputation as a producer of timber rests, grow upon soil that is unsuited for agricultural purposes.

Broadly speaking, jarrah is seen at its best on poor soil or in country that is purely laterite or largely of ironstone gravel. Such soil is of no value for farming. To this fact and this fact alone the belt of jarrah forests owes its preservation. Even when land settlement policies have alienated areas of jarrah country for agricultural purposes, these areas have sooner or later reverted to the Crown, the settler having failed to effect the necessary improvements or to make a living. In places in the jarrah belt and further south, where the Darling fault country breaks up, dykes of diorite are met with, and the soil disintegrated from this rock forms valuable agricultural land. Except in the valleys of the Capel and Blackwood rivers, and around Bridgetown, the areas of diorite soil are very small indeed. In the karri country the soil is of a better quality than in the jarrah belt, and particularly is this the case when the karri and marri are found growing mixed. The soil on which karri grows in a pure or almost pure state is disappointing agriculturally, it being of a light snuffy nature, easily washing away when cleared of timber. The soil on which wandoo grows is, generally speaking, of poor quality. It is, however, more valuable than jarrah land, and all the best of the forests have been alienated in fee simple. Tuart is entirely confined to the limestone formation along the coast. The rock lies very close to the surface, and is covered by a loose sand. It has. a value for grazing purposes, but is poor agriculturally. The savannah forest of the drier regions grows, generally speaking, on excellent heavy soils, and is in consequence necessarily fast disappearing before the wheat farmer in the assured rainfall belt. Further eastward and northward, where the rainfall is too scanty for agriculture, the savannah forest is intact, except around all mining centres, where it is being rapidly converted into firewood.

Rainfall, it goes without saying, influences forest growth very greatly, in fact, in the case of many species, an ample rainfall spread with fair regularity over the year is essential. But the eucalypt family in Western Australia have adapted themselves to their environment, and are at their best where the rainfall is large in the winter months and almost entirely absent in the summer. The eucalypts possess marvellous powers of accommodating themselves to climatic conditions. Many varieties of these trees have been planted abroad, as has already been stated, and in most of their new homes they thrive remarkably well. In California, where