8 April, 1907] Tree Planting and Forest Preservation. 227 



soil being soon washed out by the rain. The acacias and similar plants 

 gradually add humus to the soil and enrich it, so that the original forest of 

 Eucalyptus or other trees may slowly re-establish itself. Bush (ires are 

 not modern things, but were certainly frequent before the advent of 

 civilized man in Australia, and were probably frequent before the 

 appearance of aboriginal mankind. There can be little doubt that this cycle, 

 taking a hundred or more years to complete, has been repeated countless 

 times over widespread areas. In fact, we are probably correct in regarding 

 the thick, fibrous, difficultly-inflammable bark developed on the bases of 

 the main trunks of manv of the larger Eucalypti , as well as the absence of 

 branches for a considerable height above ground, as being, in part at least, 

 adaptations by the plant to constantly-recurring plutonic conditions, and 

 these adaptations enable such trees to survive the effects of the bush fire 

 which roars its way beneath. 



The danger of devastating forest fires is natural h greatest where a 

 continuous area of forest exists, whereas, Avith belts and clumps of timber 

 this danger is more localized, and the agricultural value of the tree-planting 

 better fulfilled, especially if the borders and fringes of the plantation con- 

 tain such plants as acacias or the tree lucerne, Medtcago arbor ca, i.e., 

 nitrogen-fixing plants of economic value. 



The Influence of Forests on Rainfall. 



A full account of the evidence on this point is given by ^Ir. Maiden in 

 the September number of the Agricultural Gazette of Neiv South Wales, 

 the general coaiclusion of the meteorologists being that forests do not in- 

 crease the general a\erage rainfall, but do affect local rainfall. It must 

 be remembered, however, that the rain-gauge, on which the meteorologist 

 pins his faith, is a verv crude instrument, and that it is utterly impossible 

 to measure the rainfall .accurately in a forest by means of it, wherever the 

 rain-gauge may be placed. In fact, many of the comparative observations 

 are about as valuable as it would be to attempt to detect a leak in the roof 

 by placing a rain-gauge in the garden. 



In any case it is not a question of the total rainfall, but of what 

 becomes of the rain. If the rain rims off the surface, ten times the rain- 

 fall will not keep the ground as moist and fertile as when it soaks in. An 

 excessive rainfall is as bad as a deficient one, and renders a climate equalK' 

 unfitted for agriculture, as witness the west coasts of Tasmania, Ireland, 

 and Scotland, where humus forming conditions prevail to excess. A dry 

 climate can be improA-ed bv irrigation, but an excessively wet one cannot lie 

 appreciably ameliorated. 



In an ordinary climate trees bring back the moisture and dissolved 

 minerals from the deeper layers of the soil, and retain them largely in 

 local circulation. The effects of the rain and the rain itself are made 

 to last over a longer period, and the moisture conditions of the district 

 made more equable, instead of torrential leaching and erosive rain, alter- 

 nating with devastating droughts. A forest is a sponge, to suck up 

 moisture when it rains, and gi\e it out again slowly when drv. and in the 

 term "forest'" all permanently -wooded bush or scrub land is to be in- 

 cluded. 



Tliis brief statement by no means exhausts the subject, Init tin- evidence 

 to show, for instance, how the methods of deforesting adopted in clearing 

 the land for agriculture, and still more for sheep pasturage have favoured 

 the spread of injurious weeds, is reserved for a subsequent i)aj)er. 



