INFLUENCE OF FORESTS.

Globe, Volume XXI, Issue 1827, 30 December 1879, Page 3

INFLUENCE OF FORESTS.

Some interesting observations have lately been made touching the iufl'ience of forests on rainfall, at the School of Forestry, Nancy, France. The result of these observations, made during the past six years, are summed tip by the sub-director of the school as follows :t—l. Forests increase the quantity of meteoric waters which fall on the ground, and thus favor the growth of springs and of underground waters. 2. In a forest region the ground receives as much and more water nnder cover of the trees than the uncovered ground of regions with little or no wocd. 3. The cover of the trees of the forest diminishes to a large degree the evaporation of the water received by the ground, and thus contributes to the maintenance of the moisture of the latter and to the regularity of the flow of water sources. 4. The temperature in a forest is much less unequal than in the open, although, on the whole, it may be a little lower ; but the minima are there constantly higher, and the maxima lower, than in regions not covered with wood. These results substantially corroborate those made by M. Fautrait, when sub-inspector of the forests at Senlis, and given as follows:—1. It rains more abundantly, under identical circumfltancee, over forest than over noc-wooded "ground, and most abundantly over forests with trees in a green condition. 2. The •degree of saturation of the air by moisture is greater above forests than over non-wooded {ground, and much greater over masses of Pinns sylvestris than over masses of leaved species. 3. The leafage and branches of leafed trees intercept; one-third, and those of resinous trees the half of the rain water, which afterwards returns to the atmosphere by evaporation. On the other hand, these same leaves and branches restrain the evaporation of the water which leaches tho ground, and that evaporation is nearly four times less under a mass of leafed forest than in the open, and two and one third times only nnder a mass of pines 4. The laws of t;he change of temperature out of and under ■wood are similar to those which result from the observations of M. Mathieu. The general conclusions seem to be that forests regulate the function of water, and exercise on the temperature, as on the atmosphere, an effect of " ponderation" and equilibrium.