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Page:Popular Science Monthly Volume 32.djvu/241

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moister air is found within and above the forest, which is communicated to the surroundings, and tends to bring to condensation any passing clouds, which the hot air ascending from the open field would have prevented. In this manner the forest acts exactly like a large sheet of water, as a starting-point of local winds, by which the characteristic features of the forest climate—i. e., shorter range of thermometrical extremes, and greater humidity—are communicated to the surroundings. Yet, whether under all circumstances, a direct increase of precipitation over surrounding areas may be produced through forest influence remains still unproved, and appreciable effects can only be expected from dense and extensive forest areas.

The influence of a mechanical barrier against chilling northern and hot southern blasts, such as even a simple wind-break of two or three rows of trees can produce, is well known to the prairie settler. But by far the most important function of the forest lies in the preservation of soil-humidity and in the storage and equable distribution of the water capital of the earth. The moss and leaf-mold act as a sponge, taking up all the atmospheric water which reaches them, and only gradually give up the same to the soil, from which it reappears as springs, brooks, and rivulets, forming the great water reservoir of agricultural lands, giving up its accumulations gradually throughout the season when most needed. While this beneficial action is especially noticeable in the mountainous regions, the forest of the plains acts also as a regulator of hydrologic conditions, as is apparent from the observation that on deforested areas the ground-water level sinks and aridity increases. While the large floods are probably, to a great extent, due to cosmic causes, yet it can not be denied that the deforestations at head-waters of streams must have aggravated the evil, and that local floods and their concomitants, namely, washing away of soil, pauperizing fertile valleys, etc., can be obviated by proper forestry, has been practically demonstrated by the reforestation in France and the Tyrol. On the paramount importance of the proper utilization of the water capital of the world, a volume might be written. Suffice it to say, that our agricultural development, and with it our civilization, depends upon it.

Lastly, I should recite the sanitary effects of the forest, the investigation of which has, of late, brought many important and interesting results. That the activity of individual trees in assimilating carbonic acid and exhaling oxygen improves the air we breathe has been long a recognized fact, and the healthfulness of forest air is therefore generally conceded. It is asserted that, by deforestation, malarial districts have been created, while, on the other hand, the planting of eucalyptus and other trees is said to have produced the opposite effect. It is quite possible that the manifold ramifications of the crowns of the forest act as a kind of filter in purifying the air of the spores of fungi and bacteria, thus diminishing the danger of epidemics, etc.