THE FUNCTION OF THE FOREST 



675 



A second function of great moment 

 is the regulation of the temperature. 

 They truly measure out rain and sun- 

 shine. They absorb the vast quantities 

 of water that men do not use. Close 

 observation has shown that a leaf of 

 ordinary size can absorb about fifteen 

 to forty-five grains of water in a day, 

 and a leaf of larger dimensions some- 

 times even as much as a small pailfuU. 

 But where evaporation proceeds un- 

 hampered, warmth is held bound and 

 cold produced. Forests, therefore, tem- 

 per the heat, hinder radiation and so 

 lessen also the amount of lost heat. 

 This warmth, necessary for the process 

 of evaporation, can only be taken from 

 the atmosphere, the temperature of 

 which is thereby lessened. A wooded 

 region, then, slowly warms and cools by 

 turns, and produces a corresponding 

 change in the temperature of the neigh- 

 borhood. The moisture acts as a cool- 

 ing influence in evaporating, while the 

 atmosphere and clouds hold their heat 

 because radiation is in a large measure 

 checked. The numberless vapor-laden 

 leaves facilitate the formation of mist 

 and dew. Their warm dampness as- 

 sists in cloud building; while the whole 

 wide area of vapor, inhaling and exhal- 

 ing foliage at the top of the trees, holds 

 them and the mists, to the decided ad- 

 vantage of the neighborhood. Thus, 

 this process of cooling and evaporating, 

 itself productive of rain and mist, in 

 turn benefits the forests themselves and 

 the neighboring fields and meadows. All 

 the phenomena of the atmosphere work 

 together to the great end of making 

 possible the existence and well-being of 

 earthly life. 



The forests are, however, even in 

 another sense essential to the natural 

 organization of forces, as water-gather- 

 ers and distributors and spring-builders 

 and feeders. We have seen how life 

 on earth is dependent on air and water. 

 Now, the forests absorb much moisture 

 from the air and again surrender it 

 freely. They retain a great part of the 

 moisture collected in their locality, and 

 so act as reservoirs for all atmospheric 

 condensations. In this way they become 

 the sources of numerous springs and 



streams ; prevent extremes of dampness 

 and drought and keep the precipitation 

 from flowing off too rapidly. The rain- 

 drops falling on the leaves and trickling 

 down the stems reach the ground with 

 much less force. There, if not to a 

 large extent immediately absorbed, the 

 water is at least retarded in its flow, so 

 that it gradually sinks into the real 

 ground below (which is always kept 

 open by the mass of dead leaves lying 

 on it), whereas on a bare, sloping plane 

 it flows off in large measure. The snows, 

 too, melt more slowly under the in- 

 fluence of the milder conditions foster- 

 ed by the protection of the trees, and 

 penetrate into the ground, which for the 

 same reason is seldom frozen hard be- 

 neath its blanket of grass and fallen 

 foliage. These waters are slowly and 

 constantly drained off to feed the 

 springs, wells and rivulets. Men have 

 often found the ordinary sources of 

 their water-supply exhausted, because 

 the mountain and hill-tops had been 

 cleared of their woods, and that, too, 

 at times when the water was most need- 

 ed in the houses and on the farms. 

 This also explains why after a heavy 

 rainfall the water may be so murky as 

 to be entirely unfit for use. There are 

 no cheaper, better and more sanitary 

 water reservoirs than the forests. Arti- 

 ficial water reservoirs in the shape of 

 ponds or produced by dams can never 

 equal them because their capacities are 

 limited, their contents may be diminish- 

 ed by evaporation and may become 

 poorer in quality as the drouth pro- 

 ceeds. The water that is drawn from 

 the bare floor of such a reservoir into 

 the pipes for daily consumption is often 

 contaminated, and entirely lacking in 

 refreshing carbonates. Ponds and res- 

 ervoirs must, indeed, be constructed 

 where the forest lands have been 

 cleared, but they are at best only make- 

 shifts. 



That many regions may be made un- 

 productive and even uninhabitable be- 

 cause of the destruction of their wood- 

 lands is evident from what has been 

 said. Persia, once the most productive 

 and prosperous of lands, is now nearly 

 all a desert ; it is only with grave dan- 



