190 



NEW ENGLAND FAKMEB. 



April 



FoT the New England Farmer. 



ON THE RELATION OE TREES TO THE 

 SOIL AND THE ATMOSPHERE. 



NuMBEB One. 

 BY WILSON FLAGG. 



One of the most important inquiries that can oc- 

 cupy the attention of the American public, witli 

 reference to our future agricultural prosperity, is 

 the relation of trees to the soil and the atmosphere, 

 and the consequent dependence of climate upon the 

 preservation of our forests in certain situations. All 

 persons understand and admit their importance for 

 timber and fuel ; but they are too apt to overlook 

 the intimate connection between soil and climate, 

 and the quantity and situation of trees and forests. 

 In the present series of essays, I shall speak of trees 

 as they affect the temperature and humidity of the 

 atmosphere, and the salubrity of our climate. From 

 a variety of well-authenticated facts, and from ac- 

 tual experiments, the dependence of the atmosphere 

 on trees, for preserving its electric equilibrium, has 

 been made apparent, though its full dependence on 

 them is not yet clearly demonstrated. We have 

 yet to learn many new facts and principles j but the 

 subject of my present inquiries is comparatively 

 new. The field is almost entirely unexplored. So 

 few experiments have been made with direct refer- 

 ence to it, that an intelligent and persevering ex- 

 perimenter might in a few years bring to light 

 some most interesting results. 



Brande remarks in his Chemistry — "As the plant 

 advances to perfection, it becomes dependent on 

 the air and soil for its nutriment : the roots absorb 

 moisture and other materials ; and the leaves, while 

 they exhale moisture, frequently absorb carbon from 

 the carbonic acid present in the atmosphere, and 

 evolve oxygen. This evolution of oxygen takes 

 place while the plants are exposed to the solar rays, 

 and appears one of the most efficient causes of the 

 purification and renovation of the air," 



"Under certain circumstances, the leaves of plants 

 also absorb a considerable quantity of aqueous va 

 por and water, as is shown by the resuscitation of a 

 drooping plant, on sprinkling it with water, or ex 

 posing it to a humid atmosphere. It is probable 

 that in healthy vegetation, the absorption of water 

 by the leaves takes place chiefly in the night, and 

 that their principal function in the day is that of 

 transpiration." 



It is not probable, however, that any vital absorp- 

 tion of moisture takes place in the foliage of plants. 

 Their resuscitation when exposed to humidity, af- 

 ter being wilted, is the effect of mechanical or hy- 

 grometric absorption, and ceases as soon as the leaf 

 is saturated with moisture. Hence the quantity of 

 moisture absorbed from the atmosjjhere by the 

 leaves of plants bears no proportion to that which 

 they transpire. 



As the leaves of trees and other plants have the 

 power of exhaling moisture into the atmosphere, 

 the humidity of this element must be greatly depen- 

 dent on them for an equal, regular and abundant 

 supply. A few simple experiments will prove how 

 much more rapidly and abundantly this evapora- 

 tion will take place when the earth is covered with 

 plants, than when its surface is bare. Take two 

 cups, and pour into each of them half a pint of wa- 

 ter. Place them on a table side by side. Insert 

 into one, the cuttings of any description of growing 



plants, and let the other stand without them. In 

 the course of about four hours, it will be found that 

 the water has entirely disappeared from the cup 

 containing the plants, while the water in the other 

 cup is not perceptibly diminished. The water from 

 the empty cup has been carried into the atmosphere, 

 first by the absorption at the stems, and second by 

 the exhalation from the leaves of the plants. We 

 may judge from this experiment, that a vastly greater 

 proportion of moisture must be exhaled into the 

 atmosphere from an acre or any other given extent 

 of the earth's surface, when covered with vegetation, 

 than from the same amount of surface, either of 

 naked soil or even of water ; and that plants must 

 be the general cause of the humidity of the atmo- 

 sphere, although the ocean is the ultimate source 

 of all the waters of the earth. Without plants the 

 earth must be a dry desert ; as the evaporation from 

 the ocean would not, imder present circumstances, 

 be sufficient to keep the atmosphere in a saturated 

 state. 



Admitting all this to be the effect of vegetation, 

 we must conclude that trees are more powerful agents 

 for this purpose than any other species of vegeta- 

 tion, since by means of no other kind of plants can 

 an acre of ground be covered by so great a quan- 

 tity of absorbent rootlets or exhaling foliage. It is 

 also to be taken into the account, that trees do not 

 in general prevent the growth of herbaceous plants. 

 When trees are very compact, as in a forest, there 

 is not much undergrowth ; but the amount of trans- 

 piring foliage in one of these dense forests must be 

 immense. Where trees are standing at moderate 

 distances apart, as in a grove or • an orchard, the 

 vegetation under them is generally almost as abun- 

 dant, as in similar places unsupplied with trees. If 

 a mere handful of plants will drink up half a pint 

 of water in twenty-four hours, and exhale at the 

 same time an equal quantity into the air, we can 

 easily imagine what an immense quantity must be 

 exhaled by the whole vegetation of the country, and 

 how infinitely it must exceed the amount evaporated 

 from the same extent of ocean surface, during the 

 same time. If we continue this process of reason- 

 ing, we shall soon learn why any large extent of 

 country becomes wasted by drought, when its for- 

 ests are destroyed. 



It becomes manifest, from these facts and con- 

 siderations, that any country which is well covered 

 with trees and other vegetation will be more equal- 

 ly and abundantly supplied with rain, than a coun- 

 try similarly situated which is destitute of trees. In 

 the latter case, rains will be produced chiefly by 

 meteoric agencies, they will be more nearly period- 

 ical, and come in the shape of inundating torrents, 

 instead of frequent and gentle showers. The earth 

 would be periodically flooded about the time of the 

 equinoxes, but the summers would be visited with 

 fatal droughts. But when the earth is covered with 

 a due proportion of forests, standing in those situa- 

 tions in which they will act most favorably upon the 

 climate, an equal and uniform humidity of the at- 

 mosphere is preserved by the constant exhalation 

 of moisture from the foliage of the trees ; and fre- 

 quent rains are the consequence. 



Mr. Balfour, an English botanist, remarks, "When 

 forests are destroyed as they are everywhere in 

 America, with imprudent precipitation, the streams 

 are everywhere dried up, or become less abundant. 

 In those mountains of Greece which have been de- 

 prived of their forests, the streams have disappear- 



