October 17, 1S88.] 



Garden and Forest. 



405 



The Forest. 



Forestry in California. — IV. 



The effect of forests on rainfall is not as yet sufficiently 

 determined. The total rainfall of the world would, per- 

 haps, be no less were forests not in existence, but it seems to 

 me that an examination of the subject must lead us to con- 

 clude that the distribution of the rainfall is affected by them. 



Forests continually operate to equalize temperature. The 

 capacity doubles with a mean increase of °23.4 between the 

 freezing point and 100 degrees fahr. Thus in the spring and 

 summer the cooling effects of forests on temperature must 

 diminish the water-holding power of the. air. In walking or 

 riding, every one must have noticed the difference in heat 

 between a bare verdureless spot and the shade of trees. This 

 difference is observable even in walking from a dusty road to 

 a grass-covered lawn, thus indicating that the variations of 

 temperature do not depend upon the shade alone. Conse- 

 quently a current of air saturated for a sandy waste would of 

 necessity, in passing through a forest, part with some of its 

 humidity, owing to the lower temperature. It is for this rea- 

 son that we see clouds gathered about mountains, when tlie 

 valleys are under a clear sky, 



I have often sat upon the sandy coast of Egypt and watched 

 the sea breeze, full of clouds seaward, clear itself on reaching 

 the coast : all the atmosphere over the water fleeced with 

 clouds, while to landward all was sunshine. Our own coast 

 breezes show the same phenomena ; the foggy winds of San 

 Francisco soon become the clear breezes of Sacramento, be- 

 cause the temperature of the latter will not permit the moist- 

 ure to remain condensed. 



I have records of many observations made in our Central 

 States showing that the summer rains are more frequent in 

 wooded districts, and usually follow timber lielts and water 

 courses. 



There are also a number of observations on record showing 

 that the electrical effect of trees may play an important part 

 in rainfall. Trees attract electrical discharges, as is known in 

 the case of lightning, and coupling this fact with an experi- 

 ment made with a collander so fine that water merely oozed 

 through, from which, on the application of an electrical cur- 

 rent, the water poured out of the small apertures ; we must 

 conclude that the effect of trees on rainfall through electricity 

 may be considerable. 



Whatever the effects of forests may be on the amount of 

 rainfall, it is beyond doubt that their influence on its delivery 

 is of the first importance. 



Trees offer innumerable obstacles to the running off of 

 rain. Their foliage obstructs the force of the rainfall ; when 

 this reaches the ground it is impeded by the fallen twigs, 

 leaves and the labyrinth of roots and the humus; by the latter 

 it is rapidly absorbed and held as in a sponge. The roots, at 

 least when decayed, fornr channels into the lower soil. 

 These impediments cause the water to flow very slowly, and 

 prevent it from gullying out the land and forming accumula- 

 tive channels. Thus the rain has time to sink into the earth 

 and to replenish the subterranean reservoirs of the springs. 

 The waters percolating out of forests never carry earth in 

 them, as is the case on lands denuded of vegetation. The 

 rate of delivery of a given rainfall from a wooded water-shed 

 is much slower and is much longer continued than from a 

 bare one. The importance of this will be understood when 

 we recall the French experiments at St. Phalaz. At that place 

 there are two water-sheds of nearly equal area and inclina- 

 tion ; the one wooded, the other not. From the first proceeds 

 a nearly perennial stream, from the other a dry gull v. The 

 period of delivery of flood waters in the first is five days, while 

 in the second the period is only six hours, and it is biit fair to 

 presume from the stream in the wooded one that it is a de- 

 livery of water that months before fell in rain, which amount 

 of water falling upon the other water-shed augmented its 

 flood. 



The first of these water-sheds causes no destruction to tlie 

 roads nor extensive erosions of the Ijanks of the stream, while 

 the floods from the other wash away the bridges, destrov the 

 roads and roll gravel and boulders into the valley. 



Supposing ten billion gallons of water to fall within a given 

 time upon each of these water-sheds. From the first the de- 

 livery will extend over a period of five days, or 120 hours, 

 some of it being permanently retained to supply the springs 

 and stream ; while from the other the ten billion gallons will 

 flow off in six hours with scarcely any absorption into the soil 

 itself, consequently the delivery of water during a given mo- 

 ment during the flood must be twenty times greater in the 



denuded ravine. Every second of prolongation of water de- 

 livery diminishes its height, force and danger. 



It is in denuded and mountainous water-sheds that torrents 

 are formed. The undetained waters rapidly form channels 

 and erode the land, carrying earth, sand, gravel and boulders 

 in their flow. As the inclination of water-sheds diminishes, the 

 debris is dropped, first the boulders, then the gravel, then the 

 sand, and last the earth and clay. 



Standing upon the dykes of the Talfer torrent at Botzen, in 

 the Austrian Alps, I observed the dry bed of the stream to be 

 on a level with the roofs of the three-story houses at Schlan- 

 ders, Kortsch and Lais ; the church steeples are lower than 

 the bed of the Gadribach. The water-shed of the Durance, in 

 France, was formerly wooded, as we know by the records of 

 the lumbering corporations that operated upon it. For years 

 it has been denuded, and the river now varies from a vast 

 bed of pebbles and sand to a furious torrent. It has covered 

 more than two hundred thousand (200,000) acres of one of 

 the formerly most fertile valleys of Provence. 



In Southern California the same causes are already produc- 

 ing the same results. Fires have been set and are being set 

 by sheep men, which burn the brush and forest and prevent 

 new growth. New torrents in unexpected places have formed, 

 and the old channels, such as the Tejunga, Santa Clara, San 

 Gabriel, etc., are more subject to floods than formerly with 

 the same rainfall. 



When we contemplate what has happened in other coun- 

 tries, we cannot but perceive that the mining debris of our 

 central valleys is nothing to what must be expected from tor- 

 rential action from such a chain of mountains as the Sierra 

 Nevada, with its easily disintegrated formation, should it be 

 denuded of vegetation, and the snows be unprotected and the 

 rains undetained. 



The principal sources of danger to be anticipated in this 

 direction are the fires which annually do more and more dam- 

 age, and the over-pasturage of the mountains, which packs 

 the earth, destroys the humus, and, through the hunger of 

 the half-starved sheep, causes the destruction of the natural 

 reproductive power of the forests by reason of the eating by 

 these animals of the young trees. As has been said, it 

 cannot be doubted that the sheep-men in our mountains do 

 every year a hundred times more damage to the lumber, to 

 the streams and springs, and to the retentive power of the 

 water-sheds than the scanty mountain pastures are worth. 

 Sheep-pasturage should be regulated as it is in Europe and 

 confined to particular forest tracts with such limitations as 

 the condition of the forests requires. In this way the moun- 

 tain pastures could carry more sheep than now, for under the 

 present system both forests and pastures are being destroyed. 

 The secondary effect of denudation of mountains and the 

 consequent formation of torrents is the diminution of sprinu-s 

 and streams in their summer flow. The rains rusliing oft" 

 rapidly have no time to sink into the subterranean reser\-oirs, 

 and consequently the springs must fail. 



Col. H. H. Markham, a Congressman from Southern Cali- 

 fornia, who introduced the Forestry Bill prepared Ijy the 

 California Board into the last Congress, in a letter to me, 'says: 

 "I was born, raised, and have always lived in a timbered 

 " country, and have watched the effect of timber upon natural 

 " water courses, and I am thereby fortified in my belief that 

 "your position is correct. iVIy brother owns a farm in She- 

 " boygan County, Wisconsin, a county heavily timbered. He 

 " built a single mill on the creek passing throiigh his farm and 

 " ran it by water-power, but as the land surrounding him be- 

 "came shorn of its timber and cultivated, the stream dimin- 

 " ished and soon became dry. He sold and purchased another 

 ■■ tract in the next county north, and when I first saw it, in 

 " i86r, there was a stream running through it containing suf- 

 " ficient water to allow him and others to^ float double length 

 " railroad ties by the hundreds down it to the market. The 

 "surrounding country was rapidly cleared, and within six 

 " years the stream became dry, with no water, except in rainy 

 " seasons." 



California uses much water in irrigation, and in the south 

 pays high for the fluid for domestic use. The value of water 

 here, already considei-able, nmst increase with the population. 

 Consequently it is of vital importance to preserve at least the 

 present capacity of the mountain water-sheds, to retard the 

 melting snow and the delivery of rainfall, so that torrents shall 

 not form to destroy the valley lands, and the springs and 

 streams be maintained. 



The State of California has no practical forest-system, neither 

 has the Federal Government. The forest lands of the state in 

 private hands are beyond the control of the State Board of 

 Forestry, and the State School-lands and Government-lands in 



