Page:Oregon Historical Quarterly vol. 9.djvu/413

 From Youth to Age As An American. 385 action fails altogether in periods of prolonged and heavy precipitation, which alone produce great general floods. (2) At such times the forest bed becomes thoroughly sat- urated, and water falling upon it flows off as readily as from the bare soil. Moreover, the forest storage, not being under control, flows out in swollen streams, and may and often does bring the accumulated waters of a series of storms in one part of a watershed upon those of another, which may occur several days later ; so that, not only does the forest at such times exert no restraining effect upon floods, but by virture of its uncon- trolled reservoir action, may actually intensify them, " (3) In periods of extreme summer heat forests operate to diminish the run off, because they absorb almost completely and give off in evaporation, ordinary showers which in the open country produce a considerable increase in the streams; while small springs and rivulets may dry up more than form- erly, this is not true of the larger rivers. (4) The effect of forests upon the run-off resulting from snow melting is to concentrate it into a brief period and thereby increase the severity of freshets. This results {a) from the prevention of the formation of drifts, and (&) from the prevention of snow melting by sun action in spring and the retention of the snow blanket until the arrival of hot weather. "(5) Soil erosion does not result from forest cutting in itself, but in cultivation, using that term in its broadest sense. The question of preventing such erosion of soil-wash is alto- gether one of dispensing with cultivation or properly con- trolling. The natural growth which always follows the de- struction of a forest is fully as effective in preventing erosion, and even retaining run-off, as the natural forest. ''(6) As a general proposition, climate, and particularly precipitation, have not been appreciably modified by the progress of settlement and the consequent clearing of land, and there is no sufficient reason, theoretically, why such a result should ensue. (7) The percentage of run-off to rainfall has been slightly increased by deforestation and cultivation."* forest carries a vastly heavier crop of vegetable life and roots much deeper than ordinary field crops. The leafage of the trees hold a proportion of the rainfall, but in the late summer when the land is thirsty a ripening cherry or prune crop is often injured by the bursting of the fruit — a result
 * The reason Colonel Chittenden's last proposition is true Is that a live