HOW VEGETATION HOLDS THE SOIL
H. W. Fairbanks
What the rivulets did to the hillside pastures where the grass was destroyed.
A walk up the mountains on a rainy day is not a pleasant one. There are mud and water under our feet, and overhead are the dripping branches which, if touched, send down a shower of drops. But if we keep our eyes open we shall learn something which will be of great value to us. We shall learn how it is that Nature holds the soil on the slopes—the wonderful soil which it takes her so long a time to make and which is the source of all our wealth.
Our way up the mountains is by a winding road. We first pass the foothills upon which there are scattered oaks. The rain is steadily pouring down and rivulets loaded with mud are eating little gullies all over the slopes. Along the roadside, where they have united, the rivulets form a torrent which is making a deep ditch that threatens to render the road impassable.
These slopes were once covered with grass and the rivulets ran down them without doing any harm. But so many sheep were pastured here that the grass was killed. The roots, which once formed a thick protecting sod, are now decaying. How quickly the rivulets have taken advantage of the unprotected slopes!
The road leads still upward until it brings us to where there were once pine forests. The lumbermen cut off all the trees, and then fire came and burned the decaying vegetation which once lay spread over the ground. Now all that remains is bare earth and blackened stumps.
What are the raindrops doing here? They gather in rivulets just as they do on the once grassy hillside; but because there are so many roots still remaining in the ground they have not done much work. They are not loitering, however, and by and by, when the roots have rotted, they will seize their chance and begin tearing away the soil from the mountain side.
But this is not the end of the road. Farther up we come to the primeval forests, where the giant trees stand just as they did before men came. Here we can see how the slopes are protected, for in making the road the workmen cut deep into the hillside. They first removed a layer of pine needles and decaying branches. Then they cut through a layer of soil about two feet thick which was completely filled with little roots of trees and bushes. Below this they came to the soft subsoil, which contained only a few roots, and at the bottom they reached the solid rock.