Fig. 56. Virgin Stand of Red Spruce. White Mountains, New Hampshire. U. S. Forest Service.
Fig. 57. Typical Mixed Forest,—Red Spruce, Hemlock, White Ash, Yellow Birch, Balsam Fir, and Red Maple. Raquette Lake, New York. U. S. Forest Service.
The soil in the forest is largely determined by the forest itself. In addition to the earth, it is composed of the fallen and decayed leaves and twigs and tree trunks, altogether called the forest floor. It is spongy and hence has the ability to retain moisture, a fact of great importance to the forest.
MOISTURE.
Some trees, as black ash and cypress, Fig. 58, and cotton gum, Fig. 59, grow naturally only in moist places; some, as the piñon and mesquite, a kind of locust, grow only in dry places; while others, as the juniper and Douglas fir, adapt themselves to either. Both excessively wet and dry soils tend to diminish the number of kinds of trees. In many instances the demand for water controls the distribution altogether. In the Puget Sound region, where there is a heavy rain-fall, the densest forests in the world are found, whereas on the eastern slopes of the same mountains, altho the soil is not essentially different, there are very few trees, because of the constant drouth.
Fig. 58. Cypress and Cypress "Knees." Jasper Co., Texas. U. S. Forest Service.
