Our national forests

by Richard H. D. Boerker

Studies of Forest Influences. Studies on the influence of forests upon stream flow and erosion are attempting to furnish important data for American conditions upon this subject. At the Wagon Wheel Gap Forest Experiment Station in Colorado such a study is being carried on. The purpose of the study for the first two or three years has been to determine the character of the two streams which are to be measured. The forest cover on the two watersheds is practically identical. The results so far obtained indicate that the influence upon the stream flow must be about the same in both cases, and, consequently, a comparison of these streams after the denudation of one watershed will be a very fair test of the influence of the forest cover upon the relative height of the flood stage and low-water stage, the amount of erosion, and the rate of melting of the snow.

Figure 29. At the Fort Valley Forest Experiment Station, Coconino National Forest, Arizona. A typical meteorological station Forest officer measuring precipitation. Note the shelter which contains thermometers and also the electrically equipped instruments to record the direction and velocity of the wind.

Figure 30. Forest officer ascertaining the amount of evaporation from a free water surface. Fort Valley Forest Experiment Station, Flagstaff, Arizona.

Experimental observations which have been conducted since 1908 at the various Forest Experiment Stations have shown that the forest exercises a decided moderating influence upon temperature extremes, wind motion, and evaporation. Likewise, the presence of a forest cover retards the melting of snow in the spring, and in this way huge snowbanks in the forests feed the nearby streams until late in the summer. Forests therefore have been shown to conserve the water supply and also causing this water to run off slowly rather than in sudden floods. Studies have also been conducted on determining the effect of cutting timber upon the climate within the forest.

Meteorological Observations. The climatic requirements of forest types have been studied at the Fremont Experiment Station since January 1, 1910, through experimental observations, and other stations have taken up the same problem since that date. The first step in this work at the Fremont has been to obtain a complete meteorological record as a basis for determining what climatic conditions are most important in limiting the natural range of such important species as Yellow pine, Douglas fir, and Engelmann spruce. The data collected so far have shown that soil moisture and soil temperature are the controlling factors in determining the existence of the three forest types. It has also been shown what climatic conditions each of the three types of forest must have in order to succeed. This work has since been extended to include other types of forest and a meteorological station has been established at timber line on Pikes Peak. This station, which is at approximately 11,500 feet, is equipped with self-recording instruments to measure the climatic factors which obtain at that elevation and which mark the uppermost altitudinal limit of tree growth in that locality.

Such studies as these, based upon systematic meteorological observations, have an important bearing on all other forest problems. The data secured in this way especially assist the technical foresters in solving the various problems in forest management, reforestation, fire protection, and land classification, besides giving positive knowledge of the environment in which our trees live and of the factors affecting their growth and reproduction. These systematic observations are of prime importance if we ever hope to have a science of American Forestry.

Forest Management Studies. Experiments in forest management are carried on to determine the best methods of cutting National Forest timber to secure natural reproduction and at the same time to improve the quality and productivity of the remaining stand. These studies are carried on by means of permanent sample plots, on which all the trees are carefully measured and recorded. First the timber is cut on the plots under different systems of management, or thinnings or improvement cuttings are made. An exact record is kept of the amount of timber removed and of the size and distribution of the remaining trees. Measurements taken at regular intervals show the precise effect of the method used on each plot. Close observations of the reproduction which takes place, brush and other forms of cover which may establish themselves, and changes in soil conditions are recorded. On similar sample plots methods of brush disposal, methods of marking timber for cutting, and thinning methods are studied. After logging there are several ways in which the resulting slash may be disposed, depending upon surrounding conditions. In some localities the brush must be burned immediately on account of the fire danger which its presence involves; in other places it must be removed because it interferes with reproduction; in still other places the brush may be scattered over the area because there is little fire danger and, in fact, the brush has been found to assist and protect reproduction. All these possibilities must be determined by experiments. Likewise in marking timber for cutting and in thinning practice various methods are possible, depending upon circumstances, the most important of which are the requirements of the species and the density of the forest.

Other management studies deal with the determination by actual measurement of the volumes of trees and stands, and the growth of trees and the yields of whole forests. Reliable growth and yield data for the different species and types are necessary to properly handle timber sales as well as for forest management. They are also essential for determining damages caused by fires and trespass.