Factors in Timber Production. Figs. Although the growing of wood, inasmuch as it must make use of the soil, is a part of agricultural production, yet it has many dis tinctive features which justify discussing it independently. A clear understanding of the way in which wood crops grow, and of the factors involved in their production, is essential to an in telligent treatment of the far mer's woodlot.
Three factors are invariably present in the production of all raw materials,— nature, labor, capital ; and it is the way in which these factors are combined in the production of timber crops that distinguishes the latter from all other agricultural crops.
While these factors have been brought out in the pre ceding article, it is impor tant that we here emphasize certain features, that we may more clearly compre hend their relation to forest production, and hence to the adaptation of the woodlot to the farm scheme.
Nature.
In no other agricultural crop does nature play so prominent a part as in the production of wood crops. In raising field crops the farmer deals, as a rule, with annual plants, tender and highly plas tic, which have had their original characteristics radi cally changed in accordance with the needs and wishes of man. In the production of timber, one deals with tree - species, perennial, wild plants, yielding with difficulty to human influ ence. The long period, often more than a lifetime, required by trees to grow from seed to maturity, prevents man from leaving his impress on them ; while the short cycle of development of agricul tural plants offers opportunity, year after year, to mould and adapt them to the conditions desired. This explains, to a large extent, why our farm crops are now being widely grown in climates very differ ent from those of their original home, while only compara tively few tree-species have been extended beyond the lim its of their native region. By proper planting or timely thin ning, to be sure, one can stim ulate the growth of trees in height or thickness, produce clear boles, or even improve the quality of their wood ; but the power of influencing the inherent character of the species by breeding forms adapted to new climatic or soil conditions is very limited. During the long time re .uired for the ripening of timber crops, man must practically remain a passive observer, leaving na ture to do all the work of growing the wood. Tim ber crops must be con sidered, therefore, largely the work of natural forces; at least, our American forests, with very few exceptions, are a wealth produced not by labor or capital, but accu mulated by nature with out the assistance of man. Although so essentially the product of the free forces of nature, the for est claims from nature much less than agricul tural plants (the demands which plant-life makes on nature are the require ments of climate, soil and topography). In the North and in the mountains,
the forest extends beyond the range of the hardiest cultivated plants, where, together with pasture and meadow, it is the only pos sible means of utilizing the soil.
Forest trees, as a rule, are far less sensitive to unfavorable climatic condi tions than most agricul tural plants. A prolonged drought that proves ruinous to farm crops is often not felt at all by forest trees, which depend for their water-supply on the deeper layers of the soil.
The forest, although it thrives best on good soils, will grow also on soils lacking the chemical and physical properties necessary for the support of agricultural crops. This is demonstrated by the mag nificent pine forests which grow on dry, sandy soils, and the good growth of arborvitae or balsam fir in swamps. The ability of forest trees to grow on poor soil is doubt less due partly to their roots, which penetrate deep into the ground and spread over large areas searching for water and food ; but it is due mainly to their slight demand on the nutritive substances of the soil, especially the minerals. Beech, for example, needs annually but one-third, and the pine but one-sixth of the amount of mineral substances required by a field of wheat of the same area. Roughly speaking, the amount of mineral substances required by forest growth is about one-half of what is needed by agri cultural crops, as may be inferred from the follow ing comparative analyses of the ashes of forest and agricultural products, made by Ebermayer (Physiolo gische Chemie der Ptianzen, 1882 : Vol. 1, page 761): Especially significant is the relation of wood and farm crops to nitrogen, the most indispensable ele. ment of plant life. The sources of nitrogen are precipitation, assimilation of the free atmospheric nitrogen, as by the root tubercles of the legumi• nous plants, and fertilizers. Precipitation furnishes yearly about 10.7 pounds of nitrogen per acre. An acre of beech forest consumes every year 4°. pounds of nitrogen, fir forest 37 pounds, spruce forest 35 pounds, and pine forest 30 pounds ; an average crop of potatoes consumes 54 pounds wheat 55 pounds, rye 47 pounds, and barley 3E pounds. For the building up of leaves, four to five times more nitrogen is consumed than for the building up of the wood itself. The 10.7 pounds of nitrogen conveyed annually to an acre of soil by precipitation is just sufficient for the production of the wood substance, but not for the leaves. ThE nitrogen required for the production of the leai substance is furnished by the forest itself in the form of fallen foliage and needles that have stores up large quantities of nitrogen. In farming, the need of nitrogen above the amount supplied by precipitation must be artificially introduced int( the soil by manuring or fertilizing, or by the usE of legume crops.