320 



FORESTS 



FORESTS 



Silica (SiOo) ...... 



Potash (K2O) 



Lime (CaO) 



Magnesia (MgO) 



Phosphoric anhydrid (P2O6) 

 Sulfuric anhydrid (SO3) . . 

 Other constituents .... 



Total amount 



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 

 required 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 th3 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, 

 Chestnut'( oastanea "i^eds annually but one-third, and 

 dentata). 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 Pflanzen, 1882 : Vol. I, page 761) : 



Amount of Mineral Substances Consumed by Agbicultubal and Forest Crops 

 Per Acre Per Year. 



Mixed 



agricultaral 



products 



Lbs. 

 37 

 78 

 43 

 17 

 28 

 11 

 21 



235 



Forest growth 



(a) Wood 

 and leaves 



Lbs. 



29 



11 



62 



10 



8 



3 



3 



126 



(B) Wood 

 only 



Lbs. 

 1.6 

 4 



9 



2 



1.4 

 0.4 

 0.6 



19 



Approximate ratio 

 of forest to agri- 

 cultaral demand 

 for mineral sub- 

 stances 



Fig. 446. 



Tulip tree {lAriodendron 



Tulipifera). 



Fig. 447. 

 American Elm 

 (Ulmua Ameri- 

 cana). 



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 atrnospheric 

 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 45 

 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 39 

 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 leaf 

 substance is furnished by the forest itself in the 

 form of fallen foliage and needles that have stored 

 up large quantities of nitrogen. In farming, the 

 need of nitrogen above the amount supplied by 

 precipitation must be artificially introduced into 

 the soil by manuring or fertilizing, or by the use 

 of legume crops. 



Since the bulk of all mineral substances is also 

 deposited in the foliage and not in the wood (see 

 table), the forest trees, every fall, return to the 

 soil, in the form of dead leaves, the greater part 

 of what they have taken up through their roots. 

 Thus forest trees, in addition to furnishing their 

 own fertilizer, by bringing up mineral substances 

 from the deeper layers of the soil and depositing 

 them on the surface, accomplish practically the 

 same result that is brought about in farming by 

 deep plowing. Therefore, the soil under the forest 

 (provided the leaf litter is not removed or other- 



