Correspondence Courses in Agriculture. 5 



drained away, conditions are favorable for the growth of a number 

 of other trees. If the drainage be extended to several feet below 

 the surface, many of the deep lateral-rooted trees will thrive. 

 Drained to a depth of ten or fifteen feet, conditions are favorable 

 for the development of tap-rooted trees. As a rule, trees which 

 thrive normally in wet ground do not survive transplanting to dry 

 situations, and vice versa. Under natural conditions Red Cedar 

 (Juniper), Shortleaf Pine and Red Oak are confined to dry situa- 

 tions; Walnut, Cherry, Hickory and White Oak find their best 

 development in the deep, well-drained soils of northern slopes; 

 Cypress and White Cedar thrive in saturated soils where the surface 

 of the ground is below water the greater portion of the year. 



Soil Salts. Mineral elements from the soil and carbon dioxide 

 from the air constitute the raw materials from which the tree man- 

 ufactures its food (sugar). Carbon dioxide is absorbed through 

 the leaves. Because of its universal distribution as a constituent 

 of air it has no influence in the distribution of trees. Soil salts in 

 solution are absorbed by the roots. The chief elements necessary 

 to tree growth are lime, magnesia and potash with small amounts 

 of nitrogen, potassium, iron and sulphur. In the leaves the soil 

 salts are united with carbon, hydrogen and oxygen forming sugar 

 to be used in building new tissue. The more valuable salts, as 

 nitrogen and potassium, remain in the leaves and fruit and are 

 returned to the soil as the leaves fall and decay. The wood of the 

 tree contains about one per cent mineral matter, principally potash. 

 Hardwoods contain a higher per cent of potash than softwoods. 



Trees differ markedly in their requirements for soil salts, certain 

 species (Pine) thriving in almost sterile soils (sand), others (Wal- 

 nut, Hickory, Ash) demanding a soil rich in mineral elements. 

 Excessive amounts of certain soil salts may render a soil unpro- 

 ductive for trees as well as for farm crops. An alkali soil is the 

 result of salt (sodium carbonate) or lime (calcium carbonate) in 

 excess. Such a soil often may be corrected by drainage, thereby 

 leaching out the excessive amounts of salts. Willow and Aspen 

 (Populus) thrive on a soil slightly alkaline in nature. 



Slope and Aspect. Both these factors influence tree growth in- 

 directly, as they affect light and moisture. Aspect (slope towards 

 a cardinal point) is of great importance in the distribution of trees. 

 A northern aspect receives less light (since an equal area of sun- 

 light is spread over a greater surface), has a lower rate of evapora- 

 tion than any other aspect, (since the sun's rays are not so direct),, 

 and contain more water. The southern aspect, on the other hand, 

 receives the direct rays of the sun and is drier and warmer and the 

 light is more intense. Consequently the northern aspect may sup- 

 port a forest of Hemlock, Beech, Maple, Walnut and Hickory, while 

 the southern aspect supports an open stand of Pine and Black Jack 



