SILVICS 7 



per acre. In another plantation the average accumulation was 

 7.2 pounds per year.^ 



As regards the chemical composition of soil, sour, marshy soils 

 are unsuited to most species except Scotch and white pine and 

 spruce. These are about the only species that will thrive on 

 pure peat. Ash, maple, beech, and elm require a moderate 

 amount of lime in the soil, and oak, locust, European larch, and 

 Austrian pine thrive best on soils which contain some lime, 

 while chestnut seems to do better in a soil containing very little 

 lime. Some recent investigations in soil seem to show the com- 

 manding importance of lime as a controlling factor in tree growth. 

 Most trees are lime-loving to a certain extent, but an over- 

 abundance of lime in all cases is unfavorable. The hardwoods — 

 oak, ash, maple, chestnut, beech — seem to demand the presence 

 of a considerable quantity of potash; spruce, fir, pine, and birch 

 thrive on soils rich neither in lime nor potash. For the produc- 

 tion of wood only, the demands vary as follows in high forests: 

 from 4 to 20 pounds of lime; from 2 to 10 pounds of potash, and 

 from ^ to 4I pounds of phosphoric acid per acre per year. The 

 combined influence of all these factors dependent on soil and 

 situation is shown in the amount of timber produced per acre 

 and in the quality of the timber. 



When the trees of a wood are tall and straight, free from 

 branches, and tapering but little, it is the best possible indica- 

 tion that the soil and situation are eminently suited to the wood- 

 land crops growing on them. 



These factors of climate, soil, etc., have influenced the dis- 

 tribution of trees in such a way as to form forest "types." In 

 crossing a mountain ridge we find one type of forest in the 

 swamp at its base, which is quite distinct in its composition 

 and appearance from that on the drier, rolling land just be- 

 yond. On the steeper slopes another forest type is substi- 

 tuted, just as the human type raised in the wild mountains 

 differs from that of the fertile valleys below. Scientific forestry 

 largely deals with the causes for: these varied types, while applied 



^ See Forestry Quarterly, Vol. VI, p. 290, and Vol. VII, p. 192. 



