36 IMPORTANT TIMBER TREES 



twigs and leaves all on or near the outer ends of the limbs. 

 All species require more light in old age than in early life. 



DO FORESTS IMPOVERISH THE SOIL ? 



Soil exhaustion is a very important feature when con- 

 sidering plant growth and should be well understood, and 

 it is as well to know what demands are made upon the soil 

 when we propose to grow a forest as when farm crops are 

 to be produced. Investigations made in Bavaria show that 

 an acre of wheat requires 27.9 pounds of potash and 22.7 

 pounds of phosphoric acid, while an acre of beech forest 

 demands only 13 pounds of potash and 11.9 pounds of phos- 

 phoric acid, the wood-growth requiring about one half as 

 much as the wheat. The difference is more marked between 

 potatoes and pine, the former exacting 79.5 pounds of pot- 

 ash and 26.8 pounds of phosphoric acid per acre, while pine 

 requires but 6.6 pounds of potash and 4.3 pounds of phos- 

 phoric acid, the potatoes calling for eleven times more pot- 

 ash and six times more phosphoric acid. The discrepancy 

 is nearly as great in the demands for nitrogen, for 12 

 pounds per acre for broadleaf trees and 80 pounds for 

 potatoes. 1 Conifers require less of the absolutely necessary 

 food for tree-growth than deciduous trees. 



When we take into consideration the large amount of 

 plant food given to the soil from tree-growth, one half of 

 which is received from the atmosphere, and the amount 

 drawn from the soil, and what it calls for there is mainly 

 obtained deep down in the earth, and below where most 

 farm crop roots reach, it will be seen why forests do not 



1 Were it not for the constant return to the soil, of potash, phosphoric 

 acid, and nitrogen hy the forest, this annual drain, by the trees, of the ele- 

 ments of fertility would amount to a large sum during their growth, hut hy 

 no means as great as would be the drain upon these elements by the farm 

 crops for the same length of time, and with no compensating return what- 

 ever. Dr. B. E. Fernow, in his Economics of Forestry (page 451), says : " In 

 the average there are annually returned by the fall of leaves and litter in a 

 dense forest from 1800 to 4500 pounds per acre, according to kind and con- 

 dition of growth and soil, from 22 to 220 pounds of minerals, potash, phos- 

 phoric acid, magnesia, lime, etc., and 12 to 60 pounds of nitrogen." 



