THE MOST SUITABLE GROWING SPACE. 291 



These data show that : 



(1.) The increased requirement of space is very great 



between the ages of 20 and 40 years; it then falls 



gradually up to the age of 100 years. 

 (2.) Many trees must be removed during the earlier part of 



a wood's life, and comparatively few later on, always 



assuming that the area is to remain fully stocked. 



r. Speries. 



Light demanding species require more space than shade 

 bearers ; broad-leaved species more than conifers. 



The above table shows that the light demanding Scotch pine 

 requires considerably more growing space than the shade 

 bearing spruce ; the latter less than the still greater shade 

 bearer the beech. 



Comparing the growing space of Scotch pine, larch, oak, 

 and birch with that of spruce, beech, and silver fir, the pro- 

 portion is about 100 to 65. 



<l. Soil. 



Until some time past middle age the number of trees is 

 larger on poor than on rich soil ; afterwards the dilierence 

 disappears. The reason is, that the struggle for existence 

 commences earlier and is more energetic on good than on poor 

 soil. In this I'espect considerable differences exist between 

 the various species. 



>: Allitude. 



Under otherwise equal conditions the number of trees per 

 acre increases with altitude, at any rate up to a certain eleva- 

 tion. The statistics of the Black Forest for the three regions 

 approximately indicated as below 1,200, 1,200 — 2,100, and 

 2,400 — 3,600 feet, showed the following proportion in the 

 number of trees : — 100, 126, 244, This law could not be 

 established above 3,600 feet, because at that height regular 

 woods disappeared. It was farther noticed that the difference 

 is more pronounced in the case of shade bearing species and 



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