56 PROPERTIES OF WOOD. 



and climatic optima for a species even beyond its native 

 habitat, for the possibility of the natural bridging over of 

 localities that are unfavourable for a species is much more 

 difficult than is generally believed. It is false to affirm that, 

 because a species thrives outside its native habitat, it is not 

 dependent on a decided climatic region, and that it is useless 

 to determine climatic regions as a natural basis for the culti- 

 vation of all indigenous and exotic trees. But we must not 

 overlook the fact that, in forestry, species can be cultivated 

 outside their native habitat, if, although they may yield no 

 fruit and no seed, they still produce valuable wood. In such 

 cases, however, the species would disappear as soon as the 

 hand of man is withheld [unless, like the English elm, they 

 produce suckers. Tr.]. 



With regard to the introduction of species of trees beyond 

 their native habitat, for any species there are five imaginable 

 climatic regions, three of them natural and two artificial. 



Ill c. Artificial region cooler than the natural 

 habitat. 



(II c. Region cooler than the optimum. 

 I. The optimum. 



II w. Region warmer than the optimum. 

 Ill w. Artificial region warmer than the 

 optimum. 



The law enunciated above may be expressed as follows : The 

 sp. weight of every species of wood is gradually reduced from 

 region I towards II c and II w, and towards III c and III w, 

 whether its annual zones are wider or narrower. 



The oak is the first example. Its habitat in Germany is 

 usually II c. Only the warmest localities in Germany come 

 under I ; these are districts where there are vineyards. By 

 experimental plantations oak is often grown in III c, while I 

 and II w are in the south and south-east of Germany, and 

 III w in Southern Europe. As in the first half of the rota- 

 tion of all species of trees, equality of soil and sufficient 

 moisture being presupposed, the breadth of the annual zones 

 increases with the climatic temperature, we find a general 

 increase in the breadth of annual zones of oakwood from 



