DURATION OF LIFE. 63 



they have reached the natural lioiit of their life. Never- 

 theless many cases occur, ^Yhere trees have been grown under 

 conditions which are not quite in harmony with their 

 requirements, so that they die, or at any rate fall off in 

 health and growth long before they would, in the ordinary 

 course, be cut over ; hence it is of importance to consider the 

 conditions under w'hich the growth continues to be healthy to 

 an advanced age. 



In the first place, the nourishing organs, crown and roots, 

 must be able to develop normally in accordance with the 

 requirements of the tree at the different periods of life ; 

 in other words, they must be given at all times the 

 required growing space, without, however, checking their 

 height growth or interrupting the cover overhead for 

 a lengthy period of time. Unless a tree is provided with 

 a sufficient quantity of organs, it will not be able to 

 overcome successfully internal and external damage which 

 endangers its life. The power of resistance in this respect 

 differs considerably in the various species. It is great in 

 oak, hornbeam, lime, willow, elm, yew, and Cembran pine, 

 but small in alder, Norway maple, sycamore, beech, spruce. 



The second condition of longevity is, that the locality 

 should offer to the tree all it requires for a proper deve- 

 lopment. On the whole it may be assumed that, where a 

 tree is indigenous, it finds all it requires (though this is not 

 without exceptions). Localities wdth different factors are 

 liable to be unsuited to the species, either from offering too 

 little or too much in respect of temperature and moisture, or 

 insufficient nutriment and depth in the soil, etc. Either case 

 may be injurious to the development of the tree, and 

 especially to the quality of the timber produced. For in- 

 stance, spruce is naturally fond of a cool climate ; by trans- 

 ferring it to the dry and warm air of the low lands, it 

 generally grows much more quickly, but does not jdeld 

 the same quality of timber, is shorter lived, and subject to 

 more dangers, than in its mountain home. 



