54 BRITISH FOREST TREES 



of growing-space, &c., unfavourable to the due extension 

 and steady development of the assimilative organs, and 

 thereby affecting the quality of the timber produced. Thus 

 when larch and spruce, both indigenous to the cool, moist 

 northern slopes of the Bavarian Alps, are grown in the dry 

 warm climate of the lowlands, their growth and development 

 are stimulated, but their period of life is considerably 

 shortened, the timber yielded is inferior, their power of 

 resisting injuries is weakened, and they are more liable to 

 be attacked by insect enemies and by fungoid diseases. 



As regards the attainable limits of healthy, vigorous age 

 the following classification (mainly based on Gayer' s) may 

 be made : 



Attaining 500 years and more yew, oak, lime, Scots elni, chestnut. 



,, 300 400 years English elm, silver fir, beech. 



,, about 200 years ash, maple, sycamore, spruce, larch, Scots 



pine, hornbeam. 

 Seldom attaining over 100 years aspen, birch, alders, willows, poplars. 



Many historical trees throughout Britain are known to be 

 much older than any of the limits above assigned, but to 

 attain the ages of the above classification presupposes that 

 the individual trees have grown under circumstances un- 

 usually favourable to their development. 



For trees grown in forests the attainment of an age even 

 approaching these limits is out of the question, as being 

 opposed to the economic and financial considerations which 

 ought in general to form the basis of sylvicultural operations. 

 In fixing the fall of the timber (the period of rotation or 

 reproduction, the Turnus) the object of the proprietor may 

 be to obtain the greatest quantity of timber generally, or 

 the greatest outturn of certain dimensions, or the greatest 

 returns for the capital represented by soil and growing stock 

 of timber ; but under all circumstances the due protection of 

 the soil from the deteriorating influences of sun and wind 



