78 SYLVICULTURE. 



ness principles, it is in the end more profitable to thin moder- 

 ately, and at regular intervals of about 5 years, according to the 

 given conditions, than to make heavy thinnings before the crop 

 is nearing its maturity when heavy thinnings removing about 

 15 per cent of the crop amount to partial clearances, which 

 generally give good increment on the stems, hasten maturity, 

 and promote seed-production, though increasing the risk of 

 windfall. In Conifer woods intended to be worked solely for 

 providing pit- wood timber, heavy thinnings by cutting out the 

 largest poles may, however, prove the most profitable treatment. 



Both in the early and in all later thinnings or partial clear- 

 ances with or without underplanting, the principle should be 

 carefully observed, that thinnings in young woods should not 

 be heavy enough to induce an unnecessary amount of branch- 

 formation interfering with the growth in height and depreciat- 

 ing the quality and value of the bole as timber, and that 

 thinnings in older woods should not break up the leaf-canopy 

 so far as to risk any soil - deterioration through unnecessary 

 exposure to sunlight. Where heavy thinnings and partial 

 clearances are made among light-demanding tree-crops, soil- 

 deterioration can only be prevented by underplanting (e.<j., Oak 

 with Beech or Hornbeam ; Larch and Pine with Spruce, Douglas 

 Fir, or Red Cedar), though such measures are not usually prac- 

 tised in Britain, and may perhaps seldom prove directly profit- 

 able. But soil - deterioration means a loss in capital, for it 

 diminishes the market value of the land for timber-growing. 



Pruning is not needed in highwoods grown in close canopy, 

 but may sometimes be useful on standards in copse ; but even 

 then it is seldom profitable, as it tends to produce a strong flush 

 : of shoots along the bole, and may cause the trees to die off in 

 the top (staylieadedness). Hardwoods stand pruning best, and 

 softwoods worst ; but in any case the wound-surfaces need to be 

 made smooth and to be well tarred to prevent fungi causing rot. 

 When hardwood branches over 4 inches in diameter are pruned, 



