362 SYLVICULTURAL NOTES ON TIMBER TREES 



4th or 5th year, operations being governed by good seed 

 years. 



Rotation. This should be from 90 to 1 30 years on good 

 soil. 



Average Returns from pure crops in close-canopied high 

 forest should be per acre : 



Thinnings . . . 1840 cub. ft. down to 2 in. q. g. 

 Final yield (at 1 20 years) 3000 6 



Total production . . 5390 2 



Average annual increment, 45 cub. ft. 



Equivalent net rental 1 for land only 2 } at 3% = 35. 3d. 



f at 



(from date of planting) at 4% = minus 35. 



Of Fungi. Rosellinia quercina causes root rot in 

 seedlings and young nursery plants, and often causes great 

 damage. Nectria ditissima causes a canker on the bark of 

 the stems and branches. Various species of Polyporus and 

 Fomes (Bracket Fungi) attack the stems through wounded 

 surfaces e.g., F. igniarius and Fomes fomentarius^ both pro- 

 ducing white rot. White rot is also produce by Hydnum 

 diversidens and by Stereum hirsutum. P. sulphureus produces 

 a red rot. 



Of Insects. The larvae of the Tortrix viridana often 

 defoliate the trees ; and the larvae of the Cockchafer grub 

 (Melolontha vulgaris) do considerable damage to the roots of 

 trees often killing them in nurseries and young plantations. 

 Wherever Cockchafer grubs cause trouble in a nursery, it is 

 an excellent plan to grow a few broad-leaved trees near the 

 boundaries of the nursery, and to keep these trees cut back to 

 a height of about 12 feet. When the beetles emerge, they 

 will fly to these trees to feed upon the foliage. They can 

 then be shaken down, collected, and destroyed. The larvae 

 of the Oak Boring Bark Beetle (Bostrichus dispar) often kills 

 young trees. 



The larvae of the Small Black Weevil (Orchestes querci), 



1 Vide Chapter XI I. 



2 After deducting interest on ^8, the cost of planting and establishing 

 the crop. 



