FROSTCRACK. 505 



in order to favour the interchange of air in the lower strata of 

 the atmosphere. 



ii. Preserve the natural soil-covering of dead leaves, 

 needles and moss. 



c. DiiriiKj the UfiJIsaHon of Woods. 



i. In natural regeneration-fellings, the shelterwood should 

 be only gradually removed, the final felling being delayed till 

 the plants have grown out of the reach of late frosts. In 

 frosty localities, regeneration-periods will be long — from 20 

 to 30 years. 



ii. In the case of clear-cuttings, only small areas should 

 be cleared at one time. 



iii. A protective belt should be left intact on exposed 

 easterly and north-easterly borders of a wood, at any rate 

 until the young growth which it protects is out of danger from 

 cutting winds. 



iv. Coppice-fellings must be effected in the spring; if 

 made in autumn, winter-frosts would injure the stools ; they 

 should also run from west to east, so as to protect the young 

 growth from cold winds ; this precaution is specially necessary 

 for oak coppice, as frozen oak-shoots thaw rapidly when 

 exposed to the rising sun. 



Skction II. — Fkostcrack. 

 1. External Appearance. 

 Frosfcrarkii are long splits caused in stems by winter-frost, 

 which start at the bark and proceed radially and more or less 

 deeply towards the centre of the tree. They are frequently 

 followed by the formation of projecting longitudinal ridges on 

 the stem of an affected tree, which are termed frost-ribs. 



2. Kxpla)iation. 



Frostcracks are due to the contraction of the wood along its 

 periphery and radius, owing to extreme cold. 



It has been proved by actual measurement, that the 

 diameters and girths of trees of various species are lessened 

 by tbeir loss of heat during severe winters, and tbat tliere 



