508 PROTECTION AGAINST FROST. 



attacks by insects and fungi (Xcctria and Polyporm sp.) 

 may frequently ensue. 



B. Damage done in Particular Cases. 



(a) Species. Hardwoods with large, medullary rays are 

 most subject to frostcrack. Deep roots also favour it, as they 

 pass into zones of soil which are only slightly affected by the 

 air temperature and thus keep the stem comparatively warm. 

 This difference of temperature between the outer and inner 

 zones of the wood of a tree increases its liability to crack. 



Oak, beech, walnut, elm, ash and sweet chestnut are the 

 trees most subject to frostcrack, and Turkey and sessile oaks 

 more than pedunculate oak. The sap, which pours from the 

 wound after a thaw, turns dark brown and betrays the injury 

 which the tree has received. 



Frostcracks also occur in the case of softwoods, such as the 

 horse-chestnut, lime, poplars, and tree-willows. They are 

 rare on conifers, and then chiefly on the silver-fir. 



(b) Part of Tree. Frostcracks usually occur in the lower 

 part of the stem of a tree, especially at places where the growth 

 is uneven near the root-stock, at knots, or where the stem is 

 eccentric. 



Splitting is furthered by local wounds owing to the admission 

 and freezing of sap, and is very common in the case of coppice- 

 shoots which have been allowed to grow into trees, and which 

 are always unsound at their base. Splits from the root-stock 

 proceed upwards and from a knot downwards; on eccentric 

 stems, they are always towards the largest diameter. 



In the case of stems of a regular shape, the south side 

 suffers most from frostcrack, and then the east and north 

 sides, the westerly side suffering least of all. The south side 

 suffers most, because the most vigorous circumferential growth 

 takes place there, and the tissues are consequently very 

 sappy. 



(c) Systems of Management. Standards over coppice suffer 

 most, as they are exposed to cold winds, whenever the under- 

 wood is felled. Standards in high forest, which are exposed 

 after growing in a dense wood, are also very liable to frost- 

 crack. 



