CHAPTER X 



PROTECTION OF WOODS AGAINST FROST, 

 DROUGHT, STORMS, AND FIRES 



THE measures to be taken against ordinary damage by 

 frost have already been mentioned in Chapter II, and it 

 remains only to deal with two peculiar effects of frost, frost- 

 crack and frost-lifting. 



FROST-CRACK 



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

 liable to frost-crack ; it is however found in other species, 

 though it is rare on conifers. Frost-cracks usually occur on 

 the lower part of the stem and take the form of a long crack 

 running up and down it. They usually are formed in late 

 winter, when the sap is rising, if very cold weather prevails. 

 The sapwood then contracts with the cold while the heart- 

 wood, being warm, does not ; the result is a crack in the 

 sapwood, which is often accompanied by a loud report like 

 a pistol-shot. The crack is healed over by the growth of 

 timber during the summer, but is usually opened out again 

 the following winter. Pressure of the bark being thus relieved, 

 the timber formed at the spot is laid on in thick layers, and 

 a projecting rib of wood is formed called a frost-rib. 



Frost-cracks are mostly found in open woods or in those 

 which have been over-thinned after growing in a dense state. 

 They do not affect the health of the tree, but spoil the most 

 valuable part of the timber. The best protective measure 

 is to keep woods in a properly dense state. Nothing can 

 be done when once a crack has been formed, and affected trees 

 should therefore be cut out in the thinnings. 



