FROSTCRACK. . 509 



In the Kottenforst, near Bonn, an area of 7,400 acres 

 at an altitude of 426 feet, where the treatment is that 

 of coppice-with-standards, and the soil, clay with an imper- 

 meable substratum, over twenty per cent, of the oak stan- 

 dards are frostcracked. Frostcrack is also very prevalent in 

 the seventy to eighty-year-old oak-woods in Windsor Forest, 

 owing to the absence of underwood, and it is also extremely 

 common in the open parts of the Forest of Dean, where the 

 underwood has been browsed down by sheep. 



(d) Age of Tree. Large old trees, as a rule, suffer more 

 from frostcrack than younger trees, because the differences in 

 temperature between their outer and inner woody zones are 

 greater. 



(e) Locality. Fertile and moist soils favour frostcrack. It 

 is very frequent in narrow valleys along watercourses, where 

 the night temperature falls exceptionally low in winter. 



(/) Season. Frostcracks generally occur late in the winter, 

 when the sap begins to flow, provided intense cold should 

 set in. The sapwood then rapidly cools and contracts, while 

 the inner zones of the wood retain a higher temperature and 

 do not contract. Long-protracted and gradually falling 

 temperatures are not so dangerous. Storms increase the 

 danger by blowing the frozen stems backwards and forwards ; 

 Hess even considers it probable that storms may occasion 

 frostcracks at the commencement of a thaw, but as the outer 

 zones of the wood would then be expanding, whilst the inner 

 zones remain cold, a cup-shake, or separation of the wood 

 along a portion of the whole of an annual ring, would probably 

 result. 



4. Protective Rules. 



i. Thoroughly drain wet soils. 



ii. Keep up the density of woods, and underplant all 

 pure oak high forests with a shade-bearer, such as beech or 

 silver-fir. 



iii. Establish protective belts of spruce along the north- 

 eastern, eastern, and south-eastern boundaries of a wood. 



iv. Abandon the practice of reserving oak and other 

 standards in places where frostcrack is common. 



