526 PROTECTION AGAINST INSOLATION. 



borders of a beech or spruce forest to branch freely down to 

 the ground ; this may be secured by making timely thinnings 

 in young woods. 



(e) Avoid high prunings in the case of beech standard-trees, 

 or any pruning of beech or spruce trees growing in hedgerows. 



(/) Protect the soil-covering of dead leaves, moss, etc., and 

 preserve the undergrowth along the borders of a forest. 



(g) For the protection of specially valuable avenue trees, 

 their bark may be smeared with a mixture of whitewash, clay 

 and water, cow-dung and water, etc. 



Trees that have been scorched should not be removed, as 

 they shelter trees behind them which would otherwise be 

 attacked ; it is better to form a protective belt of some shade- 

 bearing species, and not to remove the injured trees till this 

 has attained a sufficient height. 



SECTION III. HEAT-CRACK. 



Beling states that cracks in trees have been caused by 

 insolation ; this happens in the spring (April and May), when 

 there are considerable differences between the day- and night- 

 temperatures, and the ground being still cold, the centre of the 

 tree does not expand so much as the bark. Cracks are thus 

 formed on trees standing on southerly or south-westerly slopes, 

 chiefly on beech 30 to 70 years old, but also on sycamore, 

 hornbeam, oak and ash. The splits extend up the stem from 

 near the level of the ground to 20 and more feet in height. 

 Owing to the drying and loosening of the bark, local decay 

 may be introduced into the wood, but small cracks usually 

 close up again without any permanent injury resulting. 



Schlich observed in the early part of 1895, during severe 

 frost, that the bark of beech-standards cracked or split when 

 the sun rose in the morning. All such cracks or splits 

 occurred in the south-east or south side of the trees, the 

 cracking being followed by an outflow of sap. Trees which 

 had thus been injured in previous years showed a considerable 

 amount of decay in the wood, having the appearance of bark- 

 scorched trees. 



As the resulting injuries are usually unimportant, no special 

 measures need be taken to prevent heat-crack. 



