524 PROTECTION AGAINST INSOLATION. 



8. Damage done. 



(a) In general. This malady reduces the technical value of 

 the steins and frequently kills a tree. The forest-owner thus 

 suffers a loss of timber and increment, to which may be added 

 danger of breakage and of insect-attacks, and exposure of 

 young growth requiring shelter. 



(b) Species. Bark-scorching affects chiefly trees with thin 

 and persistent smooth cortext, free from cracks. 



Species of trees that produce thick bark, and the bark of 

 which is rough and fissured, do not suffer. Their dead coarse 

 bark is a bad conductor of heat, and never becomes heated to 

 the same extent as smooth bark.* The bast under coarse bark 

 offers a further protection to the cambium against insolation. 



Beech suffers most, then spruce and Weymouth pine. 

 Next come hornbeam, ash and sycamore ; next, Norway maple, 

 lime, horse-chestnut, sweet-chestnut, cherry, rowan and apple- 

 tree, sometimes silver-fir. 



Oaks, elms, field-maple, birch, most species of Pyrus, Scots 

 pine, black pine and larch never suffer from bark-scorching. 



(c) Part of the Tree. Bark-scorching affects only the clear 

 bole of a tree, and generally its lower part from the base 

 upwards. The portion of the stem which is immediately 

 above the root-stock suffers most where there is no underwood, 

 owing to the heat reflected from the ground, while the fact 

 that sap is earliest in motion near the base of trees may 

 contribute. The taller the stem and the higher the crown 

 above the ground, the more exposed is a tree to scorching. 

 Large knots or low branches localise the injury to the part of 

 the stem which is below them. Stems covered with moss or 

 lichens resist insolation, and so do trees that are branched 

 down to the ground. 



An example of the bad effects of pruning trees exposed to 

 insolation may be seen in the Mirwart Estate in the Belgian 

 Ardennes, where a number of spruce trees planted to give 

 shelter along the eastern side of a meadow have been pruned 

 of all their lower branches, and are all badly scorched. 



* Hartig states that in September, at 10 a.m., with an air-temperature of 

 69-8 F., the temperatures on the S.K. side of thin-barked beech mid spnu-e 

 were 98'6 F. and 82'4 F., while that o Scots pine was 68 F. 



