CLIMATE AND TREE GROWTH 103 



parative rate of growth on exposed and sheltered sites 

 of the same mountain range. The difficulty in obtaining 

 such data would be the variation in soil conditions which 

 might prevent exactly parallel localities, other than those 

 associated with exposure, to be obtained, but the observer 

 knows only too well that the results of strong winds are 

 beyond all dispute, and that at least two-thirds of the 

 total surface of the land are affected by them. 



The general effect of such exposure is that mountain 

 land in Great Britain and Ireland is incapable of growing 

 large timber above 700 or 800 feet, apart from glens, 

 exceptionally good soil, or eastern aspects. By large 

 timber is meant, of course, trees which will pay for sawing 

 into boards or scantlings, and leave something over for 

 the estate-owner. Pit props, fencing timber, etc., can 

 be produced at higher elevations, but at present prices it 

 is practically impossible to grow trees at a profit which do 

 not attain a total height of more than 50 feet, and an 

 average cubic content of more than 10 or 12 feet. Along 

 the eastern side of the country the effect of the wind 

 diminishes, particularly on good soil, but it is still easily 

 seen on the extreme eastern sea-board in places, particu- 

 larly in long valleys running east and west, and on high- 

 lying tablelands. Take the country between the Solway 

 and Newcastle-on-Tyne, that between Edinburgh and 

 Glasgow, or the Central Plain of Ireland, and it is difficult 

 to notice any great decrease in the effect of Avind upon 

 tree growth as one travels east. Within a few hundred 

 yards of the east coast, trees show more or less the effect 

 of the east wind off the sea, but further west the pre- 

 vailing wind again asserts itself, and few situations are 

 exempt from its influence. The influence of wind increases 

 with the height of the trees and elevation of the ground ; 

 and, according to Stevenson, an increase of nearly 100 per 

 cent, takes place in the velocity of the wind at 50 feet 



