ECONOMIC VALUE OF FOREST FLORA 197 



system, the latter on the high forest g-roup system, and 

 modifications of these may be found in most parts of the 

 British Isles. Possibly the only extensive regeneration of 

 beech on commercial lines takes place in the Chiltern 

 Hills, where it has been stated that annual nett profits of 

 20s. to 30s. per acre are obtained since the development of 

 the High Wycombe chair industry. Ash regenerates itself 

 freely in every copse and broad- leaved wood. Birch usually 

 takes the place of Scots pine in many parts of Scotland and 

 elsewhere, wherever the surface is covered with heather, 

 but only occasionally are the conditions suitable for the 

 successful regeneration of the last-named species. 



3. Power of resifitimi drouf/ht, frost, ivind, insects, fungi, 

 etc. 



Injurious drought is seldom an annual feature of the 

 British climate. It is often injurious, however, on dry or 

 thin soils in the south and east of England, where rainfall 

 is liofht. With drouyht, again, larch is often the chief 

 sufferer, and after a month or more of dr}^ hot weather it 

 shows signs of distress by yellow and withered needles, 

 -and in extreme cases by needle-shedding, subsequently 

 starting into growth after the rain comes. Spruce also 

 suffers on dry soils to some extent, but neither of these 

 species should be planted on thin soils in a dry climate, 

 Avith the idea of getting large timber. 



So far as the common species are concerned, winter 

 frost rarely causes damage in Britain. Severe winters 

 with temperatures below zero F. may occur, and occasion 

 the death of badly ripened wood in oak, chestnut, and 

 other species liable to grow late in autumn, and young 

 plants generally are often damaged by hard frost in the 

 absence of snow. Early and late frosts are often more 

 destructive, but even early frosts are only occasionally 

 injurious to a few species. The chief frost damage in the 

 British Isles, however, is invariably caused by late frosts 



