BRITISH FOREST TREES 35 



than trees, as for example the Scots pine in Scotland at about 

 2,500 feet. Similar effects are produced in localities exposed 

 to constant winds, especially those that are damp and cold. 



4. Differences of Forest Trees as to Growth in Height, 

 Girth, and Cubic Contents. 



(a) Growth in height varies considerably according to 

 species, age, soil and situation, method of formation of 

 forest, and form of treatment accorded to it. It takes place 

 by means of two shoots during the annual period of active 

 vegetation, namely the shoot from the spring flush beginning 

 in April or May, and that from the summer flush beginning in 

 July. In broad-leaved trees the latter is usually longer than 

 the former, as it falls in the warmer and more energetic period 

 of vegetation, but in conifers this is not usually the case, 

 and the later development of the spring growth is less easily 

 traceable, as no regular whorls are formed except by the spring 

 buds. In warm autumnal weather, as in 1886, some trees 

 also throw out autumn shoots early in October, but this is 

 rather a drawback than an advantage, as the shoots have not 

 time to develop, to harden naturally, and to form fresh normal 

 buds for the following spring, before the early frosts set in 

 and close the active period of vegetation for the season. 



The following table exhibits the maxima heights usually attainable 

 in forests, according to Gayer (op. cit. pp. 38, 39) : 



no 140 

 100130 



80100 



Attainable by 



Spruce, silver fir, larch, Scots and Weymouth pines. 

 Oak, ash, beech, lime maple and sycamore ; less 



frequently elm, poplar and birch. 

 Black and Cembran pines, hornbeam, alder and willow. 



These maxima heights are reached in different periods by 

 different kinds of trees ; thus the birch reaches its full 

 attainable growth in height long before the Austrian pine, 



D 2 



