CLIMATE AND TREE GROWTH 93 



sycamore, etc. In this group Plnus imignis and Oupressus 

 macrocarpa do well where the winter extremes do not fall 

 below 10° to 0° F. 



Ill 



Juli/ Means of 60° to 62° F. 



Species developing best are oak, English elm, Spanish 

 chestnut, cedars, walnut, plane, Bobinia, etc. 



The species named in each of the groups are those 

 which best reflect in a general way, the climatic features 

 in their growth and development. With the exception of 

 the four last species, all are capable of reaching timber 

 dimensions in any part of the British Isles, and given 

 suitable soils and situations, trees of large dimensions may 

 be found in most parts. But to the careful observer it is 

 evident that the farther north one travels the smaller 

 become the species associated with the third group, and 

 corresponding to the July mean of 60° to 62". North of 

 Yorkshire the English elm ceases as a common tree of large 

 size. Planes and cedars are scarce and poorly developed 

 in Scotland. Walnut and chestnut cease to ripen their 

 fruit north of the midlands, and Rohinia fails altogether 

 in Scotland and Ireland as a timber tree. 



In the first of these climatic groups or localities the 

 greater part of the north of Scotland may be placed. In 

 the second, most districts in the south of Scotland, north 

 of England and north of Ireland, and in the third, average 

 localities in Wales, the midlands and south of England, 

 and south of Ireland. The differences due to altitude de- 

 pend largely upon latitude. As seen from the following 

 list, all localities above 800 or 1000 feet possess tempera- 

 tures approximating to those in Group i. until, at 

 about 1500 feet, summer temperatures requisite for tree 

 growth, according to Mayr, probably cease altogether. 



