ALTITUDE 73 



of grass, any moisture thereon is quickly evaporated, and the 

 radiation of heat from the grass itself is very rapid, and thus 

 a frost is often induced. Also, the free circulation of air, near 

 the ground, is interfered with. 



The liability to damage by spring frosts is almost 

 always more severe on southern aspects, because on such 

 aspects the trees break into leaf much earlier than on 

 northern aspects. 1 So also the actual damage is usually 

 more severe, as, so often, the bright morning sun rapidly 

 thaws the twigs still covered with frozen rime. The slower 

 that the twigs thaw, the less will be the damage that will be 

 done. 



Aspect and Altitude in Reference to Gales. It is 

 necessary to consider these two factors together, for it does 

 not necessarily follow that the higher the altitude the greater 

 the damage that will be done by storms ; though such may 

 be apprehended when the aspect faces the direction of the 

 prevailing winds. Local knowledge is of great importance in 

 this respect, but it will usually be found that the south and 

 west of the country are more exposed to south-westerly 

 gales, whereas the north and east are more exposed to 

 north-easterly gales ; though any range of mountains or hills 

 in the neighbourhood will greatly determine this question. 



Altitude in Reference to Tree Growth. In this country 

 any reference to the actual altitude above sea level at which 

 trees will grow is liable to be very misleading ; especially 

 if comparisons be made with data as to altitudes at which 

 similar trees will grow on some big continent. The highest 

 altitudes in this country are barren, wind swept, rocky 

 peaks ; whereas the same altitudes on a big continent are 

 often at a relatively low altitude. 



In Great Britain there is very little land above 1000 feet 

 which is suitable for timber growing; and there is a great 

 deal at a lower altitude even than this which is far too 

 exposed and barren for timber growing. The relative alti- 

 tude is the determining factor. 



1 And on high altitudes the growing season is very much shorter, and 

 spring activity much later than at low altitudes. 



