LIGHT. 19 



(1.) Larch, birch. 



(2.) Scotch pine, aspen, willows, Corsican pine. 



(3.) Oak, ash, sweet chestnut, mountain pine. 



(4.) Elm, common alder, Austrian pine. 



(5.) White alder, lime, Weymuutli pine, Norway maple, 

 sycamore, Cembran pine, hazel, Douglas fir. 



(6.) Spruce, hornbeam. 



(7.) Beech. 



(8.) Silver fir. 



(9.) Yew. 



The above scale represents only general averages. In reality 

 the degree of light requirement is subject to considerable 

 modifications caused by the peculiarities of each locality. 

 Generally, all species bear more shade on good fresh soil 

 than on poor dry ground, a fact which is indicated by the 

 density of the crown. The Scotch pine, for instance, grown 

 in fresh soils in countries near the sea looks quite different 

 from the same tree seen in continental countries, and stands 

 considerably more shade than the latter. 



The length of the growing season also influences the 

 degree to which a tree will stand shade. A certain total 

 quantity of light is required to complete the annual cycle of 

 development, hence a more energetic effect of light is wanted 

 in localities with a short growing season, such as high eleva- 

 tions, or high latitudes. A species which stands a certain 

 amount of shade at the level of the sea and in a southern 

 climate, may become light demanding at a considerable 

 elevation, or in a northern climate. Again, in foggy air, 

 under a usually covered sky, or on northern aspects, the 

 same species stands less shade than in usually clear air, 

 under a sunny sky, or on southern aspects. In this respect 

 it must be remembered that the actual intensity of the light 

 is somewhat greater in high mountains than in low lands. 



The health of the trees is also of importance. Strong 

 healthy plants with a good root system stand more shade, 

 and for a longer period, than weak plants. 



c2 



