CHAP, in.] Characteristics of Trees 55 



and situation, these differences are, especially in woodlands, 

 sufficiently distinct to admit of general classification into 

 shade-bearing trees, light-demanding trees, and trees that 

 occupy an intermediate position. The different species of our 

 forest trees may accordingly be classified as : 



Light-demanding trees: 

 Larch ; Birch. 



Scots Pine ; Aspen, Poplar, Willow. 

 Oak, Ash, Elm ; Douglas Fir. 



Trees less impatient of shade : 



Alder, Maple, Sycamore ; Weymouth, Corsican, and Austrian Pines, 

 and Menzies Spruce. 



Shade-bearing trees : 

 Spruce ; Hornbeam. 

 Beech ; Silver and Nordmann's Firs. 



The capacity of the various species for bearing shade under 

 any given circumstances, or in other words, their demands for 

 light, may be gauged by the general density of the foliage of 

 the crown and the capacity of overshadowed twigs to retain 

 life. But, so far as regards the absolute quantity of light requisite 

 for the performance of the assimilative functions of any species, 

 we know as little as about the necessary amount of warmth. 

 For general sylvicultural purposes, Larch, Birch, Scots Pine, 

 Oak, Ash, Aspen, and Willow, may be considered the principal 

 light-demanding species of trees, and Silver Fir, Beech, Spruce 

 and Hornbeam the chief shade-bearers ; whilst the attitude of 

 the other woodland trees in this very important matter is 

 mainly dependent on the conditions of the soil as to depth, 

 moisture, and general quality. 



The length of the annual period of vegetation also makes itself 

 'felt to a certain degree ; for in the far north, or at high eleva- 

 tions, where this is shorter than in lower latitudes or levels, the 

 demands for light become greater than obtain under the oppo- 

 site conditions. The same may also be said of cool northern 



