CLIMATE AND SOIL 31 



shallow soil ; while the oak, which has a deep burrowing 

 root system, will not grow to fine proportions except on 

 a deep soil. 



The chief species may be arranged as follows with regard 

 to the depth of soil they require. The depths given are 

 necessary for the species to grow to large size, but they will 

 produce good saleable poles of medium size on shallower soils. 



Species which will grow on shalloiv soils, about one foot to 

 eighteen inches in depth : Spruce, mountain pine, birch, aspen, 

 mountain ash. 



Species which reqidre moderate depth, from eighteen inches to 

 two feet: Austrian pine, Corsican pine, Wey mouth pine, beech, 

 hornbeam, black poplar, willows, alder, Sitka spruce. 



Species which require greater depth, from tivo to three feet: 

 Scotch pine, elms, Norway maple, sycamore, white poplar, 

 Douglas fir, red cedar. 



Species which require the greatest depth, over three feet: 

 Silver fir, larch, ash, lime, sweet chestnut, and oaks, 



Regarding the degree of porosity of a soil neither a very 

 loose soil nor a very heavy one is favourable. In a loose soil 

 the roots cannot obtain a good hold on the ground, and the 

 trees are apt to be blown down; such soils do not retain 

 moisture, and soon dry up. In a very heavy soil the roots 

 cannot penetrate easily, air cannot get in, nor can water 

 percolate, and the surface is apt to be swampy. The best 

 soils are those of middling consistency, such as a good loam, 

 or a limy soil with a good layer of humus. On such a soil 

 most species will do well, while, as a rule, we should plant 

 broad-leaved trees on soils which are decidedly heavy, and 

 pines on very light soils. 



The moistiire contained in a soil is of first importance. 

 If the ground is very wet and swampy air cannot get in and 

 the roots decay, while if the soil is very dry the trees get 

 insufficient moisture and there is not enough water to dissolve 

 the mineral matters. The most favourable soil is one which 



