70 ON SOILS AND SUBSOILS SUSTABLE FOR PLANTING. 



growth. This mineral matter, which remains as ashes when wood is 

 completely burned, forms a small percentage of the contents of the tree, 

 and according to some (Dr. G. Heyer, director of the Forest Academy, 

 Miindeu), is found in sufficient quantity in almost all varieties of soil. 

 In addition, rain, snow, dew, and hail are continually bringing fresh 

 supplies. 



2. The amount of moisture in soil is of the utmost importance, for the 

 supply of the rootlets of trees. There is a vast quantity of water given 

 forth through the leaves during the annual period of vegetation. The 

 soil must, therefore, be able to absorb and retain moisture. Loose sand, 

 ■with a small percentage of clay, absorbs easily, but does not retain it. 

 Binding clay absorbs slowly and to moderate extent, but is very reten- 

 tive. A mixture of vegetable mold modifies both extremes. 



There are five degrees of moisture in soils : 



(1) Wet. — On lifting a handful, water drops to the ground. 



(2) Moist. — On squeezing a handful, water drops to the ground. 



(3) Fresh. — On squeezing a handful, traces of moisture remain on the 

 hand. 



(4) Dry. — On squeezing a handful, no traces of moisture remain on 

 the hand. 



(5) Arid. — On being merely rubbed, it flies off as dust. 



'6. The degree of looseness. — The more clay there is in soil the more 

 binding it is, and according as sand or lime is added the more it be- 

 comes loose. Binding clay opposes tree-growth, by not allowing the 

 free entrance of moisture and air. On the contrary, very loose soils, 

 especially if shallow, are apt to become dry, and are exposed to tiie 

 influence of frosts, while trees having no firm support in the shallow, 

 unretentive soil often fall in storms. Here, again, both extremes are 

 modified by an admixture of humus. 



4. Depth of soil favors the growth of trees, since — 

 (a) More moisture is absorbed, and is retained longer; and 

 {b) The roots are more developed, and the supply of sap is greater, 

 and the cubic contents of the tree are greater than on shallow soil. 

 The classification of soils according to depth may be — 



(1) Very shallow. — Less than 6 inches in depth. 



(2) Shalloiv. — From 6 inches to a foot. 



(3) Middle-deep.— From 1 to 2 feet. 



(4) Deep. — From 2 to 4 feet. 



(5) Very deep. — Over 4 feet. 



Mild, loamy soil, in which sand and lime are present in a higher de- 

 gree than clay — deep, fresh, and rich in vegetable mold, is favorable to 

 the growth of many forest trees, such as oak. Lime is best suited for 

 beech, ash, maples, elms, black or Austrian pine (P. austriaca), dwarf 

 pine (P. mughus of Loudon), and yew. As already remarked, a binding 

 clay, without sufficient humus, is not suitable for forest trees. In the 

 heat of summer it cracks and injures the rootlets. A soil composed of 

 quartz sand, with a small percentage of clay, fresh and rich in humus, 

 will nourish sufficiently any tree growing in Great Britain, if not too 

 shallow. Soils, if rich (minerally), although they yield trees of greater 

 height and solid contents, will, if moist, produce timber of inferior quality 

 and less durability. Dry and arid soils, if properly treated, will, as a 

 rule, nourish the Scotch fir {Finns sylvestris), along with which the 

 birch might be grown, if advisable. In the North German plain, where 

 pine forests are cut through by railroads, safety belts are planted with 

 birch, to prevent sparks from reaching the tindei-like leaves that cover 

 the soil. 



