REFERENCES
Muldrew: Sylvan Ontario. Briggs.
Keeler: Our Native Trees. Scribners' Sons. $2.00.
TREES IN RELATION TO THEIR ENVIRONMENT
Consider the influences at work and their effect under the following heads:
1. Character of the Soil and Subsoil.—It may be gravelly, pure sand, sandy loam, clay or clay loam, muck or humus, shallow or rocky, and the subsoil may be sand, clay or hard clay with stones (hard-pan). Notice what species are most common in each kind of soil.
2. Water Supply.—What species are found naturally in moist ravines or along the margins of rivers and lakes, in bogs or swamps, on dry, sandy plains, or rocky hillsides. Consider also the rainfall.
3. Exposure to Sunlight.—Account for the lack of symmetry in the shapes of trees. Branches grow only where their leaves can get the light. Account for the pith in many tree stems not being in the geometric centre. Account for the rapid growth in height made by young trees in the woods. Their light supply is chiefly from above, and they stretch up toward it as rapidly as possible. Dim light causes rapid growth at the expense, however, of strength of tissue, but as these young trees are protected in the woods from the strain of wind storms, their slimness and lack of toughness is a benefit rather than a hindrance to them. Also, the limbs near the ground die off while the trees are still young and small, giving us the clear timber tree, free from large knots, tall and straight. Make further application of this principle of light in relation to the planting of trees for shade and for wood or lumber. Account for the large size of the leaves of young trees in the dimly lighted woods as compared with the leaves of older trees. The principle of rapid growth in dim light is seen here also. It will be noticed that the large leaves of the young trees are more thin, soft, and flexible.
4. Wind.—Observe the tops of tall trees that have always been exposed to a strong prevailing wind as, for instance, those growing on the tops of hills or the eastern shore of a lake which has a prevailing west wind. The tops lean in the direction in which the prevailing wind blows. Does strong wind help or hinder the growth of a tree? Examples of stunted trees on wind swept hills or shores readily show this. It will be seen also that the higher branches are poorest on the side most exposed to the wind.
5. Suitability of the Species to the Climate.—Observe that some trees retain their leaves much later in the autumn than do others. The beech, hickory, red oak, and chestnut are good examples. These are on the northern extreme of their territory of growth. The tree best suited to a rigorous climate is the one that finishes its work early in the autumn and has all its tissues well matured before cold weather sets in. Examples: maple, elm, birch, and willow.