THE ENEMIES OF TREES. In every treetop we can read the story of a long fight. Leaf, flower and fruit, bud, twig and branch, contest unceasingly for room and food and sun. Underground, the roots have their own struggle for the bounty of the soil. Always the struggle is un equal, the weak succumbing to the strong. Where tens succeed, hundreds and thousands fail.
In the woods the story is the same. Neighbour trees contend as do neighbour branches. Nature thins and prunes, discarding all but the fittest. Many people understand that the best forests are those in which Nature has her own way. But only from Nature's point of view. She is the great impartial all-Mother, and is as much interested in the well-being of a fungus that de stroys a tree as in the tree itself. A virgin forest is a battleground where varied and multitudinous natural forces meet and fight for supremacy.
The noble forests of the Cascade range in Washington and Oregon best illustrate the victory of trees over all other forms of vegetation. The pine forests of the Great Lakes and of the South, the broad-leaved forests of the Ohio and lower Mississippi Valleys, all showed how trees triumphed in days gone by over inimical forces of Nature. The meagre fringe of trees along streams in the arid West, the stunted growth of northernmost woods, show how trees are affected by drought and cold. The dis tribution of forests and their condition are traceable to well known causes.
Some of the enemies of the forest are natural; some are attributable to man and his civilisation. In many instances responsibility is divided. One enters and leaves the door open for others.
The chief enemies of forests are fires and insects. Winds, frost, lightning, snow, hail; ice, drought and flood are atmospheric in origin. Fungi decompose dead wood, doing the forest a service by enriching the soil. But many of them menace sound trees wherever their bark is broken. Grazing and wasteful lumbering are two abuses of the first magnitude. Beside these, man is responsible for most forest fires.
Cold is the barrier that sets a limit to each species of trees at a certain degree of latitude and at a certain altitude above the sea. Few species are hardy enough to reach into British America, or to climb high up on mountains.
Frost damages forests by nipping the buds and tender shoots, by actually causing tree trunks as well as branches to burst open after the freezing of sap in spring, and by heaving the porous soil so that saplings of all ages are uprooted. Frost often destroys seeds before they are ripe, and while they are germinating.
Snow and ice burden trees in winter time, doing great damage to their tops—often maiming young trees for life. Broad leaved trees avoid much injury by their deciduous habit, but evergreens suffer where snows are heavy and winters long. Ex treme toughness and flexibility of limb characterise trees that successfully throw off their snow burdens spring after spring. The Western mountain hemlock, crouching on the most exposed ridges of the coast mountains, is a good example.
Hail beats off the leaves and tender shoots of trees, especially in the warmer states. It destroys flowers and unripe fruits, and bruises young growth.
Lightning shatters trees, and leaves them a prey to the attacks of insects and fungi. The chief harm caused by it is the starting of forest fires. Compared with this, the other damage it does is slight.
Winds lash the trees, breaking and maiming them. Hurri canes plough their paths through the woods. This exposes the trees left on the border of the swath to a new danger. Their support on the open side is gone; they fall by reason of the inade quacy of their roots to hold them securely in the ground. Roots do not go deep unless they must. Winds fan small fires into conflagrations. Beneficent carriers of pollen and distributors of seed, they also carry infection from diseased trees to sound ones, lodging spores in fresh wounds to eat down to the tree's heart or to prey upon leaf or twig or bark. Each species finds its habitat.