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The Winds and the Woods: March: Black
TREES AS ATHLETES Of course if you happen to be born a Black Spruce, and your home is on the edge of the treeless plains of the far north, as that of some of the Black Spruces is, your best policy may be to cling as close to the ground as they do -- like a creeping vine, almost. Otherwise you're liable to be torn up by the roots, for the robust winds of that part of the world are apt to be rather rough at times.
But in the regions farther south and in all the forest-lands of the United States, you've got to stand up and wrestle with these boisterous playfellows, from time to time, if you hope to grow up to be anything of a tree and hold your place in the world. The foresters who undertake to train the youngsters of Treeland in the ways they should go know this perfectly well. In thinning out a group of saplings that are too dense for strong and rapid growth, because there isn't enough light, food, and moisture for so many in one spot, they also have in mind the develoment of the strength of the trees so as to prevent wind-throw and breakage. Not only do the selected trees -- always the best in the group, or "stand" -- develop stouter bodies and roots because of the increased opportunities for growth, but the very winds themselves help give them the strength to resist the winds!
When the body of a tree or a branch or a twig is bent by a gust of wind, the sap-cells are compressed on one side of the bend and stretched on the other. In both cases the result is that, as the bent branch or body straightens again, and the sap-cells reopen, an extra supply of sap is pumped, by suction, to these points of strain. Thus the tree is not only made to grow larger and stronger at these points, but the whole tree grows faster and stronger; just as the exercise of your legs and arms not only strengthens them, but affects your whole body.
Where a limb joins the trunk of a veteran that has weathered many storms, you'll sometimes see a big, bulging mass like the muscles of the strong man's shoulders. The bending strain is especially great in the case of horizontal branches bearing thick clusters of leaves that are always catching and being tossed about by the winds. Following the admirable methods of tree architecture, the branch not only springs upward in an arch -- evidently designed, as arches are in human architecture, to resist strain -- but, in the case of the older branches, you'll notice a heavier growth of wood on the under-side. In other words, it is not only an arch but a buttressed arch! The sap-cells in the wood of trees not only conduct water and sap -- and, it is now thought probable, store water, much as a camel's stomach does -- but co-operate with the fibres in stiffening the tree. The fibres are long, narrow cells with sharp, tapering points which are spliced into each other as a sailor or a Boy Scout would splice a rope. This is accomplished by the fibres sliding into each other as the tree grows. These fibres don't hold sap. Their sole business seems to be to help stiffen the tree's backbone -- and other parts of its anatomy.
THE GUY-ROPES OF THE ROOT SYSTEM But, let a high wind come along, and, no matter how stout your trunk and your limbs and your branches may be, it's all over with you unless you've got a firm grip on the earth under your feet! A tree, to hold its own, must be well rooted in the soil; and its roots must constantly tighten their grip in proportion to the strain on the wind-tossed branches. So, by the same automatic pumping system that strengthens the body of the tree, the roots are strengthened for their work. For this reason you'll see more surface roots on trees growing in thick woods, or in the shelter of hills, than on trees in the open, and standing wide apart. Trees in the open strike their lateral roots deeper to resist the wind strain. Trees of the thick woods, finding plenty of food near the surface of the ground and being protected from the winds by each other, don't feel any necessity for paying premiums for high-wind insurance by sinking their roots deep. But some of them overdo this kind of economy -- the Spruces, for example. They don't do any more digging than they have to, and, therefore, keep pretty close to the surface of the ground. The result is that an uprooted Spruce is a common sight.
It is on the lateral roots rather than on its tap-root that a tree must depend for bracing against the wind. These roots serve a similar purpose to that of the guy-ropes of a tent or a ship spar or the cables of a suspension bridge. The tap-root is like the tap in the kitchen sink in one respect -- its business is to furnish water for the preparation of food for the "family," which goes on in the innumerable little kitchens, the leaves. In situations where they are most exposed to the wind, trees not only have an extra thick coat of wood and bark on the side of the highest winds -- usually the north -- but they sometimes throw out special roots to secure themselves; roots that have no connection whatever with either the tap-root or the lateral roots!