Part 9 (1/2)
CHAPTER SIXTEEN
WHAT ARE THE ENEMIES OF THE TREES?
Every living thing is engaged in a struggle for air to breathe and for something to eat. Those that make their homes on the land also have to struggle for water. The stronger rob the weaker; for, among all of them except man, might always makes right. Men are learning that unselfishness is the better way, although they do not always practice it.
In this struggle the animals have an advantage over the plants, for if food fails in one place they can move to another. Among the animals also the mother tries to protect her children; and, in the case of some,--the wolf, for example,--a number will hunt together for the common good.
It is quite different with the plants. They must grow where the seeds take root. If there is little sunlight or water or the soil is poor, they must make the best of what they have.
The plants have to struggle not only with such enemies as insects, winds, fire, and browsing animals, but with each other, for every tree is the real or possible enemy of every other tree. Brother seeds sprouting under the same parent maple struggle with each other for the food and moisture in the soil and for the best place in the sunlight.
The one that gets the most of these will grow the faster and choke some of its weaker brothers.
[Ill.u.s.tration: _Edward S. Curtis_ Trees that struggle with cold and storm.]
In yonder grove of pines there are trees of all ages and sizes. The older ones have much the advantage and take a part of the food and sunlight that the smaller ones require. How the little ones stretch up and grow tall and slender in their attempt to get the sunlight!
But in spite of all their efforts some of them must die.
Some kinds of trees grow faster than others. Where a number are springing up together, the slow-growing ones will stand less chance of ever becoming great trees. In this way the yellow pine sometimes chokes out the cedar, and the fir gets the advantage of the sugar pine.
The bright, warm sun is the enemy of the tree that loves the shady hillsides. The swamp is the enemy of the tree that must have loose, dry soil. The cold is the enemy of the tree that is used to a hot climate.
Is it not strange that what is good for one tree is an enemy of another?
Many kinds of trees have their own particular insect enemies which attack them and no others. Some of these insects live upon the leaves, others eat the sapwood under the bark, while a few attack the roots.
Certain insects burrow in and eat the heartwood. Although this does not always kill the tree, it weakens it and makes the wood unfit for use.
The cedar and the hickory are among the trees injured in this manner.
The foliage of the broad-leaved trees is the delight of many insects.
They sometimes eat the leaves so closely that the tree is killed; for the trees breathe through their leaves and can no more do without them than they can without their roots.
The gypsy moth, which did no great harm in its European home, was brought to this country and accidentally set free. It at once began to attack the leaves of the elm, that beautiful tree of the old New England villages. Now it is destroying other trees and, notwithstanding the fight which we have made against it, we have not yet been able to exterminate it.
[Ill.u.s.tration: _American Forestry a.s.sociation_ Insects are destroying the trees of this forest.]
The chestnut tree, which every Eastern child loves for its nuts, is now being destroyed by a fungus which may kill every one of these trees in the country.
The white-pine blister, also brought over from Europe, is now threatening all the white pines and the related trees of our country.
This disease has already such a start in the East that we may not be able to stop it.
The dainty mistletoe, about which there are so many pretty Christmas legends, is a deadly enemy of many trees. The seed of this fungus is carried, by the birds or by the wind, from one tree to another. When it sprouts, tiny roots go down through the bark to the sap, on which it feeds until the tree is killed.
All our fruit trees have their deadly enemies which cause a loss of many millions of dollars every year. Among the worst of these is the San Jose scale, which was carelessly brought into the country from China.
[Ill.u.s.tration: _Pillsbury's Pictures, Inc._ A dwarf white pine which has found a foothold in the rocks on a mountain top.]
The pear blight has destroyed whole orchards of pear trees in the Western states. The citrus canker is now threatening the orange orchards of the Southern states.
For years we have been searching over the world for new and better varieties of fruit trees. With the s.h.i.+pments of such trees we have brought some of the worst of the diseases that we have just mentioned.