A year among the trees

by Wilson Flagg

RELATIONS OF TREES TO BIRDS AND INSECTS.

“My neighbors,” said my philosophic friend, “are the cause of more than half the injury my crops receive from caterpillars and other insects. They will not allow the birds a harbor of wood and shrubbery upon their own grounds, and they shoot those which I endeavor to entice by offering them a shelter in my farm. It is strange they cannot understand the mischievous character of their operations of smoothing and grubbing. That little rising ground you see before you, covered with trees and shrubs, is hardly more than a bare rock. It occupies about an eighth of an acre; but no other possible use could be made of it, except as a quarry. The little grove, or coppice, that stands upon it, is the most beautiful object in sight from my house. I have never allowed it to be disturbed or frequented by social assemblages. I keep it sacred for the use of the birds, and it is a perfect aviary. The birds that feed upon the destructive insects that infest my grounds are raised in that temple of the gods, which is watered by numerous little springs that ooze from the crevices of the rock. While they are rearing their young, all species, even if they live exclusively upon seeds after they have left their nest, feed their offspring upon larvæ, which they collect from the nearest ground that affords them a supply. Hence I consider that bare rock, with its trees and shrubbery, the most profitable division of my farm, from the shelter it affords the birds, which are in an important sense my most profitable stock.”

I have often thought of my neighbor’s remarks, especially when I have observed the diligence of our farmers in destroying upon their grounds every acceptable harbor for the birds. When we are traversing a wood, if we discover an apple-tree growing in a little clearing or open space, we find it invariably exempt from the ravages of the common apple-borer. The same exemption is observed in those fruit-trees that stand very near a wild wood, or any wood containing a spontaneous undergrowth. The explanation of this fact is that the wood affords a harbor to the birds that destroy these insects in all their forms. Orchards and gardens, on the contrary, which are located at any considerable distance from a wood, have not this security. Robins, it is true, are very abundant in orchards, which are their breeding-places; but robins, though the most useful birds that are known to exist, take all their food from the ground. They destroy vast quantities of cutworms and chrysalids buried in the soil, but they take no part of their insect food from the trees. The birds that perform this work are the sylvias, woodpeckers, creepers, and other species that live only in woods and thickets. Hence an orchard that is nearly surrounded by a wild wood of much extent is not badly infested by borers and other injurious insects.

All species of insects multiply in cultivated grounds, while the birds, with a few exceptions, that feed upon them, can find a nursery and protection only in the woods. “The locust,” says George P. Marsh, “which ravages the East with its voracious armies, is bred in vast open plains, which admit the full heat of the sun to hasten the hatching of the eggs, gather no moisture to destroy them, and harbor no bird to feed upon their larvæ. It is only since the felling of the forests of Asia Minor and Cyrene that the locust has become so fearfully destructive in those countries; and the grasshopper, which now threatens to be almost as great a pest to the agriculture of North American soils, breeds in seriously injurious numbers only where a wide extent of surface is bare of woods.”

Some men destroy trees and shrubbery in their borders, because they are supposed to harbor insects. But if this be true, it is because they are not sufficient in extent to shelter the birds that feed upon them. The insects that multiply upon our lands deposit their eggs some in the soil, some on the branches of trees and upon fences and buildings. They are nowise dependent on a wild growth of wood and shrubbery. These pests of agriculture need nothing better than the under edge of a clapboard or a shingle whereon to suspend their cocoons or lay their eggs. So minute are the objects that will afford them all the conveniences they need, when hatching and when passing through all their transformations, till they become perfect insects, that no artifice or industry of man can deprive them of their nurseries, or appreciably lessen their numbers. All inventions and appliances used to rid the trees and grounds of these pests never destroyed more than one in a million of their whole number. It is not in the power of man, with all his science, unassisted by birds, to prevent the multiplication of insects from being the cause of his own annihilation. But the farmer, when he destroys the border shrubbery in his fields and the coppice and wood on his hills, exterminates the birds by hosts, while the mischievous boy with his gun destroys only a few individuals. The clipped hedge-row, which is often substituted for a border of wild shrubbery, may assist in breeding insects; but the birds never build their nests in a hedge-row, unless it be a long-neglected one.

I have in another essay spoken of the scarcity of birds and other animals in the primitive forest. They are not numerous there, because the forest would yield them only a scanty subsistence. The forest border is their nursery and their shelter, but their best feeding-places are the cultivated grounds. There is not a single species whose means of subsistence are not increased by the clearing of the forest and the cultivation of the land; but they require a certain proportion of wild wood for their habitation. Very few species build their nests in the trees and shrubbery of our gardens, unless they are near a wood. In that case the catbird often nestles in the garden, that during the rearing of its young it may be near the grounds that produce larvæ. Most of the woodpeckers, the sylvias, and the small thrushes, including some of our most valuable birds, cannot rear their young except in a wild wood. Yet all these, solitary as they are in their habits, increase under favorable circumstances with the multiplication of insects consequent upon the culture of the soil. It may be affirmed as an indisputable truth, that if their increase were not checked by the sporting habits of men and boys, and the clearing and grubbing habits of “model farmers,” birds of every species would increase in the same ratio with the multiplication of their insect food, and proportionally diminish their ravages.