The Earth as Modified by Human ActionMarsh, George P. (George Perkins)
History
The Earth as Modified by Human Action
Marsh, George P. (George Perkins)
Conservation of natural resources; Human geography; Nature -- Effect of human beings on; Physical geography
bushel, carts were filled with them as fast as if picked up on dry land,
and in the fishing season they were commonly sold at a shilling
(eightpence halfpenny, or about seventeen cents) a bushel. The increase
in the size of the trout was as remarkable as the multiplication of
their numbers.
The construction of dams and mills is destructive to many fish, but
operates as a protection to their prey. The mills on Connecticut River
greatly diminished the number of the salmon, but the striped bass, on
which the salmon feeds, multiplied in proportion.--Dr. Dwight, Travels,
vol. ii., p. 323.]
Geographical Importance of Birds.
Wild birds form of themselves a very conspicuous and interesting feature
in the staffage, as painters call it, of the natural landscape, and they
are important elements in the view we are taking of geography, whether
we consider their immediate or their incidental influence. Birds affect
vegetation directly by sowing seeds and by consuming them; they affect
it indirectly by destroying insects injurious, or, in some cases,
beneficial to vegetable life. Hence, when we kill a seed-sowing bird, we
check the dissemination of a plant; when we kill a bird which digests
the seed it swallows, we promote the increase of a vegetable. Nature
protects the seeds of wild, much more effectually than those of
domesticated plants. The cereal grains are completely digested when
consumed by birds, but the germ of the smaller stone fruits and of very
many other wild vegetables is uninjured, perhaps even stimulated to more
vigorous growth, by the natural chemistry of the bird's stomach. The
power of flight and the restless habits of the bird enable it to
transport heavy seeds to far greater distances than they could be
carried by the wind. A swift-winged bird may drop cherry stones a
thousand miles from the tree they grow on; a hawk, in tearing a pigeon,
may scatter from its crop the still fresh rice it had swallowed at a
distance of ten degrees of latitude, and thus the occurrence of isolated
plants in situations where their presence cannot otherwise well be
explained, is easily accounted for. [Footnote: Pigeons were shot near
Albany, in New York, a few years ago, with green rice in their crops,
which it was thought must have been growing, a very few hours before, at
the distance of seven or eight hundred miles. The efforts of the Dutch
to confine the cultivation of the nutmeg to the island of Banda are said
to have been defeated by the birds, which transported this heavy fruit
to other islands.] There is a large class of seeds apparently specially
fitted by nature for dissemination by animals. I refer to those which
attach themselves, by means of hooks, or by viscous juices, to the coats
of quadrupeds and the feathers of birds, and are thus transported
wherever their living vehicles may chance to wander. Some birds, too,
deliberately bury seeds in the earth, or in holes excavated by them in
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