The following is from an address delivered by Mr. Robert Douglas
before the Association of American Nurserymen at the meeting in
Chicago recently.
It is the prevailing and almost universal belief that when native
forests are destroyed they will be replaced by other kinds, for the
simple reason that the soil has been impoverished of the constituents
required for the growth of that particular tree or trees. This I
believe to be one of the fallacies handed down from past ages, taken
for granted, and never questioned. Nowhere does the English oak grow
better than where it grew when William the Conqueror found it at the
time he invaded Britain. Where do you find white pines growing better
than in parts of New England where this tree has grown from time
immemorial? Where can you find young redwoods growing more thriftily
than among their giant ancestors, nearly or quite as old as the
Christian era?
The question why the original growth is not reproduced can best be
answered by some illustrations. When a pine forest is burned over,
both trees and seeds are destroyed, and as the burned trees cannot
sprout from the stump like oaks and many other trees, the land is left
in a condition well suited for the germination of tree seeds, but
there are no seeds to germinate. It is an open field for pioneers to
enter, and the seeds which arrive there first have the right of
possession. The aspen poplar (_Populus tremuloides_) has the advantage
over all other trees. It is a native of all our northern forests, from
the Atlantic to the Pacific. Even fires cannot eradicate it, as it
grows in moist as well as dry places, and sprouts from any part of the
root. It is a short-lived tree, consequently it seeds when quite young
and seeds abundantly; the seeds are light, almost infinitesimal, and
are carried on wings of down. Its seeds ripen in spring, and are
carried to great distances at the very time when the ground is in the
best condition for them. Even on the dry mountain sides in Colorado,
the snows are just melting and the ground is moist where they fall.
To grow this tree from seed would require the greatest skill of the
nurseryman, but the burnt land is its paradise. Wherever you see it on
high, dry land you may rest assured that a fire has been there. On
land slides you will not find its seeds germinating, although they
have been deposited there as abundantly as on the burned land.
Next to the aspen and poplars comes the canoe birch, and further north
the yellow birch, and such other trees as have provision for
scattering their seeds. I have seen acorns and nuts germinating in
clusters on burned lands in a few instances. They had evidently been
buried there by animals and had escaped the fires. I have seen the red
cherry (_Prunus Pennsylvanica_) coming up in great quantities where
they might never have germinated had not the fires destroyed the
debris which covered the seed too deeply.
A careful examination around the margin of a burned forest will show
the trees of surrounding kinds working in again. Thus by the time the
short-lived aspens (and they are very short-lived on high land) have
made a covering on the burned land, the surrounding kinds will be
found re-established in the new forest, the seeds of the conifers,
carried in by the winds, the berries by the birds, the nuts and acorns
by the squirrels, the mixture varying more or less from the kinds
which grew there before the fire.
It is wonderful how far the seeds of berries are carried by birds. The
waxwings and cedar birds carry seeds of our tartarean honeysuckles,
purple barberries and many other kinds four miles distant, where we
see them spring up on the lake shore, where these birds fly in flocks
to feed on the juniper berries. It seems to be the same everywhere. I
found European mountain ash trees last summer in a forest in New
Hampshire; the seed must have been carried over two miles as the crow
flies.
While this alternation is going on in the East, and may have been
going on for thousands of years, the Rocky Mountain district is not so
fortunate. When a forest is burned down in that dry region, it is
doubtful if coniferous trees will ever grow again, except in some
localities specially favored. I have seen localities where short-lived
trees were dying out and no others taking their places. Such spots
will hereafter take their places above the timber line, which seems to
me to be a line governed by circumstances more than by altitude or
quality of soil.
There are a few exceptions where pines will succeed pines in a
burned-down forest. _Pinus Murrayana_ grows up near the timber line in
the Rocky Mountains. This tree has persistent cones which adhere to
the trees for many years. I have counted the cones of sixteen years on
one of these trees, and examined burned forests of this species, where
many of the cones had apparently been bedded in the earth as the trees
fell. The heat had opened the cones and the seedlings were growing up
in myriads; but not a conifer of any other kind could be seen as far
as the fire had reached.
In the Michigan Peninsula, northern Wisconsin and Minnesota, _P.
Banksiana_, a comparatively worthless tree, is replacing the valuable
red pine (_P. resinosa_), and in the Sierras _P. Murrayana_ and _P.
tuberculata_ are replacing the more valuable species by the same
process.
In this case, also, the worthless trees are the shortest lived. So we
see that nature is doing all that she can to remedy the evil. Man only
is reckless, and especially the American man. The Mexican will cut
large limbs off his trees for fuel, but will spare the tree. Even the
poor Indian, when at the starvation point, stripping the bark from the
yellow pine (_P. ponderosa_), for the mucilaginous matter being formed
into sap wood, will never take a strip wider than one third the
circumference of the tree, so that its growth may not be injured.
We often read that oaks are springing up in destroyed forests where
oaks had never grown before. The writers are no doubt sincere, but
they are careless. The only pine forests where oaks are not intermixed
are either in land so sandy that oaks cannot be made to grow on them
at all, or so far north that they are beyond their northern limit. In
the Green Mountains and in the New England forests, in the pine
forests in Pennsylvania, in the Adirondacks, in Wisconsin and
Michigan--except in sand--I have found oaks mixed with the pines and
spruces. In northwestern Minnesota and in northern Dakota the oaks are
near their northern limit, but even there the burr oak drags on a bare
existence among the pines and spruces. In the Black Hills, in Dakota,
poor, forlorn, scrubby burr oaks are scattered through the hills among
the yellow pines. In Colorado we find them as shrubs among the pines
and Douglas spruces. In New Mexico we find them scattered among the
piñons. In Arizona they grow like hazel bushes among the yellow pines.
On the Sierra Nevada the oak region crosses the pine region, and
scattering oaks reach far up into the mountains. Yet oaks will not
flourish between the one hundredth meridian and the eastern base of
the Sierras, owing to the aridity of the climate. I recently found
oaks scattered among the redwoods on both sides of the Coast Range
Mountains.
Darwin has truly said, "The oaks are driving the pines to the sands."
Wherever the oak is established--and we have seen that it is already
established whereever it can endure the soil and climate--there it
will remain and keep on advancing. The oak produces comparatively few
seeds. Where it produces a hundred, the ash and maple will yield a
thousand, the elm ten thousand, and many other trees a hundred
thousand. The acorn has no provision for protection and transportation
like many tree seeds. Many kinds are furnished with wings to float
them on the water and carry them in the air. Nearly every tree seed,
except the acorn, has a case to protect it while growing, either
opening and casting the seeds off to a distance when ripe or falling
with them to protect them till they begin to germinate. Even the
equally large seeds of other kinds are protected in some way. The
hickory nut has a hard shell, which shell itself is protected by a
strong covering until ripe. The black walnut has both a hard shell and
a fleshy covering. The acorn is the only seed I can think of which is
left by nature to take care of itself. It matures without protection,
falls heavily and helplessly to the ground, to be eaten and trodden on
by animals, yet the few which escape and those which are trodden under
are well able to compete in the race for life. While the elm and maple
seeds are drying up on the surface, the hickories and the walnuts
waiting to be cracked, the acorn is at work with its coat off. It
drives its tap root into the earth in spite of grass, and brush, and
litter. No matter if it is shaded by forest trees so that the sun
cannot penetrate, it will manage to make a short stem and a few leaves
the first season, enough to keep life in the root, which will drill in
deeper and deeper. When age or accident removes the tree which has
overshadowed it, then it will assert itself. Fires may run over the
land, destroying almost everything else, the oak will be killed to the
ground, but it will throw up a new shoot the next spring, the root
will keep enlarging, and when the opportunity arrives it will make a
vigorous growth, in proportion to the strength of the root, and throw
out strong side roots, and after that care no more for its tap root,
which has been its only support, than the frog cares for the tail of
the tadpole after it has got on its own legs.
There is no mystery about the succession of forest growths, nothing in
nature is more plain and simple. We cannot but admire her wisdom,
economy, and justness, compensating in another direction for any
disadvantage a species may have to labor under. Every kind of tree has
an interesting history in itself. Seeds with a hard shell, or with a
pulpy or resinous covering which retards their germination, are often
saved from becoming extinct by these means.
The red cedar (_Juniperus Virginiana_) reaches from Florida to and
beyond Cape Cod; it is among the hills of Tennessee, through the
Middle States and New England. It is scattered through the Western
States and Territories, at long distances apart, creeping up the
Platte River, in Nebraska. (I found only three in the Black Hills, in
Dakota, in an extended search for the different trees which grow
there. Found only one in a long ramble in the hills at Las Vegas, New
Mexico.) Yet this tree has crept across the continent, and is found
here and there in a northwesterly direction between the Platte and the
Pacific Coast. It is owing to the resinous coating which protects its
seeds that this tree is found to-day scattered over that immense
region.
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[NATURE.]