NATURAL ENEMIES OF THE FOREST.
The natural enemies of the forest--as distinct from its human
enemies--fall into three groups: (1) Meteorological, (2) Vegetable,
(3) Animal.
METEOROLOGICAL FORCES.
[Illustration: Fig. 74. Effect of Wind, July, 1902, Cass County,
Minnesota. _U. S. Forest Service._]
_Wind._ "Windfalls" are not an uncommon sight in any forest.
Frequently only small areas are blown down, one large tree upsetting a
few others, or again a vast region is destroyed by great storms, Fig.
74. An area of many square miles in Florida covered with long-leaf
pine was thus destroyed several years ago. The "slash" thus formed,
when well dried, is particularly liable to catch fire and burn
furiously. Windfalls are especially common among shallow-rooted trees,
as hemlock, basswood and spruce, on sandy soil and on shallow soil
underlaid with solid stone, especially where open spaces give the wind
free sweep. It follows that an unbroken forest is a great protection
to itself. The only precautions against wind therefore, that can be
taken by the forester, are to keep the forest unbroken by selecting
only the larger trees for felling or to cut down a given tract by
beginning at the side opposite the direction of prevailing storms and
working toward them.
In sandy regions, the wind does immense harm by blowing the sand to
and fro in constantly shifting dunes, Figs. 75 and 76. These dunes
occupy long stretches of the Atlantic coast and the shore of Lake
Michigan. Such dunes have been estimated to cover 20,000 square miles
of Europe. Along the Bay of Biscay in France, the sand dunes formerly
drifted in ridges along the shore, damming up the streams and
converting what was once a forest into a pestilential marsh. This
region has been reclaimed at great expense by building fences along
the shore to break the wind and thus keep the moving sand within
limits. In this way a million acres of productive forest have been
obtained.
[Illustration: Fig. 75. Sand-dunes, Cape May, New Jersey. _U.S. Forest
Service._]
[Illustration: Fig. 76. Sand-dune. Oregon. _U.S. Forest Service._]
On the other hand winds are beneficial to the forest in scattering
seeds, weeding out weak trees, and developing strength in tree trunks.
_Drouth_ both injures the foliage of trees and causes defects in the
grain of wood, the latter appearing as "false rings." These arise
from the effort of the tree to resume growth when the water supply is
restored. See p. 19.
_Water._ Certain trees have become accustomed to living in much water,
as cedar and cypress have in swamps, and certain trees have become
accustomed to periodical floods, but other trees are killed by much
water. So when lumbermen make a pond which overflows forest land, the
trees soon die, Fig. 77.
[Illustration: Fig. 77. Effect of Flooding. First Connecticut Lake,
New Hampshire. _U. S. Forest Service._]
_Lightning_ frequently blasts single trees, and in dry seasons may set
fire to forests. This is a much more important factor in the west than
in the east,--in the Rockies, for instance, where there are electrical
storms without rain.
_Fires_ will be considered later under man's relation to the forest.
[Illustration: Fig. 78. Slim Trees Bent Over by Snow; Stouter Trees
Unharmed. Zurich, Switzerland. _U. S. Forest Service._]
_Snow and ice_ often bring serious harm to saplings by permanently
bending them over, Fig. 78, or by breaking off tops and branches.
_Frost_ kills young plants; and sudden changes in temperature
seriously affect grown timber, producing "frost checks" and "wind
shakes." When there is a sudden fall in temperature, the outside
layers of the tree, which are full of sap, contract more rapidly than
the inner portions, with the result that the tree splits with a sudden
pistol-like report, the check running radially up and down the tree.
This is called a "frost check" or "star shake," Fig. 41._a_, p. 47,
and such wounds rarely heal, Fig. 79.
On the other hand when the temperature rapidly rises, the outside
layers of the tree expand so much more rapidly than the inside, that
they separate with a dull muffled chug, the check extending in a
circular direction following the annual rings. Such checks are often
called "wind shakes" and "cup shakes," Fig. 41._c_, p. 47. These
injuries are found in regions where sudden changes of temperature
occur, rather than in the tropics or in very cold climates.
[Illustration: Fig. 79. Contraction Frost Check. _U. S. Forest
Service._]
VEGETABLE ENEMIES.
Under this head may be classed, in addition to fungi, a number of
unrelated plants, including such as: moosewood and dogwood, Fig. 80,
which crowd out young trees; vines, like bitter-sweet, which wind
about trees and often choke them by pressure, cutting thru the bark
and cambium; saprophytes, which smother the foliage of trees, of
which Spanish moss, Fig. 47, p. 201, is an example; and finally such
parasites as the mistletoes, which weaken and deform the trees.
[Illustration: Fig. 80. A "Forest Weed," Flowering Dogwood. North
Carolina. _U.S. Forest Service._]
The most important of the vegetable enemies of trees are fungi. It
should be remembered, however, that, without the decay produced by
them, the fallen trees would soon cover the ground, and prevent any
new growth, thus destroying the natural forest.
Every tree, as has been noted (p. 17), is composed of two parts, one
part, including leaves, young branches, roots and sap-wood, living,
and the other part, namely, the heart-wood, practically dead.
Fungi that attack the live parts of a tree are called parasites,
while those that live on dead trunks and branches are designated as
saprophytes. The line, however, between these two classes of fungi is
not well defined, since some parasites live on both living and dead
wood. The parasites are of first importance, for, since they kill many
trees, they control to a large extent the supply of living timber.
Nearly all parasitic fungi have two portions, an external fruiting
portion which bears the spores--which correspond to the seeds of
flowering plants--and an internal portion consisting of a tangle of
threads or filaments, which ramify the tissues of the tree and whose
function is to absorb nutriment for the fungus. Fungi are classified
botanically according to the spore-bearing bodies, their form, color,
etc.
The parasitic fungi which are especially destructive to wood are
those that have naked spores growing on exposed fruiting surfaces (the
_Hymenomycetes_). In toadstools (the _agarics_) these exposed surfaces
are thin, flat plates called gills. In the polypores, which include
the shelf fungi, the spore surfaces are tubes whose openings
constitute the pores. In the dry-rot, or tear fungus (_Merulius
lacrymans_), the spore surfaces are shallow cavities.
Some varieties, called _true_ parasites, develop in uninjured trees,
while others, called _wound_ parasites, can penetrate the tissues of
trees, only where a cut or injury makes a suitable lodgment for the
spores. Some fungi attack only a single species of trees, others whole
genera; some attack only conifers, others deciduous trees, while a few
attack trees of nearly all kinds alike.
Fungal spores when brought in contact with a wound on a tree or other
suitable place, and provided with suitable conditions of growth,
germinate, penetrate the tissues and grow very rapidly. These spores
send out long threads or filaments which run thru the cells lengthwise
and also pierce them in all directions, soon forming a network in the
wood called the mycelium.
Rotting, in a large number of cases, is due to the ravages of fungi.
This sometimes shows in the color, as the "red rot" of pine or the
"bluing" of ash. Sometimes as in "pecky" or "peggy" cypress, the
decayed tracts are tubular. More commonly the decayed parts are of
irregular shape.
The decay of wood is due to the ravages of low forms of plant life,
both bacteria and fungi.
A few of the more destructive forms may be noted.
_Trametes pini_ (Brot.) Fr. Foremost among the timber
destroying fungi is the large brown "punk" or "conch" found in
its typical development on the long-leaf and short-leaf pines,
_Pinus palustris_ and _Pinus echinata_, Fig. 81. The
fruiting bodies form large masses which grow out from a knot,
oftentimes as large as a child's head. They are cinnamon brown
on the lower surface, and much fissured and broken, on the
black charcoal-like upper surface. This fungus probably causes
four-fifths of the destruction brought about by the timber
destroying fungi. It occurs on most of the conifers in the
United States which have any value as lumber trees, and brings
about a characteristic white spotting of the wood, Fig. 82,
which varies with the kind of tree attacked. (Von Schrenk,
_Agric. Yr. Bk._, 1900, p. 206.)
[Illustration: Fig. 81. A "Conch," the fruiting body of _Trametes
pini_, on Sugar Pine. [_Agric. Year Book, 1900_, Pl. XXII, Fig. 2.]]
[Illustration: Fig. 82. Effect of Fungus. (_Trametes pini._) _U. S.
Dept. Agric._]
[Illustration: Fig. 83. "Shelf" Fungus on Pine. _a._ Sound wood; _b._
Resinous "light" wood; _c._ Partly decayed wood or punk; _d._ Layer of
living spore tubes; _e._ Old filled-up spore tubes; _f._ Fluted upper
surface of the fruiting body of the fungus, which gets its food thru
a great number of fine threads (the mycelium), its vegetative tissue
penetrating the wood and causing its decay. [_After Hartig._]]
Of the shelf fungi, which project like brackets from the stems of
trees, and have their pores on their under surfaces, one of the
commonest in many localities is the yellow cheese-like _Polyporus
sulphureus_, Fig. 83. This is found on oak, poplar, willow, larch, and
other standing timber.
Its spawnlike threads spread from any exposed portion of
cambium into the pith-rays and between the annual rings,
forming thick layers of yellowish-white felt, and penetrating
the vessels of the wood, which thereupon becomes a deep brown
color and decays.
Of the umbrella-shaped gill-bearing fungi, a yellow toadstool, called
the honey mushroom (_Agaricus melleus_), is a good example, Fig. 84.
[Illustration: Fig. 84. Honey Mushroom. _Agaricus melleus._ 1. Cluster
of small sporophores. 2. Larger sporophore with root-like organ of
attachment. _Forestry Bulletin 22._ Plate XII, Figs. 1 and 2.]
This fungus, of common occurrence in the United States as well
as in Europe, is exceedingly destructive to coniferous trees,
the white pine in particular suffering greatly from its
attacks. It also fastens upon various deciduous species as a
parasite, attacking living trees of all ages, but living as
well upon dead roots and stumps and on wood that has been cut
and worked up, occurring frequently on bridges, railroad
ties, and the like, and causing prompt decay wherever it has
effected an entrance. The most conspicuous part of the fungus
is found frequently in the summer and fall on the diseased
parts of the tree or timber infested by it. It is one of the
common toadstools, this particular species being recognized by
its yellowish color, gills extending downward upon the stem,
which is encircled a little lower down by a ring, and by its
habit of growing in tufts or little clumps of several or many
individuals together. It is also particularly distinguished by
the formation of slender, dark-colored strings, consisting of
compact mycelium, from which the fruiting parts just described
arise. These hard root-like strings (called rhizomorphs)
extend along just beneath the surface of the ground, often
a distance of several feet, and penetrate the roots of sound
trees. By carefully removing the bark from a root thus invaded
the fungus is seen in the form of a dense, nearly white,
mass of mycelium, which, as the parts around decay, gradually
produces again the rhizomorphs already described. These
rhizomorphs are a characteristic part of the fungus. Occurring
both in the decayed wood from which they spread to the
adjacent parts, and extending in the soil from root to root,
they constitute a most effective agency in the extension of
the disease. * * *
External symptoms, to be observed especially in young
specimens recently attacked, consist in a change of the leaves
to a pale sickly color and often the production of short
stunted shoots. A still more marked symptom is the formation
of great quantities of resin, which flow downward thru the
injured parts and out into the ground. (_Forestry Bulletin_
No. 22, p. 51.)
Of the irregular shaped fungi, one of the most destructive is a
true parasite, _i.e._, one that finds lodgment without help, called
_Polyporus annosus_ and also _Trametes radiciperda_, Fig. 85. It is
peculiar in developing its fructifications on the exterior of
roots, beneath the soil. Its pores appear on the upper side of the
fructifications. It attacks only conifers.
Its spores, which can be readily conveyed in the fur of mice
or other burrowing animals, germinate in the moisture around
the roots: the fine threads of "spawn" penetrate the cortex,
and spread thru and destroy the cambium, extending in thin,
flat, fan-like, white, silky bands, and, here and there,
bursting thru the cortex in white, oval cushions, on which the
subterranean fructifications are produced. Each of these is
a yellowish-white, felt-like mass, with its outer surface
covered with crowded minute tubes or "pores" in which the
spores are produced. The wood attacked by this fungus first
becomes rosy or purple, then turns yellowish, and then
exhibits minute black dots, which surround themselves with
extending soft white patches. (Boulger, p. 73.)
[Illustration: Fig. 85. 1. Stump of Norway Spruce, with a sporophore
of _polyporus annosus_ several years old; the inner portions of the
stump wholly decayed.
2. Roots of a diseased spruce tree, with numerous small sporophores
of _polyporus annosus_ attached. _Forestry Bulletin 22_, Plate XIII,
Figs. 1 and 2.]
Of the fungi which attack converted timber, the most important is "dry
rot" or "tear fungus" (_Merulius lachrymans_), Fig. 86. It flourishes
on damp wood in still air, especially around stables and ill
ventilated cellars. It gets its name lachrymans (weeping) from its
habit of dripping moisture.
The fungus destroys the substance of the timber, lessening its
weight and causing it to warp and crack; until at length it
crumbles up when dry into a fine brown powder, or, readily
absorbing any moisture in its neighborhood, becomes a soft,
cheese-like mass. * * * Imperfectly seasoned timber is most
susceptible to dry rot: the fungus can be spread either by its
spawn or by spores, and these latter can be carried even by
the clothes or saws of workmen, and are, of course, only too
likely to reach sound wood if diseased timber is left about
near it; but on the other hand dry timber kept dry is proof
against dry rot, and exposure to really dry air is fatal to
the fungus. (Boulger, p. 75.)
[Illustration: Fig. 86. Portion of the mycelium of dry rot or tear
fungus, _Merulius lachrymans_. This cakelike mass spreads over the
surface of the timber. In a moist environment pellucid drops or
"tears" distil from its lower surface: Hence its name. [Ward:
_Timber_; Fig. 21.]]
About all that can be done to protect the forest against fungi is to
keep it clean, that is, to clear out fallen timber and slash, and in
some cases to dig trenches around affected trees to prevent spreading
or to cut them out and destroy them. Such methods have heretofore been
too expensive to employ in any ordinary American forest, but the time
is at hand when such action will prove profitable in many localities.
For the preservation of cut timber from decay, several methods are
used. Fungi need heat, air, moisture and food. If any one of these is
lacking the fungus cannot grow. Air and heat are hard to exclude from
wood, but moisture and food can be kept from fungi. The removal of
moisture is called seasoning, and the poisoning of the food of fungi
is a process of impregnating wood with certain chemicals. Both these
processes are described in _Handwork in Wood_, Chapter III.
ANIMAL ENEMIES.
The larger animals working damage to our forests are chiefly rodents
and grazing animals. Beavers gnaw the bark, while mice and squirrels
rob the forest of seed and consequently of new trees. The acorns of
white oak are particularly liable to be devoured because of their
sweetness, while those of red and black oak, which afford timber of
comparatively little value, are allowed to sprout, and thus come to
possess the land. Hogs annually consume enormous quantities of "mast,"
_i.e._, acorns or other nuts, by pasturing in oak and other forests.
They, together with goats and sheep, Figs. 87 and 88, deer and cattle,
work harm by trampling and browsing. Browsing destroys the tender
shoots, especially of deciduous trees, but trampling entirely kills
out the seedlings. The cutting up of the soil by the sharp cleft hoofs
injures the forest floor, by pulverizing it and allowing it to be
readily washed away by storms until deforestation may result, as was
the case in France after the Revolution. It has cost the French people
from thirty to forty million dollars to repair the damage begun by the
sheep. In this country, this matter has become a very serious one
on the Pacific Coast, where there are enormous flocks of sheep, and
therefore the government is trying to regulate the grazing on public
lands there, especially on steep slopes, where erosion takes place
rapidly.[1]
[Footnote 1: The evils of grazing are increased by the fact
that fires are sometimes started intentionally in order to
increase the area of grazing land.]
[Illustration: Fig. 87. Goats Eating Foliage, New Mexico. _U.S. Forest
Service._]
[Illustration: Fig. 88. Sheep Grazing in Forest, Idaho. _U.S. Forest
Service._]
The most destructive animal enemies of the forest are the insects.
The average annual loss of trees in the United States from this cause
alone has been estimated to be one hundred million dollars.
Insects have two objects in their attack on trees, one is to obtain
food, as when they are in the larval stage, and the other is to
provide for offspring, as do certain beetles.
The number of insect enemies of the forest is enormous. At the St.
Louis Exposition, there were on exhibit nearly three hundred such
insects. These belong to some twenty orders, of which the beetles
(_Coleoptera_), which have horny wings and biting mouth parts, and
the moths and butterflies (_Lepidoptera_), with membraneous wings and
sucking mouth parts, are the most destructive. Insects attack every
part of the tree, the seed, the shoot, the flower, the root, the leaf,
the bark and the wood, both standing and cut.
Of the fruit and seed pests, the most destructive are weevils, worms
and gall insects.
Of the twig and shoot pests, beetles, weevils and caterpillars are the
worst.
Among insects that attack roots, the periodical cicada (17 year old
locust) may be noted.
The leaf pests are far more serious. They include the true and false
caterpillars, moths, gall insects and plant lice.
Of the bark pests, the bark beetles are the most destructive. These
are also called Engraver Beetles from the smoothly cut figures which
are their burrows under the bark, Figs. 89, 90, 91.
[Illustration: Fig. 89. Work of the Spruce Destroying Beetle: _a._
Primary gallery; _b._ Borings packed in side; _c._ Entrance and
central burrow thru the packed borings; _d._ Larval mines. Note how
the eggs are grouped on the sides. [_Agric. Year Book_, 1902, Fig. 24,
p. 268.]]
[Illustration: Fig. 90. Complete brood Galleries of the Hickory Bark
Beetle in Surface of Wood. [_Agric. Year Book_, 1903, Fig. 28, p.
316.]]
[Illustration: Fig. 91. Brood Galleries of the Oak Bark Beetle,
showing Character of Primary Gallery at _b_; Larval or Brood Mines at
_a._ [_Agric. Year Book_, 1903, Fig. 30, page 318.]]
Many pairs of beetles make a simultaneous attack on the lower
half of the main trunk of medium-sized to large trees. They
bore thru the outer bark to the inner living portion, and thru
the inner layers of the latter; they excavate long, irregular,
longitudinal galleries, and along the sides of these at
irregular intervals, numerous eggs are closely placed. The
eggs soon hatch and the larvae at once commence to feed on the
inner bark, and as they increase in size, extend and enlarge
their food burrows in a general transverse but irregular
course, away from the mother galleries (see illustration).
When these young and larval forms are full grown, each
excavates a cavity or cell at the end of its burrow and next
to the outer corky bark. (Hopkins, _Agric. Yr. Bk._, 1902.)
Some of the species attack living trees, causing their rapid death,
and are among the most destructive enemies of American forests.
All of the above indirectly affect both the quantity and quality
of the wood supply. They can be studied more in detail in the
publications of the U.S. Bureau of Entomology.
Of the insects directly attacking wood, the most important are the
ambrosia or timber beetles, the borers, the ants, and the carpenter
bees. The most remarkable feature of the beetle is the manner of its
boring into the harder parts of the wood. Its jaws are particularly
constructed for this work, being heavy and strong. The boring is
done something after the manner of countersinking, and the jaws are
believed to be self-sharpening, by reason of the peculiar right to
left and left to right motion.
_Ambrosia_ or _timber beetles_, Fig. 92. This class of insects
attacks living, dead, and felled trees, sawlogs, green lumber,
and stave-bolts, often causing serious injury and loss from
the pin-hole and stained-wood defects caused by their brood
galleries. The galleries are excavated by the parent beetles
in the sound sap-wood sometimes extending into the heart-wood,
and the young stages feed on a fungus growth which grows on
the walls of galleries. (Hopkins, Entom. Bulletin No. 48, p.
10.) The growth of this ambrosia-like fungus is induced or
controlled by the parent beetles and the young are dependent
on it for food. (Hopkins, _Agric. Yr. Bk._, 1904.)
[Illustration: Fig. 92. Work of Ambrosia Beetle, _Xyloborus celsus_,
in Hickory Wood: _a_, Larva; _b_, Pupa; _c_, Adult beetle; _d_,
Character of work in lumber cut from injured log; _e_, Bark; _f_, Sap
wood; _g_, Heartwood. [_Agric. Year Book_, 1904, Fig. 44, p. 384.]]
[Illustration: Fig. 93. Work of Ambrosia Beetles in Oak: _a_,
_Monarthum mali_, and work; _b_, _Platypus compositus_, and work; _c_,
Bark; _d_, Sap-wood; _e_, Heart-wood; _f_, Character of work in lumber
from injured log. [_Agric. Year Book_, 1904, Fig. 45, p. 384.]]
There are two general types or classes of these galleries, one
in which the broods develop together in the main burrows, the
other, in which the individuals develop in short separate side
chambers extending at right angles from the primary gallery,
Fig. 93. The galleries of the latter type are usually
accompanied by a distinct staining of the wood, while those of
the former are not. (Hopkins, _Agric. Yr. Bk._, 1904, p. 383.)
_Bark_ and _wood borers_, Fig. 94. This class of enemies
differs from the preceding in the fact that the parent beetles
do not burrow into the wood or bark, but deposit their eggs
on the surface. The elongate, whitish, round-headed
(_Cerambycid_), flat-headed (_Buprestid_), or short, stout
(_Curculionid_) grubs hatching from these eggs cause injury
by burrowing beneath the bark, or deep into the sap-wood and
heart-wood of living, injured and dead trees, sawlogs, etc.
Some of the species infest living trees, Fig. 95, causing
serious injury or death. Others attack only dead or dying bark
and wood, but this injury often results in great loss from the
so-called wormhole defects. (A. D. Hopkins, _Entom. Bull._, No.
48, p. 10.)
[Illustration: Fig. 94. Work of Round-Headed and Flat-Headed Borers
in Pine: _a_, Work of round-headed borers, "sawyer," _Monohamnus_
sp.; _b_, _Ergates spiculatus_; _c_, Work of flat-headed borer,
_Buprestis_, larva and adult. [_Agric. Year Book_, 1904, Fig. 46, p.
385.]]
[Illustration: Fig. 95. Hemlock Killed by Buprestid Worms. Hoquiam,
Washington. _U.S. Forest Service._]
The pine sawyers are among the most troublesome pests in the
mill yard, and their large, white larvae often do much damage
to logs by eating great holes thru their solid interior. While
burrowing in the wood the larvae make a peculiar grating sound
that may be heard on quiet nights at a considerable distance.
This is a familiar sound in the lumber camps of the North,
and has probably given rise to the name of the pine sawyers by
which these insects are known. (_Forestry Bulletin_, No. 22,
p. 58.)
_Powder-post beetles_, Fig. 96. This is a class of insects
representing two or three families of beetles, the larvae of
which infest and convert into fine powder many different kinds
of dry and seasoned wood products, such as hickory and ash
handles, wagon spokes, lumber, etc., when wholly or in part
from the sap-wood of trees. Oak and hemlock tan-bark is
sometimes injured to a great extent, and the structural
timbers of old houses, barns, etc., are often seriously
injured, while hop poles and like products are attacked by one
set of these insects, the adults of which burrow into the wood
for the purpose of depositing their eggs. (Hopkins, _Forestry
Bulletin_ No. 48, p. 11.)
[Illustration: Fig. 96. Work of Powder Post Beetle, _Sinoxylon
basilare_, in hickory pole: _a_, Character of work by larvae; _b_,
Exit holes made by emerging broods. [_Agric. Year Book_, 1904, Fig.
49.]]
_Timber worms_, Fig. 97. This class of true wood-boring
"worms," or grubs, are the larvae of beetles. They enter the
wood from eggs deposited in wounds in living trees, from
which they burrow deep into the heart-wood. Generation after
generation may develop in the wood of a tree without affecting
its life but the wood is rendered worthless for most purposes
by the so-called wormhole and pinhole defects resulting from
their burrows. The same species also breed in the wood of
dying and dead standing trees, and in the stumps and logs of
felled ones, often for many years after the trees are felled.
One species sometimes attacks freshly sawed oak lumber, new
stave bolts, etc. They are among the most destructive enemies
of hardwood forest trees, especially in reducing the value of
the wood of the best part of the trunks. (Hopkins, _Forestry
Bulletin_ No. 48, p. 10.)
[Illustration: Fig. 97. Work of Timber Worms in Oak: _a_, Work of oak
timber worm, _Eupsalis minuta_; _b._ Barked surface; _c._ Bark;
_d._ Sap-wood timber worm, _Hylocaetus lugubris_, and its work; _e._
Sap-wood. [_Agric. Year Book_, 1904, Fig. 47, p. 386.]]
The _carpenter worms_, Fig. 98. These are large pinkish
caterpillars which are the larvae of stout-bodied moths. They
enter the bark and wood of living oak, locust, poplar and
other trees, from eggs deposited by the moths in the crevices
of uninjured bark, or in the edges of wounds. They burrow deep
into the solid wood, where they live for two or three years
before transforming to the adult. The wood is seriously
injured by the very large wormhole defects, and while the
life of the tree is but slightly, if at all, affected by the
earlier attacks, the continued operations of this class of
borers year after year, finally results in the decay of
the heart-wood, or a hollow trunk and a dead top. (Hopkins,
_Forestry Bulletin_, No. 48, p. 11.)
[Illustration: Fig. 98. Worm Holes in Red Oak, Work of the Oak
Carpenter Worm. [_Agric. Year Book_, 1903, Fig. 37, p. 324.]]
_Columbian Timber-beetle_ One of the commonest wormhole defects
in white oak, rock oak, beech, and tulip ("whitewood" or
"yellow poplar") is one known to the lumber trade as grease
spots, patch-worm, or black holes, Fig. 99, steam boats, Fig.
100, etc., caused by the Columbian timber beetle (_Corthylus
columbianus Hopk_.) The characteristic feature of this
wormhole defect, which will enable it to be readily recognized
in oak and beech, is transverse series of two or more black
holes about the size of the lead in an ordinary lead pencil,
with a streak of stained wood extending with the grain two
or three or more inches each side, as in Fig. 99. In
quarter-sawed oak or split or sawed staves, a short
longitudinal section of one of these black holes is seen
attended by the stained streak on one side of a thick or curly
growth or grain, Fig. 100. It is this form which is called
"steamboats." In whitewood (yellow poplar) the black holes
are attended by very long black, greenish, or bluish streaks,
sometimes five or six feet long. When this is common in the
lumber it is called "calico poplar." Fig. 101 represents the
characteristic appearance of this defect greatly reduced.
(Hopkins, _Agric. Yr. Bk._, 1903, p. 327.)
[Illustration: Fig. 99. Work of the Columbian Timber Beetle: Black
holes and "grease spots" in white oak. [_Agric. Year Book_, 1903, Fig.
38, p. 325.]]
[Illustration: Fig. 100. Work of the Columbian Timber Beetle:
"Steamboats" in quartered or Split white oak. [_Agric. Year Book_,
1903, Fig. 39, p. 326.]]
[Illustration: Fig. 101. Work of the Columbian Timber Beetle in Tulip
Wood, "Calico Poplar," [_Agric. Year Book_ 1903, Fig. 40, p. 326.]]
_Carpenter bees._ The work of this class of woodboring bees
is shown in Fig. 102. The injury consists of large augerlike
tunnels in exposed, solid dry wood of buildings and other
structures. It is most common in soft woods, such as pine,
poplar, redwood and the like. (Hopkins, _Agric. Yr. Bk._,
1904, p. 390.)
[Illustration: Fig. 102. Work of the Carpenter Bee, _Xylocopa
orpifex_, in Redwood Lumber: _a_, entrance; _b_, galleries; _c_,
cells; _d_, larva; _e_, adult. [_Agric. Year Book_, 1904, Fig. 53, p.
390.]]
_Horn tails._ This is a class of borers which are the larvae
of the so-called wood wasps. They may enter the exposed dead
wood of wounds of living trees, but more commonly attack the
wood of dead standing conifers and hard woods, in the sap-wood
of which they excavate irregular burrows, which are packed
with their borings. When the adults emerge they leave the
surface perforated with numerous round holes. Water and fungi
entering these holes cause a very rapid decay of the wood.
(Hopkins, _Entom. Bull._ No. 48, p. 11.)
The tunnels of these various wood pests are most frequently to be seen
in chestnut, ash, hickory, oak, tulip, and cypress.
One would think that with such an array of enemies, the forest would
hardly survive, but on the other hand there are many enemies of these
pests. The most destructive are the predaceous and parasitic insects.
Many insects are simply predaceous, pouncing upon and destroying such
other insects as they can overcome. Still others are parasites, some
external, but most of them living within the bodies of their victims
where they pass their entire larval life. The eggs are laid on or
in the body of the victim, so that as soon as one hatches, it has
suitable food. The ichneumon fly, Fig. 103, is such a parasite;
it destroys millions of insect pests. It has a long and peculiar
ovipositor with which it drills a hole into the tree and deposits the
egg in a burrow of the Pigeon Horntail, a wood wasp that burrows into
deciduous trees. The larva soon finds its victim, the grub of the
Pigeon Horntail, and lives on it to its destruction.
[Illustration: Fig. 103. Ichneumon Fly whose Larva Feeds on the Larva
of the Pigeon Horn-tail.]
It would seem that it is a hopeless task to control the insect enemies
of forest trees and forest products or to prevent losses from their
ravages, but the writer is informed by Dr. A. D. Hopkins, the expert
in the Bureau of Entomology in charge of forest insect investigations,
that the results of their investigations show conclusively that there
are many practical and inexpensive methods of control now available
thru the suggestions and recommendations in recent Department
publications on forest insects, as well as thru direct correspondence
with the Department. These methods are based on the principle of
prevention and not on that of extermination. It has been shown that
thru proper adjustment of the details in management of forests and of
the business of manufacturing, storing, transporting, and utilizing
the products a large percentage of the losses can be prevented at
small additional expense, and that even when considerable cost is
involved the amount saved will often represent a handsome profit.
THE NATURAL ENEMIES OF THE FOREST.
REFERENCES:[A]
(1) Meterological.
Pinchot, _Primer_ I, pp. 75-76.
Roth, _First Book_, _pp._ 198-202.
Bruncken, pp. 27-29.
Water.
Roth, _First Book_, p. 27.
Snow, ice and frost.
Pinchot, _Primer_, I, p. 76.
Bruce, _For. and Irr._, 8: 159, Ap. '02.
(2) Vegetable.
Roth, _First Book_, p. 4.
Boulger, pp. 70-75.
Spaulding, _For. Bull._, No. 22.
Ward, Chaps. V, VI, VII.
Sickles, pp. 41-45.
von Schrenck, _For. Bull._, No. 41, Pl. III.
Sherfesee. _For. Circ._ No. 139.
von Schrenck, _Bur. Plant Ind. Bull._ No. 36.
von Schrenck, _Bur. Plant Ind. Bull._ No. 32.
von Schrenck, _Agric. Yr. Bk._, 1900, p. 199.
(3) Animal.
Grazing.
Pinchot, _Primer I_, pp. 69-73, II, p. 73.
Pinchot, _Agric. Yr. Bk._, 1898, p. 187
Coville, _For. Bull._ No. 15, pp. 28-31.
Roth, _First Bk._, p. 130, 178.
Insects.
Comstock, passim.
Hopkins, _Agric. Yr. Bk._, 1902, pp. 265-282.
Roth, _First Book_, pp. 115-130.
Howard, _Entom. Bull._, No. 11, n. s.
Hopkins, Spaulding, _Entom. Bull._, No. 28.
Hopkins, _Entom. Bull._, No. 48.
Hopkins, _Agric. Yr. Bk._, 1903, pp. 313-329.
Hopkins, _Agric. Yr. Bk._, 1904, pp. 382-389, Figs. 43-56.
Pinchot, _Primer_, I, p. 73.
Felt, N. Y. _State Museum Bull._, 103, Ent. 25.
Hopkins, _Entom. Bull._ No. 32.
Hopkins, _Entom. Bull._ No. 56.
Hopkins, _Entom. Bull._ No. 58.
Spaulding and Chittenden, _For. Bull._ No. 22, pp. 55-61.
[Footnote A: For general bibliography, see p. 4.]