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Sylviculture
of Norway Spruce, Picea Abies
INDEX
(added by webmother)
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AND
THEIR
SYLVICULTURAL CHARACTERISTICS
AND TREATMENT
BY
JOHN NISBET, D.OEc.
OF
THE INDIAN FOREST SERVICE;
TRANSLATOR
OP FÜRST'S "PROTECTION OF WOODLANDS."
London
MACMILLAN AND Co.
AND
NEW YORK
1893
The
Right of Translation and Reproduction is Reserved
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Our
reproduction starts from page 83 from the section:
"CHIEF SPECIES,
forming, or capable of forming, Pure Forests."
"Conifers"
and
includes all pages up to page 114
SPRUCE, NORWAY SPRUCE, OR
SPRUCE FIR (Pinus abies, L = Pinus picea, Du Roi = Pinus
excelsa, Lam. = Abies excelssa, D.C. = PICEA EXCELSA,
Link).
Distribution.
---In this respect the spruce is inferior only to the Scots
pine. It extends from latitude 690 N. throughout the whole of
northern and central Europe, southwards to the slopes of the Alps,
Cevennes and Pyrenees. It forms extensive forests in Scandinavia,
Finland, Lapland, and Russia, although its growth there is not to be
compared with that attained on the hilly land and mountain masses in
central Germany. It seems not to have been indigenous to Scotland or
England, for no fossil traces of it have been found, and no
historical record exists of it having ever formed forests on the
hills of ancient Britain; it was probably only introduced toward the
middle of the sixteenth century.
In France, as well as in Scotland on an altogether smaller scale, it
has been cultivated to a much less extent than other conifers, and
in Spain, Italy and Greece it is seldom met with forming forests.
The eastern limit of the species is not easy to fix, as it gradually
merges into another variety, the Siberian spruce (Picea obovata).
It ascends the Harz mountains to about 3,300 feet, the Black Forest
and the mountains of Silesia to 3500---4000 feet, the Bavarian Alps
to nearly 6,000 feet, and the central Alpine ranges to over 6600
feet. In Germany and Switzerland the spruce is the principal
forest tree on all mountain ranges and hilly tracts, often forming
pure forests over large tracts of country, whilst below it there is
a girdle of deciduous broad-leaved trees into whose domain it is
always trying to extend its frontiers.
On the lower hills it is frequently found mixed with the silver fir
and the beech, and at higher elevations in lower latitudes with the
larch; in Silesia and East Prussia it forms extensive forests, often
in company with the Scots pine. It is emphatically a tree of the
upper hilly region, the more so in proportion as the hills and
mountains are massive in formation, instead of consisting of a
series of ridges and chains; it ascends to its greatest height when
the general elevation of the surrounding country is considerably
above the sea-level. Where the uplands fall away towards warm, dry,
lowland tracts the spruce is not indigenous, and though pure forests
of it are frequently to be found on indifferent soils in these
localities, they are almost always the result of artificial
production, and too often but poor in their production of timber.
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Tree-form
and Roof-system of the spruce exhibit many differences from,
and indeed direct contrasts to, those of the Scots pine. Its roots
are mostly confined to the upper layer of the soil, and these of one
tree often interlace with those of its nearest neighbours, thus
obtaining some little protection during high winds. Its horizontal
root-system, seldom going lower than 18-20 inches, and unprovided
with any deep-reaching tap-root, stamps it indeed as the tree of
shallow-soiled mountains, but offers it too often a sacrifice to the
winds. It develops great numbers of rootlets, and as it also
possesses the property of extending its roots to a great distance,
it has a comparatively large area from which to draw supplies of
nutriment, although owing to its density when forming pure forests
the individual growing-space is limited beyond that of any other
tree except perhaps the silver fir.
Although slower in growth during youth than the Scots pine, it
maintains a much steadier rate of increase in height and grows up in
dense canopy without much tendency to branch formation or
interruption. In height, length of bole, straightness and full-woodedness
of stem, freedom from branches, greatest quantitative production of
wood and of useful timber per acre, it is rivalled only by the
silver fir. Its crown is cone-shaped, and when grown in isolated
positions the whole foliage is retained in more or less conical form
from the summit downwards to near the ground; the short leaves or
needles on the branches are retained for five to seven years.
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Requirements
as to Soil and Situation. -----Shallow-rooted though the
spruce undoubtedly be, yet it demands freshness in the soil, and
cool, damp, mountain atmosphere is beneficial to its growth. Where
other woods shelter it from the wind it also finds a suitable abode
in the vicinity of the seacoast, but its best development is
attained in protected localities on mountain sides. In its true home
the average temperature in July does not much exceed 660° Fahr. (Willkomm,
Die forstliche Flora Deutschlands und Oesterreichs, 887, p. 81.) and
the total minimum warmth requisite during each annual period of
active vegetation has been ascertained to be about 2,610° Fahr.,
which is about the annual average quantity of warmth developed at
latitude 69° north. Its growth seems best when the enjoyment of the
warmth, and thereby the period of active vegetation, is confined to
a short summer season, during which there is daylight for the
longest possible
time, as in the north of Scotland and in Norway and Sweden. Drought
is less easily borne by the spruce than by any other tree.
In regard to the quality of the soil, spruce shows a considerable
degree of indifference, or at any rate adaptability; it makes
greater demands on mineral strength than the Scots pine, but is
content with less than the silver fir. Being at the same time one of
the thickly-foliaged species of trees that improve the soil, and
recruit such soils as have become impoverished, it is frequently
found where broad leaved deciduous trees have previously allowed the
soil to become deteriorated and impoverished.
Spruce thrives on soils of the most varied description, from the
strong, friable mountain soil down through the binding varieties to
the sandy-loamy, and the drained moors and bogs. Soils that show any
good growth of weeds like Epilobium, Senecia, Atropa,
or Digitalis, or of grasses like Carex are generally
fresh and capable of producing good spruce forests, as also are
those with high growth of whortleberry; but on tracts covered with
heath and heather plantations should more frequently be made with
spruce and Scots pine, than with spruce alone. It is not indifferent
to mineral strength, but the chief factor in determining the
suitability or non-suitability of any particular locality is
certainly the equable distribution of a moderate quantity of
moisture throughout the soil. The older sand formations, and loamy
deposits resting on limy subsoil found in Alpine districts bear good
spruce forests, but on limy soils it is apt to suffer from fungous
diseases. On marls, loams, and rich clayey soils, deciduous
broad-leaved trees find a more suitable home than the spruce. Low
sandy plains with dry gravelly soil, soured undrained stretches with
stagnant soil-moisture, moorpan with excess of sesquioxide of iron,
or tracts liable to inundation are not the localities on which
spruce can be expected to attain its normal development.
The most suitable aspect depends on the locality, and the elevation
above the sea-level. Towards the lower limit of its proper region it
prefers the cool, moist, north and north-east exposures, whilst
towards the upper limit it seeks the southern and south-western
aspects in order to obtain the requisite degree of warmth, and to
escape from the drying-up influence of the east winds.
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Requirements
as to Light.---The ability to retain its branches in foliage
for five to seven years, and the consequent density of its crown,
give indication of the large capacity with which the spruce is
endowed as regards bearing shade; but the extent to which the demand
for some measure of enjoyment of light exists, is mainly dependent
on how far any particular locality varies from the normal situations
suitable to it.
Where these various climatic changes are distinctly discernible, the
demand for light becomes greater, and the capacity for bearing shade
smaller. Where soils are wanting in moisture, young spruce cannot
thrive under standards which intercept and partially retain the
atmospheric precipitations. Excess of light on the other hand
stimulates to increased assimilation of sap and too rapid growth in
the earlier stages, which in consequence seriously affects the
quality of the timber produced. In its true home, as, for example,
on the fresh loamy soil of the Bavarian plateau, it frequently has
to content itself for the first fifteen to twenty years of its
existence with only a moderate supply of light under scattered
standard parent trees, before being gradually admitted to the full
enjoyment of unrestricted light and sunshine and the opportunity of
normal development.
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Attainment
of Maturity and Reproductive Capacity.--- Spruce is generally
grown with a rotation of seventy to eighty years for ordinary
timber, or one hundred to one hundred and twenty years for the
production of larger assortments, but local market considerations
must determine when the fall can most advantageously take place;
higher periods of rotation are only advisable where the quality of
the soil is above the average. Good money returns on the capital
represented point decidedly towards the growth of spruce (and
Douglas Fir) as being one of the most remunerative and profitable
ways of utilising forest soils of about average quality.
Good seed years are less frequent with the spruce than the Scots
pine, but are generally - reckoning from the fiftieth to sixtieth
year - more productive when they occur; on the Harz mountains one
good and one minor seed year are expected in every six years. Seed
years can be foretold by the flower-buds, and the twigs showing
these, broken off by squirrels and birds which feed on them. The
ruddy-brown seed ripens in the October after the flowering, and is
scattered from the cones in spring; it is somewhat larger and
heavier than the greenish-black or brownish seed of Scots
pine, and is reckoned good in quality when test experiments show a
germinative power of seventy-five to eighty per cent. lit thus has
not only a greater germinative power than the Scots pine, but it
retains this somewhat longer, especially when kept in the cone. Each
cone has 200 to 250 seeds, and one pound contains from 55,000 to 60,000
seeds.
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Liability
to suffer from External Dangers.---As an offset against its
many excellent qualities, spruce has unfortunately to contend with
many external dangers at all periods of its existence, here of
course to a greater extent, and there to a less, according to the
soil and situation. Sharp, biting winds hinder reproduction at high
elevations, except under the shelter of protective standards. Frost
is only liable to damage the young growth at its earliest stage.
Accumulations of snow, and of ice formed after rain on the heavy
foliaged branches, bend down saplings in thickets, break the poles
in young forests, snap off the tops of trees, and make large holes
here and there in the canopy, especially at moderate elevations (on
the Harz mountains, particularly those between 1700 - 2300 feet)
where the snow is larger in flake than at high altitudes. Dense
forests suffer most from snow, whilst a larger growing-space
increases the danger from hanging ice.
No other species of forest tree is less able than the spruce to
resist the violence of storms. Its shallow root-system, the long
lever formed by the bole, and the purchase obtainable by the wind on
the dense crown of foliage near the summit, all combine to weaken
the resistance it is able to offer, especially in early spring and
late autumn when strong winds are frequent just at the time when the
foliage is often heavy with moisture and the soil sodden and
softened by continuous rainfall. Whole forests are then often thrown
down. The danger from wind is considerably lessened when other
species are grown in admixture with it, or when natural reproduction
takes place by the annual or periodical removal of the largest trees
only.
Drought is injurious in the youngest stages of growth especially
when accompanied by dry winds.
On unsuitable localities the mature stems are somewhat liable to die
off, and old tree forests often suffer from fungous diseases,
occasioned chiefly by Trarnetes pini and Nectria cucurbitula
on the stem and branches, and by Trametes radiciperda and Agaricus
melleus in and near the roots, which diminish the value of the
timber. Cotyledons and leaves of seedlings are demolished by Phytophthora
omnivora. In young plantations, and particularly in nurseries
and young seedling crops, blanks are often caused after wet summers
by Pestalozzia Hartigii. Red-rot in the timber is occasioned
by Polyporus vaporarius, and white-rot by Polyporus
borealis or, less frequently, P. fulvus.
But even the climatic dangers and fungous diseases combined are
surpassed in importance by those to which spruce is exposed at all
periods of its growth and development from the attacks of insect
enemies. Extensive tracts of pure spruce forest have recently in
Germany been severely damaged, partially destroyed, and even often
killed outright by insects, the lower elevations suffering far more
severely than those situated within the true mountainous region.
To enumerate merely the more important of such enemies, larvæ of Melolontha
vulgaris and hippocastani, and Gryllotalpa vulgaris,
and the full-grown Hylastes cunicularis and Gryllotalpa
do great damage to the roots of seedlings and young plants, whilst
the beetles Hylobius abietis and
pinastri and Hylastes cunicularis gnaw the tender bark
of their stems; later on the cortex and sap-wood suffer from both
the larvæ and the fully-developed beetle of three varieties of Bostrychus
- amitinus, calcographus, and typographus, whilst
the mature wood is damaged by both the active forms of Xyloterus
lineatus. Buds and foliage are destroyed completely, and
valuable forests utterly ruined over immense tracts of country, by
that scourge of the coniferous forests of Germany, Liparis monacha,
the voracity of whose caterpillars is only equalled by their almost
unlimited numbers in bad years like 1889, 1890, 1891 in southern
Bavaria, where alone the extent of forests devastated by the black
arches, "nun," or spruce moth (Liparis monacka) is
estimated to be about 42,500 acres or sixty-six square miles, of
which by far the greatest portion was pure forest of spruce. (For
a detailed account of this insect and its ravages, see the
Transactions of the Highland and Agricultural Society for 1893.)
In the mixed forests attacked, the beech and Scots pine suffered
comparatively much less than the spruce, although they were also
badly injured; the spruce, however, was usually killed outright,
owing to the much smaller reserves of starchy matters stored up by
this species for subsequent constructive purposes.
In recuperative power with regard to injuries received, whether
caused by insects or by deer, the thin-barked spruce is not well
endowed. Where a strong head of game is maintained, red-deer do more
damage in spruce forests than elsewhere, by stripping the bark with
their teeth during summer, as well as for food during winter. The
damage caused is often very serious, and is generally most
widespread in pole-forests from twenty to forty years of age,
although it is often done also in tree-forests up to sixty years of
age. For the healing of the wounds thus caused, spruce has
unfortunately less recuperative power than the silver fir or even
the Scots pine.
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Sylvicultural
Treatment of Spruce.---The economic value of spruce is by no
means small, if its cultivation takes place under suitable
circumstances. Moderate in its demands on soil, which it also
protects and improves in quality, and seldom giving much trouble in
the formation and reproduction of forests, spruce yields on
favourable localities a larger outturn of timber than any other tree
usually grown in pure-forests (vide table on page 44),
without requiring a high period of rotation to attain marketable
proportions. It remains long in close canopy, and forms lofty,
cylindrical, straight stems, that are valuable and of great general
utility. It also yields fair returns in the way of thinnings, and
occasionally affords good grazing for cattle. From the actuarial
point of view many advantages point towards the cultivation of
spruce as one of the most remunerative forms of high forest; but the
relatively high returns promised can only be realised on soils and
situations which admit of the normal development of this species,
and these are to be found chiefly in sheltered localities of
mountainous regions haying a moist and moderately good soil.
Misled by tempting actuarial calculations, it would be a mistake to
transform existing crops into spruce woods without other definite
reasons, for most other trees, and particularly the broad-leaved
deciduous species, have undoubted advantages over spruce in respect
to the greater security they afford against destruction of the crop
from snow, storms, or insects. But in mountainous tracts, on
undulating soil temporarily reduced by too open crops of deciduous
trees, or where timber prices are good, but fuel is little in
demand, spruce forests generally as a matter of fact yield the most
remunerative returns on soils of about the average quality.
Young crops of spruce do not form canopy so soon as those of Scots
pine, though in plantations it is attained earlier than by sowing or
with natural reproduction. On sunny localities the soil is apt to
become overgrown with weeds like Atropa, Digitalis, Epilobium,
Rubus and Urtica, with Vaccinium, Carex,
Scirpus and Juncus on the moister patches, which
usually interfere with the growth of the young plants and
occasionally choke them altogether; but on dry and shallow soil the
dangers arising from dry winds and direct insolation are greater.
Frost in general does more damage, by lifting the young plants out
of the ground, than is occasioned by the actual degree of cold to
which they are exposed. Young growth, particularly in woods that
have been formed by planting, is greatly exposed to danger from the
large brown pine weevil (Hylobius abietis), which bores into
the young shoots, and often ruins whole crops formed where the
stumps of the mature crop have neither been grubbed up nor barked
after the harvesting of the mature fall of timber.
Until the young crop forms canopy, the growth of the individual
plants is rather towards lateral extension than in the direction of
increase in height, but when once they have closed up (which usually
occurs about the twelfth or twentieth year according to the quality
of the soil), and the twig-shoots begin to interlace, the
development of the leading shoot becomes vigorous, the more so in
proportion to the density of the crop and the quality of the soil.
As they are densely foliaged and make little demand on
growing-space, young thickets of spruce generally stand very thick,
and completely cover the soil. So much so is this the case, that,
where sowings have been too thick, the development is greatly
interfered with; but in general the natural selection of the
predominating stems, to form the future crop, goes on normally and
quickly, the current annual increase in height culminating with
shoots averaging one and a half feet on soils of the best quality
between the twenty-sixth and fortieth year, and later, with of
course smaller averages, on those of merely average or inferior
quality (vide tables on page 36 - 38). Throughout this period
of energetic development, the natural suppression of dominated stems
gradually progresses, but without any practical interruption of the
canopy taking place, so that the boles are enabled to assume that
full-wooded cylindrical shape which renders them so valuable. According
to Baur this maximum of approach to the cylindrical is attained when
the average height of the crop is from sixty-six to eighty feet, but
with advancing age it sinks only gradually.
One decided drawback of the close canopy and even development of
spruce woods at this stage of their life-history is the consequent
danger from accumulations of snow, which often occasion serious
damage---a danger however not so much to be feared in either
Scotland or England as on the Continent with its severe winters.
Later on the density of the crop also gradually diminishes without
the continuity of the canopy being very seriously interrupted,
whilst from the time that it has reached the tree-forest stage of
development, a rich growth of mosses (Hypnum) covers the
soil, which, however, gives place to whortleberry (Vaccinium) and
similar weeds when self-thinning with consequent interruption of
canopy has gone too far. It is at this stage of growth that pure
forests of spruce of equal age are most exposed to the danger of
windfall and to attacks of bark-beetles (Bostrichini). No
species is so little able to resist the force of storms as the
spruce, and when once violent winds succeed in breaking up the
canopy, they seem to act in a concentrated and cyclonic manner,
throwing down everything that offers resistance to their passage.
According to Burckhardt (Säen
und Pftanzen, 1880, p. 329. The introduction of the silver fir and
the re-introduction of beech into these spruce forests has been
occupying the attention of foresters there for many years past.)
in the Hanoverian portion of the Harz mountains, aggregating 134.350
acres, of which four-fifths, or 107,480 acres, are under spruce,
during the present century (up till 1870) over two millions of
mature spruce were thrown by wind, or the equivalent to full crops
on about 10,500 acres, nearly 8 per cent. of the total area. He also
estimates that wind and snow combined have during the present
century destroyed at least four millions of stems in the tree-forest
stage of growth, without including those that have been merely
damaged by wind or snow, and have consequently fallen victims
afterwards to bark-beetles, which first of all attack the sickly
stems, breed there, and then attack sound and healthy trees, unless
all unsound individuals are removed.
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Pure
Forests of Spruce.---Localities with a short period of
vegetation being the natural home of spruce, its cultivation in pure
forests in Scotland would seem advisable wherever the upper soil has
the requisite moisture. In the generally damp climate of both the
lowlands and highlands of Scotland with their comparatively short
summer, the factors are given which hold out promise of the normal
development of spruce, although its growth may perhaps not be so
rapid as in warmer southern localities. At higher elevations or in
the far north it takes perhaps a hundred to a hundred and twenty
years to attain the same average dimensions in pure spruce forests
that can be arrived at in lower or warmer localities in eighty to a
hundred years, but this shortening is to a great extent
counterbalanced by the better quality of the timber produced.
Tempted by the remunerative promises held out, spruce forests have
often been formed on heavy loams and clays, or on sandy soils apt to
suffer from want of moisture. When the climate is mild, and the
period of vegetation prolonged through warm spring and autumn
weather, plantations show rapid growth in youth, which, however,
does not always continue throughout the whole period of rotation,
but not infrequently shows signs of loss of energy about the
fortieth to sixtieth year. The too rapid development during the
youthful period produces soft wood of indifferent quality, which
offers but little resistance to `dangers threatened by snow, by the
attacks of insects, through infection with fungous disease, or to
diseases originating in other causes. Although of course this is by
no means necessarily the case, it is not unusual to find such spruce
woods early interrupted in canopy, and unable to afford sufficient
protection to the soil, so much so in fact that their clearance may
be advisable before they have attained sixty years of age. On such
localities spruce is not necessarily out of place, but may, grown in
patches along with a ruling species for which the soil and situation
are more suitable, attain very satisfactory growth, and assist very
materially in increasing the ultimate returns from the crop. The
periods of rotation of spruce usually vary from seventy to eighty up
to a hundred or a hundred and twenty years, the former supplying the
ordinary assortments of timber requisite for building purposes, the
latter yielding large squares. Local demands of course to a great
extent determine the most remunerative period of rotation, but where
the forests are extensive, fixing the fall at an early age is apt to
swamp the market with small timber, whilst entailing the harvesting
of large quantities of top-ends and small material of very little
value. The postponement of the fall to a hundred and twenty or a
hundred and forty years, for the production of large- girthed
timber, can only be advisable in very sheltered localities, owing to
the dangers to which the spruce then becomes exposed; and for the
same reason the retention of standards, when mature crops are being
cleared, is always combined with more risk than is prudent. Here
again, however, the same end can be better attained by growing the
spruce in admixture with other species, such as the beech, silver
fir, or pine.
The thinning out of pure forests of spruce is usually confined to
the removal of suppressed individuals, and of those likely to be
immediately suppressed, and in localities where damage from snow is
not improbable the operations must be conducted carefully. As the
natural habit of spruce is to grow in close canopy, any premature
removal of poles can only be an unnecessary diminution of the number
of individual stems per acre. In the weedings and clearings which
take place in young crops before thinnings are begun, (Under
clearings and weedings are classifiable all the operations in young
woods which necessitate an outlay that cannot be covered by sale of,
the material cut out; when the costs involved are covered, or more
than covered, by the proceeds obtained, the operations are then
properly termed thinnings. ) all
soft woods and coppice shoots of trees forming part of the former
crop should be removed in order to avoid the formation of blanks
later on,---birches if left standing often do great damage by
rubbing and chafing leading-shoots of the spruce,---and when the
crop has been formed by thick sowing or planting in wisps of two or
three on the poorer classes of spruce soil, these early protective
measures for improving the growth of the young stock often occasion
great trouble and considerable expense. In the thickets formed by
planting in wisps on inferior soil, it is especially necessary to
repeat the thinnings as frequently as possible, in order to assist
nature in the selection of the predominating stems to form the
future crop; the longer such operations, are delayed the more
difficult and expensive do they become as the roots interlace and
the lower portions of the stems grow into each other. Localities
exposed to the danger of snow-accumulation require the most careful
thinning, and even dominated individuals should be left standing, as
reserves in case of accidents, if their crowns are' still green;
broken stems also should not be removed if three or four green
whorls give hope of some side spray assuming the rôle of
leading-shoot. Where a strong head of game is maintained, deer often
do greatest damage by stripping the bark in woods directly they have
been thinned, and in particular just after the first time of
thinning out; from such wounds spruce suffers more serious permanent
damage than Scots pine or silver fir, owing to its weaker
recuperative power. For the same reason the removal of green
branches with the bill or axe is not advisable; when it is desired
to remove branches for the purpose of producing clean-stemmed timber
free from knots, the operation should invariably be performed with
the saw in the case of both living and of dead branches, and
confined to those under 4" diameter.
Soils that are somewhat inferior for the production of mixed forests
of broad-leaved species, or areas where long- continued or badly
managed copse, or coppice under standards, has allowed the soil to
become more or less deteriorated, frequently afford good localities
for the growth of spruce in pure forest, although it is not
advisable to confine it to soils below the average in quality if the
production of the larger, more valuable, and under certain
circumstances more remunerative assortments of timber be desired.
Where pure forests of spruce exist on an extensive scale over large
tracts, it is exceedingly desirable to frame the working plan so
that the annual fall should take place in several places apart from
each other, instead of being combined in one large area annually, as
it is to a great extent the latter method of procedure which causes
so many of the drawbacks under which pure forests of spruce suffer.
With the cessation of total clearances over large areas it is beyond
all doubt that dangers from insects during the youthful period of
growth, from snow during the pole-forest stage of development, and
from wind when approaching maturity, would all be practically, and
very considerably, lessened by the formation of several blocks, each
with its growing stock of successive annual crops from one to eighty
or a hundred years according to the period of rotation fixed on, in
place of having the total area divided simply into eighty or a
hundred compartments as the case may be, from the oldest of which a
total clearance of the mature timber is annually made.
The usual method of regeneration of pure forests of spruce is, as
above indicated, total clearance with artificial reproduction,
except at very high altitudes where considerations of treatment are
usually secondary to those relative to the general economic value of
maintaining the higher mountains under forest in order to prevent
landslips, and to regulate the flow of moisture through the soil and
ensure the perennial feeding of the streams which have their sources
there.
The unsuitability of the method of natural reproduction under parent
standards that is customary in the case of the other two densely
foliaged shade-bearing species, silver fir and beech, finds easy
explanation in the indifferent resistance which the spruce is able
to offer to the violence of storms, otherwise the diminished
increment that is attained by the young crop during the earlier
stage of growth would be amply compensated by the protection against
various dangers which the parent trees would secure to their progeny
during the first ten to twenty years. Experience has, however, shown
that attempts at natural reproduction in this manner, except in very
sheltered localities, usually lead to the parent standards being
thrown by wind, when a rank growth of weeds soon covers the soil,
and chokes a large proportion of the seedlings; and again, when the
reproduction takes place by sowing or planting, the retention of
standards is more likely to be injurious than beneficial.
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Mixed
Forests with Spruce as the Ruling Species. ---Spruce is
found forming pure forests over very extensive areas, as it is one
of the species which can thrive and attain normal development
without an admixture of other kinds of timber trees in the crop. At
the same time there is hardly any other species of forest tree in
Britain which gains so much as the spruce by the formation of mixed
forests, both as regards the unquestionable, protection thus
afforded to it against dangers, whether of organic or inorganic
nature, and in respect to the stimulus thereby secured for the total
production of timber per acre, and the better quality of the timber
produced.
In its Alpine home, the larch is frequently to be found naturally
associated with spruce at the higher elevations, although artificial
admixture of these two species in other localities has often been
far from satisfactory. Throughout the mountainous tracts of eastern
France, and of central and southern Germany, in particular in the
Black Forest, mixed forests of spruce and silver fir are a favourite
form of timber crop,---except on the Harz mountains, where the
climatic factors do not seem to be favourable to the development of
the latter. Beech is also often an associate of the spruce, and is
to be found frequently in mixed forests of spruce and silver fir.
Towards its northern and `eastern limits, the species chiefly found
growing along with spruce is undoubtedly the Scots pine. These are
the trees which are usually found growing as subordinate species in
mixed forests where spruce forms the ruling species or matrix, and
although other mixtures have been tried artificially, the
above-named are those which hold out the best sylvicultural and
economical promises.
When the silver fir finds the soil and situation congenial, it is
the most important associate of the spruce; and though during the
earlier years of growth it must be granted some protection against
the more rapidly developing spruce, it requires no special tending
throughout the later stages of growth. In many respects it adapts
itself better for admixture with the spruce than with any other
ruling species of forest tree. In tree-form and natural development
they have many close resemblances, but as silver fir is
deeper-rooted than spruce, the two species, admixed, can develop
unhindered a much larger aggregate of roots than if either species
were grown in pure crop; and as this maximum of root-system has
practically the opportunity of drawing the requisite supplies of
nutriment from two different layers of soil, it follows naturally
that the number of stems and the total production of timber per acre
will under ordinary circumstances be considerably greater than can
be shown by pure forests of either species. By interlacing of the
two root-systems also, no inconsiderable support is given to the
shallow-rooting spruce against windfall.
The main condition for the formation of mixed forests of spruce and
silver fir is a good deep soil without excess of soil-moisture, as
unless that essential condition be satisfied the latter is unable to
maintain itself against the former. Even although developing slowly
at first as compared with Scots pine, spruce has a more rapid early
growth than the silver fir, and the advantage thus won it maintains
throughout the pole-forest and into the tree-forest stage of
development. Although the silver fir can thrive in the side-shade
cast by the spruce, measures must be taken to prevent the latter
shooting so far ahead as to form canopy above the silver fir in the
thicket stage of growth, otherwise the latter dies off. Where the
two species are planted out alternately in equal numbers, the silver
fir soon gets defeated in the life-struggle, unless the soil is of
better than average quality. Even when the admixture takes place by
planting in alternate rows, the silver fir transplants should have
the advantage of being older than those of the spruce. Where such
mixed forests are formed or reproduced, it L is advisable to allow
the silver fir the advantage of five to ten years of growth in order
to enable it to protect itself against the spruce without
necessitating considerable outlay for tending,
Beech is not of so much importance as silver fir as a minor
species in spruce forests, for though its root-system is
heart-shaped like that of the former, its general habit of growth
and development as a forest tree is greatly different from that of
the latter; it requires to be grown in groups or patches in order to
maintain itself at all against the much quicker growing spruce.
Although it yields better fuel than any other species of forest
tree, the wood of the beech is in poor demand as timber for
technical purposes, so that in Britain it will usually only be found
in forests on account of its soil-improving qualities.
Important though the considerations regarding increased annual
production and better quality of timber be, yet the chief advantages
to be gained through the introduction of silver fir and beech are
beyond all question or doubt the greater security afforded to the
spruce in respect to all the dangers and enemies to which this
species is exposed. In localities where spruce can thrive safely
till maturity, measures for increasing the production are hardly of
the first importance, as the returns from pure forests of spruce are
in themselves so good that further outlay for the introduction of a
minor species might often seem uncalled for; but where, as in most
localities under spruce, storm, snow and ice-accumulations, attacks
of insects, fungous diseases especially (Trarnetes radiciperda
and Agaricus melleus), and other dangers cannot be left out
of reckoning, an intermixture of one or other of these species - and
on suitable soils and situations preferably the silver fir, - is in
the highest degree advisable in the light of recent experience
throughout Germany.
On many parts of the northern slopes of the Bavarian Alps, the larch
also occurs as a subordinate species along with silver fir and beech
in spruce forests. Its growth at first is much more rapid than that
of the spruce, and on deep fresh soil the advantage thus early won
is maintained till the sixtieth to seventieth year, or under
favourable circumstances longer, although only too often it is
caught up and overtopped by the spruce. Where the soil, however, is
wanting in depth and strength, or where, as in Britain, both species
are removed far from their natural homes, and cultivated under
conditions in many respects dissimilar from their normal
requirements, it not infrequently happens that the spruce,
stimulated to lively growth in height, catches up the larch as early
as the twentieth to thirtieth year, when nothing remains but to cut
out the latter, and allow the spruce to form pure forest. Even when
the larch has been introduced in patches among the spruce, little
can be done in such cases to protect it, as its further growth is
prejudiced by the side-shade, and it can no longer develop
satisfactorily. As a rule, the larch should only be grown in spruce
forests on parts where the soil is of better quality than the
surrounding ground, and on such patches it generally thrives better
in groups than when planted out alternately with spruce, or only
simply here and there,---although it maybe remarked here that
Burckhardt recommends its being planted out singly only, except
along the edges of compartments where it may form rows or belts. The
groups should not, however, be too large, as otherwise there is the
same tendency towards crooked, sabre-like growth as is.
characteristic of pure larch forest away from its Alpine home.
Experience shows that when grown along with spruce, the larch is
less liable to be attacked by fungous disease (Peziza Wilkommii)
than when it forms pure forest. As a rule large transplants should
be used in introducing the larch into spruce woods, so as to assist
in giving it the greatest possible advantage in growth, - but
unfortunately where roe-deer are maintained, these are specially
sought out by the bucks at the. time of brushing the velvet from the
horns in early summer, and much damage may be caused in this way.
Scots pine is seldom to be found as a minor species on the better
classes of spruce soil, where the preference is usually given to
those others already mentioned; but it forms a valuable associate on
the poorer qualities of soil, and wherever the satisfactory
development of the spruce is likely to prove questionable. The rôle
that it then plays is partly that of a purely subordinate species,
partly that of a nurse or protector. In such cases the object in
view is to raise the spruce in as large a quantity as possible, but
at the same time to have the pine represented to as great an extent
as can be grown along with the spruce, or as is necessary for the
maintenance of closed forest. That, under such circumstances, what
was originally intended as a spruce forest with the admixture of
Scots pine, ultimately approaches maturity as a crop of pine with
admixture of spruce, can easily be understood, as on such debatable
land consideration must be duly given to the factors influencing the
growth of both species at many critical periods of the life-history
of the growing-stock. Any stencil-like regularity and uniformity of
treatment of such mixed crops is out of the question, and it can
only be expected that, with proper and prudent treatment, the mature
fall will consist here and there of spruce with pine, and in other
parts of pine with spruce intermixed. When there is doubt about the
soil suiting the spruce, it is perhaps a good rule always to form
the young crop by means of an equal admixture of both species in
rows or bands proceeding later on with the clearings and thinnings
as may seem advisable each time these operations are under
consideration.
Such cases of doubtful success are just as frequent on the dry
slopes of low hills and uplands, as on the more level tracts or
plateaux. Pure pine forests are often just as much out of the
question as pure forests of spruce, for whilst the latter is slow in
closing up to form canopy, and inactive in growth generally, the
former is apt to become interrupted in canopy at too early a stage
of development, and to fail in affording to the ground the
protection so specially requisite on soils of inferior quality. In
mixed forests consisting equally of spruce and Scots pine, - or of
spruce to half the number, and Scots, black and Weymouth pines
forming the other half, - the best possible attainable results are
perhaps achievable, the ultimate tending of the crop being dependent
on the relative development of the different species. In Hanover it
was usual, at the time when sowing stood in greater favour among
sylviculturists than planting, to mix and sow spruce and Scots pine
seed in the proportion of five to one, the pines being regarded
[solely as nurses, and cut out as soon as they began to
inconvenience the spruce with their shade.
That, in equally mixed spruce and pine forest, the latter often
becomes the dominant species, is due to inefficient tending more
than anything else, for, unless some special attention be paid to
the spruce during the clearings and thinnings, it either remains
dwarfed as underwood, or at any rate has no fair chance of
developing until the canopy of the pine becomes naturally
interrupted. Many mixed woods of this description yield good returns
if the pines are cleared away wherever the spruce shows need of
freer enjoyment of light and air, and stems are left only here and
there on the better patches to increase rapidly in girth over the
well-protected soil.
The oak is not naturally a common associate with the spruce, from
which it differs essentially in many sylvicultural characteristics.
The oak is generally found on the milder situations on plains and
uplands with a long warm period of vegetation, the spruce at higher
elevations and on shallower soils. Still, in many parts of northern
Germany such mixed forests do exist, and are often spoken well of.
Even when oaks are given a few years' advantage at first, they are
soon overtaken and topped in growth by the spruce, unless they are
planted in clumps of considerable diameter. If planted in rows or
small groups, though they may reach the pole-forest stage of growth
evidently thriving and well above the spruce, they seldom maintain
these advantages till maturity, but have usually to be cut out long
before they attain good marketable dimensions.
Softwoods are often found associated with spruce, as nurses where
the reproduction of the latter is difficult, or as protective
standards in situations exposed to frost. But their artificial
production is seldom necessary, as they usually occur self-sown, and
if not, a more desirable substitute for parent shelter can generally
be found in the pine. More frequently they in reality become weeds,
whose coppice-shoots occasion much trouble and annoyance. This is
particularly the case with coppice-growth of the birch, whose long
whip-like twigs damage the leading-shoots of the young spruce
growing around; but where seedlings of birch occur merely scattered
here and there individually throughout spruce woods in places where
late and early frosts are to be feared, their retention till they
are caught up in growth by the spruce, often yields good preliminary
returns as well as useful aid sylviculturally.
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Formation
and Reproduction of Spruce Forests. ---Except at high
elevations, where the ordinary methods of reproduction of spruce
forests cannot be carried out~ and where their profitable working
must be subordinated to the main object of maintaining the
mountain-tops under woodland, there are three distinct forms of
reproduction, all of which are practised in regular annual falls.
These are:
1. Natural reproduction under parent standards.
2.Total clearance in narrow strips, with natural
reproduction from neighbouring woods.
3.Total clearance of annual fall, with artificial
reproduction (usually by planting).
Natural reproduction under parent standards is especially
practicable in respect to mixed crops of spruce with silver fir and
beech, but is, however, also adopted in pure spruce forests on level
soil, where late frosts or attacks of cockchafer grubs (Melolontha
vulgaris) are to be feared on an extensive scale, and experience
has further shown that in forests thus reproduced the dangers from. Curculionidae
are likewise diminished. Other local circumstances must of course be
taken into consideration, and this method of reproduction will often
recommend itself in outlying and sheltered localities, where the
proprietor does not wish to incur the usually moderate costs of
artificial regeneration. The results of natural reproduction under
parent standards are varying. In some situations the parent
standards are not much exposed to the violence of storms, but in
most localities this is unfortunately not the case. The young crop
often varies much in quality; in some situations a moist soil is
favourable to germination and the seedlings stand too thick, whilst
in other places reproduction is slow and unequal, resulting in thin
patches of seedling growth of different ages, necessitating some
artificial assistance, and adding considerably to the costs of
tending later on.
The method of total clearance with natural reproduction from
neighbouring woods, was formerly much more frequently adopted than
is now the case. The fall for reproduction should not be more than
100---120 yards broad, and must of course be so located that the
adjoining mature woods lie to the windward, in order that seed may
be evenly shed over the area when the cones open with dry warm winds
in late spring and early summer. Some measure of soil preparation
for the reception of the seed is absolutely requisite, and when
seed-years turn out disappointing, artificial reproduction or
assistance becomes a necessity to a greater or less extent, as
otherwise a rank growth of grasses and other weeds covers the soil
and shuts out the hope of seedlings being subsequently able to force
their way through these successfully.
The total clearance of the annual fall of the mature crop with
artificial reproduction by planting, is now the usual method of
treatment of spruce forests in Germany. Independent of seed-years,
untrammelled by considerations regarding the protection of standard
parent trees against the violence of storms, and far less threatened
with danger from growth of weeds, reproduction can thus be carried
out quickly and satisfactorily at a moderate cost, whilst the
extraction of the mature timber is easier, and the grubbing up of
the roots less difficult in localities where there is any good
market for fuel. This method has many advantages to recommend its
adoption,---it is an easy system, involving the minimum outlay for
supervision, tending, and ultimate harvesting of the crop, the
annual fall of timber is regular, and varies little in quality or
cubic contents, and the working plan is based on the simplest and
safest of all foundations, viz, equality of the areas (modified
according to their relative productive capacity) from which the
mature crop is annually cleared; it has, however, drawbacks and
disadvantages which have previously been referred to.
In whatever manner spruce forests are reproduced, a general
principle should be followed of not making the annual fall comprise
too large an area, as it is in every way of unquestionable advantage
to have a series of self-contained blocks, each comprising within
itself crops varying from one to eighty or a hundred years, instead
of one large block simply divided into eighty or a hundred annual
compartments or falls.
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Natural
Reproduction.---When reproduced naturally under parent
standards, no preparatory fellings are necessary to stimulate the
production of seed and prepare the soil for its reception. When a
good seed-year seems favourable for reproductive fellings, they are
made so as rather to resemble those in beech and silver fir, than in
Scots pine forests; but on account of the danger from wind the
number of trees left per acre is greater, only from ¼ to ⅓
of the total number of trees forming close canopy being removed, so
that during storms the crowns can afford each other some measure of
support. On moist soil, a lighter disposal of the parent trees would
also favour a rank growth of weeds, which is more prejudicial to
young spruce than even a considerable degree of shade from lofty
standards. The period of reproduction is much shorter than with
beech or silver fir, as the seed-years are more frequent, and the
amount of seed produced greater, besides which the young seedling
growth is not so absolutely shade-demanding as with these other
species. From the pine it also differs essentially, not only in the
more abundant, though not more frequent, production of seed, but
also in that the seed ripens in about six months, in place of being
delayed till eighteen months after the flowering.
The shape that it is advisable to give the area to be reproduced is
dependent on the extent of the danger from wind; the greater the
danger, the more should reproduction take place in long narrow
strips on which the number of trees along the middle should be
greater than towards the edges, so as to ensure speedier
regeneration and earlier clearance of the parent trees, in order to
minimise the damage caused to the ~ seedling growth at the time of
extraction. Where good patches of self-sown spruce occur they should
be retained, but all other species of trees should be cut out. When
practicable, large branches should be sawn off to decrease the
leverage obtainable by the wind, but care should be taken to carry
out this operation during winter, in order to prevent the outflow 6f
sap from the wounds. Whatever soil-preparation can be conveniently
undertaken yields its reward in easier and better growth of
seedlings ; the layer of thick moss should at any rate be removed
with the rake. In Prussia, breaking up of the soil roughly into
clods in bands or strips one to one and a half feet broad and six
feet apart has been found a judicious outlay, the operation being
performed in the autumn of the seed-year.
The clearance of the standard parent trees commences in the winter
of the year following the seed-shedding, and the extraction should
take place, so far as possible, whilst snow lies on the ground, in
order to minimise the injury done to the seedling crop; clearance
must be effected as speedily as possible, as the danger from wind
increases greatly when once this operation has been begun; even in
sheltered localities the final clearance should be completed by the
time the seedlings have attained a height of one foot. Where
reproduction has not been equally and uniformly successful, it is
not advisable to retain the standards; blanks can easily be filled
up by sowing or planting, or an excellent opportunity is thus given
for introducing other species such as silver fir, beech, pine or
larch, whose admixture along with spruce has been shown by
experience to be so desirable for many good reasons. Douglas fir
should also yield good results.
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Artificial
Reproduction and Formation.---During the last century,
sowing was the usual method of forming or reproducing spruce forests
artificially, but towards the beginning of the present century
planting, in place of being confined merely to the filling up of
blanks in sowings, became a rival of the older method, and for the
last fifty years it has been the favourite system. Sowing, besides
not always being so successful, is on the whole not so very much
cheaper than planting that one can afford to overlook the difference
of two to four years' growth won for the future crop when seedlings
or transplants are utilised. But planting of spruce has other
advantages over sowing. Plantations suffer less from rank growth of
grass, run less risk of being lifted out of the ground by frost, and
also suffer less where large herds of deer are maintained, whilst
they can be opened earlier to grazing; they thrive as a rule better
than young crops raised from seed, and can be formed in autumn as
well as in spring.
The material for filling up the blanks in crops raised from seed was
formerly usually taken from reserve plots or temporary nurseries
prepared by sowing thickly in the proportion of about 150 lbs. of
seed per acre actually sown. By the time the seedlings were four or
five years old they could only be used in wisps of three to five, in
place of individually, as they had grown quite entangled, a method
that is even now intentionally practised under certain
circumstances, but which is hardly recommendable, as it renders
subsequent tending difficult, and interferes too often with the
normal development and the early selection of predominating poles.
The distances at which seedlings and transplants were planted out in
the great home of the spruce, the Harz mountains of central Germany,
has varied at different times. At first plantations used to be made
at 2½ feet x 2½ feet, but later on the plants were made to stand
at from 3 feet x 3 feet to 5 feet x 5 feet, the wider distances
being preferred where there was heavy snowfall; recent experience in
Germany has shown, however, that 4 feet x 4 feet is preferable to
any wider distance.
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Sowing.
---Although planting is now generally admitted to be preferable to
sowing, yet under certain circumstances the latter method finds its
proper uses, as, for example, where seedlings or transplants are not
conveniently obtainable, or where the soil is too rocky or otherwise
unsuitable for planting, or when a good market for small material
like pea-sticks can be tapped early and remuneratively. More seed
per acre is used for spruce than for Scots pine, for not only do
fewer seeds go to the lb. (55,000 to 57,000), but a denser crop is
also desirable. As a rule about 10 to 12 lbs. per acre are
used, although this quantity must be increased in proportion to the
magnitude of the danger from drought, weeds, or lifting of the
seedlings by frost. Sowings are less frequently made broadcast than
in rows, or strips, or on small patches, and clean seed is now alone
used, a soil-covering not exceeding a quarter of an inch being
provided by light raking. The operation is carried out towards the
end of April or the beginning of May, as a rule, and only
exceptionally in autumn. Except where rank growth of weeds demands
broader strips the soil is generally prepared
to a breadth of 1½ to 2 feet and in rows 3 to 4 or at most 5 feet
apart; patches are usually 1½ to 2 feet square and about 4 feet
apart. On hilly situations the rows should run horizontally, and not
vertically, to prevent the seed being washed away.
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Planting.
---The best results are obtained with transplants from regular
nurseries, although younger seedlings taken from seeds beds, or
wisps (three to five) from rills in temporary nurseries, also at
times find favour. Plants from two to five years are usually put
out, in preference to yearling seedlings, as the planting of the
latter often costs nearly as much as if two-year-old plants be used,
whilst the results are generally not so good as with these.
Notching, and the use of naked seedling or wisps, are only suited
for the more favourable soils of a light character; on tenacious
soils, or where there is a strong tendency to growth of weeds, this
otherwise cheap and good method is not advisable. In general, too,
this method seems to affect the rootlets of the spruce to a greater
extent than those of the pine, which latter do not so long retain
the flat shape induced by the pressure employed at the time of
planting.
The use of transplants with earth attached is on the whole far more
advisable, and usually leads to better results, than the use of
naked seedlings; and in localities where growth of weeds does not
call for the use of older material, the operations, of transport and
planting can be carried out at a very reasonable rate if the
preparation of the holes on the area to be planted, and the lifting
of the material from the nurseries, be carried out with small
cylindrical spades (Heyer's - These
useful instruments were first, described in a report "On the
Corsican Fir,' printed in the Transactions of the Highland and
Agricultural Society, 1876),
which besides have the additional advantage of rendering too deep
planting impossible,---one of the worst, but most common mistakes
made in regard to the spruce, particularly in tenacious soil.
Planting should take place in spring to as great an extent as is
practicable; but at high latitudes or elevations, or where a moist
soil has first to get rid of some of its superfluous moisture,
autumn planting also yields good results. On windy situations, and
on dry soil, the most favourable time for planting is is spring,
just before the buds flush and form the new shoots. Plantations
formed in autumn are less able to resist the action of frost during
their first winter than those formed in spring, whilst the plants
can more easily be pulled out of the ground by deer.
The best average distance between the plants has been found to be
four feet; whether greater or less distances recommend themselves in
any particular case depends upon local circumstances and on the
funds available, the principal advantages of closer planting being
in the speedier attainment of close canopy and protection of the
soil, in greater freedom from branches, and in earlier returns from
small material removed during the operations of thinning out. When
requisite, it is better to give the individual poles more
growing-space by means of the bill or the axe, than to endeavour to
secure it from the very outset by means of planting at wide
distances; but where there is a poor market for pea-sticks and the
like, and where labour is neither plentiful nor cheap, a preference
will often be justified in favour of somewhat wider planting. Where
the soil is fresh and good, and only sound four to five-year- old
transplants are set out, wide planting at 5 feet x 5 feet should be
sufficient; but care must be taken to fill up any blanks promptly,
as with only 1,742 plants per acre to start with one cannot afford
to lose any prematurely (vide tables on pages 22 and 43). But
where, on the other hand, the soil is dry, or where rank growth of
whortleberry, heather, or other weeds has to be contended with,
considerations as to the speedy formation of close canopy and
suppression of weeds may determine in favour of closer planting, for
2,725 plants per acre at 4 feet X 4 feet effect the purpose much
more quickly and effectually than 1,742 at 5 feet x 5 feet. On dry
slopes, or deteriorated soil, even closer planting is advisable when
funds are at disposal, although a judicious admixture of Scots pine
along with the spruce often leads to the attainment of the object in
view at less cost than close planting of spruce alone. When planted
for shelter, as a protective mantle along the edge of pine or other
forests, they should not be put out closer than five or ~ix feet in
order that the individual trees may develop fully in foliage and be
able to maintain themselves against storm-winds by a free formation
of their' root-systems towards the windward side.
Whether the setting-out of the plants should take place in squares,
or triangles, or rows, is of less importance than the actual number
of plants per acre; practically, planting in squares is the usual
method adopted, although in situations where plantations are liable
to suffer from accumulations of snow or ice, planting in rows of 6
feet x 4 feet, or 6 feet x 3 feet are said to yield the most
satisfactory results. Close planting increases the danger from snow,
whilst ice causes most breakage when the individual plants have a
fair amount of free growing-space.
As previously remarked, notching is not so well applicable to the
spruce as to Scots pine, but recommends itself on account of its
cheapness wherever the nature of the soil is suitable. The usual
methods adopted are planting by means of Heyer's cylindrical spade
for one and two- year-old seedlings and three-year-old transplants,
and pit-planting,---or on wet soil, tumping or planting on. mounds
--- when older material is put out.
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