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By William Gilchrist, Cluny
Castle, Aberdeen. [Premium—Five Sovereigns.]
As a general rule, soils
and subsoils that are considered suitable for growing the various species
of forest trees are those that are unsuitable for agricultural purposes,
consequently trees are often planted in soils and subsoils quite
uncongenial for their growth and development. Although there is no doubt
that soil and subsoil exercise a considerable influence on the development
of trees it is not altogether paramount, as, however suitable they may be,
if the exposure is too severe, or the altitude too high, the trees will
not succeed. Altitude and exposure must, therefore, be taken in connection
with soil and subsoil, as suited for the growth of timber trees. Altitudes
are generally described as low, medium, and high—low being under 350 feet,
medium from 350 to 800 feet, and high from 800 feet upward.
In describing the different
soils and subsoils we lay no claim to a scientific knowledge of the
subject, but simply base our report on practical experience and
observation. Relying on this basis, the chief difficulty is to get
examples alike in every respect, as almost every situation has some local
peculiarity that, in some way or other, tends to stimulate the growth of
trees. In some parts of the country the soils are so variable that it is
often difficult, without a chemical analysis, to distinguish between peat
and loam, the one running so much into the other; and there is no doubt
that many of the inaccurate statements, regarding the suitableness of
certain soils and subsoils for the development of forest trees, may be
traced to this cause.
1. Peat.—This is generally
understood to be the natural accumulation of vegetable matter on the
surface of waste lands, and is always more or less saturated with water.
Considered as suitable for the growth of wood, it must be divided into two
distinct classes—first, the natural accumulation of wooded vegetable
matter; and second, the natural accumulation of succulent vegetable
matter. The former of these is generally suitable for growing wood, while
the latter is only occasionally, and under special circumstances, fitted
for that purpose.
1st, Brown peat, with an open subsoil on the granitic formation. This is
the prevalent soil on hill sides and moorland that is covered with heath.
It is well suited for the growth of Scots fir at low and medium altitudes.
In many cases the Scots fir produces good timber on this sort of soil at
altitudes ranging above 1000 feet; but these are exceptional cases, and
are generally found to be in sheltered and otherwise favourable
situations. The quality of the timber on this sort of soil depends
entirely on the depth of the soil and the openness of the subsoil. If the
peat soil is deep the young trees succeed very slowly for a number of
years, until their rootlets get through into the substratum, after which
they grow more rapidly; but at the best the wood is soft and rough in the
grain. When the trees are cut down the concentric rings for the first
fifteen or twenty years are found to be comparatively small, after that
period they gradually increase. When the soil is shallower the trees grow
more equally throughout, provided always that the subsoil is open, and are
smaller in the grain, and the timber of superior quality. When in a young
state they generally grow with a good deal of taper; but with a medium
altitude and a suitable situation they will, at the age of sixty, have
from 30 to 35 feet of bool, and average about 10 cubic feet. Some of them
will be considerably larger, but in all plantations of that age there is a
certain amount of spar-wood, and sometimes even props, which take down the
average size. This
variety of peat is also very suitable for birch and plane, especially the
former, which in many parts of Scotland grows naturally on soil of this
description. Still, although the birch is a graceful tree, and a rapid
grower at low and medium altitudes, and on soil and subsoil most suitable
for its growth, it is not to be compared, as a profitable tree, with the
Scots fir, and should never be planted for profit except at high altitudes
and hill sides, where, owing to the severe exposure, Scots fir does not
succeed. We have never met with any large quantity of plane trees growing
on this sort of soil, but, judging from what we have seen of it in mixed
plantation, as also in groups and single trees, there is no doubt that the
soil is suitable for its growth, especially over whinstone formation at
medium altitudes. At
low altitudes this soil is also suitable for the growth of spruce in
masses, and where a good demand exists for spruce it is a remunerative
crop. When grown singly or wide apart they are, in general, very rough and
branchy; but when grown in masses they are the reverse, and are very
suitable for many country purposes. Willows and alders may also be grown,
but the former almost invariably gets stagheaded when about forty years
old, and the latter is not a profitable tree at the best. It may, however,
be grown as copse wood with advantage.
On low altitudes this sort of peat generally
requires to be regularly drained from 2 to 2½ feet deep; but on medium and
high altitudes it seldom requires to be close drained, except where the
formation is flat.
2d, Peat containing a proportion of sand, and resting on a clayey bottom.
This, at low and medium altitudes, will grow oak, lime, and elm to fair
sizes, but not so profitably as it would Scots fir, spruce, and larch. The
latter often succeeds very well and grows to good sizes on light soil,
provided it has a cool subsoil such as referred to. What a number of
contract planters call "fern ground" comes very near to this description,
and it is invariably selected by them as a soil suitable for the growth of
larch. No doubt, it is also quite suitable for the growth of the other
trees mentioned, but larch is the most profitable and remunerative crop
when the situation is suitable. The timber, when matured, is generally
clean grown, with very little taper; tough, but only a small proportion of
heart-wood, as compared with larch grown on heavier soils. Elm grown on
this soil is soft and open in the texture, and more brittle than when
grown on stronger soil. The same remarks apply to the ash; and a strange
coincidence is, that both shed their foliage from ten to fourteen days
earlier, when grown on peat soil, than they do on loam,—especially is this
the case if the bottom is damp. On peat soil the timber of the oak—even
the heart-wood—is brittle, soft, and open, with a comparative small
proportion of heart-wood. The bark is also more corky, and does not
contain the same percentage of tanning properties. However, the soil is
quite suitable for its growth; and where it is desirable to grow oak as an
ornamental tree, or for variety, a peat soil with a proportion of sand
need not be considered any drawback; but it cannot be grown profitably on
such soil. The lime
tree and willows (Huntingdon and Bedford) also grow to fair sizes on this
soil, but in general they are very branchy, except when they have been
artificially pruned. The former is the most suitable tree for the soil,
although the willows at from forty to fifty years old are the most
profitable, especially when grown at low altitudes. One of the chief
drawbacks to growing willows on this sort of soil is their tendency to be
blown over. Thorough drainage, so as to allow the roots to get down into
the subsoil, is the only remedy. Of course, the tops can be lightened, but
that is taking away the vital energies of the trees, and besides, the
remedy is only temporary. The poplars do not succeed so well as the
willows, and are liable to all their drawbacks, although they are often
planted, and sometimes even grow to fair sizes. At low and medium
altitudes the Norway spruce can be grown profitably on this kind of peat,
especially on the former and in sheltered places. In such situations
spruce is one of the most profitable crops that this soil will produce.
The Abies Douglasii, also grows in similar situations, at least to a
certain age, but of course it is of too recent introduction to form a
positive opinion as to the soils on which it will succeed; but in a young
state, it promises well.
If the altitude is high and the situation
exposed, this sort of soil and subsoil is best suited for growing Scots
fir, and they will be found to be as safe and as profitable a crop as the
soil can produce. The quality and durability of the Scots fir is much
improved by a proportion of sand amongst the peat, especially if the
subsoil be granitic. If on a limestone formation, the Scots fir is of a
branchy habit, and the timber rougher than when on granite. They grow
rapidly up to a certain stage, when they generally branch off into
numerous leaders and get flat-headed. The stage at which this appearance
occurs depends on the depth of the subsoil, as it is generally allowed to
be caused by the roots coming into contact with some substance
antagonistic to their development. Under the same circumstances, larch,
besides losing their leaders, are affected with blisters and ulcers, and
when such is their state, it is considerably reduced in value, and as a
profitable crop is a failure. The hardwood stated as suitable for growing
on a granite formation is more suitable for growing on a limestone
formation under similar circumstances; thus showing that on the granite
formations the fir tribes are the most suitable, while on the limestone
formation the planter can have a wider choice.
3d, Peat of various depths, but generally
shallow, with a moorband pan and hard subsoil, is very common in some
parts of Scotland, especially on flat moorland. The soil is invariably wet
on the surface, and in its natural state is quite unsuitable for the
growth of trees. If thoroughly drained and the pan broken, Scots fir and
spruce will grow on it to be a fair average crop. Unless thoroughly
drained, the trees either die off young or get twisted into all
conceivable shapes, and never attain to anything like timber proportions.
The spruce is only suited for growing on low and medium altitudes, but the
Scots fir will grow on either. Birch will do the same; but as mentioned
before, it is not so profitable, and should only be grown where variety is
wanted. 4th, Deep
black peat, such as is generally used for fuel, is not suitable for the
growth of trees under any circumstances; still, if it can be got
thoroughly drained and a portion of the subsoil spread over the surface, a
fair crop of spruce may be got to cover the ground; but unless the roots
can get through the peat and into the subsoil, this sort of peat will not
grow a profitable crop of trees. Some good crops of spruce and Scots fir
are grown at low and medium altitudes on peat where the great proportion
has been cast off for fuel, and only about one foot in depth left for
surface; and where this is practicable, it is the safest way to secure a
crop. Under such circumstances, neither the spruce nor the Scots fir grow
to a large size, and at from fifty to sixty years old they may be
considered at their best as a crop.
5th, Peat on a soft tilly or "boiling" clay
bottom is unsuitable for the growth of trees, especially if the "boil" is
near the surface. If there is as much surface soil as keep down the soft
clay, any of the surface-rooting varieties may be grown, but they never
grow to great dimensions, and are liable to be blown over at all stages.
If the "boiling" clay can be got under by drainage the case is different,
and wood may be grown profitably; but it is of the utmost importance that
the drains should be kept at all times clear and in good working order.
Spruce and alder are the varieties that will succeed best. The former is
the most profitable, except in districts where a demand exists for alder.
6th,. Bog peat, or the natural accumulation of
succulent vegetable matter with a soft bottom. This, in its natural state,
is the most unsuitable of all for the growth of trees. Still, if it is
desirable to grow trees or shrubs, it can be made suitable by thorough
drainage, digging over and exposing the peat to atmospheric influence, and
adding sand. Treated thus it will grow good spruce, alder, and lime.
Taking everything into account, it cannot be said that the undertaking
would be profitable; but circumstances might arise where it would be very
desirable to have such ground occupied, or partly occupied, by a crop of
trees or shrubs and treated in the manner indicated; this has been
accomplished at low altitudes.
2. Loam is a soil consisting of clay, sand,
and oxide of iron, with more or less of chalk. The qualities are various,
from a light sandy loam to a heavy clay loam. If the subsoil and situation
are suitable for growing trees, all the different qualities of loam are
found to be adopted for the growth of some of the ordinary varieties of
forest trees. 1st,
Light loam on a sandy or gravelly bottom. This is a likely soil for the
growth of trees, and yet there is perhaps no soil so unsuited for the
profitable growth of the trees that are generally found growing upon it,
especially larch; and it js a matter of surprise that, with so many
examples of failure, arch is still persistently planted on such soils.
Even when they grow to fair sizes and present a fair exterior, we have
found upwards of three-fourths of them to be unsound at the root, and
consequently a great portion of the root comparatively useless. This
heart-rot is found to begin at an early period; and if larch is to be
grown profitably on this sort of subsoil, they must be cut at an early
stage for props and spars. During the summer of 1868, on such a soil and
subsoil, in a mixed plantation eight years old, most of the larch and
poplars died out; while the Scots fir, Laricio, Austrian pine, and plane
stood apparently unscathed. The birch and beech were seriously checked,
and have not yet recovered from the effects, but have still a languid and
sickly hue. The larch were taken out and the blanks made up with Austrian
pine, and they have stood the test of 1874. The plantation referred to is
at a medium altitude. Scotch fir grown on this subsoil wants the dark
green foliage that it has on heavier soils, and does not grow so tall, but
the timber is generally pretty clean and of fair quality. The Austrian
pine and Laricio do not change so much in the colour of foliage, and grow
more freely; but we have not seen any of their timber cut up into
scantling. Larch generally grows pretty freely up to thirty or forty years
old, when it invariably begins to have a sickly appearance, becomes
shorter in the foliage, and sheds its foliage from ten days to a fortnight
before trees grown on heavier soils. Beech are generally short in the
trunk, with scraggy, spreading tops, and of little value as timber trees.
Birch and plane do not lose much of their ordinary habits, only they are
of a great deal smaller dimensions than when grown on favourable soils. If
the subsoil is damp, although of sand, it is more suitable for the growth
of trees. Instances of this are invariably met with in plantations with an
undulating surface, where, on the dry subsoil of the heights, the trees of
all varieties are a great deal smaller than those in the hollows and low
portions of the ground,—the only perceptible differences as to soil and
subsoil being that the latter is more moist in the hollows. Of course,
shelter must not be lost sight of; but all the difference cannot be
attributed to it. This damp subsoil must not be considered as opposed to
drainage for plantations, or apologising for stagnant water, as no soil
that is surcharged with water is suitable for the growth of trees. On the
other hand, where the water percolates freely through the soil and
subsoil, it is not as a rule injurious to the growth of trees, but rather
favourable. Under such circumstances, larch is the most profitable tree
that can be grown, provided the altitude and situation are such that it
will not be liable to be damaged by spring frosts. In inland districts the
larch suffers most from frosts on southern exposures, and at altitudes
ranging from 300 to 450 feet. In such situations, the crop should consist
of two-thirds larch and one-third of Scotch fir, plane, oak, or beech, for
all of which the soil and subsoil referred to is suitable, at altitudes
not exceeding 1000 feet; above that altitude, the Scotch fir alone is most
suitable. 2d, Light
loam, with a hard clay or gravelly and clay subsoil, on a granitic
formation, and at low and medium altitudes, is well suited for growing
silver-fir, lime, plane, and beech. Scotch fir and larch are also often
grown—in fact, commonly grown; but on this soil the Scotch fir does not
produce the same quantity of timber as the silver fir; and the larch only
succeeds for about fifty years, when it is very frequently affected with
heart-rot. On such a subsoil as this, very fine silver firs, plane, and
beech have been grown at medium altitudes. Compared with the spruce,
Scotch fir, larch, oak, and elm growing in the same plantation, the silver
firs were much healthier, and contained at least one-third more timber
than the other varieties; while the plane had grown as rapidly as the
beech. The same sort of soil and subsoil, over limestone or whinstone
formation, is best suited for the growth of oak, plane, elm, ash, larch,
and silver fir, provided the ground is naturally dry, or has been
previously drained. Under such circumstances the oak continues to grow
rapidly, until the hard subsoil becomes too hard for the roots to
penetrate, when its top loses the leading shoots, and becomes more bushy,
and its growth as to height is generally at an end. The wood is, however,
tough at all periods of its growth; but in general it is from sixty to
seventy years old before much heart-wood is formed. On heavy loams, over
limestone, we have seen large oaks with only one inch of sap-wood; while
on light loams we have often seen the very reverse. Plane trees are more
surface rooters; consequently they are not so much affected with the
quality of the subsoil, provided the soil is deep enough; but on a light,
shallow loam, they are invariably of small dimensions, unless they are
supported and derive nourishment from the subsoil. Elm and ash grow
freely, especially in glens or hollows; but neither of them attain the
same size as they do on heavier soils. The ash is, however, generally of
good quality. Larch is not so much affected with heart-rot on the
limestone as it is on the granite ; but it grows with more taper, and is
shorter, and is very frequently affected with blisters. The silver fir
grows freely on booth, and the difference is not so perceptible.
3d, Medium loam, of good
depth and open subsoil. This variety of soil is well adapted for oak,
elms, and planes, as also most of the newer conifera3, at low and medium
altitudes. On this soil the plane grows to great size, and being generally
sound, commands a high price. In fact, for some years back, good plane
trees of large size have been about the best selling of our home wood. On
deep loams they are proportionately larger in size; but we have not been
able to detect much difference in the quality of the timber. Elms also
prefer a deep loam; in act, the deeper the soil the larger is the elm,
both Scotch and English; but both require a considerable amount of shelter
to produce good timber. In exposed situations both varieties are
frequently affected with ring-shake, which is sometimes aggravated by
heart-rot. When such is the case, the value of the timber is considerably
deteriorated. This sort of soil is also well suited for growing larch,
limes, chestnuts, and in fact almost all the ordinary varieties of forest
trees ; but larch, and the kinds first mentioned, are those that are
considered to be the most profitable, except at high altitudes, when the
Scotch fir must be preferred.
4th, Medium loam, with a clayey subsoil, in
glens or sheltered places, is the most suitable for ash. In such
situations, it is the most profitable tree that can be grown, as, besides
producing a heavy crop if allowed to grow to maturity, it yields a fair
revenue during the whole period of its growth, young ash being in great
request at all stages. When grown on the granite formation, the wood is
more brittle and shorter in the grain than when it is grown on limestone ;
but a clayey bottom is preferable to either. As an ornamental tree, the
ash grows well at high altitudes and in exposed places; but under such
circumstances, the trunks are invariably short and rough, and consequently
the wood is not of so much value as when grown on suitable soils and under
favourable conditions. This sort of soil is also suitable for oak, plane,
Spanish chestnut, black Italian poplars, beech, elm, silver birch, and
Scotch fir; and, at low altitudes, spruce and willows. In fact, this is
one of the soils in which there can scarcely be a mistake made in
selecting suitable trees, as, under ordinary circumstances, it will grow
to fair dimensions all the common varieties. Of course, there is a
difference as to the value of crop; but there is no doubt that the ash,
plane, black Italian poplar, larch, silver and Scotch fir are the most
remunerative. Poplars and larch being the most rapid growers, attain to a
large size on this sort of soil when about fifty or sixty years old.
5th, Heavy loam or clay. This is most common
at low altitudes. Oak, ash, elm, and plane are the varieties most commonly
met with on this soil, and they all grow to fair sizes and are of good
quality, especially the oak and ash, many fine specimens of which are
growing on clay soils, and often under very adverse circumstances as to
situation. However, as a profitable tree for the growth of which this soil
is suitable, the black Italian poplar is the best. It generally contains
as many cubic feet of timber at 50 years old as the oak does at 100 years,
and the price of poplar per cubic foot is sometimes as high as the oak,
but in general it averages about one-fourth less. Owing to the branches of
the poplar being wide-spreading and brittle, they are often damaged with
the wind when grown in exposed places; but being free and rapid growers,
they soon recover their appearance. When grown among other trees the
poplar soon overtops the whole, and it is therefore more suitable for
growing in masses than in mixed plantations. To plant this sort of soil
successfully, good-sized well-rooted plants must be used, as small plants
are always stiff to grow on clay soils; but when once they are fairly
established, they grow rapidly.
6th, Sand. Until recently sand was considered
to be unsuitable for the growth of anything but bent, but the success that
has attended the planting of the Culben Sands, in Morayshire, has proved
that sand is capable of growing a fair crop of Scots fir. The Pinaster
also grows well on the Continent on sandy soils, and there is no reason
why it should not be considered as suitable in this country. The
successful growing of Scots fir on sand has been attended with a good deal
of expense, but the results have been very encouraging, and such as ought
to induce the proprietors of such lands to turn them to some better
account than lying waste, exposed, and carried away by almost every wind
that blows.
Conclusion.—Such is a description of the soils and subsoils suited for the
various species of forest trees, coniferous and hardwood. The conclusions
arrived at are the result of careful observation of the different
varieties of forest trees under all circumstances. More species could
easily have been enumerated, but our study in this report and our object
in daily practice is to recommend the varieties from which the largest
amount of revenue can be obtained, coupled with the varieties for the
growth of which the soil and subsoil is most suitable. We feel that had
the nature of the different soils and subsoils been more scientifically
described and designated, this report would have been more interesting and
readable to the savans of the Highland and Agricultural Society; but we
believe that the soils and subsoils, along with the altitudes and
situations as described, will be understood by the greater part of those
who are interested and engaged in the planting of forest trees, or the
management of plantations and wood lands. |
