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•entering into intimate union with the roots of mountain pine are, according
to Melin, the same as those which occur on Scots pine, and no such stimulating action on spruce is claimed on behalf of that species. Mountain pine, therefore, must exercise its influence through some medium other than that of free
nitrogen fixation.
The above notes, though brief, represent, in the writer's opinion, the salient
points of a paper which is replete with information of the utmost value, not
only to the investigator into problems connected with tree growth and development, but also to the silviculturist.
A Note on Hesselman's 'Barrskogens Humustacke' (Study on the
Humus Covering of Coniferous Forests, their Properties, and their
Relation to Silviculture), {Report of the Swedish Institute of
Experimental Forestry, 22, 1925.)
By G. K. FRASER.
' I 'HE problem of the classification of soils and estimation of site-values is
JL always of considerable importance and, at the present time to a marked
degree, is occupying the minds of most soil investigators whether in agriculture
or in forestry.
In this country only a commencement has been made in systematic grouping,
but abroad a fair degree of progress has been made. This progress has followed
the investigation of wide stretches of land of regularly varying topography and
causal conditions (climatic,&c), and has led to the grouping of soils into a comparatively small number of what may be described as climatogenic soil groups
of world importance; the fundamental theory underlying the classification is
that soil type is produced predominantly, if not entirely, by climatic conditions,
whatever be the nature of its geological base, if a sufficiently long time is given
for the action of this climatic process. Along similar lines has been developed
in Finland, by Cajander,the well-known system of assessment of quality classes
by what is termed the Forest Types (Waldtypen) method, a system which may
be justly considered the natural development of the principles ofvegetational
ecology applied to regularly varying habitat conditions by the silviculturist.
Into the broad issues of the question of principles of classification involved
it is not advisable to enter here, although both systems may be attacked on these
grounds, but our main objection to both systems is that their chief scope lies
in world classification or at least classification of wider areas than most soil
workers can become familar with, and that the application of either Glinka's
Soil Classification or of Cajander's Forest Types to a limited area such as
Great Britain must necessarily result in confusion and mistake, even although
one admits the fundamental utility of both.
These reflections are suggested by the perusal of a paper bearing the above
title published by Hesselman in the Reports of the Swedish Institute of Experimental Forestry (summary in German). Hesselman is not only convinced that
Cajander's 'Waldtypen' cannot be applied to Swedish forests, but also that it
is quite misleading; and he has produced good evidence for his assertions. We
feel that his results may be equally well applied to Glinka's classification of
soils in its application to conditions in this country as well as in Sweden.
There may be no doubt that, as Cajander maintains, 'in a Forest Type,
therefore, as a rule, only those primary—climatic and edaphic—factors of
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121
locality are reflected, which may be assumed to remain active even when the
locality is laid bare of all plants,' but the crux of the question is really not
whether those factors 'remain active' but whether those factors exert their
activity along identical lines or such similar lines as to obliterate for all practical
purposes the effects of vegetation, crop, method of treatment, and so on. It
seems that there are too many large assumptions—Glinka assumes that all types
of humus are (or will become under identical climatic conditions) the same,
Cajander assumes that the effects of all types of vegetation, &c, upon climate
are similar. Hesselman shows that both assumptions are invalid.
This paper is a continuation of earlier work into the nitrogen economy of
Swedish forest soils, wherein the importance of nitrogen metabolism in the soil,
as a factor of soil fertility, was fully demonstrated. From this it was concluded
that a fuller knowledge of the properties and effects of acid types of humus
must be obtained in order to place soil fertility problems on a more exact basis,
and to classify the relationships of methods of practice to soil improvement.
Comparing Swedish soils with those of Central Europe Hesselman concludes
that whereas the fertile mull type ofhumus (with 'brown earth' soil) is the characteristic soil covering of Central European forests, raw humus (with 'podsol') is
the characteristic Swedish Northern type, a type considered a 'pathological' type
by German foresters, probably the result of inefficient silvicultural operations.
Can the podsols of North Sweden be changed into mull types ?
In the first instance it is shown that topography may have a determinant
importance in the soil itself apart from—in fact opposing—topographically
determined climatic variation. For example, the downward percolation of
lime-laden water from higher to lower levels in a sloping surface, removing
acid constituents as well as neutralizing these, produces in place of raw humus
a mull type of soil bearing a vegetation which possesses constituents found in
areas where the mull type is general, upon drier rather than wetter soils; that
is to say, a dynamic process conditioned by topography may produce results,
so far as vegetation is concerned, equivalent to a static climatic condition
totally different in its outward appearance.
Examples are also given where under different climatic conditions different
or indeed diametrically opposed methods of silvicultural treatment must be
used to obtain a corresponding result; for example, under the Atlantic climate
of the Black Forest clear cutting is followed by rapid formation of raw humus,
invasion of heath sub-shrubs, and soil deterioration; in the Norrland area
(Sweden) with a continental climate raw humus is general in the old selection
forests, but disappears on clear cutting, the warmth of the summer being
responsible for the more rapid decay of humus; again, at higher elevations in
Sweden, where high rainfall occurs and temperature is lower, raw humus occurs
both in close and cleared conditions, and drastic operations such as burning are
necessary to remove the raw humus so. as to obtain natural regeneration. The
operation, successful in one case, is directly injurious in the second and ineffective
in the third; silvicultural method of treatment is sufficient to determine quality
of locality against the tendency of climate and soil in some cases but not in all.
Reference is also made to soil flora and fauna in relation to their effects on
humus covering and this might be extended to vegetarian fauna and their relation to vegetation and hence to the soil.
Apart from the concluding descriptions of the areas investigated the main
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portion of Hesselman's paper consists of a large series of determinations of the
reactions and of related data of these forest soils, their humus, leaf-litter, &c,
and of the connexion existing between these and soil type, soil nitrogen metabolism, and general fertility. On the whole a case is made out for. a general
inverse causal connexion between acidity and available nitrogen in the soil,
but acidity may be due to different fundamental causes producing different
effects in this and other respects. Very striking are the differences shown in the
leaf-litter, humus, and hence soil under different species of trees and ground
vegetation, e.g. birch, pH = 5-3-6-1, beech 5-3-6-6, conifers about 4, &c,
reaction in each species varying somewhat from place to place. Considerable
stress is laid upon the presence in leaf-litter and humus of buffer-bodies
(Tufferstoffe5) which under given conditions tend to retain their acidity and
to intensify acidity, these occurring to a marked degree in species of plants
which have been considered liable to show (or cause) soil deterioration, e.g.
pines, heath plants, Sec. Plants in which the buffering agent has a reaction of
a more favourable type, such as birch, beech, and broad-leaved trees in general,
counteract this acid-buffering and in turn tend to impress their reaction upon
the soil; e.g. a mixture of pine and birch upon a given soil produces better soil
conditions than a pure pine forest does, owing to the action of birch leaf-litter
in reducing the acidity, and so with any of the broad-leaved trees. In other
words the forest type is influenced in a very definite way by the artificial introduction or natural occurrence of broad-leaved 'soil improvers' in a coniferous
crop—reference is of course made to beech in this connexion as the 'Mutter des
Waldes' in the eyes of the German forester.
All the implications of Hesselman's paper cannot be touched upon, but the
points mentioned indicate its value and great interest; it may not contain a
great deal which will modify practice but it places, amongst other things, the
necessary practice of including 'soil improver' broad-leaved species in a coniferous crop on poorer localities upon a more satisfactory scientific basis than
has hitherto been set forth; it emphasizes the danger of the direct application
of insufficiently understood silvicultural systems or methods from one climatic
or edaphic region to another, only because successful in the first instance; it
clearly shows that the application of vegetational ecology to the silvicultural
determination of quality of locality must be undertaken with caution, especially
with regard to exact numerical evaluation, since a vegetational or forest type
is not such a definite and invariable entity in fact or under artificial treatment
as it tends to become in the mind and with limited outlook or experience; and
finally, as the author indicates, it points the way to further investigation and
comprehension of the interrelations of soil and crop.
1. Aims and Methods in the Study of Vegetation, edited by A. G.
TANSLEY and T. F. CHIPP, 1926.
2. The Theory of Forest Types, by A. K. CAJANDER, Helsinki, 1926.
A Note by A. S. WATT.
i p H E natural order is not necessarily the order in which things are studied.
JL Man has used what lay to his hand without staving his action to consider
causes and consequences. Indeed consequences have in many cases directed his
attention to values hitherto unsuspected or ignored. For example, Palestine,