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Sustainability of Forests
Written by Linc on Tue Aug 18 18:36:09 1998 GMT
Came upon this and thought it was worth posting. - Linc
Sustainability of Forests: An Attempt at a Biological
1992 Professor Dr. Peter Schutt
A couple of years ago, the term "sustainability" was introduced
environmental discussions, and it is still in fashion. Meanwhile,
been discovered and utilized by several disciplines, which,
do not always give it the same meaning. I think this is reason
to invite you for a short analytical excursion.
As a matter of fact, sustainability is not a recent neologism. To
knowledge it was first used by foresters. In the 18th and early
century, after a long period of plundering the Central European
resources, a new system of forest management was created, called
"Schlagweiser Hochwald". It was based on harvesting old growth
forests through clearcutting to the same extent that new wood was
formed by growth processes.
In a rotation period of 100 years, a quantity of timber equivalent
1/100 of the total volume is cut every year. By this procedure
permanent economic use of the forest is guaranteed. Foresters
it "nachhaltige Nutzung" (sustainable use) or "Nachhaltigkeit"
(sustainability). So, in its original forestry meaning and in its
practical application, the term sustainability has to be understood
an economic concept. A priori it has little to do with biological
In order to bring these two terms into congruity--I mean so that
permanent economic success would run parallel to the entirety of
biological system--it is necessary to fulfil a number of important
KEYWORD NO. 1: CLEARCUTTING
Per definitionem sustainable forests are originally based on
repeated clearcuttings, followed by artificial reforestation with
species of economic importance. No doubt, the system has many
technical and organizational advantages. In the course of time,
however, soil scientists and ecologists found out that the practice
clearcutting automatically leads to considerable drawbacks:
- Wounding of soil surface through logging operations. Risk of
- High irradiation and higher climatic extremes alter the
the flora and microflora, and deteriorate the growing conditions
number of valuable tree species. Soil compression and a reduction
species richness occur. - An accelerated decomposition of organic
matter occurs, combined with a wash out of nutrients and the
eutrophication of groundwater, rivers and lakes. - Mycorrhiza-fungi
partners in an important symbiosis with tree roots disappear within
less than a year.
Altogether, clearcuttings obviously have economic advantages, but
they are burdened with ecological and biological risks, especially
Clearcuttings are not allowed at all in Switzerland and they are
permitted up to a size of 1 and 2 hectares respectively in Germany
and Austria. The reason: they influence biological sustainability
negative way. It is internationally known that large clearcuttings
reduce soil productivity, disturb the balance within forest
ecosystems, and via afforestation diminish biodiversity.
KEYWORD NO. 2: ECOSYSTEMS
Ecosystems are often defined as a kind of biocoenoses--in other
words, as associations of plants, animals and microorganisms, which
live together in a given area, always in close contact with each
influenced by volatile, fluid or solid metabolic substances, which
stimulate or inhibit, can act as antagonists or synergists, and
are ruled by the chemical and physical conditions of the soil and
The number of biotic inhabitants is far beyond our imagination. The
same is true of the possible interactions. What we know, however,
that this complicated and reactive accumulation of mutual
dependencies is very flexible and finally has the effect of a
system which protects the given forest as an ecosystem.
One prominent example may demonstrate how far-reaching the
consequences of inter-specific interactions in forest ecosystems
be. I am talking about mycorrhization, a symbiosis between
soil-inhabiting fungi and the feeder roots of forest trees, which
considerable benefit to both partners. The fungus earns
carbohydrates which he is not able to produce himself. The
and water-absorbing root surface of the tree is enlarged up to
hundred fold by fungal hyphae. Consequently the water and nutrient
supply of the tree increases. Moreover the susceptibility against
attack by root pathogens is considerably reduced, and finally,
are indications that heavy metals are hindered from invading the
On the other hand, a weakened tree-partner occasionally may
become subject to pathological attacks by his own fungal symbiont.
Forest ecosystems are characterized by a high degree of stability.
They can lose single biotic components without running into
imbalances. Diversity stands for stability. By the way: an almost
world-wide disease syndrome is sometimes defined as a toxification
forest ecosystems--not by politicians, however.
KEY WORD NO. 3: BIODIVERSITY
Biodiversity in the sense of species richness is accepted to be a
valuable indicator of stability in ecosystems. If this is so, then
forests would be more sustainable than artificially established
monocultures, and tropical rainforests should be more stable than
relatively uniform boreal conifer forests near the Arctic Circle.
the first relationship has been proven to be true many times, the
second conclusion cannot be correct, because comparisons like
these ought to be made on the same climatic and edaphic base.
Monocultures are defined as plantations comprised of even-aged
plants belonging to the same species. For economic reasons they
have often replaced natural mixed forests of higher
during the past two centuries. In these cases the negative
consequences of clearcutting, of disturbed ecosystems and of
reduced biodiversity, have most probably led to a decrease in
biological sustainability, but not necessarily already to a
In agriculture, crop plants are cultivated almost entirely in
monocultures. Agricultural plants have long since been selected and
crossbred by man, with the consequence that these species became
more and more uniform genetically. This is not the case with tree
populations which are still to a high degree heterozygous. And
heterozygosity is, to a certain degree, identical with genetic
So trees from natural populations have, so to speak, a genetic
potential large enough to adapt to a certain change of environment.
This statement, of course, has a direct connection with biological
sustainability, but it is restricted to natural populations. Even
are, to a certain extent, influenced by anthropogenic stress
(like air pollution) which reduce the gene pool of forest stands,
according to the results of recent investigations and genetic
in beech and spruce.
In general, genetic uniformity within a population means that its
stability and productivity will be at risk when the environmental
conditions change, or when new types of pathogens appear. In this
case the reserve of genes necessary to produce new, better adapted
progeny has become too small.
There are numerous impressive examples of sudden breakdowns of
high production cultivars of corn, potato, wheat, poplar, and pines
a single mutant of a pest or a disease. This is why plant breeders
around the world try to preserve germ plasm and biological
for future food production.
Replacing natural forests with modern plantations of fast- growing
trees therefore creates a number of important genetic and
risks. This is especially the case in the tropics:
- An indigenous well-balanced multifactorial forest ecosystem with
high buffering capacity against biotic and abiotic stress-effects
disturbed. Many species become extinct. The new monoculture,
separated from its natural environment, needs time to adapt. Life
structure of the soil is altered, the original vegetation and flora
disappears, and the risk of erosion increases.
- The broad genetic base of the ecosystem, in which the presence of
many species minimizes the risk of disturbance, has been replaced
the much smaller gene pool of one single species--possibly by a few
clones of this species. This kind of plantation is a vulnerable
endangered by losses due to pests, pathogens and abiotic stresses,
and is often detrimental to landscape and biology. A re-
of the original forest vegetation will at least be complicated and
Under these conditions, biological sustainability tends toward
spite of that, an economic profit may be available for a couple of
years. This, however, has little to do with sustainability.
Let me try to give a short intermediate summary. With respect to
forests, the term sustainability can have a traditional economic
biological meaning. In the long run, both types have to be
a forest ecosystem shall remain alive, and remain productive and
flexible enough to withstand biotic and abiotic stresses.
Several ecological, biological, and genetic suppositions have to be
fulfilled to reach this aim.
In general, natural populations not only express higher stability
do monocultures and clonal plantations: they also have a much
adaptability to environmental changes, for instance to global
warming, and they obviously rank first in biological
At present, two cases of large-scale deforestation have induced hot
discussions in many countries: - the destruction of tropical
rainforests. - the overuse followed by transformation of natural
into monocultures in North America.
With respect to sustainability, these events can be looked upon as
Tropical rainforests are characterized by a tremendous richness of
species--plants, as well as animals and microorganisms. Up to 500
tree species grow on a hectare. This means strong competition
between species and individuals, but also an enormous degree of
biodiversity. As a consequence, there are no diseases or pests
threatening the system. The biological sustainability is evident.
the existence of this almost ideal ecosystem is very significantly
correlated with one important presupposition: the nutrient cycle is
to be altered. What does this mean?
The majority of tropical rainforests grow on poor soils, with a
small reserve of nutrients bound to the soil. The greatest quantity
nutrients in this system is deposited in the organic matter of the
vegetation: trees, shrubs, epiphytes. If you cut and remove the
the nutrient circulation is interrupted, a large quantity of
gets lost, and another amount is washed out. A re-establishment of
this type of forest will not succeed.
DIAGNOSES: High biological but no economic sustainability for an
undisturbed tropical rain forest. Neither biological nor economic
sustainability after cutting.
Reforestation with foreign species or cultivation of agricultural
will very seldom be successful because of the poverty of the soils,
disturbance of the natural ecosystem, and difficulties of the new
species to adapt. Under these conditions, a sustainable forestry
an economic point of view) can only be possible when the given
ecosystem can be kept alive and productive- -in other words, if it
kept biologically sustainable.
There are encouraging examples for a successful forest management
of the tropical rainforest. But they consequently renounce
clearcuttings of every size. Very, very careful selective cutting
single trees, very, very careful logging operations by oxen, and a
more than patient and tender handling of natural regeneration is
adequate recipe. The result is a true combination of biological and
economic sustainability: promising for farmers and for owners of
forests, but little attractive for big companies, I think.
Primary forests of the Pacific Northwest belong to the most
productive conifer-ecosystems on earth. Ideal climatic conditions
make trees grow almost up to heaven. For a European forester it is
just a dream to go on a pilgrimage to these examples of a
intact system with a maximum output of timber. Nobody would
hesitate to attribute to these stands a high degree of biological
In this area, selective cutting has never been the dominant method
silvicultural practice (most probably with the exception of the
Indians). But in earlier times, the clearcuts were small enough to
the establishment of NATURAL REGENERATION by and by, so that
the species composition of the original forest was not, in general,
This practice, however, has changed considerably during the past
to fifteen years, as you all know. Numerous clearcuts of an
size characterize the present forest scenery. Not only experts ask
themselves how it could happen that such a discrepancy between
forest science and forest administration and/or management could
From our point of view, most of these forests had and still have a
degree of sustainability, from both a biological and an economic
of view. But since the next generation will be recruited not by
populations but by artificial plantations which are frequently
composed of only one or two conifer species, and which in a
distinctive manner are called "industrial tree farms," a reduction
biodiversity, an impoverishment of the ecosystem, and a diminution
the gene pool is to be expected.
The continuation of this modern form of forestry is inevitably
by a loss of both forms of sustainability, and this in one of the
vital and intact forest regions we have. Well established
methods of silviculture instead of industrialized clearcutting
have led to these negative consequences, however the owners of the
forest would not have earned so much money in such a short period
The term sustainability, when used in connection with forests needs
detailed direction for using it. Economic profit may be possible
biological sustainability, but economic sustainability is not.
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