Sustainability of Forests

Don Staples dstaples at
Thu Aug 20 09:32:34 EST 1998

Copied and forwarded to the news groups, original credit to LINC.

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,
it has
     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
long, long
     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


     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
for a
     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
     mountainous regions. 

     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
in a
     negative way. It is internationally known that large clearcuttings
     reduce soil productivity, disturb the balance within forest
     ecosystems, and via afforestation diminish biodiversity. 


     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
is of
     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. 


     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
reduction in
     economic sustainability. 

     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
zero. In
     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
and a
     biological meaning. In the long run, both types have to be
congruent if
     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
     economic sustainability. 

     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
would not
     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. 
Don Staples
UIN 4653335

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