A global trend away from monoculture tree plantations towards multiple uses of native forests is good for conserving forest ecosystems, but progress is hampered by a dominant paradigm that treats forests like cornfields. Dr. Mae-Wan Ho
Dr. Erkki Lähde, Finlands foremost forestry scientist, is convinced that forests can no longer be divided into those focussing on timber production and others with multiple uses. Instead, all commercial forests, in Finland and elsewhere on our planet, should be treated with their multiple uses in mind, in order to sustain their ecology and biodiversity in a close-to-nature state. Merely safeguarding the productivity of timber and pulp in monoculture plantations - while preserving key biotopes in their natural state is no longer considered sufficient for species conservation.
I met Dr. Erkki Lähde very briefly while on a hectic lecture tour in Finland in November-December 2004 as guest of Finlands Peoples Biosafety Association, and immediately recognized the profound significance of his work.
The emphasis on multiple uses of commercial forests is particularly important for many indigenous peoples who have been an integral part of forest ecosystems for millennium; whose livelihoods are being threatened by deforestation, which includes replacing native forests with monoculture tree plantations.
Monoculture tree plantations are anathema to the biodiverse native forest ecosystems of the world. The United Nations Environment Programme (UNEP) estimated that about 60 percent, and possibly closer to 90 percent of all living species are found in tropical forests. Thus, adopting multiple uses of forests that can sustain their biodiversity is extremely significant for conserving the earths species; and there has been a growing trend towards doing just that, though not quite fast enough.
Recent research in Mexico also shows that cacao and coffee-based agroforestry systems managed with low inputs by small holders harbour significant biodiversity compared to the monoculture plantations (see "Agroecology versus ecoagriculture", SiS 25).
One major obstacle to adopting multiple uses of forests is the lack of a good model of the natural forest ecosystem. "The prevailing paradigm still treats natural forests as if they are cornfields," says Lähde, "The entire stand is supposed to be destroyed at certain intervals by natural disturbances such as forest fires or storms. After that a new forest would grow from the saplings."
Based on that model, thinning and clear-cutting forests are routinely carried out to this day. The smallest and youngest trees and the under storey are cleared away, leaving uniform trees standing like "rows of carrots"; and when the trees are ready for harvesting, they are clear-cut, and the stock replaced. This is said to mimic nature. More accurately, it is supposed that natural forests imitate their cultivated counterparts, producing stands of trees that are uniform in size or age.
However, when real forests are examined, they tell a very different tale; there are no uniform or even stands of trees. Instead, native forests - especially mature and long established forests - tend to have diverse, uneven-sized mixed stands.
Finland was the first country in the world to carry out a national forest inventory as early as the beginning of the 1920s. The inventories have since been repeated once every decade. Measuring tree diameter at breast height has been one of the ways to investigate forest stand structure. It fell to the lot of Lähde and his research team to carry out the ninth inventory in the early 1990s; and for the first time since inventory began in Finland, the distribution of stem diameters of the trees was published.
Lähde went through the old inventory data for advanced and mature forests in Southern Finland for 1920s, 1950s and 1985. He found four possible distributions in the data: even or uniform sized, two-storeyed, "moundy uneven-sized" (normal distribution), and "regularly all-sized" (see Fig. 1). The vast majority of advanced and mature forests had the "regularly all-sized" distribution. This was also true of data from the Swedish National Forest Inventory.
Fig 1. Different distributions of tree sizes and their percentage occurrence in natural or mature forests in three surveys carried out in 1921, 1951 and 1985.
The "regularly all-sized" distribution discovered by Lähde and colleagues for the stem diameter of forest trees is commonly referred to as the 1/f distribution, where f is the frequency of the size class. It says that the frequency of the size class varies inversely as the diameter: the bigger the trees, the less frequently they occur. The 1/f distribution is possibly the most significant law discovered within the past 15 years for natural processes ranging from earthquakes and avalanches to the branching of trees; and is especially relevant for biology (see "Living energies" series, SiS 21). This distribution is characteristic of fractals such as coastlines and trees - which have fractional dimensions between the usual 1, 2 or 3; as well as the same or similar structure over many scales.
I have suggested that the "regular all size" or fractal distribution applies to the totality of species in an ecosystem, which enables the ecosystem to maximize energy capture and storage and minimize dissipation. Translated into biological terms, it would predict an increase in biodiversity and productivity (see "Energy, productivity & biodiversity" and "Why are organisms so complex? A lesson in sustainability", SiS 21).
Sure enough, there is evidence for that in forest ecosystems. The "regular all size" distribution supports more biodiversity of trees and higher productivity, and any measure that destroys that fractal structure diminishes both.
Lähde and his colleagues calculated the diversity index of trees in forests with the four different distributions: the even sized stands scored 7, the two-storeyed stands scored 15, the "moundy", 21.5, and "regular all-sized", a clear winner at 39.5.
Researchers in the Canadian Forest Service in the forests of North Central British Columbia had previously shown that the impact on biodiversity was dependent on the method of harvesting, with single-tree selection and group selection causing the minimum damage (see Table 1).
|Table 1. Harvesting method and diversity|
Lähde and colleagues compared the productivity of even-sized stands with uneven-sized stands in experimental plots in southern Finland.
The results (Table 2) showed that clear cutting leads to unstable wood production. During regeneration and sapling stages, growth remains low, reaching its peak only when maturing. At maximum, it is still lower than the average production of regularly all-sized stands. Thus, the latter are more productive and more profitable on average than even-sized stands. The quality of the wood produced is better and it is able to sustain multiple uses on account of its higher diversity.
|Table 2. Productivity of even-sized and uneven-sized stands|
|Stand/developmental stage||Volume m3||CAI* m3|
|Clear cut area||0||0.0|
|Regeneration area with seed trees||28||0.8|
|Regeneration area with sapling stand||26||2.7|
|Young thinning stand||140||5.1|
|Advanced thinning stand||178||5.1|
|Regularly all sized stand||194||5.9|
|*Current Annual Increase|
In the short-term, clearcutting is a cheap and technically easy option, and hence "an obvious favourite of the forest industry" which enjoys the full benefits while leaving forest owners to bear the costs of long and often expensive process of regeneration. "Then, not only the timber production is at its minimum but the multiple use and sales values of the forest are also at the lowest." Furthermore, the risk of failure remains high throughout the regeneration process.
Somewhat surprisingly, low thinning of small trees - a common practice in forestry carried out in the belief that it favours the growth of large trees by removing "competition" also reduces wood productivity (see Table 2). And this was confirmed in another set of experiments involving 23 Norway spruce-dominated experimental stands extending from southern to northern Finland, where Lähde and coworkers found that CAI averaged 5.4 m3ha-1 in single-tree selection plots compared with 4.6 m3ha-1 in low thinning plots.
The reason why single-tree selection favours wood growth, they suggest, may be because removing slow-growing dominant trees releases space and nutrients to enable small trees to grow more rapidly; while removing small trees in low thinning results in little or no benefit for the remaining dominants.
In order to counter the market-driven economic arguments all too often used to justify the destruction of our natural resources, there have been valiant attempts to estimate the value of ecosystem goods and services in monetary terms.
An international team of conservationists led by Andrew Balmford in Cambridge University, UK, estimated the monetary value of benefits from relatively intact biomes compared with those converted to intensive human use. These include the tropical forest in Malaysia under reduced impact logging as opposed to conventional logging, and the tropical forest in Cameroon under reduced-impact logging or small-scale farming as opposed to conversion into oil-palm and rubber plantations.
In the case of Malaysia, the high-intensity, unsustainable logging was associated with greater private benefits through timber harvesting, but reduced social and global benefits through loss of non-timber forest products, flood protection, carbon stocks and endangered species. Summed together, the total economy value of the forest was some 14% greater when placed under more sustainable management.
In the case of Cameroon, conversion to oil palm and rubber plantations yielded negative private benefits, while social benefits from non-timber forest products, sedimentation control, and flood prevention were highest under sustainable forestry, as were global benefits from carbon storage and other values. Overall, the total economic value of sustainable forestry was 18% greater than that of small-scale farming, whereas it was negative for plantations.
The total economic value of sustainable uses of the forests were underestimated in that report, as only a handful of well-established ecosystem services were considered, while some particularly valuable services, such as nutrient cycling, waste treatment and the provision of cultural values were not examined.
It would appear that forestry is in for a complete shake-up, if we are to make the best use of a resource thats essential to the survival of our planet and its teeming biodiversity.
Article first published 03/03/05
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