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In as far as mankind is contributingto the rise in the concentration ofatmospheric carbon dioxide gas

(CO2), and thus to the likelihood of achange in the global climate, scientists have been turning theirattention to the forests, which act asreservoirs for this greenhouse gas.Whenever a change in the extent orthe biomass density of forests takesplace it induces an exchange of CO2

between forest and atmosphere:when the area occupied by the for-est expands, or the stocks of bio-mass in existing forests increase,CO2 “flows” into the forest. Con-versely, should the forest be de-stroyed, or its wood content re-duced, then the concentration ofCO2 in the atmosphere increases.

In its 1995 report, the Intergovern-mental Panel on Climate Change(IPCC) stated that between 1980and 1989, human activities, mainlytree-felling in the tropics, had led toforests releasing an approximateannual amount of 1.6 billion tonnesof carbon (C), whereas, in the sameperiod, approximately half a billiontonnes of the element were taken upby the forests in the northern hemi-sphere. Both figures are subject tofluctuations of up to 100 per cent;the lack of any reliable regional dataleads to a considerable degree ofuncertainty when estimating globalcarbon stocks and flows. Moreover,a transformation in the utilization ofa forest which involves a complexchange in the carbon cycle is diffi-cult to quantify due to the problemspresented by the measurement ofthe extent of the change in area.Changes often take place over a

The Clothes-cupboardas a Carbon ReservoirWhat happens when primaeval forest is transformed into a “commercial” forest? Scientists have been studying the effects on the atmosphere

Rotten wood in forests (above) alsoprovides a major reservoir for atmosphericgreenhouse gases. Below: On opening up a primaeval forest for commercial use the first task is to build vehicle tracksthrough it.

very great number of areas, each ofwhich is in itself small. And, finally,ignorance also often prevails con-cerning the original state of the forest before the change took place.

It was against this backgroundthat a DFG-supported study of thetransition from primaeval to com-mercial forest was undertaken. Theactual case in point was the pro-posed commercial exploitation ofseveral hundred thousand hectaresof completely untouched forest inTierra del Fuego. If the Chileanparts of Patagonia are also included,

Life Sciences

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balance, a number of other counter-productive aspects have to be takeninto account.

Due to the fact that the CO2 theybind equates roughly to that whichthey release, the huge amounts ofcarbon present in primaeval forestshave no impact on the global cycle.Moreover, the wood in naturalforests rots unused, whereas in thecase of commercial exploitation alarge proportion of the wood pro-duced is harvested and worked astimber, ensuring that the carbon re-mains stored in the wood – of aclothes-cupboard, for example.

Wood can even be used to replace fossil fuels, thusavoiding the emission of

fossil carbon into the atmosphere.Direct substitution here implies thatfossil energy sources such as coal oroil are directly replaced by the com-bustion of wood. In contrast to fossilenergy sources, the combustion ofwood produced by sustainable for-est management is CO2-neutralwhen it is burnt as the CO2 releasedinto the atmosphere on combustionis offset by that bound by regenerat-

then this figure rises to over a mil-lion hectares! The aim of the studywas to measure the carbon stocks inthese forests and to estimate the effects of commercial exploitationon the carbon balance.

The study was based on an areaof 49 hectares of virgin forest in theArgentinian part of the region. Inorder to discover how much carbonwas bound up in it, the amounts pre-sent in the soil, above-ground vege-tation, deadwood and the living treemass had to be calculated. The datarelating to the trees, deadwood andsoil were gained by sampling. Thebelow- and above-ground biomass-es were estimated on the basis of theexperience gained from analysingindividual trees. Chemical analysesrevealed the carbon content of thesoil and wood.

304 tonnes of carbon per hectarewere found in the area of forestunder study, of which two thirdswere stored in the living tree mass,in other words, in the trunks,branches, roots and leaves of thetrees. Nevertheless, a good 20 percent of the carbon was stored in thesoil.

In the area of virgin forest understudy, the deadwood, which incommercial forests is of little

significance, is of great importance– after all, it does account for elevenper cent of the total carbon stored,since in natural forests all the dead-wood remains in situ, where it issubjected to more or less rapid natural decomposition. Commercialforests, in contrast, are thinned out,which ensures that trees are re-moved before they die, thus practi-cally eliminating the presence ofdeadwood. Compared to that con-tained in the primaeval forest understudy, the amount of carbon storedin commercial forests is consider-ably smaller. Stands of beeches inBavaria store just on two thirds ofthe amount found in the primaevalforest in Tierra del Fuego. This un-derscores the significance of naturalforests as major carbon reservoirs. Ifthey were to be commercialised weshould have to expect a marked reduction in storage capacity. How-ever, before any final judgementcan be made on the global carbon

“Virgin” forests in Tierra del Fuego coverseveral hundred thousand hectares, withmuch deadwood lying on the forest floor.In commercially used woodland, incontrast, dying trees are felled and worked in sawmills (below).

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ed forest. This substitution is alsopossible in an indirect manner: ifproducts, whose extraction, manu-facture or final disposal demandlarge amounts of fossil energy (forexample, aluminium or steel) are replaced by equally good productsmade of wood, which require onlyvery little fossil energy, no CO2 iseven released in the first place, andthe avoidance of emissions – thegreat goal of climate policy – hasthus been achieved!

It is against this background thatthe question is constantly beingraised as to whether it is more eco-nomical to transform “unproduc-tive” natural forests, which, howev-er, form vast reserves of carbon, intohighly productive commercialwoodland. Model calculations showhow the carbon balance developswith different forms of use: the di-rect or indirect replacement of fossilforms of energy by wood has a long-term and cumulative effect, where-as the storage effect from woodproducts is time-limited dependingon their useful life and the amountstored. The conversion of wood fromone hectare of virgin forest wouldmake it possible in this way to avoidthe emission of 267 tonnes of fossilcarbon over a period of 200 years, inother words, half a tonne per year.However, should this potential notbe exploited consistently, the con-version of primaeval into commer-cial forest would produce a negativecarbon balance extending over sev-eral centuries. Since the wood inTierra del Fuego cannot be utilisedfor energy production at the mo-ment, model calculations show thatcommercialisation could be expect-ed to release some 70 tonnes of car-bon per hectare on average over thenext 190 years. This highlights theneed for the protection of primaevalforests as carbon reservoirs. Quiteapart from this concrete situation,the calculation provides an idea ofthe enormous potential for reducingthe rise in atmospheric CO2 achiev-able by the purposeful utilisation ofwood from sustained commercialforestry.

PD Dr. Michael WeberTechnische UniversitätMünchen

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