A study on potentiality of carbon storage and [CO.sub.2] uptake in the biomass and soil of coppice stand.

Author:Khademi, A.
 
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INTRODUCTION

The universal phenomenon of global warming originates mainly from continual increase in the production of greenhouse gases such as [CO.sub.2], fossil fuels consumption, forest destruction, irregular grazing of pastures, land use change and some other activities resulting in human life development (4). The density of greenhouse gases increased considerably during the period of industrial revolution, especially in the contemporary century when the concentration of carbon dioxide rose from 280 ppm before industrial revolution to 386 ppm in 2006. Carbon dioxide is one of the most important greenhouse gases that gradually increase the temperature of the Earth. Climatic changes lead to the decline of carbon uptake by plants which may finally result in a considerable decrease of soil carbon storage to 11% by the year 2100 (5). In terrestrial ecosystems, plants are regarded the most important [Co.sub.2] up-takers. Plants absorb [CO.sub.2] from atmosphere and store it in their biomass during a photosynthesizing process. Some of the stored carbon is emitted into atmosphere during respiration and the difference between these two is called net primary productivity.

Since the rate of respiration is high in older forests, the annual uptake of carbon in these areas is low. The difference between the absorbed carbon and that of emitted is called'' carbon sequestration '' which is recognized as a very important universal issue (10). The forests in China store annually 118.1 million tons of carbon as a result of growth of trees as well as storing 18.4 million tons in the soil but they release 38.9 million tons of carbon in the atmosphere. So, the pure uptake of carbon would be 97.6 million tons (11). Forest as one of the major components of terrestrial ecosystems, plays an important role in energy matter and momentum exchange between the land surface and atmosphere. About 75% of carbon storage in such ecosystems is taken up by forest (3). Likewise, 40% of total carbon storage is spread on trunks of trees, 27% on humus, branches and other wooden products and the rest on soil and forest floors (10).

With regard to the amount of carbon storage, there is a direct relationship between soil fertility, leaf surface index, trees growth and biomass level (1). For instance, the level of stored carbon in Eucalyptus camaldulensis afforested in Iranian southern city of Fassa in fertile growing land was estimated to be 3.67 tons [ha.sup.-1] whereas in less fertile growing land it was only 2.27 tons [ha.sup.-1] in a year.

Carbon purification or refining with artificial methodologies such as filtering, etc. is costly. For example, in the U.S.A, the estimated cost for each ton of carbon would be 100-300 US dollars (2). Most of the carbon absorbing cost is spent on preserving and protecting the forests which is about 46.6-260.3 US dollars per ton (7).

By examining and measuring the level of carbon sequestrated in a biomass as well as in the soils of forests with different stands and types, it is possible for us to assess whether the cost of scientific management or control over these resources and increased contraction of heaps of soil can be reverted through [Co.sub.2] uptake in plant organs or not. The investigations show that the ever green wide-leaved forests have much further potentials to emit [Co.sub.2] and directing needle-leaved forests into those of wide leafs can increase the rate of carbon absorption (7). Similarly, the amount of carbon storage in plants' biomass in controlled forests is 335 tons [ha.sup.-1], in traditionally controlled forests it is 145 tons and in pastures this would be 46 tons [ha.sup.-1]. Storing takes place up to the depth of 40 centimeters below the soil surface (6).

Given the fact that dominant species in the area of study was oak tree and also considering that this tree exists in different types and stands, especially in the form of oak coppice, it is possible...

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