The forest environment carbon cycle can be viewed at a number of scales. Measurements can be made at the scale of an individual leaf or tree, stand-scale measurements can be made, and models can be developed that examine forest-level, regional, and global carbon cycles. The role of the forest in the global carbon cycle has become increasingly important as it is realized that forests and forestry have a role to play in mitigating the so-called greenhouse effect. This article examines the sources, sinks, and ﬂuxes of carbon as they relate to forests and then places this information within the context of global change. Finally, the potential contribution of forests to the mitigation of climate change is assessed. The main components of the natural global carbon cycle are the sources, sinks, and ﬂuxes between the land, oceans, atmosphere, and geological reservoirs. Current estimates suggest that the atmosphere contains about 730 PgC, the land 2000 PgC, the oceans 38 000 PgC, and that an unknown amount remains in geological reservoirs. The greatest natural ﬂux (120 PgC per year) is between the land and the atmosphere, with a smaller ﬂux occurring between the atmosphere and the oceans (90 PgC per year).
[...] Trees are seen as a potential means to sequester carbon. This is based on the idea that a one-time beneﬁt can be obtained by planting forests in areas where forests have previously been lost. Tree plantations in the boreal, temperate, and tropical zones are thought to have sequestered about 11.8 GtC. The IPCC has estimated that slowing the rate of deforestation combined with the promotion of natural forest regeneration and afforestation could increase terrestrial carbon stocks in the period 1995– 2050 by between 60 and 87 PgC. [...]
[...] For example, emissions of carbon associated with forest ﬁres in Russia are very uncertain, with information on both the extent and severity of forest ﬁres in Siberia being very unreliable. Despite these difﬁculties, there are increasing numbers of indications that carbon stocks in the world's forests may be increasing. In the tropics, data from permanent sample plots indicate that tree growth is increasing, although the ﬂux is more than balanced by losses caused by deforestation. In temperate and boreal forests, an increasing forest area has been accompanied by increasing carbon stocks in existing forests. [...]
[...] The Forest Carbon Cycle All higher plants take up carbon dioxide. Globally, the amount of CO2 that is dissolved in leaf water has been estimated to be 270 PgC per year, representing more than one-third of all the CO2 stored in the atmosphere. Most of this carbon leaves the plants without being involved in photosynthesis. The fraction that remains and which is converted from CO2 to carbohydrate is known as the gross primary production (GPP). The total amount of terrestrial GPP has been estimated at 120 PgC per year. [...]
[...] This assumption is based on looking at the carbon balance over a fairly extensive area of forest, as local stand dynamics can result in substantial changes in the carbon balance as the forest is disturbed and regrows. Using the terms described above, NPP should more-or-less equal RH. While this may be the case for some mature forests, more often forests are in a state of dynamic equilibrium, with some net carbon either being gained or lost from the forest ecosystem. [...]
[...] These include ﬁre prevention and control, protection against pests and disease, changes to rotation lengths, control of stand density, enhancement of nutrient supply, control of the water table, selection of useful species and genotypes, use of biotechnology, reduced regeneration delays, selection of harvesting methods such as reduced-impact logging, recovery of degraded forest, management of logging residues, recycling of wood products, increased use of wood, and efﬁciency of the conversion process from wood to products, and the establishment and maintenance of forest reserves. These methods all provide means by which the forest sector could contribute to the global effort to reduce anthropogenic impacts on the global carbon cycle. SUMMARY The forest environment carbon cycle can be viewed at a number of scales. Measurements can be made at the scale of an individual leaf or tree, stand- scale measurements can be made, and models can be developed that examine forest-level, regional, and global carbon cycles. The role of [...]
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