Forests play a significant role in the current perturbation of the global carbon cycle, which needs to be understood in order to translate CO2 emission scenarios into predictions of future atmospheric CO2 levels and hence into projections of climate change. This review outlines the projections and sources of uncertainty about future global warming and puts it in the context of relevant climate changes that have occurred in the past. The current perturbed global carbon budget is described, including recent statistics on the magnitude of global deforestation and forestation as carbon sources and sinks. Constraints on the global carbon budget suggest that an additional 'missing sink' has appeared in recent decades. The evidence for this sink being on land and attributable to increases in temperature, atmospheric CO2 and nitrogen fertilisation are discussed. The future global options for planting and conserving forests to sequester carbon may be limited to offsetting 12-15% of projected fossil fuel emissions over the next 60 years. The principles of managing forests to sequester carbon are described. Different forest types should be chosen depending upon the need to maximise the short-term rate of carbon storage or the total storage at equilibrium. Replacing mature forests with plantations may lead to a loss of carbon unless the plantations grow rapidly and have lon-lasting products. The optimum rotation period for carbon storage coincides with the period to maximum mean annual increment only when the products have a long lifetime. Finally, the effects of draining peatlands and planting trees on the fluxes of greenhouse gases is described, concluding that sooner or later planting on deep peats will lead to a net contribution to global warming.
161.32 (Assimilation des Kohlenstoffes. Photosynthese) 181.2 (Beziehungen zum Klima. Akklimatisation. [Siehe vorzugsweise Untertitel von 4; Einflüsse durch Verunreinigungen der Umwelt siehe 181.45])
