Carbon sequestration in forest trees of the EU as affected by long-term changes of land use.

The biomass of forest vegetation expands in all EU countries. This review analyses the long-term development of forest vegetation and, thereby, the sequestration of carbon in forest biomass in the EU, country by country. The sequestration estimates and their uncertainties are assessed focusing on the period 1990-2006. The most recent estimates are compared with those for earlier times. A case study from Finland is presented, which helps understand the causal mechanisms affecting long-term sequestration of carbon in forest vegetation on a centennial scale. The forests of the 27 countries of the European Union (EU-27) represent approximately 4% of global forest area and 5% of global growing stock volume [1]. Despite their relatively small global shares, the region's forests remove carbon from the atmosphere at a surprisingly high rate. During 1990 to 2006 within the 27 countries (that were members of the EU in 2008) the expanding woody biomass annually sequestered 360 to 495 million tonnes CO&#60;sub&#62;2&#60;/sub&#62; from the atmosphere (<i>high confidence</i>). The rate of sequestration accelerated over time during the same period (<i>low confidence</i>). Over a more extended decadal scale from 1900 to 2006, the rate accelerated (<i>high confidence</i>). The biomass sink was mainly driven by increasing density of average European forests and to a lesser extent by increasing forest cover (<i>high confidence</i>). Changes in forestry, nature conservation and other land management practices were the main drivers of carbon sequestration (<i>medium confidence</i>). The contribution of carbon sequestration in forests to the national carbon budget varied among countries depending on the extent of forests. Estimates for individual years varied and the accuracy and precision of the national estimates was not high, typically ±30%. A three-year moving average can be recommended as a basis for calculations, because it evens out inter-annual variation. Biomass sequestration has potential to continue in the EU for at least 50 years into the future. If land use trends revert and consumption patterns change, for example, if the demand for agricultural and wood products increases and bioenergy is developed on a large scale, sequestration can decelerate in the very long term. Climate change in itself is a risk factor to forest ecosystems in terms of increasing risks of storm damage, forest fire, forest pests and drought. Losing the biomass sink in EU, notably only a theoretical scenario in the next 20 to 30 years, would become an obstacle to reaching the main goal of climate policy: a stable atmosphere in terms of greenhouse gases. Promoting the sink on the other hand would make a contribution to achieving that goal. If the global trends of deforestation and forest degradation are reverted, forest sequestration of carbon can make an important contribution to stabilizing the atmosphere and preventing a serious climate change. Forest biomass has a potential to expand significantly worldwide.