Aug 22, 2013. /Lesprom Network/. The carbon sink services provided by European forests were predicted to be functional for decades. However, since 2005 there have been signs of sink saturation, states the international team of authors led by former EFI's Assistant Director Gert-Jan Nabuurs, currently from Alterra, Wageningen, in their recent paper in Nature Climate Change. The authors suggest that declining volume increment of trees, deforestation rates and higher vulnerability to natural disturbances such as fires, storms and insects play a part in this slow-down, as European Forest Institute (EFI) said in the press release received by Lesprom Network.

Carbon sinks remove CO2 from the atmosphere and the Kyoto Protocol has promoted their use as a form of carbon offset. Nabuurs and colleagues looked at forest inventories for the whole European area and found that since 2005 there has been a decline in the rate of tree volume increase, and therefore also in sink capacity.

This was calculated using the average annual volume of forest increment minus the average annual volume of harvest and other losses of trees. The authors suggest that a few conditions may explain this. As European forests are increasingly mature, they are dominated by older trees.

This condition, combined with reduced nitrogen deposition from the atmosphere and decreased summer air humidity due to climate change, can explain the lower growth in forest volume that curbs the carbon sink. In addition, urban sprawl and infrastructure expansion are driving deforestation rates, even if only on a modest scale, with effects on the sink strength. Finally, evidence shows that the older European forests are more susceptible to damage caused by natural disturbances, leading to release of carbon into the atmosphere.

The authors conclude that although managed European forests are closer to capacity than previously thought, changes in management practices can improve volume growth and slow down saturation of the carbon sink.

A more regional spread of forest functions over Europe may be needed; where there are regions with enhanced conservation, and regions where the production of wood receives more attention, with enhanced rejuvenation.

“Countries should realise that a carbon sink in the forest biomass cannot be sustained forever. Only through a locally adapted management a balance can be found between a sink in the forest, and a continuous flow of wood products and biomass for bioenergy. A carbon sink is only one function of the forest, and should be valued with respect to other services and products, sometimes going beyond the boundaries of the forest sector. This calls for better coordination of policies beyond those that deal directly with forest and forest management,” says Nabuurs.

The European Forest Institute is an international organisation established by European States.