Volume increment and carbon dynamics in boreal forest when extending the rotation length towards biologically old stands

This study documents volume increment and natural mortality in 1379 old boreal forests plots during four consecutive inventory cycles in the Norwegian national forest inventory. The stands age up to 100 years beyond recommended rotation length (close to economical optimal rotation length) and comprise a wide range of site productivity classes in both pine-and spruce-dominated forests. The annual gross volume increment was stable and nearly constant up to 50?100 years beyond economically optimal rotation length. In parallel, there was very low natural mortality (0.22?0.66% of standing volume) with minimal risk of stand collapse. Stands with satisfactory stocking had volume increment equal to or higher than the reference volume increment in managed stands harvested at recommended rotation length, while poorly stocked stands had inferior volume increment. From a climate change mitigation perspective, it seems to be a good strategy to extend the rotation length beyond what is currently recommended, provided that the stands have satisfactory stocking.