Sensitivity of growth of Scots pine, Norway spruce and silver birch to climate change and forest management in boreal conditions

An assessment is made on how climate change and thinning may affect the total stem wood growth of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and silver birch (Betula pendula), and the resulting effects on the total timber yield and the consequent distribution of timber between pulp wood and saw logs. A process-based model used in the study links the flows of carbon, energy, nitrogen and water in trees and soils as affecting the physiological and ecological performance of trees under the control of climatic and edaphic factors and management. The simulations represent the boreal forest in Southern and Northern Finland. Under thinning, the climate change increased the growth of Scots pine up to 28% in the south and up to 54% in the north, whereas the increase for Norway spruce was up to 24% in the south and 40% in the north. The response of silver birch was smaller than that of conifers; i.e. growth increased by 21% in the south and 34% in the north. The enhanced growth implied an increase in the timber yield regardless of tree species and site. The increase for Scots pine was up to 26% in the south and 50% in the north. For Norway spruce, the increase was somewhat smaller, up to 23% in the south and up to 40% in the north. For silver birch, the increase was the smallest, up to 20% in the south and up to 33% in the north. The thinning regime had, however, a clear effect on total growth and timber yield. Any thinning regime increasing the mean stocking over the rotation increased the total growth and timber yield regardless of the tree species and site. An adaptation of the current management rules might be needed in order to exploit the benefits that climate change seems to provide in the form of increased growth and timber yield in the boreal conditions.