Impacts of thinning on growth, timber production and carbon stocks in Finland under changing climate

A gap-type ecosystem model was used to assess how climate change may affect the growth (stemwood production), timber production (sawlogs and pulpwood) and carbon stocks in the forest ecosystem (trees and soil) under varying thinning regimes in Finland. Simulations were carried out over a 100-year period under current and changing climate for seven thinning regimes by changing both the basal area threshold when the thinning is performed and the remaining basal area after the thinning. The management recommendations, currently applied in Finnish forestry, were used to define the “business-as-usual” treatment. The results indicated that climate change may substantially increase the growth, timber production and carbon stocks in the forest ecosystem. The largest relative changes were found in northern (above 64° N) Finland (south: growth 37-45%, timber production 23-40%, carbon stocks 8-10%; north: 75-78%, 59-70%, 21-23%, respectively, depending on the thinning regimes applied), although the absolute (mean) values were higher in southern (below 64° N) Finland. Regardless of climate scenarios, a reduced level of tree stocking in thinnings may result in cuttings exceeding the growth and result in lower carbon stocks in the forest ecosystem. Conversely, increased tree stocking level up to 30% reduced timber production, but did not remarkably affect the growth and carbon stocks under the current or changing climate. Hence, it may be suggested that if thinning is made at 15-30% higher stocking than current level it would result in a positive compromise; beyond that, timber production could be reduced drastically.