Effects of thinning intensity and rotation length on albedo- and carbon stock-based radiative forcing in boreal Norway spruce stands

Abstract

We investigated how thinning intensity and rotation length affect radiative forcing, and thus climate warming or cooling, through changes in albedo and carbon stocks in Norway spruce (Picea abies Kart. (L.)) stands. Forest ecosystem model simulations were conducted under the current climate on sub-mesic sites in central Finland (62oN). Even-aged management regime with a business-as-usual (baseline) thinning from below over an 80-year rotation length was used as the reference management regime with which others were compared. Other even-aged management regimes included baseline thinning with ±20 per cent changes in basal area thinning thresholds over rotation lengths of 80, 100 and 120 years. Additionally, we used as a comparison an uneven-aged management regime, with selective cuttings (from above) at ca. 15-year intervals, and no management regime, over the simulation periods of 80–120 years. Under even-aged management, a simultaneous decrease in thinning intensity and extension of rotation length from 80 to 120 years reduced total radiative forcing compared to the reference management regime. Thus, it had an overall net cooling effect. Under even-aged management with baseline thinning and/or higher thinning intensity with rotation lengths of 80–100 years, and under uneven-aged management, there was little net climatic effect. This was because the opposing effects of changes in albedo and ecosystem carbon stocks largely cancelled each other out. No management regime resulted in the highest net cooling effect but provided no harvest income for timber. Thus, proper incentives for forest owners would likely be required to promote such potential cooling effects in forest management.