Accumulation of standing aboveground biomass carbon in Scots pine and Norway spruce stands affected by genetic variation

Abstract

Abstract The area of planted forests increases worldwide and those forests have a potential to contribute to climate change mitigation. Often the genetically improved planting material is used for reforestation, but its potential to accumulate more carbon (C) in biomass through enhanced or faster growth is not fully appreciated. The aim of this study was to investigate variation among native Scots pine and Norway spruce populations in terms of their growth and ability to accumulate C in standing aboveground biomass when transferred into non-local environments. For that purpose we modeled aboveground C in a series of replicated provenance experiments with both species at the age close to half of the rotation. We used the sets of allometric equations and compared the obtained estimates of accumulated C between experimental series and the commercial reference stands of the same species and age. Significant variation in aboveground C accumulation was found among examined populations, that reached up to 91% for Scots pine and 74% for Norway spruce, depending on testing site. The site-averaged estimates of C accumulation varied between 74.0 (±2.1\xa0s.e.) and 120.0 (±3.7) Mg ha−1 for Scots pine at age 52, and between 37.4 (±3.7) and 184.4 (±5.9) Mg ha−1 for Norway spruce at age 47–53. Those values would be by 23% lower or by 25% higher for pine, and from 9% lower to 11% higher for spruce, depending on the allometric equation used. The accumulated aboveground C was not significantly different at the research sites compared to the nearby reference stands when accounting for differences in stand density. Norway spruce experimental stands had a reduced stand density because of the damage by wind and insects. Those stresses and the observed trends of decreasing stand productivity for spruce populations when transferred to warmer and drier conditions would jeopardize the ability of pure spruce stands to contribute to climate change mitigation in the future. Norway spruce would likely benefit from planting in mixtures with other tree species for increased stand stability and resistance. The results of our study indicate a possibility to increase C sequestration in forest stands through selective breeding, perhaps linking it with protection of natural forests as an option for climate change mitigation. For increased C sequestration in planted forests the use of seed sources which accumulate biomass faster and in a greater amount would need to be combined with silvicultural operations that maintain proper stand density and structure.