Carbon sequestration at land use conversion – Early changes in total carbon stocks for six tree species grown on former agricultural land

Abstract

Changing land use from agriculture to forestry affects global carbon (C) balances. In addition to reduce using fossil fuels, climatic benefits may be reached by increasing forested areas where appropriate. At present, there is limited data concerning whether differences in C sequestration rates occur among tree species. In this study we evaluated the effects of various species on C sequestration at an early stage of afforestation. Total C stocks, i.e. C in biomass, litter and soil, were compiled for hybrid aspen, poplar, silver birch, Norway spruce, larch and willow. The species were planted in random blocks on five sites at different latitudes. Soil, litter and plant biomass were sampled repeatedly, except for root biomass which was calculated from functions found in the literature. There were no differences between species in total C stocks after 8–9 years growth, except for short rotation coppice (SRC) willows that reached a high production early due to a higher stand density compared to the species managed with short rotation forestry (SRF). Total C sequestration rates for sites varied from zero to 2.3–4.9 Mg C ha−1 year−1. There were no effects of species on soil organic carbon (SOC), but significant decreases were noted for sites with high initial amounts, while SOC was unchanged or increased on sites with lower initial amounts. Mean SOC sequestration rates for sites ranged between −3.0 to 0.78 Mg C ha−1 year−1. Thus, former land use and time since abandonment rather than species seemed to influence the SOC pools at this early stage of afforestation. There were few differences between species in litter C in these young stands. We conclude that increased tree productivity had a positive effect on total C sequestration. It is crucial to include C in both biomass and soil when discussing C capture at land use change. The time factor is important and experiments like this should be followed for an extended time.