Carbon sequestration in willow (Salix spp.) plantations on former arable land estimated by repeated field sampling and C budget calculation

Abstract

Short rotation coppice (SRC) plantations are of interest as producers of biomass for fuel, but also as carbon (C) sinks to mitigate CO2 emissions. Carbon sequestration in biomass and soil was estimated in 5-year-old replicated SRC plantations with willows (Salix spp.) on former arable land at five sites in Sweden. Total standing C stocks, i.e. C stored in woody biomass above- and belowground, fine root standing crop, litter, and soil organic carbon (SOC) were estimated by repeated field sampling and C budget calculation.Overall, the SRC willow plantations represented a C sink after five years. Estimated increase of total standing C stock was 15% on average compared to pre-planting conditions. There was no change in SOC when including all sites. Analyses within sites revealed a decrease in SOC at one site, although the decrease was compensated for by C stored in willow biomass. After removal of stem biomass, C in other plant pools was sufficient to compensate for the SOC decrease. Remaining C in stumps, stool, and coarse roots was estimated at ca 20% of stem C.There was a discrepancy between SOC sequestration rates from soil sampling and C budget calculation, −2.1–1.0 and 0.15–0.45 Mg ha−1 y−1, respectively. Mineralization of old organic material from previous land-use and input to SOC from understory vegetation were not included in the calculations, which may explain part of the differences. The importance of understory litter in C budgets for young plantations was apparent, as it comprised 24–80% of aboveground litter C.