Biomass turnover time in terrestrial ecosystems halved by land use

The terrestrial carbon cycle is not well quantified(1). Biomass turnover time is a crucial parameter in the global carbon cycle(2-4), and contributes to the feedback between the terrestrial carbon cycle and climate(2-7). Biomass turnover time varies substantially in time and space, but its determinants are not well known(8,9), making predictions of future global carbon cycle dynamics uncertain(5,10-13). Land use-the sum of activities that aim at enhancing terrestrial ecosystem services(14)-alters plant growth(15) and reduces biomass stocks(16), and is hence expected to affect biomass turnover. Here we explore land-use-induced alterations of biomass turnover at the global scale by comparing the biomass turnover of the actual vegetation with that of a hypothetical vegetation state with no land use under current climate conditions. We find that, in the global average, biomass turnover is 1.9 times faster with land use. This acceleration affects all biomes roughly equally, but with large differences between land-use types. Land conversion, for example from forests to agricultural fields, is responsible for 59% of the acceleration; the use of forests and natural grazing land accounts for 26% and 15% respectively. Reductions in biomass stocks are partly compensated by reductions in net primary productivity. We conclude that land use significantly and systematically affects the fundamental trade-off between carbon turnover and carbon stocks.