Enhanced woody biomass production in a mature temperate forest under elevated CO2

Abstract Enhanced CO 2 assimilation by forests as atmospheric CO 2 concentration rises could slow the rate of CO 2 increase if the assimilated carbon is allocated to long-lived biomass. Experiments in young tree plantations support a CO 2 fertilization effect as atmospheric CO 2 continues to increase. Uncertainty exists, however, as to whether older, more mature forests retain the capacity to respond to elevated CO 2. Here, aided by tree-ring analysis and canopy laser scanning, we show that a 180-year-old Quercus robur L. woodland in central England increased the production of woody biomass when exposed to free-air CO 2 enrichment (FACE) for 7 years. Further, elevated CO 2 increased exudation of carbon from fine roots into the soil with likely effects on nutrient cycles. The increase in tree growth and allocation to long-lived woody biomass demonstrated here substantiates the major role for mature temperate forests in climate change mitigation.