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

Enhanced CO₂ assimilation by forests as atmospheric CO₂ concentration rises could slow the rate of CO₂ increase if the assimilated carbon is allocated to long-lived biomass. Experiments in young tree plantations support a CO₂ fertilization effect as atmospheric CO₂ continues to increase. Uncertainty exists, however, as to whether older, more mature forests retain the capacity to respond to elevated CO₂. 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 CO₂ enrichment (FACE) for 7 years. Further, elevated CO₂ 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.