Decadal biomass increment in early secondary succession woody ecosystems is increased by CO 2 enrichment

Increasing atmospheric CO2 stimulates photosynthesis which can increase net primary production (NPP), but at longer timescales may not necessarily increase plant biomass. Here we analyse the four decade-long CO2-enrichment experiments in woody ecosystems that measured total NPP and biomass. CO2 enrichment increased biomassincrement by 1.05 ± 0.26 kg C m−2 over a full decade, a 29.1 ± 11.7% stimulation of biomassgain in these early- secondary-successiontemperate ecosystems. This response is predictable by combining the CO2 response of NPP (0.16 ± 0.03 kg C m−2 y−1) and the CO2-independent, linear slope between biomassincrement and cumulative NPP (0.55 ± 0.17). An ensemble of terrestrial ecosystemmodels fail to predict both terms correctly. Allocation to wood was a driver of across-site, and across-model, response variability and together with CO2-independence of biomassretention highlights the value of understanding drivers of wood allocation under ambient conditions to correctly interpret and predict CO2 responses.