Global Patterns of Stem CO2 Efflux in Forests and its Biotic and Abiotic Controls

Abstract:

Forest stem CO₂ efflux (E_S) plays an important role in the carbon balance of forest ecosystems. However, its primary controls at the global scale are poorly understood and observation-based global estimates are lacking. We synthesized data from XX published studies across global forest ecosystems and examined the relationships between annual E_S and abiotic factors (mean annual temperature (MAT), mean annual precipitation (MAP)) and biotic factors (gross primary production (GPP), net primary production (NPP), leaf area index (LAI), soil CO₂ efflux (R_S), root CO₂ efflux (R_A), foliar CO₂ efflux, basal area, and stand age). Based on our compiled datasets, the mean annual E_S was 90 ± 43 g C m^-2 yr^-1, 160 ± 79 g C m^-2 yr^-1 and 501 ± 363 g C m^-2 yr^-1 for boreal, temperate, and tropical forest ecosystems, respectively. Average apparent Q₁₀ of E_S for boreal forests was 1.85, 2.29 for temperate forests, and 2.26 for tropical forests. Globally, MAT and MAP explained 32% and 24% of the variation in annual E_S, respectively. Positive linear relationships exist between E_S and forest production (GPP and NPP), LAI, R_S, and R_A in different forest ecosystems. These correlations hold for the global dataset, as well as for temperate and tropical forest ecosystems independently. In addition, we found no correlation between E_S and both R_S and R_A after accounting for temperature and GPP effects. The predicted a global annual E_S was about 6.1Pg C yr^-1.