Biomass increment and carbon balance of ash (Fraxinus excelsior) trees in an experimental stand in northeastern France

Abstract

In this study, we compared the annual biomass increment of ash trees to their annual carbon balance calculated from the end of the growing season in 1994 to the end of the next one in 1995. In 1995, three trees of variable competitive status and aged 25 were studied. Stem, branch and root biomass increments were derived from detailed measurements. Tree crowns were divided vertically into three layers. In each crown layer, the foliage biomass and area were determined, net CO2 assimilation (An) and global radiation (Rg) were measured regularly throughout the growing season. Outside this period, Rg was estimated from global radiation measured above the canopy and from estimations of light transmittance. Net assimilation of trees (AN) was obtained by scaling leaf An to the tree level, using relations established between An and Rg for each crown layer, the distribution of foliage area, and measured climatic data. Above- and below-ground tree respirations, not measured, were estimated. A n was correlated to Rg and potential evapotranspiration. It decreased from the upper to the lower crown layers, but was independent of tree competitive status. Total estimated respiration of trees accounted for about 37% of gross assimilation. The proportion of carbon allocated to the stem was more than 45%. Net productivity of trees obtained from simulated annual carbon fluxes compared reasonably well with the biomass increment of trees.