Stem CO 2 efflux in six co‐occurring tree species: underlying factors and ecological implications

Stem respiration plays a role in species coexistence and forest dynamics. Here we examined the intra‐ and inter‐specific variability of stem CO 2 efflux ( E ) in dominant and suppressed trees of six deciduous species in a mixed forest stand: F agus sylvatica L., Q uercus petraea [ M att.] Liebl, Q uercus pyrenaica   W illd., P runus avium   L ., S orbus aucuparia   L . and C rataegus monogyna   J acq. We conducted measurements in late autumn. Within species, dominants had higher E per unit stem surface area ( E s ) mainly because sapwood depth was higher than in suppressed trees. Across species, however, differences in E s corresponded with differences in the proportion of living parenchyma in sapwood and concentration of non‐structural carbohydrates ( NSC ). Across species, E s was strongly and NSC marginally positively related with an index of drought tolerance, suggesting that slow growth of drought‐tolerant trees is related to higher NSC concentration and E s . We conclude that, during the leafless period, E is indicative of maintenance respiration and is related with some ecological characteristics of the species, such as drought resistance; that sapwood depth is the main factor explaining variability in E s within species; and that the proportion of NSC in the sapwood is the main factor behind variability in E s among species.