The tree height‐related spatial variances of tree sap flux density and its scale‐up to stand transpiration in a subtropical evergreen broadleaf forest

Abstract

AbstractThe sap flux method generates problems when it is applied in a subtropical evergreen broadleaf forest. In this study, 6 dominant species in such a forest were selected to investigate the spatial variances on the stem and individual variances within the forest. The sap flux density (Fd) at 20–40 and 40–60 mm of the xylem for the upper canopy species (Schima superba, Castanea henryi, and Machilus chinensis) accounted 18–60% and 16–37%, respectively, of that at 0–20 mm. For the lower canopy species (Ilex ficoidea, Symplocos ramosissima, and Schefflera octophylla), the highest Fd occurred at 20–40 mm. Tree height (H) was closely related to the radial variances of sap flux in the xylem. Vertically, the mean Fd increased with tree height among different species (p < .01). On this basis, the proportion of mean whole tree transpiration for the 6 tree species was 37.10% (S. superba), 17.73% (C. henryi), 7.15% (M. chinensis), 15.88% (I. ficoidea), 17.36% (S. ramosissima), and 4.76% (S. octophylla). The annual stand transpiration for the 6 tree species was estimated of 366.4 mm. The observed distinct stratification of the water flux that highly related to their importance for different tree species revealed the critical role of tree water use in determining the development of vegetation succession.