Allometric Equations between Stem Diameter and Sapwood Area of Japanese Cedar and Japanese Cypress for Stand Transpiration Estimates Using Sap Flow Measurement

Abstract

 Total sapwood area of a stand (A_{S_stand}) is an important factor to determine stand transpiration by scaling up from sap flux densities. A_{S_stand} is generally calculated from all the stem diameter at breast height (DBH) using the regression equation between DBH and tree sapwood area (A_{S_tree}) made in each stand. We collected the data of A_{S_tree} measured in Japanese cedar (Cryptomeria japonica) and Japanese cypress (Chamaecyparis obtusa) stands, and compared the relationships between DBH and A_{S_tree} across the stands to develop general equations for A_{S_tree} of Japanese cedar and Japanese cypress stands. We observed no clear differences in the relationships between DBH and A_{S_tree} across the stands. Using all the collected data, we developed the equations; A_{S_tree} = 10.0DBH-41.5 (DBH<30 cm) and A_{S_tree} = 19.1DBH-314.8 (DBH>30 cm) for Japanese cedar, A_{S_tree} = 8.2DBH-27.4 (DBH<32 cm) and A_{S_tree} = 19.1DBH-374.7 (DBH>32 cm) for Japanese cypress. Mean errors of A_{S_stand} estimates by the equations were 5 % for Japanese cedar stands, and 8 % for Japanese cypress stands. The equations are useful for predicting A_{S_stand} on the basis of DBH data for Japanese cedar and Japanese cypress stands.