Canopy transpiration in two Japanese cypress forests with contrasting structures

Abstract

Canopy transpiration (EC) varies among forest stands with different structures. To evaluate different EC for Japanese cypress we observed EC for 5 months, by use of the sap flow technique, in two adjacent stands of different ages with contrasting structures. Mean diameter at breast height was 13.5 and 44.6 cm and stem density was 2100 and 350 trees ha−1 for the Sakuta and Hiwada plots, respectively. Mean EC measured was 1.3 mm day−1 for the Sakuta plot and 0.7 mm day−1 for the Hiwada plot (or 53 % of that for the Sakuta plot). This difference between EC was caused by differences between both mean stand sap flux density (JS) and stand sapwood area (AS__stand): JS for the Hiwada plot was 69 % of that for the Sakuta plot and AS_stand for the Hiwada plot was 75 % of that for the Sakuta plot. The difference between JS was primarily caused by different reference JS for given meteorological conditions, not by the different response of JS to meteorological conditions. Previous studies of coniferous plantation forests in Japan reported that differences between EC among stands with different structures were mainly caused by different AS_stand. This study revealed this is not always true, and that differences between JS should also be considered when predicting differences between EC among stands with different structures.