Estimating transpiration of Japanese Larch (Larix kaempferi): monitoring and calibration

Abstract:

We evaluated transpiration of Japanese Larch (Larix kaempferi (Lamb.) Carr.) based on monitoring and calibration of thermal dissipation method. Japanese Larch is a unique deciduous needle tree and dominated in the northern hemisphere including high altitude and northern Japan. Because Larch is rapid growth hardwood species, the timber demand of larch has been elevated in recent decades, and plantation has been continued. Two stem segments with 47-year-old Larch (19.4 cm mean DBH and 22 m mean height) were collected for calibration between the actual sap flux density and k dimensionless estimated from temperature difference obtained from thermal dissipation method. We developed a 20 m x 20 m plot in 45-year-old Japanese Larch forest for monitoring transpiration. Within this plot, six stems out of 24 stems (28.5 cm mean DBH, and 20 m mean height) within the plot were monitored using thermal dissipation method in from June to September, 2019. By combining data from two sampled trees, estimated new coefficient values of a and b were 40 and 0.32, respectively. Overall, the application of original parameters underestimated the actual SFD of Larix kaempferi by 85%. Transpiration of each stem varied from 20.4 to 32.4 kg day^-1, which corresponding to the differences of sap wood area from 85 to 221 cm². The total transpiration of 24 Japanese Larch stems was 72.5 mm with daily stand transpiration ranging from 1.0 to 2.0 mm day^-1 (mean: 1.5 mm day^-1; SD: 0.16). Estimated daily transpiration using the calibration equation was from 1.2 to 3.0 times higher than estimated values of the original equation (0.4 and 1.4 mm day^-1). During our studied period, daily transpiration significantly correlated to daytime VPD and PAR.