Change in evapotranspiration partitioning after thinning in a Japanese cypress plantation

Thinning resulted in evapotranspiration decrease and caused the relative contributions of each component to evapotranspiration to become very close. To increase the understanding of forest management to control water cycles, we examined the effect of 50% strip thinning on evapotranspiration (ET) and its partitioning into canopy interception (E (i)), tree transpiration (E (t)), and forest floor evaporation (E (f)) in a Japanese cypress (Chamaecyparis obtusa Endl.) plantation. Intensive measurements were employed to monitor each component of ET during the pre- and post-thinning periods. The results showed the annual E (t) was the dominant component of ET followed by E (i), whereas E (f) was the smallest component in both periods. Thinning has significant impact on the process of ET partitioning. In such that it decreased from 42.3 to 33.7% in E (i)/ET and from 45.0 to 34.9% in E (t)/ET, and increased from 12.7 to 31.4% in E (f)/ET on an annual scale. The relative contributions of each ET component to the whole ET became more or less the same after thinning. Additionally, the monthly E (i)/P (g) had relative stable values in both pre- and post-thinning periods, contributing significantly to the ET/P (g) during heavy rainfall conditions. After thinning, ET decreased by 21.4% from 629.3 to 494.8 mm during the growing season and by 20.4% from 979.8 to 780.1 mm at the annual scale, demonstrating that thinning results in an increase in water availability in the forested watershed. This study can improve the understanding of forest water budget in response to thinning and aid in development of appropriate forest management practices accordingly.