Effects of clear‐cutting, meteorological, and physiological factors on evapotranspiration in the Kamabuchi experimental watershed in northern Japan

• Published in: Hydrological processes Vol. 35; no. 4
• Main Authors: Kubota, Tayoko, Kagawa, Akira, Abe, Toshio, Hosoda, Ikuhiro
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.04.2021; Wiley Subscription Services, Inc
• Subjects: Carbon dioxide; Carbon dioxide atmospheric concentrations; Carbon dioxide concentration; Carbon fixation; Cellulose; clear‐cutting; Cutting; Cuttings; Evapotranspiration; global warming; Hydrologic data; Interception; Interception loss; intrinsic water‐use efficiency; Mathematical analysis; paired watershed experiment; Photosynthesis; Physiological effects; Physiological factors; Physiology; Solar radiation; Transpiration; tree‐ring cellulose; Water temperature; Watersheds; δ13C; δ18O; Japan
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.14111

This study investigated the effects of clear‐cutting and the meteorological and physiological factors on forest evapotranspiration (ET), by using the water‐budget method in the Kamabuchi experimental watershed (KMB; 38° 56′ 21″ N, 140° 15′ 58″ E) in northern Japan. Meteorological and discharge data collected during no‐snow periods (from June to October) from 1939 were used to compare ET in three sub‐watersheds: No. 1, where the forest had been left undisturbed, and No. 2 and No. 3, where Cryptomeria japonica was planted after clear‐cutting. Paired watershed experiments revealed that clear‐cutting caused ET to decrease by approximately 100 mm yr−1, and this reduction continued for more than 20 years, even after C. japonica was planted. ET fluctuated similarly across all watersheds, regardless of clear‐cutting or planting. This fluctuation is mainly caused by solar radiation and temperature. Intrinsic water‐use efficiency (iWUE) calculated using δ13C of tree‐ring cellulose in C. japonica increased due to elevated atmospheric CO2 concentration. We estimated annual carbon fixation in a single tree as the annual net photosynthesis (A). Subsequently, transpiration (E) was calculated from the relationship between iWUE and A. The results showed that A and E per tree increased as the tree grew older; however, the trees' responses to increasing ca suppress the increase in ET. Moreover, the fluctuation of ET from the watershed was small compared to the fluctuation of P during the observation periods because the increase and decrease in E and interception loss complemented each other. Clear‐cutting has had a large impact on evapotranspiration in forests. Inter‐annual fluctuation and long‐term trends in evapotranspiration are mainly caused by meteorological factors. CO2‐induced stomatal closure did not cause a basin‐wide reduction in transpiration but has suppressed the increase in evapotranspiration promoted by global warming.