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The effect of strip thinning on forest floor evaporation in a Japanese cypress plantation

Xinchao Sun, Yuichi Onda, Kyoichi Otsuki, Hiroaki Kato, Takashi Gomi
Agricultural and forest meteorology 2016 v.216 pp. 48-57
basins, canopy, solar radiation, soil water content, stems, forest litter, models, lysimeters, environmental factors, evaporation, soil water, forest thinning, vapor pressure, Chamaecyparis obtusa, hydrologic cycle, forests, Japan
Thinning results in more open-stand canopies and then immediately modifies the environmental factors that influence forest floor evaporation (Ef). Thus, the changes in Ef induced by thinning would play an important role in the forest water cycle, whereas few studies have reported this topic. This study analyzes the effect of strip thinning on Ef, its spatial variation and identifies the factors influencing it in a Japanese cypress (Chamaecyparis obtusa Endl.) plantation in Tochigi Prefecture, Japan. Strip thinning, which removed 50% of the stems, was conducted in a headwater basin during the period of October 11–November 5, 2011. The Ef was monitored by weighing lysimeters before and after thinning. The daily Ef was strongly correlated with the daily solar radiation (R2=0.62) followed by vapor pressure deficit (R2=0.41) below the canopy, whereas the soil water content had a poor effect on it in post-thinning. After thinning, the daily Ef among the measuring points had no significant difference, indicating that the daily Ef had a small spatial variation. This responded to the small spatial variability in the daily solar radiation under the canopy. Additionally, on an annual scale, thinning resulted in the daily mean Ef increasing from 0.34±0.23 to 0.68±0.47mmd−1. The total Ef increased by 97.6% from 124.0 to 245.0mm. These findings indicate that Ef composes a significant part of the forest water budget after thinning and emphasize the importance of Ef measurements for management practices. This study also provides useful information for modeling the changes in hydrological processes at the forest floor and for evaluating the Ef response to different management practices.