17:15 〜 18:30
[AHW20-P02] 飛沫蒸発説のエビデンスとしての2種類のスギ高密度林分における雨水配分
キーワード：樹冠遮断、樹冠通過雨、樹幹流、飛沫蒸発
1. Introduction
Rainfall partitioning in two Japanese cedar stands with the stand densities of 5700 trees/ha (the stand A) and 9700 trees/ha (the stand B) was measured, which were the highest densities in measurements of rainfall partitioning in Japanese coniferous plantations (Jeong et al. 2019). Gross rainfall GR, throughfall TF, stemflow SF and canopy interception CI were analyzed. The results were discussed from the viewpoint of splash droplet evaporation hypothesis that claims splash droplets generated by raindrops impacting on the canopy surface evaporate that is a major mechanism of CI (Murakami, 2006).
2. Site and methods
Both stands were 7 years old and located at Kyushu Research Center, Forestry and Forest Products Research Institute, Kumamoto, Japan. Four tipping bucket type flowmeters were used to measure TF and SF of each stand for some 6 months. Data were recorded with an interval of 10 minutes, and analysis was conducted on a rain event basis. Hourly analysis was also made and the results will be shown at the time of the presentation.
3. Results
Total GR during the period was 1405.0 mm. The percentage of CI/GR, TF/GR and SF/GR in the stand A (B) was 18.2% (13.1%), 38.6% (24.7%) and 43.2% (62.2%), respectively. TF/GR and SF/GR in the stand B were, respectively, the smallest and the largest record in Japanese coniferous stands referring to Jeong et al. (2019).
As shown in Fig. 1 CI, TF and SF increase with GR in both stands on a rain event basis. However, in each stand data do not fit with a single linear regression line except for SF of the stand B in Fig. 1c. Instead, there are threshold values, over which data are not placed on the regression line. In Fig. 1a the increment in CI with respect to GR abruptly becomes large for GR > 107.0 mm (162.5 mm) in the stand A (B). Inversely, in Fig. 1b the increment in TF reduces for GR>107.0 mm (37.0 mm) in the stand A (B). In Fig. 1c SF has a single linear relationship with GR in the stand B, but the increment in SF declines for GR>139.5 mm in the stand A.
4. Discussion
High stand density restricts wider extension of branches because of limited canopy area per tree that forces the tree to grow branches upward with steeper angle. The branches collect rainwater effectively and produce much SF.
There exists a possible mechanism to reduce TF and SF for large rain events that are often accompanied by high rainfall intensity. Bassette and Bussière (2008) pointed out that the steeper the leaf angle was the smaller the production of splash became and that the proportion of splash increased with drop kinetic energy. Similar mechanism can work for branches. Upward branches collect rainwater efficiently like a funnel and generate SF without producing much splash for rainfall with low intensity. TF is also large for low-intensity rainfall because raindrops generate less splash with less splash droplet evaporation on upward branches. Nonetheless, when rainfall intensity becomes high the production rate of splash is boosted that reduces TF (Fig. 1b) and SF (Fig. 1c, the stand A) because of active splash droplet evaporation. As a consequence CI is augmented for heavy rainfall, though we have no idea why the threshold values exist.
References
Bassette and Bussière. 2008. Partitioning of splash and storage during raindrop impacts on banana leaves. Agricultural and Forest Meteorology. 97, 9-19. doi: 10.1016/j.agrformet.2008.01.016
Jeong, S. et al. 2019. Marked difference of rainfall partitioning in an unmanaged coniferous plantation with high stand density. Journal of Forest Research. 24, 107-114. doi: 10.1080/13416979.2018.1551116
Murakami, S. 2006. A proposal for a new forest canopy interception mechanism: Splash droplet evaporation. Journal of Hydrology, 319, 72–82. doi:10.1016/j.jhydrol.2005.07.002
Rainfall partitioning in two Japanese cedar stands with the stand densities of 5700 trees/ha (the stand A) and 9700 trees/ha (the stand B) was measured, which were the highest densities in measurements of rainfall partitioning in Japanese coniferous plantations (Jeong et al. 2019). Gross rainfall GR, throughfall TF, stemflow SF and canopy interception CI were analyzed. The results were discussed from the viewpoint of splash droplet evaporation hypothesis that claims splash droplets generated by raindrops impacting on the canopy surface evaporate that is a major mechanism of CI (Murakami, 2006).
2. Site and methods
Both stands were 7 years old and located at Kyushu Research Center, Forestry and Forest Products Research Institute, Kumamoto, Japan. Four tipping bucket type flowmeters were used to measure TF and SF of each stand for some 6 months. Data were recorded with an interval of 10 minutes, and analysis was conducted on a rain event basis. Hourly analysis was also made and the results will be shown at the time of the presentation.
3. Results
Total GR during the period was 1405.0 mm. The percentage of CI/GR, TF/GR and SF/GR in the stand A (B) was 18.2% (13.1%), 38.6% (24.7%) and 43.2% (62.2%), respectively. TF/GR and SF/GR in the stand B were, respectively, the smallest and the largest record in Japanese coniferous stands referring to Jeong et al. (2019).
As shown in Fig. 1 CI, TF and SF increase with GR in both stands on a rain event basis. However, in each stand data do not fit with a single linear regression line except for SF of the stand B in Fig. 1c. Instead, there are threshold values, over which data are not placed on the regression line. In Fig. 1a the increment in CI with respect to GR abruptly becomes large for GR > 107.0 mm (162.5 mm) in the stand A (B). Inversely, in Fig. 1b the increment in TF reduces for GR>107.0 mm (37.0 mm) in the stand A (B). In Fig. 1c SF has a single linear relationship with GR in the stand B, but the increment in SF declines for GR>139.5 mm in the stand A.
4. Discussion
High stand density restricts wider extension of branches because of limited canopy area per tree that forces the tree to grow branches upward with steeper angle. The branches collect rainwater effectively and produce much SF.
There exists a possible mechanism to reduce TF and SF for large rain events that are often accompanied by high rainfall intensity. Bassette and Bussière (2008) pointed out that the steeper the leaf angle was the smaller the production of splash became and that the proportion of splash increased with drop kinetic energy. Similar mechanism can work for branches. Upward branches collect rainwater efficiently like a funnel and generate SF without producing much splash for rainfall with low intensity. TF is also large for low-intensity rainfall because raindrops generate less splash with less splash droplet evaporation on upward branches. Nonetheless, when rainfall intensity becomes high the production rate of splash is boosted that reduces TF (Fig. 1b) and SF (Fig. 1c, the stand A) because of active splash droplet evaporation. As a consequence CI is augmented for heavy rainfall, though we have no idea why the threshold values exist.
References
Bassette and Bussière. 2008. Partitioning of splash and storage during raindrop impacts on banana leaves. Agricultural and Forest Meteorology. 97, 9-19. doi: 10.1016/j.agrformet.2008.01.016
Jeong, S. et al. 2019. Marked difference of rainfall partitioning in an unmanaged coniferous plantation with high stand density. Journal of Forest Research. 24, 107-114. doi: 10.1080/13416979.2018.1551116
Murakami, S. 2006. A proposal for a new forest canopy interception mechanism: Splash droplet evaporation. Journal of Hydrology, 319, 72–82. doi:10.1016/j.jhydrol.2005.07.002