Transpiration of trees in a cool temperate forest on Mt. Aso, Japan: comparison of model simulation and measurements
In the large caldera of Mt. Aso, Japan, artificial grasslands were converted into forests of different species due to the decline of the livestock industry in this region. These changes in species composition are thought to have changed not only the transpiration rates (E), but also the responses in E to variations in environmental conditions. For three introduced forest types, we monitored E using sap flux sensors and computed E with a multilayer model parameterized by independently obtained leaf-scale ecophysiological traits. Modeled E replicated the time series of measured E reasonably well, but did not reproduce a decrease in E lasting 20 days after a short rainless period in conifer plantation. Mean leaf-scale stomatal conductance of two deciduous broadleaved tree species was as low as that of trees under dry conditions in other studies, possibly an adaptation for the avoidance of excessive E during rainless periods. These results suggest that land use change influenced E and its response to the rainfall patterns of the region and that drought plays an important role in influencing species-specific E characteristics in this rainy region. The multilayer model in combination with sap flux measurements was found to be a useful tool not only for the extrapolation of E, but also for the detection of the unexpected events, as long as the measured parameter values capture the species-specific seasonality in leaf ecophysiological traits.
KeywordsDrought Leaf ecophysiological traits Mt. Aso Multilayer model Transpiration
We thank Keiji Nakashima for the preparation of this study, staff of the Aso Nature Conservation Office (Ministry of Environments) for their support in securing permission for field research in Aso-Kuju National Park. We also thank the staffs of Minami-Aso Visitor Center, Kyukamura Minami-Aso, Stock-farming Association of Nakamatsu and Kobori, and Aso Green Stock for the use of the field sites. Dr. Yoshitaka Takahasi (NARO), Aso Grassland Restoration Committee and Kumamoto Ground Water Foundation provided information about the history and the social basis for the land cover changes in the Aso region. Drs. Ryuji Ichihasi, Yoshitoshi Uehara, Fumiko Iwanaga and Kenichi Shinozuka supported the field work for the monitoring of sap flux and environmental variables.
Compliance with ethical standards
Conflict of interest
The authors declared that they have no conflict of interest.
This study was supported by the Environment Research and Technology Development Fund of the Ministry of the Environment, Japan (4RF-1301 to YM) and JSPS (26292088 to AI) which funded the cost of field trips and maintenance of instruments.
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