[Eco-hydrological characteristics of a subtropical evergreen broadleaved forest in Japan].

A three years (1998-2000) observation on the eco-hydrological characteristics of Castanopsis sieboldii and Schima wallichii dominated subtropical evergreen broadleaved forest on the Okinawa Island of Japan showed that during the observation period, the mean annual precipitation was 3325 mm, and 42.3% of it was directly or indirectly contributed by typhoon rainfall, implying that typhoon played a very important role in the hydrology of the forest. Through-fall and stem-flow contributed to 53.9% and 30.9% of the annual rainfall, respectively. The higher stem-flow could be due to the high wind velocity, intense rainfall, and the crown morphology of dominant species C. sieboldii with inclined branches and concave-shaped leaves. Interception loss occupied 15.2% of the total rainfall, being the lowest in the range of 15%-30% widely reported for many broadleaved evergreen forests. The annual surface runoff and lateral flow were 1092 mm and 613 mm, respectively, and the high proportion of surface runoff (32.8%) was probably due to the poor physical properties of soil, particularly the low noncapillary porosity (8%-12%), high clay content (51.9%-60.5%), and low infiltration rate (12 ml x min(-1)) in deeper soil layers. The effective and maximum water storage capacity of 0-70 cm soil layer were 85 mm and 324 mm, respectively, and the maximum water-holding capacity of forest floor was 2. 8 mm, which were close to or lower than those of the subtropical and tropical rain forests in China.