The Kiryu Experimental Watershed: 50-years forest dynamics and hydro-biogeochemical studies in Central Japan

Kiryu Experimental Watershed (KEW; 5.99 ha) was established in 1967. It locates at Shiga prefecture, Central Japan (34 °58' N, 136 °00' E). Since then, various studies such as water cycle, rainfall-runoff processes, biogeochemistry, and gas exchange, related with forest dynamics have been ongoing.

The climate is warm temperate, with rainfall distributed year round, peaking in summer, but producing little snowfall in winter. The mean annual precipitation is 1664.0 mm. The mean annual air temperature is 13.6 ℃. The entire area of KEW is underlain by Cretaceous biotite granite, called the Tanakami granite. Around this region, it was bare mountains because of historically overuse of tree and timbers. The erosion control works had started about 120 years ago, and forest had recovered. Now, the vegetation of KEW is uniform, mainly consists of Chamaecyparis obtusa Sieb. et Zucc. (Japanese cypress) planted in 1959 for forestry purposes.

KEW is one of a leading experimental forest with long-term monitoring data in Japan. One of the main topics of the biogeochemical studies is long-term dynamics of streamwater nitrate concentration in relation to the forest conditions. In 1990's and early 2000's, the concentration was affected by the disturbance with pine-wild disease. After that, it has already passed about 25 years. However, the concentration is still higher than the level before disturbance occurred. The recent higher concentration may be the result of attenuation of unmanaged mature Japanese cypress forest. This is our new hypothesis, and the monitoring data of NEP support it. We have been keeping the site to understand how the climate change effect on the forest dynamics, and following hydrological and biogeochemical in a warm temperate zone.