Soil properties and nitrogen utilization of hinoki cypress as affected by strong thinning under different climatic conditions in the Shikoku and Kinki districts in Japan

The effect of climate conditions and strong thinning on the soil organic layer, surface soil, and nitrogen and water utilization by plants was evaluated for hinoki cypress forests in Shikoku and Kinki districts in Japan. Thirty-five forests were selected in Kochi, Ehime, Kagawa and Kyoto prefectures. The mean annual temperate of the studied forests ranged from 9.6 to 16.3°C, and the mean annual precipitation ranged from 1,350 to 3,960 mm. Carbon and nitrogen content in the organic layer decreased with increasing mean annual precipitation. In high precipitation areas, carbon and nitrogen content in the organic layer would be lower due to rapid decomposition with low soil acidity and due to loss of litter because of heavy rainfall. Carbon and nitrogen content in the surface soil at 0–5 cm depth decreased with increasing mean annual temperature, but was not related to mean annual precipitation. The results indicate that loss of organic layer by raindrops in a high precipitation area causes lower nitrogen availability for plants. Strong thinning significantly reduced carbon and nitrogen content in the organic layer but did not affect nitrogen concentration and δ¹³C in leaves. These results suggest that climate conditions and strong thinning can affect carbon and nitrogen content in the organic layer and subsequent nitrogen availability in soil, but strong thinning does not appreciably affect nitrogen and water utilization by hinoki cypress.