Effects of thinning on leaf-fall and leaf-litter nitrogen concentration in hinoki cypress (Chamaecyparis obtusa Endlicher) plantation stands in Japan

The effects of thinning on fresh-leaf nitrogen concentration, leaf-litter nitrogen concentration, and leaf-fall phenology were evaluated over 3 years in two evergreen hinoki cypress (Chamaecyparis obtusa Endlicher) plantations at different elevations (TNG and FMY) and with different site characteristics on Shikoku Island in southern Japan. Two adjacent study plots (400 m2) were selected: in one plot thinning was conducted in 2002 where about 50% of trees were removed and in the other plot no trees were cut as the control.The plantation at a higher elevation (TNG) was characterized by higher soil nitrogen mineralization, higher fresh-leaf and leaf-litter nitrogen concentration and earlier leaf-fall than that at a lower elevation (FMY). The net nitrogen mineralization in the surface soil and fresh-leaf nitrogen concentration in the thinned plots was significantly greater than in the control plots across both sites. Leaf-litter nitrogen concentration was marginally higher in the thinned plots than in the control plots and was negatively correlated with the time of 50% annual leaf-fall. When severe typhoons affected the area in 2004, leaf-fall became earlier and the leaf-litter nitrogen concentration was greater in the thinned plots. The results suggest that the time of leaf-fall is an important factor affecting leaf-litter nitrogen concentration. The results imply that the effects of severe typhoons are greater in the thinned plots and plantations at a higher elevation.