Abstract
We investigated relationships between the phenology of leaf-fall and nitrogen use by trees in eight Hinoki cypress (Chamaecyparis obtusa Endlicher) plantations in three areas (Otoyo, Kochi, Tsuno) in Kochi prefecture. The time of 10% annual leaf-fall ranged from 7 September to 22 October, and time of 50% annual leaf-fall ranged from 25 October to 3 January of the following year. The time between 10% and 90% annual leaf-fall ranged from 30 to 189 days. Although the mean annual temperature of the forests ranged from 9.6 to 16.7℃ and differed greatly, mean annual temperature was not correlated with the phenology of leaf-fall. By contrast, the time of 10% annual leaf-fall was negatively correlated with the nitrogen concentration of litter-fall. These results suggest that in nitrogen poor environments, plants have longer growth period. The time of 50% annual leaf fall was positively correlated with the relative height growth of the forest. The leaf-fall in the forest with lower height growth is earlier probably due to water stresses. These results suggest that the time of leaf-fall of the Hinoki cypress forests in the region occurs earlier in water-limited conditions and later in nitrogen limited conditions.
