Pattern and chemical composition of fine litterfall in a subtropical forest in northern Okinawa Island, Japan

The aim of this work was to analyze the pattern and chemical composition of litterfall and to investigate relationships between the contents of nutrient elements in senescent and fresh mature leaves of two dominant species: Castanopsis sieboldii and Schima wallichii, in two forest sites differing in edaphic condition on the northern Okinawa Island, Japan. In this subtropical forest, the mean annual rates of litterfall (including premature litter generated by windstorm) were 684 and 737 g m(-2) yr(-1) at site A and B, respectively. The leaf litter contributed 67% of annual total litterfall. The peak leaf fall occurred in March. Woody litter showed no particular pattern, and its peak fall varied with windstorm. The mean annual nutrient inputs by fine litterfall were, respectively, N 80.1, P 3.2, K 25.8, Ca 58.6 and Mg 17.1 kg ha(-2) yr(-1) at site A; and N 80.6, P 2.9, K 20.7, Ca 65.9 and Mg 17.8 kg ha(-2) yr(-1) at site B. A marked seasonal variability was observed in the concentrations of N, P and K, with no important differences for Ca and Mg, in leaf litter for the two dominants. N, P and K were retranslocated to other tree organs and Ca, Mg, Mn and Al were accumulated in mature leaves. The comparison between leaf litter and fresh mature leaves suggests that the analysis of leaf litter cannot substitute for that of living leaves to evaluate the nutritional status of the species studied for essential elements N, P and K. However, the index of nutrient use efficiency in litterfall can be used as an indicator of soil nutrient conditions. We found site-dependent and between-species differences in nutrient content and nutrient remobilization. The nutrient cycling in this subtropical forest follows a pattern similar to tropical forests, with inefficient within-stand use of N and more efficient cycling of P.