Litter production, nutrient return and leaf-litter decomposition in natural and monoculture plantation forests of Castanopsis kawakamii in subtropical China

The amount and pattern of litterfall, its nutrient (N, P, K, Ca and Mg) returns, and leaf-litter decomposition associated with its quality were studied in a natural forest of Castanopsis kawakamii (NF) and adjacent monoculture plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata, CF) in Sanming, Fujian, China. Mean annual total litterfall over 3 years of observations (from 1999 to 2001) was 11.01 t·hm -2 in the NF, 9.54 t·hm -2 in the CK and 5.47 t·hm -2 in the CF respectively. Of the total annual litterfall in the three forests, leaf contribution constituted 59.70%, 71.98% and 58.29%, respectively. Litterfall in the NF and CK showed similar litterfall pattern with a distinct peak in April of each year. While for the CF, the litterfall peaks occurred in April (or May), August and November, respectively. Except for the highest annual Ca returns in the CF and Mg returns in the CK, the three forests could be arranged in this sequence with respect to annual nutrient returns: NFCKCF. The annual percent leaf litter mass loss was the highest for C. kawakamii in the NF (98.16%) and the lowest for Chinese fir (60.78%). Ratios of C/N and lignin/N had significantly negative influences on decay rate coefficients, while initial N and water soluble compounds exerted significantly positive influences. The results of this study demonstrate that the natural forest has a greater capability for maintaining site productivity than monoculture plantations due to higher amount and quality of litter coupled with greater nutrient returns and faster litter decomposition. Therefore, conservation of the natural forest is recommended as a practical measure in forest management to realize sustainable development of forestry in mountainous areas of southern China.