LEAF LITTER DECOMPOSITION ALONG THE TEMPERATE - TROPICAL TRANSECT (EAST CHINA): THE INFLUENCE OF STAND SUCCESSION, LITTER QUALITY AND CLIMATE

The relationship between litter decomposition and forest succession in addition to the influence of climate variables on the rate of litter decomposition in forest ecosystems are poorly understood. In this study, the effects of forest successional stages, climate, and litter quality on litter decomposition rates were investigated in five sites located in China. The selected sites cover 29 degrees of latitude from 18 degrees N to 47 degrees N and spans more than 5,000 km in length along a temperature gradient that transverses across eastern China. This zonal gradient includes five climate zones from temperate to subtropical to tropical zones. Forest types include broad-leaved Korean pine, deciduous broad-leaved, evergreen broad-leaved, monsoon evergreen broad-leaved, and tropical rain forests. The North-South Transect of Eastern China (NSTEC) is one of fifteen international standard transects setup by Global Change and Terrestrial Ecosystems (GCTE). NSTEC is a key component of the International Geosphere-Biosphere Programme (IGBP). The litterbag method was used in this study to determine mass loss and annual decomposition rates of eight tree species (Pinus massoniana Lamb., Cunninghamia lanceolata (Lamb.) Hook., Schima superba Gardn. et Champ., Cinnamomum camphora (L.) Presl., Cyclobalanopsis glauca (Thunb.) Oerst., C. gracilis (Rehd. et Wils.) Cheng et T. Hong, Michelia chapensis Dandy, and Castanopsis eyeri (Champ.) Tutch. through a timeframe starting in May, 2006, and ending in May, 2008. Litterbags 15 x 15 cm and 0.5 x 1.0 mm mesh were filled with 10 g of leaf litter collected from the subtropical forest region and then placed onto the forest floor in triplicate samples for each eight species in all five sites. Three litterbags per species were retrieved from each of the five sites at two month intervals during the two year experimental period. Results suggest that species litter in the climax stage (C. glauca, C. gracilis, and M. chapensis) tended to decompose faster than those in the pioneer stage (P. massoniana and C. lanceolata). Initial phosphorous (P) and nitrogen (N) concentrations of leaf litter were the most critical variables of litter quality in relation to the impact on the rate of litter decomposition. Litter decomposition at different successional stages was found to be directly related to climatic variables such as mean annual precipitation (MAP) and mean annual temperature (MAT). MAP and initial P and N concentrations could therefore be considered good indicators of rates of decomposition.