Comparison on nutrient cycling in different generation plantations of Chinese fir

Chinese fir Cunninghamia lanceolata (Lamb.) Hook., a fast-growing evergreen coniferous tree with high yield and excellent quality, is one of the most important tree species of timber plantations in South China with a planting history extending over more than 1000 years. The total plantation area of Chinese fir in China is around 9.11 million (hectors). One of the critical issues faced in Chinese fir plantation management is the decline of site productivity under traditional intensive regime, of which the imbalance of nutrients has been assumed to be one of potential causes. It is (extremely) important to understand the reasons for productivity decline in Chinese fir plantations in successive rotations in (order) to develop sustainable management of these plantations in China. In order to compare nutrient distribution and (nutrient) cycling between Chinese fir plantations of different generations and evaluate whether there is a relationship (between) nutrient availability and decline in productivity in Chinese fir plantations, nutrient cycling in different generation and age plantations of Chinese fir were studied in Jianou, Fujian Province, South China. The results showed that there were (significant) differences in nutrient cycling of different generation plantations. As the planting generation increased, annual nutrient return, absorption and (return/absorption) ratios of Chinese fir plantations declined. They were in the (sequence of) the first-generation plantations the second-generation plantations. It indicated that successive planting was not beneficial for soil fertility recovery of Chinese fir plantation. As the stand age increased, annual nutrient return, (uptake) and return/absorption ratios of Chinese fir plantations increased. They were in the sequence of mature plantations middle-aged plantations. Compared with the middle-aged plantations, nutrient accumulations in first-generation and (second-generation) (mature) plantations decreased by 14.74% and 11.86%,respectively. Therefore, long cutting cycle is beneficial for nutrient return of Chinese fir plantations.