[Dynamics of biomass- and nutrient accumulation in a Chinese-fir plantation]

Based on the over 30 years observation data in Huitong National Research Station of Forest Ecosystem under Chinese Academy of Sciences and related literatures, this paper analyzed the dynamics of the biomass- and nutrient accumulation and allocation in a Chinese-fir (Cunninghamia lanceolata) plantation, and the effects of rotation length and harvest intensity on the nutrient input/output. The results showed that stand age was the main factor affecting the biomass- and nutrient accumulation and allocation, and different organs had significant differences in their biomass- and nutrient storage. Stand age and different organs explained 37.1% and 40.3% of the variations of biomass- and nutrient storage, respectively. With the increase of stand age, the proportions of biomass and nutrients allocated to stem increased, while those allocated to foliage decreased. The accumulation rates of biomass and nutrients peaked at the age of 17 and 13, respectively, indicating that the nutrients reached their maximum accumulation rate ahead of the biomass. The nutrient requirement per unit dry biomass production decreased rapidly from the stand age 3 to 20 and reached a steady state after then, suggesting that the nutrient use efficiency increased with stand age. The analysis of different harvest scenarios showed that to prolong rotation length and to lower utilization intensity could reduce nutrient output. For example, if the rotation length was prolonged from 28 years to 56 years and only stem was harvested, the harvested biomass would be decreased by 31.57%, and the output of N, P, K, Ca, and Mg would be decreased by 42.02%, 58.93%, 27.70%, 31.07%, and 45.26%, respectively.