Impact of Growth and Development Characters of Chinese Firand Its Plantation on the Long-term Site Productivity

A systematic study was made on the impact of the growth and development characters of Chinese fir (Cunninghamia lanceolata) and its plantation on the long term site productivity. The results show that many growth and development characters of Chinese fir and its plantation have negative impact on the maintenance of site productivity, i.e. (1) the falling of needles and branches occur lately and mainly concentrative occurs when it is 14-,16 years old in the plantation. (2) the dead needles and branches keep staying on stem long and most of them keep staying on stem when it is 13-,15 years old, which results in non immediate decomposition of dead needles and branches. (3) the litters of Chinese fir contains less nutrients, e.g. the content of N is only 30%-,50% of that in the litters of broad leaved trees that results in less back of the nutrients to the soil in Chinese fir plantations. (4) the decomposition rate of Chinese fir litters is relatively slow with annual decomposition rate below 45%. (5) as a fast growing tree species Chinese fir needs much nutrients to grow especially before 15 years old, which is not compatible by the amount of nutrients given back from the decomposition of litters so that the nutrient cycling rate is less than 40% in Chinese fir plantations. (6) since the density is high for Chinese fir plantation, little or no undergrowth vegetation develop in the Chinese fir plantation before thinning at around 15 years old that results in no contribution of undergrowth to the improvement of soil nutrient status until the plantation grows to 20 years old. It is concluded that the growth and development characters of Chinese fir and its plantation are also the important factors resulting in the degradation of soil fertility or the reduction of long term site productivity in Chinese fir plantation.