Ecological Functions And Processes In Successive Replanting Stand And Natural Regrowth Following Fallow On Clear-cutting Forestland Of Chinese Fir Plantations Ecosystem

Chinese fir (Cunninghamia lannceolala) is a fast-growing native Chinese species with valuable timber attributes in subtropical area of southern China. The statistics from the 5th National Forest Resources Inventory showed that the total area and stocking volume of Chinese fir plantations have reached 12.39 million ha and 473.57 million m-3, respectively, accounting for 26.55% and 46.89% of those of plantations in the whole nation. Chinese fir plantations will contribute a great deal to alleviating the huge timber demand from rapid economic growth and assisting natural forest conservation at the national level. However, the possibility whether the current management system following the mode of industrial forestry can sustain long-term productivity of Chinese fir plantation has been questioned. Based on the data collected from long-term located observation, the hypothesis that the successive replanting Chinese fir will cause the decline in productivity was verified in this dissertation. Hydrological processes and nutrients cycling in Chinese fir plantation were studied by using small watershed technique combined with closure runoff field, to figure out functional explanation of productivity change in two rotations of Chinese fir plantation. Nutrients management in the process of timber harvest and fallow were put forward as optional biological solutions to achieve the goal of sustainability of Chinese fir plantation. The main results of the research are as follows.In contrast to the first rotation, diameter structure in the second rotation of Chinese fir plantation deviated from normal distribution. The fast-growing period of height and diameter at breast height (DBH) of the second rotation was shorter than that of the first rotation. The biomass and productivity declined to some extent in the second rotation. The fact that the median of diameter distribution increased and the shape of distribution curve became flat with increase of stands age demonstrated that strong competition among trees gave rise to differentiation of growth class grade. Although the value of median of diameter structure in two rotations at age of 10 was 12 cm. the curve of diameter distribution in the second rotation was shaper with more trees skewing in lower diameter than that of the first rotation.There was no difference of DBH growth in two rotations during the period from 3 to 6 years old. However, it was after 6 years old that DBH grew faster in the first rotation than that in the second rotation. The maximum current annual increment of DBH occurred at the age of 3 in two rotations. During the period from 3 to 5 years old. the second rotation had larger current annual increment of DBH than the first rotation. This trend was reversed after 5 years old and the difference between two rotations increased with stand development. Both rotations had the maximum mean annual increment of DBH at age of 5 and no difference in mean annual increment of DBH before 5 years old. The fast-growing period of the first rotation started atage of 3 and ended at age of 8 while that of the second rotation started at age of 3 and ended at age of 7. The active growing periods of diameter of the first and second rotation were 15 years and 11 years, respectively.The average height of two rotations increased slowly in the first 3 years following replanting and there were no differences in height growth in two rotations. After 3 years old, the height increased faster in the first rotation than that in the second rotation. The highest value of current annual increment of height appeared at age of 6. The first rotation entered fast-growing period from 2 to 13 years old. The highest value of current annual increment appeared at age of 5. The period of fast-growing of the second rotation started at age of 3 and ended at age of 10. The period of fast-growing was 4 years shorter in the second rotation than that in the first rotation. The maximum mean annual increment of the first rotation appeared at age of 10 while that of the second rotation occurred at...