Abstract: Chinese fir (Cunninghamia lanceolata) is a fast-growing species native to China,and has a very important status in production of commercial timber.In response to the growing need for timber,pure Chinese fir plantations have been extensively replanted on the same site in successive rotations,which has resulted in serious problems of soil fertility degradation and productivity decline,and these problems have caused considerable attention from foresters,microbiologists,soil scientists and ecologists.They have also done a lot of work on these problems and studied the mechanism of productivity decline of replanted Chinese fir plantation.In this article,the author described the characteristics of productivity decline and soil degradation,and summed up the factors caused lower productivity,and analyzed the degradation mechanism of replanted Chinese fir plantation.In sum,productivity decline and soil physical and chemical characteristics deterioration were the main properties of replanted Chinese fir plantation.The factors summarized primarily as two kinds of reasons.One was the unreasonable management that was the edogenic factor,and another was the biotic self-characteristics of Chinese fir that was the intrinsic factor of poor establishment of replanted Chinese fir plantation.The combination of the edogenic and intrinsic factors reduced the productivity decline and soil degradation of the replanted Chinese fir plantation.

Key words: Chinese fir, Productivity, Allelopathy, Phenolics, Autotoxicity