In this paper,the root system and their associated effect of mixed forest of Cunninghamia lanceolata and Sassafras tsumu at eight-year-old were investigated and analyzed.The results showed that Sassafras tsumu might play a important role in improving the root system of Cunninghamia lanceolata growth due to the single root weight of Cunninghamia lanceolata in mixed forest of Cunninghamia lanceolata and Sassafras tsumu was evidently more than that of Cunninghamia lanceolata in pure forest,and that there were different mixed effects in mixed forest of Cunninghamia lanceolata and Sassafras tsumu in different slope situation,which meant that the associated effect was better in higher slope situation than in lower slope situation,and which reflected in the effect of Sassafras tsumu to the height and D.B.H. growth of Cunninghamia lanceolata. This study indicated that the associated effect was positively related to the effect of roots system.
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