Abstract: Baed on the field experiment and laboratory analysis, characteristics of ecological processes, such as nutrient return, uptake, and of productivity of mixed Cunninghamia lanceolata. and Michelia mncclurei plantations was investigated in comparison with pure C. lanceolata plantations. The results show that in the mixed plantations, the process of nutrient return was greatly enhanced, and the soil fertility and the productivity were raised significantly. For example, in a 15 years old mixed plantation. the branch and leaf litters were respectively twice and triple that in the pure one with the same age, and the litter was mainly corn of fallen leaf of M'macclurei, which decomposes much easier. As a result, the amount of nutrients returned to the soil in the mixed plantation was 2-3 times as much as that in the pure. The annual mortality of fine roots Of the mixed plantation. corresponding to 65.9% of aboveground litter fall, was about twice as much as that in the pure. Tile soil total N, NH₄⁺-N and available K contents of mixed plantation were increased by 64.3, 82.3 and 63.1 % respectively against the pure, soil porosity and water status were also improved. The productivity, measured as annual net production, of mixed plantation was increased by 52.7%. The ratio of return/uptake of five major elements in mixed plantation is twice as big a, that in the pure, indicating that the mixed plantation cycles its nutrients more efficiently, and sustains ifs productivity at a higher level with a minimal human support.

Key words: Mixed plantations, Pure plantation, Nutrient return, Productivity, Ecological process, characteristics of geo-spectrum, space separating degree, land use change, arable land occupation and supplement, Jiangsu Province.