Abstract:

The species relations were studied by comparing the biomass of tree, root system, vegetation under tree crown, forest floor in the mixed forests with that in the pure forests. The effects of different mixed spacings on the growth of pine trees were observed in the mixed forests in Longhua County, Hebei Province. The results showed that the relations of two tree species in the mixed forests were basically in harmom state in spite of the existence of restraining role of Betula trees on the growth of pine trees when the mixed distance was less than 250cm. The vegetation biomass under tree crown in the mixed forest stands was much more than that in the pure pine stands, while litter accumulation was less in the mixed stands than in the pure pine stands because of high decomposition rate of litter in the mixed stands. These factors benefit the improvement of physical and chemical properties of soil as well as stand nutrition state. The paper suggests that the mixed forest should be planted in the model of group mixture and the distances of two species should be larger than 250cm.

Key words: Pinus tabulaeformis Carr., Betula platyphylla Suk, Mixed forest, Biomass, Mixing dislance