Abstract: Based on the data collected from 27 plots of Pinus armandii community in the Qinling Mountains, this paper studied the spatial distribution pattern, its scale, and gap characteristics of P. armandii population. The results showed that P. armandii population had a contagious distribution before age 50. At the age from 15 to 20, though the population tended to distribute randomly, the distribution was still contagious. The population at the age from 40 to 50 was at the transitional stage from contagious to random distribution. After age 50, the population started to be senesced, with the distribution pattern turned from contagious to random. The distribution pattern scale of P. armandii always changed with the development stage of the population, being 100 m² in general. The gap size of P. armandii population was similar to its distribution pattern scale, and the gaps of 80～130 m² occupied 59% of the total. Because of the better light and nutrient conditions in the gap, P. armandii seedlings grew well, which helped the population kept its stability though ‘mobile mosaic circle’.

Key words: Mn availability, Calcium-nitrate, Soil moisture, Wetting-drying cycles