Abstract: To investigate the natural regeneration of Pinus tabuliformis, thirtytwo plots wereselected inP. tabuliformisforests in Songshan National Nature Reserve. The effects of terrain factors (altitude, slope, aspect, and slope position) and forest stand structural indicators (crown index, proportion of large trees, stand density, shrub coverage and herb coverage) on the natural regeneration ofP. tabuliformis were examined. The results showed that the regeneration density ofP. tabuliformiswas significantly negatively correlated with altitude. The regeneration density of seedlings at different slope positions followed the pattern: bottom slope > middle slope > upper slope. The regeneration density ofP. tabuliformis was negatively correlated with the magnitude of slope. The relationship between the regeneration density and the proportion of large trees could be explained by a parabolic model. The regeneration density was the lowest when the proportion of large trees reached about 50%. Furthermore, the regeneration of seedlings was positively correlated with stand density and herb coverage.

Key words: Loess Plateau, microbial community abundance, real-time PCR, long-term fertilization