Abstract: The study with sampling plot method showed that in Pinus tabulaeformis secondary forests in Qinling Mountains, there were 36 tree species in regeneration layer, occupying 51.4% of the total. The dominant species were Quercus glandulifera, Quercus aliena var. acuteserrata, and Corylus heterophylla. The seedling bank was abundant, and with lower height class and age class. The main regeneration type was seedling, showing the forest being at its middle succession period. Stand density had significant effects on sapling and seedling densities (P<0.01). The sapling and seedling densities increased when the stand density increased from 580 trees·hm^-2 up to 1500 trees·hm^-2, but decreased with the further increase of stand density. Slope aspect also had significant effects on the seedling and sapling densities (P<0.05). The sapling density decreased gradually when the slope aspect changed from SW10° to
SW40°, but increased with the slope aspect changed to shady slope (NE10°). The forest regeneration characteristics differed at different slope positions,with the sapling and seedling densities being relatively higher in flat stand. From foot to top, the seedling density decreased, while the sapling density increased. The sapling density increased from the altitude 1159 m up to 1449 m but decreased from 1449 m up to 1658 m, while the seedling density all along had an increasing trend from lower altitude to higher altitude. It was suggested that the medium stand density on shady slope had the best natural regeneration. To rationally regulate stand density could be an effective way to accelerate the regeneration process of P. tabulaeformis forest.

Key words: Qinling Mountains, Pinus tabulaeformis secondary forest, regeneration characteristics, stand density, environmental factor, Xiongan New Area, urbanization., remote sensing ecological index, ecological quality