Abstract: Mechanism of directive restoration artificially induced by creating gaps in Pinus tabulaeformis plantations of protection forest for water resources was studied.The seedling density regenerated in closed stands is 5 375 ind.·m~(-2),which age was 1～2 yr-old.In artificial gaps,the seedling density was 17 062.5 ind.·m^-2,in which 1～2-yr-old seedling,3～4-yr-old seedling and 5～6-yr-old seedling were 73.44%,13.97% and 12.59%,respectively.Daily light intensity in growth season at the height of 0 m,1.5 m,2.0 m was 289.0×100 lux,542.0×100 lux and 589.0×100 lux respectively in the gap,and 139.0×100 lux,146.0×100 lux and 246.0×100lux in closed stand,respectively.In daylight,average air temperature in gaps was higher than that in closed stands in summer at the same time,and the difference was about 2～3 ℃.At night,average air temperature in gaps was less than that in closed stands in summer,and temperature difference was about 0.5～1 ℃;Average air humidity in gaps was higher than that in closed stands at 6:00～11:00 AM in daylight and almost similar in other times a day.Soil temperature in the gaps was higher and change more acutely than that in closed stands in the same depth.The maximum extent of soil temperature difference between gaps and closed stands in 0cm,10cm,20cm depth was 10 ℃,5 ℃ and 2 ℃,respectively.Average soil water content in the layers of 0～10 cm,10～20 cm,20～30 cm was 16.9%,15.1% and 12.3% respectively in the gaps,and 14.6%,12.5% and 9.9% in closed stands.The result showed that the artificial gaps,created as disturbance patch through cutting the trees in the closed stands,induced the changes of the value of ecological factors such as light intensity,air temperature,soil temperature,soil water content,and then caused to accelerate the regeneration of Pinus tabulaeformis in the gaps.

Key words: Pinus sylvestris var.mongolica, Sand-fixation plantation forest, Decline, Decline cause