Abstract: This paper analyzed the height,diameter of breast height(DBH),and age structure of hillsides-closed afforested Pinus tabulaeformis population,with its density characteristics forecasted by Markov matrixes.The results indicated that the population growth at different hillsides-closed afforested stages presented visible difference.The dominant height ranges and DBH classes of P.tabulaeformis individuals were 2～4 m and 6～8 m,and 0～2 cm and >20 cm,respectively,and the population with medium and larger DBH classes had a larger density probability than that with smaller DBH class.There was a larger proportion of old trees if the hillsides-closed afforestation was less than 45 years,while young trees and seedlings were more but died with high proportion if the afforestation was more than 45 years.It could be concluded that natural forest in this area should be protected for at least 45 years.

Key words: Phosphorus, Urban soil, Groundwater