Assessment on effect of fully hillsides-closed and afforested mode on natural Pinus tabulaeformis forest
完全封育方式对天然油松林的影响

Huanglong Mountain forest zone is one of the main natural secondary forest zones on the southern Loess Plateau in Shaanxi province. Since 1950, a mode of fully hillsides-closed and afforested (FHA) has been applied in the forest. In some special sites, the forest age even exceeds 80 years. Pinus tabulaeformis forest is the most important vegetation in warm temperate region in China. Similarly, population of P. tabulaeformis is dominant in the formed forest ecosystem. Quercus Liaotungensis, Syringa oblate, Populus davidiana, Prunus davidiana,, Betula platyphylla and Toxicodendron vernicifluum can be occasionally found in arbor layer and species of shrub are abundant. Based on the data collected from 31 plots and 93 soil samples, health of the forest ecosystem has been discussed and appropriate FHA age has been pointed out.12 indexes manifesting traits of vegetation and soil in natural secondary P. tabulaeformis forest ecosystem were acquired by sensitive analysis and the assessment index system for FHA mode was established. According to equal distance method, 5 grades of integrated index for evaluating FHA mode were compartmentalized. Effect of FHA mode on natural secondary P. tabulaeformis forest was evaluated by methods of integrated index and analytic hierarchy process (AHP). The results are follows: values of integrated index in FHA 16, 25, 30, 45, 60a and 75a were 7.25,6.88,7.82,5.51,4.78 and 2.79 respectively. With the FHA age increase, the effect of FHA mode became worse. It could be concluded that natural forest should not be protected in FHA way more than 45a. After 45a, mixing suitable tree species, select cutting and other cultivating and managing measures should be adopted.