Growth Law And Seed Germination Of Pinus Sylvestris Var. Mongolica In Yulin,Shaanxi

Pinus sylvestris var. mongolica is an important greening tree for desertification control in the Three-North Area of China. Its growthand regeneration directly affect the sand-fixing and environmental improvement efforts. Therefore, we collected the anatomical samples of P. sylvestris var. mongolica of different ages to identify its growth characteristic and climatic factors. Meanwhile, we conducted series of experiments on seed germination and emergence involving soil moisture, sand burials, seed storage and soaking to explore the regeneration process. The main results are as follow.(1) The total growth of DBH, tree height and volume increased with tree ages increased. The 1990s Pinus sylvestris var. mongolica is still in the fast-growth period, while the 1970s and 1960s are into the growth steady period, which all does not reach the maturity age for largest volumequantitative maturity, and having a large cultivating potential.(2) Fitting the total growth of DBH and tree height and ages of different years, the best equationfor the 1990s Pinus sylvestris var. mongolica is quadratic polynomial and Sloboda, the best for the 1970s is Yoshida and Levacovic, and Levacovic is the best equation for the 1960s.(3) Temperature and sunshine hours are the man affecting factors of DBH growth, temperature, sunshine hours and wind speed are the man affecting factors of tree height growth, and precipitation, evaporation and temperature are the main affecting factors of volume of Pinus sylvestris var. mongolica.(4) The optimal soil moisture content was 8%-10%or seedling emergence of P. sylvestris var. mongolica, which is equivalent to the topsoil moisture content of 5 mm rainfall in a single rain, in which the emergence percentage arriving 58%. Seeds, storing in the low temperature or soaking in the 25-30℃ water, have emergence advantages when the soil water content is 2%-6%. The emergence percentage is only 19.7% when the soil water content is 20%.(5) Seed emerged mostly under no burial, reaching to 68.9%. Emergence percentage decreased with sand burial depths increased, which cannot emerge more than 3 cm burial depths. The seeds experienced low temperature environment or air drying after wetting have emergence advantages.(6) In Yulin, the surface soil water content is 4%, and more than 5mm rainfall is less than once in 3-4 month, which is the main germination period of Pinus sylvestris var. mongolica. The water supply does not meet the need of the seed emerged is an important factor of restricting natural regeneration. While, rainfall does not the mainly affect thegrowth of DBH and tree height of Pinus sylvestris var. mongolica. Therefore, Pinus sylvestris var. mongolica of different years grew well but natural renewal in severe danger.This improved information will contribute to a better understanding of the growth characteristic and the factors of restricting natural regeneration of P. sylvestris var. mongolicain Yulin, Shaanxi. This study will also be essential to provide a firm basis for planting cultivation and regeneration management of other areas in China.