Nursery And Silviculture Practice On Introduction Of Pinus Ponderosa On Loess Plateau

With dry climate, scarce afforestation and trees on Loess Plateau, it is great significance in production to introduce trees on foreign land to enrich the local resources of trees.Pinus ponderosas are widely spread in North America with strong adaptability and high economic value. The climate and ecological conditions in its distribution area are similar to that on Loess Plateau. Thirty years' trial plantation in Yan'an Trees-garden indicated that Pinus ponderosa is a good conifer with fast growth and strong resistance to adversity.For further understanding its growth on Loess Plateau in different areas and its growing regulations, it is necessary to find out its growing regulations, seek appropriate nursery and afforestation approaches, define a suitable expansion area, and conduct the researches on Pinus ponderosa nursery and afforestation with the help of the past introduction.Over ten years, the researchers have introduced 20kg seeds of Pinus ponderosa from the region in America with similar climate, conducted nursery trials in eight trial bases located on Loess Plateau, and the north slope of Qinling Range respectively. About 40 acres experimental forests are cultivated in Yan'an, Linyou County, Longxian County and Zhouzhi County. We have found some growing characteristics and regulations of seedlings and young plants. The results of the researches have provided some theoretic basis for the introduction of Pinus ponderosa.The nursery trial showed that the seeds of Pinus ponderosa has a high percentage of germination, can sprout without any treatment (e.g. stored in sand), but it is irresistant to moisture. If lack of sunlight, much moisture would spoil the seeds. Little seedlings of Pinus ponderosa present weak resistance to damping-off. Delay in sowing, high temperature and much moisture are the three major reasons for damping-off. The effectiveness on damping-off prevention and control of new medicines like Nordox, Previcurn is as high as 85%. There is no any physiological draught in the course of growing. The seedlings tolerate low temperature, they can live through winter without cover in Yan'an, and its southern region. Compared with the native Pinus tabulaeformis, the diameter growth of 1-year-old Pinus ponderosa seedlings is obviously faster, the height growth of which is close to that of Pinus tabulaeformis. Strong roots, long vertical roots in particular, enable the plants to resist draught. Early sowing and effective moisture control are the crucial techniques in nursery.The growth analysis on the experimental plantation showed that young plants of Pinus ponderosa grow differently in different areas on Loess Plateau. The height of 6-year-old Pinus ponderosa in Longxian County is 31.4 % more than that in Qinjiagou of Linyou County; the height of the 7-year-old plants is 46.5% more than that in Yan'an Trees-garden. The growth of plants in the same age in Houzhenzi hilly area (North Slope of Qinling Range) of Zhouzhi County is far slower than that in Qinjiagou and Badu Forest Farm of Longxian County, but 30.4% faster than that in Yan'an Trees-garden. In the circumstances of Loess Plateau, the diameter growth of Pinus ponderosa is faster than that of Pinus tabulaeformis (the native plant), but the height growth is slower than that of Pinus tabulaeformis. The diameter growth of 9-year-old Pinus ponderosa is 118.9% that of Pinus tabulaeformis, the height growth, 91.5%. The third year is the growth accelerating period (later than that of Pinus tabulaeformis), before it grows comparatively slowly, after the third year, it grows faster steadily. In the above mentioned four afforestation bases, Pinus ponderosa presents great resistance to adversity. The 6 or 9 year-old young plants grow well with relatively strong adaptability to local climate and ecological environment, not injured by freeze, without plant diseases and insect pests.On the basis of the previous research by the predecessors, nursery and experimental afforestation in multiple areas showed that basically Pinus ponderosa grow fast, resistant to adversity, adaptable to different areas. It equals Pinus tabulaeformis with great worth of expansion.