The Analysis And Discussion On Technique Of Mountain And Sandland Closure In Loess Plateau Of Shaanxi

Through closing off hill of 5 years, the vegetation succession speeds up with the stable plant community.Woody tree height has increased by 12.5% in closing-off areas comparing with 16.4% of un-closing-off areas. DBH increased by 31.3% and 23.4%,tree crown increased by 24.0% and 22.2% respectively. The stock volume of sea buckthorn and Chinese pine forest mixing with Chinese arbor vitae(侧柏) grew 67.4% and 56.9% than the non-fencing area.The forest grows not only highly. The quality of forest and natural tending keep good level in closing forest areas. Chinese pine biomass reaches 7.1 tons /mu, which is 48.8% higher than.Chinese arbor vitae (Platycladus orientalis) is 5.1 tons / mu, 35.3%.higher than the area without fencing.In closing-off areas, the total biomass ratio of stem, bark, branches, and roots is basically the same as compared with the un-closed area. But average leaf volume reaches 33.3% higher than in un-closed area. Due to better stand growth, timber volume high, making the more nutrients.In the second year after closing-off, canopy density increased by 0.03, shrub cover increased by 2%, herbaceous cover increase in by 3%. After 5 years, canopy density increased by 0.16, shrub cover increased by 6% herbaceous cover increased by 9%.All this promote tree, shrub and grass grow thickly as well as improves soil erosion controlling. The regional plant communities become more stable, changing the local ecological environment.The measures of forest management taken, such as Turning Cutting, thinning ,building sand barrier, preserve the relative amount of vegetation, and fixing sand, and soil and water conservation to ensure the closing-off effect.These measures resolve firewood which can be used to solve the people's life (heating, cooking). Thinning measures promote young tree health growth and become stratified structure of uneven-aged stands.In the sand closing-off area, especially in the strong flow of sand dune,it is to take measures of building sand barrier, planting trees and shrubs ,closing sand area that promote tree growth. The closing hill and sand land is systematic project. It needs to study forward for harmonious society.