Effect Of Hillsides Enclosure For Afforestation Of Water Conservation Forest In Eastern End (North Slope) Of The Qilian Mountains

The water conservation forest of Qilian Mountains is a major ecological barrier of Hexi corridor, which plays an irreplaceable important role to economic and social development of Hexi corridors and Gansu Province. Water conservation forest in Tianzhu Tibetan Autonomous County is located in the easternmost (North Slope) of Qilian mountains. As an important component, water conservation forest accounts for 44 percent of the total area and plays an important role in economic and social development of the Hexi area. From the 1960s, in Tianzhu Tibetan Autonomous County, degraded lands of water conservation forest started to be recovered and developed to a certain extent by measures of enclosure operation. However, there are no systematic research about its effectiveness of closing hillsides to facilitate afforestation, reasonable manner and duration of exclusion, policy-oriented investment costs, etc.The main purpose and significance of this paper is: comprehensively and systematically introduced basic situation of water conservation forest district in Tianzhu Tibetan Autonomous County of the eastern end of Qilian Mountains (North Slope), investigated and researched growth conditions of forest in enclosure area, the impact factors of water conservation, different ways and exclusion period, investments and the existing problems of closing hillsides to facilitate afforestation. In addition, effects of enclosure on water conservation forest construction were further comparatively analyzed, which could provide a scientific basis in restoration of forest resources for government at all levels, forest authorities in charge and the forest management units of Qilian Mountain.Based on survey and research of the enclosure of water conservation forest in the eastern end of the Qilian Mountains (North Slope), we draw the following concussions:1.Stand growth significantly improved in enclosure areas by hillsides enclosure to facilitate afforestationIn enclosure area, natural regeneration saplings in enclosure zone increased by 5.6 times than the control area, height growth of 6 to 20-year-old spruce saplings increased 28.7 percent, coverage and height growth of shrubs increased 2.2 times and 1.8 times, respectively. The survival rate of trees increased 26 percent, save rate increased by 75 percent.2.Water Conservation capacity increased The forest litter in enclosure zone increased by 1.1 times of the control area; moss litter increased by 69 percent; water capacity of moss litter increased by 37; soil moisture content of 0 to 50cm soil layer increased 26.5 percent.3.Remarkable effects of hillsides enclosure to facilitate afforestationIn enclosure area and control area, plant species (tree, shrub and grass) per unit increased 1.32 species, increased by 18.8 percent, including an increase of 18.3 percent of herbaceous, 19.3 percent of woody. Plant species richness index increased by12.7 percent; abundance of plants increased 12.7 percent and was Soc grade. Interference grade of enclusion area was A - in enclosure zone. Vegetation coverage increased by 49 percent and restoration rate of exclusion zones was faster than artificial afforestation and earier 3～4 a.4.Forest ecosystem function of closures was more effective than semi-closureIn enclosure condition, 10 to 14 plants increased and forest lands formed a complex multilayers crown forest, soil thickness increased 15～25 cm, vegetation coverage increased by 50 to 80 percent. The average diameter of main forest crown increased about 8 to 12cm. In semi-enclosure condition, indices of plant species, soil thickness, vegetation coverage were less than enclosure areas.5.The deadline of hillsides enclosure to facilitate afforestation decided by the biological characteristics of plantsIn enclosure condition, broad-leaved trees grew into forest needing 10 to 15 years, conifer trees needed 20 to 25 years to grow into forest.6.Less input, more output of hillsides enclosure for forest conservationAfforestation cost of hillsides enclosure was the 34.3 percent cost of artificial afforestation. Adopting hillsides enclosure for forest conservation method to restore and construct forest and grass vegetation was the fastest and most simple operation, with least cost and investment, and had the quick and effective results to realize restoration of vegetation succession progress.