Study On The Community Stability Of Hippophae Rhamnoide And Populus Simonii Plantations In Hilly-gully Region Of Loess Plateau

Hilly-gully region of Loess plateau is one of the places where there the problem of erosion of water and soil is very serious, and the ecology environment is very brittle in the world. Because of the human population of this area increasing sharply, the field reclaimed blindly, immoderate graze, and the irrationality utilization of land resource, the environment was made even worse. Natural forests were all destroyed. The main vegetation types are only Sophora davidii, Ostryopsis davidiana undershrub etc. and Hippophae rhamnoide, Populus simonii and Robinia pseudoacacia etc. built to restore the environment. Some phenomena were found these years that parts of plantations were not stable, and yet were deteriorated gradually for maladjustment to the location environment. Those plantations could not preserve the soil and water, and not improve the environment. So this research studied on the population structure, species diversity, moisture and nutrient in soil, and the infection of environment elements of the main plantations, Hippophae rhamnoide and Populus simonii. Systemically, and confirm the suitable environment of the main plantations, in order to offer theory bases to vegetation renewal and rebuilding. The result is showed as follows. Hippophae rhamnoide is a nicer shrub species for plantation becoming savageness. This population could renew very well in Hilly-gully region of Loess plateau. With the time going, the population structure took on a developing trend, biodiversity, moisture and nutrient in soil increased gradually, and community was more stable in a development sequence. The number of youth and adults was large on half-sunny, half cloudy slope and cloudy slope, which showed that this population was a developing one, and could survival in the future. There were higher biodiversity, strong intensity of Interspecific association, and better moisture and nutrition in soil in this plantation on the half-sunny and half cloudy slope which provided a guarantee for community stabilizing gradually. So, some measures should be adopted to build Hippophae rhamnoide plantations on half-sunny and half-cloudy slope by using its characters of biology and ecology, in order to exert its ecologic function to strengthen the water and soil retained, improve the soil physical and chemical structure. The Populus simonii population renew difficultly in Hilly-gully region of Loess plateau. In one development sequence, the renewal seedling appeared when the population developed at 20 years, and more renewal seedlings, higher species diversity, more reasonable community composing and structure at 30 years. However arbor layer was still only one species, and this plantation appeared to decline at 45 yeas. Although the soil nutrient had certain improvement, the community could not get the guarantee of enough nutrition for stably. The result of research on different habitats showed that this population could not renew at sunny slope. Compare with in the sunny slope, there were growing well Populus simonii, several seedlings appeared higher biodiversity and better soil nutrient content in the cloudy slope. But these could not change the declining trend of the whole population, the Populus simonii population disappeared gradually. So the Populus simonii should be planted at places where there has more soil water, such as cloudy slope, gully and so on, and some suitable upbringing measures should be adopted at a time, in order to prevent this community from declining and promote the population to renew. The fact that how to improve plantations'stability and productivity was a problem solved urgently in the eco-environment rebuilt field now. This research showed that some aspects should be taken into account to improve the plantation stability. First, to build certain vegetation types, arbor, shrub and herb, which should be adapt to the local environment, especially the water and hot, according to the distributing rule of the zone vegetation. Second, t o have important attach to selecting and using local species. Third, to select species which have strong resistance and adaptability. Forth, to adopt suitable upbringing measures for promoting plantations renew. Fifth, to pay more attention to reasonable configure fashion, and simulate the block pattern of natural vegetation to improve plantations evolving naturally, and form a stabile one.