The Study On Community Characteristics And Species Distributing In Yunwushan Reservation

The vegetation of Loess Plateau has been destroyed seriously. And the area is one of most fragile ecosystems in China. Severe desertification on the Loess Plateau as a result of improper land utilization has caused critical soil erosion and water shortages. To prevent further soil erosion, it is very important to cover the bare land surface with natural vegetation. Restoring the ecological balance is the main task to improve the region environment. For getting the fundamental data for restoring the ecosystem balance in Loess Plateau, the characteristics of plant community structure, the pattern of species distribution and the relationship with environmental factors at natural grassland in Yunwushan Reservation were studied in this paper.The important value and the niche breadth of species in different communities were investigated, and the box-counting dimensions of dominant species in the Reservation were studied with fractal theory, and the relationships between species distribution and environmental factors was analyzed by canonical correspondence analysis. Main results were as follow:1 Stipa bungeana, Stipa grandis, Artemisia sacrorum, Thymus mongolicus, Aneurolepidium dasystachys were dominant species in Yuwushan Reservation in terms of higher important value than other species, and both Stipa bungeana and Stipa grandis had the highest important value in all the enclosed, grazing grassland and weed community. Only in the grazing grassland, had Euphorbia fischeriana, Leontopodium leontopodioides, Artemisia scoparis, Potentilla acaulis, Poa sphondylodes, Gentiana squarrosa high important value. In the weed community, however, the important value of Thymus mongolicus was higher than Artemisia sacrorum.2 Stipa bungeana, Stipa grandis, Aneurolepidium dasystachys had great niche breadth in this area. The niche overlaps among the 3 species were comparatively greater than these between the 3 species and other species in the reservation. The niche overlaps among the 3 species Artemisia sacrorum, Thymus mongolicus, Leontopodium leontopodioides and other species except Stipa bungeana, Stipa grandis, Aneurolepidium dasystachys were at comparatively middle level, and the niche overlaps among other species except these 6 species above were at comparatively low level.3 Both Stipa bungeana and Stipa grandis communities hosted comparatively greater plant species diversity than both Artemisia sacrorum and Thymus mongolicus communities, the grazing grassland had the lowest plant species diversity in the same way. Thymus mongolicus community was the most similar with Stipa bungeana community; however, Artemisia sacrorum community and weed community had the contrary result. 4 Each mean box-counting dimension value of Stipa bungeana, Artemisia sacrorum, Thymus mongolicus was more than 1.3. In the samples with different enclosing years, the box-counting dimensions respectively ranged from 1.3 to 1.8, 1.3 to 1.7 and 0.7 to 1.8, and the mean values were 1.6831, 1.5083, and 1.2968 corresponding species Stipa bungeana, Artemisia sacrorum and Thymus mongolicus. Stipa bungeana and Thymus mongolicus got the highest box-counting dimension at the sample plots which has been enclosed for 20 years, and the highest box-counting dimension of Artemisia sacrorum presented in the sample plots which has been enclosed for 25 years.5 The active soil moisture layer existed in 60㎝-100㎝ depth soil layer in all communities. Soil moisture content in May had no significant difference among 6 communities. The soil moisture content of Stipa grandis community was comparatively higher than other 5 communities in June, however the lowest one was Artemisia sacrorum community in August. The soil moisture content of Stipa grandis community and Stipa grandis community were comparatively higher than other communities in September. The weed community had the highest soil moisture content in all the four months. According to the Gray Theory and the gray correlation coefficient, the soil water content between May and September had a little of change in same as June and August.6 Enclosure measure, aspect and the soil water of 0-80㎝ depth were dominant factors affecting species distribution. There were Artemisia scoparis, Potentilla acaulis, Mentha haplocalyx, Potentilla discolor and Potentilla bifurc in the grazing grassland, however, Bupleurum chinensis, Mentha haplocalyx, Heteropaappus altaicus presented in the enclosed sample plots. These environmental factors had no significant effect on the distribution of Stipa bungeana, Stipa grandis, Artemisia sacrorum, Thymus mongolicus, Aneurolepidium dasystachys.