Studies On Coupling Relationship Between Vegetation And Environment In Malan Forest Area On The Loess Plateau

Malan forest area is situated in the northeast of Xunyi County, Shaanxi province. It belongs to the south of Ziwuling in the middle part of the Loess Plateau. Choosing different plant communities in the typical sites of Malan forest area, the relationship among plant communities and the coupling relationship between plant communities and environmental factors of topography and soil were studied by multivariate analysis of plant communities and their members. Based on the grey relational analysis, two problems were both studied. The first was the biological and ecological characteristic from long mutual interaction of species and environment. The second was the relative dominant factors influencing tree species. The coupling relationship between vegetation and environment was studied by analyzing the distributing law of soil nutrient and comprehensively evaluating the properties of soil nutrient.40 plant community samples collected from Malan forest area of the Loess Plateau were multivariate analyzed by two-way indicate species analysis (TWINSPAN) and the detrended correspondence analysis (DCA). The quantitative environmental interpretation of various plant community types was given by regression analysis that connects the ordination scores and environmental parameters. The primary community types, ecological gradients and their quantitative relation with environmental factors were studied. The result showed that slope direction and slope position were the dominant factors to determine plant community distributing pattern of Malan forest area on the large scales, litter thickness, soil humus thickness, soil total phosphorous, available phosphorous content and soil pH values were the dominant factor to determine plant community types and distribution of this area on the small scales. Meanwhile, comparing the ordination chart of plant communities and species, comparing the relationship of environment and plant species, and the result of analyzing plant communities, the result indicated that the character of plant communities had close relation with its members. It was a comprehensive reflection of character of each species. DCA distributing pattern of main species in dominant layer of plant communities decided to larger extent the distributing pattern of the types of plant communities.The relationship of main species in arboreal layer and ecological factors, relative dominant factors influencing main tree species were studied by the grey relational analysis in Malan forest area. The results showed that different plant species have different reflection to environment. Pioneer tree species including Populus davidiana and Malus baccata etc. live in the environment that has lager disturbing. These species were fond of light and have high anti-aridity and tolerance. Pinus tabulaeformis, Carpinus turczaninowii and Quercus liaotungensis have close relation with soil factors. Slope direction, litter thickness and the density of tree were the relative dominant factors to influence main tree species.Compared the soil nutrient of artificial P. tabulaeformis forest of different age, the results showed that the content of available nitrogen, organic matter and total nitrogen of all age stage artificial P. tabulaeformis forest were higher than that of pasture, but PH value was lower than pasture. The artificial P. tabulaeformis forest had improved the properties of soil nutrient to some extent. Samples of plant communities investigated integrally indicated that the properties of surface soil nutrient were better that of deep soil in Malan forest area. It reflected surface enrichment of soil nutrient.The soil nutrient factors affecting the growth of the trees could be lined by the arrangement of grey relating degrees in forest communities of Malan forest area. The result indicated that humus and organic matter were the dominant soil factors to influence the growth of the trees;the following in turn were total nitrogen, available nitrogen, available kalium, available phosphate, total phosphate and pH.Based on the grey relational analysis method, the properties of soil nutrient in main forest types of Malan forest area were comprehensively evaluated. The properties of soil nutrient in Q. liaotungensis dominated forest was the best, it validated the result of Zou Hou-yuan, the stability of Q. liaotungensis dominated forest was high, and it was the climate climax in the succession of Ziwuling area. P. tabulaeformis forest and P. davidiana mixed forest was in the middle, Betula platyphylla dominated forest was worse, especially Q. liaotungensi+B. platyphylla mixed forest was the worst.Using the space series to replace time courses, the evolvement of soil nutrient properties in artificial P. tabulaeformis forest was studied. The result showed that the soil nutrient of P. tabulaeformis forest planted for 20 years was the best, the following was lower, but still was better than that of the forest planted for 10 years.The soil nutrient properties of P. tabulaeformis+ B. platyphylla mixed forest was better than that of the forest types which dominant species was P. tabulaeformis or B. platyphylla. The soil nutrient properties of Q. liaotungensis+P davidiana mixed forest was better than that of the forest dominanted P. davidiana. While soil nutrient properties of forest dominated by Q. liaotungensis showed better than that of Q. liaotungensis and some tree species mixed forest, and the bigger the important value of Q. liaotungensis in the mixed forest, the better the soil nutrient properties. It was a characteristic of Q. liaotungensis forest.