Research On Habitat Conditions And Evaluation Of Vegetation Restoration Of Microtopography In The Loess Plateau,Noth Shaanxi

Habitat conditions affecting the population structure of space and time, community composition and biomass, as a result, conducting research on the habitat differences between microtopographies constitutes the basis of and key issue in the ecological construction of the hilly-gully region in Northern Shaanxi. Therefore, the five types of microtopographies, collapse, gully, furrow, gently-sloped terrace, and scarp, as well as natural vegetation were selected as the research objects, and we located the observation site in the drainage basin of Hegou, Wuqi County. Multiple statistical methods, field survey and index measurements were combined, to reveal the soil, water and nutrient characteristics of the various microtopography; establish a soil quality evaluation system and methods for an integrated evaluation; and explore the evolution of vegetation for an ecological effect evaluation. The results of the present study indicated that:(1) In the 0-40cm soil layer, the moisture content was the lowest in the gently-sloped terrace and gully and the highest in the scarp, with the collapse, furrow and undisturbed slope falling in between; the overall variations were very drastic.The moisture content in the 80-160cm soil layer was always higher than that in the 40-80cmsoil layer. With an increase in soil layer depth, the variation in moisture content tended to be small and stable, and accompanied by a decreasing effect of precipitation recharge. In terms of the moisture content of soil in the growing season, it was gully> gently-sloped terrace>collapse> undisturbed slope>furrow>scarp.The moisture content of the soil was relatively low in July and August, and variations were more drastic than in other months.(2) The organic matter, total nitrogen, available nitrogen, total potassium, available potassium and CEC of various microtopography tended to decrease with an increase in the soil layer depth. Certain variabilities and sensitivities were observed among the 22 physical, chemical and biological soil quality evaluation indexes of the microtopography that were used, among which there were seven weakly variable and insensitive indexes while no strongly variable or highly sensitive indexes were determined. The soil quality evaluation results obtained by the correlation coefficient method and by the factor analysis method were basically the same, and show certain differences from the results obtained by the Nemerow index method, in that the latter had a higher sensitivity than the former two. However, on the whole, the three evaluation methods were all reliable and suitable when applied for an integrated evaluation of soil quality. There were certain differences among the microtopographies in terms of soil quality index (SQI), that is, gently-sloped terrace>gully>collapse>furrow>undisturbed slope>scarp.(3) The systematic cluster analysis method divided the vegetation succession of the microtopographies into five stages. Diversity index can reach their maximum levels after land abandonment for 10 or 11 years. There were significant differences between the sunny slope and the half-shaded slope in terms of Simpson index only. The biomass presents a linear increasing tendency with an increase as the years of land abandonment increase.There were significant differences between the sunny slope and all other slope aspects in terms of biomass, and the differences follow the order of shaded slope>half-shaded slope>half-sunny slope and sunny slope. There was no linear correlation between the diversity of species and the biomass.(4) Fourteen biological effect evaluation indexes (from a total of 27) were screened out. The present paper proposed five grades of biological effect indexes regarding the microtopography of the study region, which are, low (Ⅴ), relatively low (Ⅳ), medium (Ⅲ), relatively high (Ⅱ) and high (Ⅰ). The grades of the biological effect indexes were basically consistent as the weighting & index method model, weighted composite index method model, adoption of all the indexes or only simplified indexes did not have an effect, as most of them fell within the scope of grade Ⅲ. The ranking of their ecological effect indexes is consistent with that of their integrated effect indexes:gently-sloped terrace>gully>collapse >furrow>undisturbed slope>scarp.