| Based on the international frontier topics of ecology-the basic thought of restoration and reconstruction of ecosystem, taken Loess Plateau with flimsily ecological and economical system as case, through social investigation of two years and experiment of one year, the system was studied by combination of macroscopic with microscopic. Through ascertained the stage of ecological restoration in Loess Plateau, the structure and service function of ecosystem were diagnosed. Follow the diagnostic results, the main ecological effects during process of ecological restoration of Loess Plateau were researched as well. At last, the study discussed the interaction mechanism between regressing arable land to forestry (grass) project and change of ecosystem. The main results and conclusion are given as follows:(1) Stage determination of degenerate ecological system of Loess Plateau Triggering factor-ecological response model for degradation and control of ecology inLoess Plateau was proposed, and ascertained the stage of ecological degradation and interaction mechanism between ecosystem and interference factors. Iinitial validation of the model indicate that ecological dominant force of Loess Plateau ecosystem was weak to maintain itself developing. Deviation of the climax of ecological succession from its preconcerted status was ahead of time because influenced by interference factors, and degradation of ecosystem was in stage II. All these changes needed suitable artificial design to impel the ecosystem turn to resumptive direction of self-design.(2) Determination of structure and service function of the ecosystem and influencing mechanism on function of ecological restoration in Loess PlateauThe study analyzed the structure of the ecosystem of Loess Plateau, ascertained and constructed framework of service function of the ecosystem, and discussed the way and mechanism that effects of restoration vegetation on service function of the ecosystem. It was considered that the effects of restoration vegetation on service functions of the ecosystem was completed by function of soil conservation and soil and water conservation, biodiversity and adjustment of climate. Restoration vegetation shown different ecological effect with change of time scale and spatial size.(3) The main ecological effect of restoration vegetation in Loess PlateauFrom function of soil conservation and soil and water conservation, maintenance of biodiversity, ecological effect of restoration vegetation in Loess Plateau was analyzed by experiment and observation.Soil and water conservation effect: soil water content shown seasonal variation. The average soil water content was increased because of significantly difference between water consumption and sequestration by different vegetation type. The increased extent of water content shown natural vegetation > artificial vegetation > control. The natural vegetation was made for accumulation of average soil water content. Soil water-holding capacity was closely related with type and growth of vegetation.The capacity of sequestrating water in different plant shown arbor > shrub > herbage. Different way of restoration vegetation could aroused change of soil physical properties that was closely related with soil water-holding capacity. The physical properties of control soil become bad under long term human disturbance. The main manifestations were increase of bulk density and sand content, decrease of field water capacity, total porosity and soil permeability capability. The soil physical properties were obviously improved under natural vegetation and artificial vegetation, especial natural secondary forest soil shown stronger function for adjustment of hydrology.Ecological effect of soil conservation under restoration vegetation: different way of restoration vegetation result in significantly difference on soil quality. The soil quality of natural and artificial vegetation was higher than control soil that was under long term human disturbance. The quality of natural secondary forest soil was higher than artificial vegetation soil. The main reasons for lower quality in control soil and artificial vegetation soil was that periodically forest tending made decrease in quality and amount of litter, biological function become bad, soil physical structure was break and soil nutrient loss was seriously. The study of effect of different way of restoration vegetation on biological characteristics indicated natural vegetation > artificial vegetation > control. The reason was higher quality of litter, amount of root biomass and abundant species in forest land, which formed benign ecological condition in soil.(4) Climate effect of restoration vegetation in Loess PlateauThe study analyzed the date of NDVI and climate during 1982-2003, and discussed the relationship between vegetation coverage and climate factors on different middle scale and county scale. The experiment of observation on climate in region was used to analyze climate in small scale.Change of vegetation coverage: the vegetation in Loess Plateau was significantly improved in 22 years, especially in recent 3years. NDVI was increased highest with 11.54%. The restoration vegetation in spring and summer was faster than other seasons, increased with 7.0×10-4·a-1. The vegetation in spring and summer determined the distribution of vegetation in whole year. In addition the change of vegetation has obviously difference among region, the NDVI shown increasing trend from northwest to southeast.The relationship between change of vegetation in middle scale and climate factors indicated there was not obviously correlation between NDVI and temperature at middle scale, however it was similar in change of spatial structure of them. Analyse of correlation in county scale indicated that restoration vegetation in typical growth season have significant influence on climate of whole year, spring and summer. The summer climate was the most sensitive to restoration vegetation. When NDVI in typical growth season increased 0.01, the precipitation of summer was increased 86.75mm, evaporation and wind velocity were decreased 115.77mm and 0.08 m·s-1 respectively. Annual wind velocity was decreased 0.09 m·s-1 when annual NDVI of Loess Plateau was increased 0.01.Comparison of microclimate ecological effect strength by different vegetation in recovery of local ground on Loess Plateau: The results of the microclimate effect comparison of vegetation in the same year indicated that artificial vegetation > natural restoration > control. In the range of local ground ,the wind speed and temperature of the artificial vegetation was lower than the abandonment.we see from the strength of effect that the microclimate condition of the artificial vegetation was relatively proper, the process of natural restoration vegetation was slower, adopting artificial recovery could accelerated the successional process of vegetation, so as to promote the increase of diversity, optimizate the service function of ecosystem. But from the stability of the microclimate environment, artificial vegetation has accelerated the process of vegetation restoration to a certain extent, but the proportion of its soil water content was significantly lower than natural restoration.Sum up above, ecological effect of artificial vegetation and natural vegetation has been shown. But effect of artificial vegetation still did not fully shown. There some disadvantages in soil water and fertility, which same with conclusion of factor-ecological response model. So artificial vegetation should be further improved.(5)The study of interaction mechanism between forestry (grass) engineering and ecosystem in Loess PlateauBased on the DPSIR model, we build the interactional framework between the loess plateau forestry (grass) engineering and change of ecosystem, use the interaction index to quantify interaction and analyze scene, and form systemic interaction analysis and quantitative methods. We research from the five aspects of forestry (grass) engineering construction and change of ecosystem, including the driver, pressure, state, impact and response, to construct systemic index, and analyzed the complete interaction inner and outer liaison mechanism. In detailed analysis of internal interaction process, we used the valuable analytical methods and the energy analysis to unify, which makes comparative analysis possible between different types, different states and different forms parameters. The interaction between the forestry (grass) project construction and the change of ecosystem in Ansai were researched. The study concluded that the positive effect was the dominant stage in the Ansai currently. The effect-driven index IIDI was 3.92> 0, which indicated that the project was in income condition after six years. The response index IIIR was 14.35, indicated that the carrying capacity of the system was very strong. Synthesizing all elements, we concluded that the impact of Ansai county's forestry (grass) project on ecosystem environment was conducive to the overall regional ecology, environment and the sustainable economic development. |
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