| As one of the regions which has the worst water and soil loss problem in China even the whole world, the ecological environment in Loess Plateau is very hard, so in order to improve the feeble ecological environment and control water and soil loss, the vegetation restoration project mainly including converting farmland into forest and grassland was carried out in this region. Research on the ecological effects of different vegetation restoration has great importance in instructing the ecological environment construction in this region as well as objectively evaluating the effects of vegetation restoration project.The experimental site of this research was located in a small village called Ranjiagou, which is a typical hilly and gully region of Loess Plateau. Based on field observation and laboratory experiment, the ecological effects of different vegetation restoration with different implementation times were researched and compared respectively from vegetation population, community diversity, soil evolution and hydro-ecological effect, etc., also the total ecological effects of vegetation restoration in this region was evaluated by adopting the comprehensive analysis method and the main results were concluded as follows:The vegetation population and community changes of different restoration with different implementation times varied evidently. Along with the increase of implementation time, the canopy density of forest and grass coverage of abandoned land increased, which indicated an evident community ecological effect; as for the community richness, abandoned land was higher than forestland, natural vegetation was higher than artificial vegetation under the same growing time, and the final sequence of community richness was 5-year abandoned land>3-year abandoned land>20-year Robinia pseudoacacia >5-year Robinia pseudoacacia (1-year abandoned land)>30-year Robinia pseudoacacia > Platycladus orientalis >Vitex negundo var.heterophylla >orchard (Medicago sativa L)> farmland, and so as the Gleason richness; the final sequence of Simpon dominance index, which reflects the dominant conditions of communities, was 30-year Robinia pseudoacacia > Platycladus orientalis >5-year Robinia pseudoacacia>20-year Robinia pseudoacacia >orchard>Vitex negundo var.heterophylla> Medicago sativa L>1-year abandoned land>3-year abandoned land>5-year abandoned land>farmland; the Shannon-Wiener diversity index reflects the difference of species, and in this research that of forestland was higher than that of shrubbery and grassland, the detailed sequence was 20-year Robinia pseudoacacia >5-year Robinia pseudoacacia> Platycladus orientalis >30-year Robinia pseudoacacia >3-year abandoned land>5-year abandoned land>Vitex negundo var.heterophylla>peach orchard>1-year abandoned land>farmland; the sequence of Sheldon evenness index, which reflects the distribution conditions of species, was Platycladus orientalis >30-year Robinia pseudoacacia >20-year Robinia pseudoacacia >5-year Robinia pseudoacacia> Vitex negundo var.heterophylla>orchard> Medicago sativa L>5-year abandoned land>3-year abandoned land> farmland>1-year abandoned land.The effects on soil quality of different vegetation were different, too, including the physical, chemical and biological characteristics. Along with the increase of restoration time, the physical conditions of soil were improved as well as the promotion of soil stability. As for the physical effects of soil, forestland was better than shrubbery and grassland, natural vegetation was better than artificial vegetation; As for the chemical effects, the contents of organic matters and total nitrogen increased gradually while the changes of available nutrients and total phosphorus were no so evident, and of all the restoration, several kinds of nutrients in fruit orchard, Medicago sativa L land and farmland were much higher, which probable because of artificial fertilization; the biological conditions of soil changed with vegetation restoration, too, the content of soil microbes and enzyme activity were higher than farmland, also forestland was better than shrubbery and grassland.The hydro-ecological effect reflects the absorption and utilization capability of different restoration, mainly including changes of soil water content, soil water retention capability, vegetation interception and water retention capability of litter. The soil water contents of all the restoration increased compared to farmland except the 20-year Robinia pseudoacacia. The vegetation interception and water retention capability of litter were influenced both by vegetation canopy and undergrowth vegetation, and the results shown that forestland>shrubbery> grassland. The water retention capability of surface soil was influenced both by root system and upper part of vegetation, the comparison of curve analysis shown that forestland and grassland were better than farmland, and the detailed results indicated that compared to farmland, the water retention capability of Platycladus orientalis, Vitex negundo var.heterophylla, 30-year Robinia pseudoacacia, 20-year Robinia pseudoacacia, 5-year Robinia pseudoacacia, orchard, Medicago sativa L, 5-year abandoned land, 3-year abandoned land, 1-year abandoned land increased respectively by 32.98%, 24.0%, 28.53%, 25.37%, 12.80%, 10.90%, 10.76%, 10.98%, 7.22% and 0.57%.The results of relativity analysis indicated that Simpon dominance index had a positive correlation with Shannon-Wiener diversity index and a much significant positive correlation with Sheldon evenness index; Shannon-Wiener diversity index had a positive correlation with Sheldon evenness index; soil bulk density had a much significant negative correlation with all the physical factors except the dispersion coefficient and destruction rate, which were much significant positive correlations; unlike the good correlation between organic matters and total nitrogen, the correlation between total nutrients and available nutrients was no so good; the content of soil microbes and enzyme activity had a significant positive correlation, as well as the a value of water characteristic curve and vegetation interception capability.As a conclusion, the research established an index system for assessing the ecological effects of different vegetation restoration in Loess Plateau, determined the weight of each factors by the method of principal component analysis and factor analysis, and by adopting fuzzy mathematics method the membership values of all the ecological factors were calculated and compared with the same dimension. The ecological effects results calculated by two different methods, comprehensive EEI and IEI, tended to be the same and had significant positive correlation with each other. So the ecological effects of different vegetation restoration could be concluded as forestland>shrubbery>grassland, and the ecological effects of different restoration time could be concluded as 30 year>20 year>50 year>3 year>1 year, which indicated that the ecological environment in gully regions of Loess Plateau was improved evidently though the implementation of vegetation restoration project.
|
PDF Full Text Request