| The North Farming-Pastoral Ecotones of China(NFPE)was a transition zone where the semi-humid agriculture area and arid & semi-arid pasturing area meet here.The significances of studying NFPE were as follows;first of all,the geographic position of NFPE was important and the ecological environment was quite fragile; secondly,the ecological environment was deteriorated and the grassland was destroyed,resulting in large numbers of poor people in recent years.Thus,the studies about the vegetation dynamics in NFPE were significant in the meaning of ecology and actuality. This dissertation takes Yanchi County in NFPE as an example to study the characteristic of grassland vegetation dynamic from 3 scales;plant species,community and landscape(RS scale).The sample-plots were distributed according to different measures of vegetation protection and restoration in population and community scales.The quadrat method and sample line approaches were quoted according to the biotope gradient to investigate vegetation and soil in annual June to August,2002-2006. The data was analyzed by the means of TWINSPAN,DCA and indices analyse of species and community by using community classification software WinTWINS,community ordination software CANNCO,biodiversity analysis software Biodiversity Pro and other ecological statistics software.On this base,the present status and dynamic of grassland vegetation community and plant species in NFPE were studied systematically.In the scale of landscape(macroscopic scale),the vegetation dynamic characteristics from the year of 2002 to 2005 were studied by using NDVI.At the same time, correlation analysis between meteorologic data and mean NDVI values had been done to discuss the main meteorologic factors that influence the vegetation dynamic in NFPE.At the same time,as a special vegetation dynamics type,community edge effect was also studied in this dissertation The grassland vegetation dynamics were studied on 3 scales in Yanchi County in NFPE,2002-2006. Results showed that the best vegetation growth was in 2003 and the less vegetation growth was in 2005 & 2006 and the main phasic research findings were as follows; 1)The vegetation in study area was classified into 3 types and 20 associations.The three vegetation types were;grassland vegetation,which distributed widely and was the main vegetation type in Yanchi County; meadow vegetation,which distributed in the wetland-grassland ecotones and low lying land; halophytic marsh vegetation,which was mainly distributed in the wetland zone.Soil moisture content, organic matter,soil salt content,total nitrogen and so on were the main environmental factors which influence the vegetation distribution pattern along the biotope gradient.Also,the microtopography and grazing pressure were the other influencing factors. 2)Population fluctuation study showed that there were 4 dynamic types;fluctuation increase, representative species was Artemisia ordosica; fluctuation decline,representative species was Pennisetum flaccidum; stable community,representative species were Sophora alopecuroides and Cynanchum komarovii; type of climate fluctuation,mainly included annual plant whose growth status was influenced easily by investigation antecedent precipitation.Plant species mainly present gathering distribution from 2002-2006,but gathering degree was different because of species' biological and ecological characteristic.Otherwise,precipitation,temperature and so on were the other factors influencing populations gathering degree. 3)Based on the meanings of ecology and statistics from community scale,this paper defined the grassland vegetation fluctuation and fluctuation ratio,and built the fluctuation ratio formula as follows; The grassland vegetation quantitative fluctuation and fluctuation ratio in Yanchi,2002-2006 were calculated.Results showed the maximal positive fluctuation ratio was 0.685,meaning a better vegetation growth,which was in 2003.The most negative fluctuation ratio was -1.098,meaning a less vegetation growth,which was in 2005. 4)Community structure fluctuation study showed;all of the values of ecological indices such as community ecological dominance,evenness index and so on were maximal in the year of 2003.In the year of 2005 & 2006,the values of the ecological indices were smaller,especially 2006,the minimum. Thus,the year of 2003 was a better vegetation growth year and 2006,a vegetation less growth year. 5)Community fluctuation of different measures of vegetation protection and restoration showed that nature grassland,rehabilitated fields,abandoned land and so on were effective grassland vegetation restoration measures,especially nature grassland and rehabilitated fields.The study outcomes also discovered that the fenced taming grassland,one of the measures of vegetation restoration was special. After 2-3 years' fencing cultivation,dominant plant community reinforced their dominant position with some companion species dying out in the competition.Plant characteristic number peaked during this time and descended later.In addition,both plant species diversity and the main plants' importance value showed the same trend. 6)Based on the regression analysis between NDVI and biomass,the inversion model applicable for NFPE was built up as follows; Y = 887841NDVI~3 - 710288NDVI~2 + 198232NDVI-15935(R=0.809) On this base,the grassland vegetation quantitative attribute in study area from 2002-2005 was studied. Results showed that the vegetation growth status was best in 2003 and worst in 2005.Rank correlation between values of month-mean NDVI and meteorologic factors presented that precipitation and temperature were the main vegetation dynamic influencing factors in NFPE.Other meteorologic factors such as wind etc.had no obvious correlation to grassland vegetation dynamic in NFPE. 7)The study about edge effect of wetland and grassland ectone discovered that all of the ecological induces such as species richness,community ecological dominance and species diversity were maximal in ecotones than in other two vegetation zone(wetland zone & arid grassland zone)excepting the community evenness index.This indicated community ecotones had higher edge effect.
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