Remote Sensing Dynamic Monitoring And Eco-security Assessment Of Grassland Degradation In Northern Tibet

Grassland resources is an important component of terrestrial ecosystem, and playsan important role in the ecological environment. Grassland resources also is one of theimportant economic resources for development of animal husbandry, and is the basis ofsurvive in pastoral area and semi pastoral. At the same time,grassland resources ishelpful to windbreak and sand-fixation, purify air, adjusting the climate, keep soilmoisture, reduce water loss and soil erosion, which has important ecological protectionfunction.Northern Tibet plateau is located in the hinterland of qinghai-tibet plateau,whichwith a total area of3.9×105km2and with an average altitude above4500m.This area isroughly one third of the Tibet autonomous region, and is one of the largest regionaldistribution of alpine meadow area in our country.Northern Tibet plateau is the importantgreen ecological barrier for ecological safety in the Tibet and even the whole country,andalso is our country important green gene pool. With the rapid population growth,increasing demand material, the increasingly prominent contradiction between humanbreeding, grassland overload is serious, northern Tibet grassland appear different degreeof degradation.Although the grassland protection construction projects (such as grazingban, set of grass livestock) has be implemented, there is no improving in the prairieecology “partial improvement, overall deterioration”, which poses a serious threat toherdsmen’life and the national ecological security.In this paper, we take the grassland ecosystem in northern Tibet plateau as theresearch object, based on the theory of landscape ecology and the extensive collection ofthe natural geography and social economic data in northern region, using different phaseremote sensing image (TM、ETM+and CBERS during1990、2000、2009),take theBange county which with grassland area and serious degradation as exampel, interpretedthe grass coverage information and established the evaluation index system of remotesensing monitoring grassland degradation, analyzed dynamics of grassland degradationand the spatial distribution pattern during the past20years in Bange county.The paper established an improved ecological footprint model: the productivegrassland ecological footprint model which using the grassland production instead ofconsumption is first established which taking the single grass land type as the research object. Combined with the GIS spatial analysis and visualization technology, realizingthe ecological footprint of visual expression creatively. In this paper, we measure thesustainable development by the unit area land productivity instead of the amount of land.Using the remote sensing image and CASE model, we calculated the net primaryproductivity of land instead of using the yield factor calculate grass actual bearingcapacity. Implements the ecological footprint, ecological capacity, ecological deficit andecological security space display and regional differences.The paper also used theimproved ecological footprint model to measure the dynamic change of Bange countyecological security in the past20years, evaluated the main factors and influencemechanism that influence the grassland ecological security in the region.Mainachievements and innovation of this paper is:(1)Grassland degradation dynamic monitoring in the study area.With the support of3“S” technology, taking the Landsat ETM and TM images andCBERS data in three different phase of1990,2000and2009as basic information sources,the paper extracted the difference phases NDVI images through data preprocessing,analyzed spectral characteristics of grassland resources and established the remotesensing interpretation signs of grassland resources based on field investigation and theanalysis of historical data. The paper also calculated the vegetation coverage with modelmaker of ERDAS and extracted the vegetation coverage depending on unsupervisedclassification methods to acquire the vegetation classification diagram on variousperiods.At the same time, this paper assigned different color according to theclassification results, while ranked grassland degradation and extracted the time-spacedistribution information of grassland degradation.(2) The space-time changes of grassland degradation in the study areaOn the basis of remote sensing image from1990to2009, we analyzed the threephase variation trendency of vegetation coverage in Bange county. The vegetationcoverage of Bange county experiences great changes from1990to2009. Generaltrendency showed that the vegetation degradation area has been increasing and themoderate,severe degradation area in the proportion of the total degradation area is rising.Grassland degradation in1990mainly emerged in the northwest, northeast, center andsoutheast of Bange county. The total degradation areas are78.39×105hm2, and gavepriority to mild degradation which occupies24.74%of the degradation area. Besides, themoderate and severe degradation took the part of5.97%and2.39%respectively. In2000,grassland degradation occurred mainly in the north of the Bamucuo in Bange county. Themild degradation only accounted for40.35%; the proportion of moderate and severe degradation occupied31.36%and12.54%respectively. In2009, Bange county grasslanddegradation occurred mainly in the north of the Bamucuo. The overall vegetationdevelopment situation in Bange county is west better than the east, south better than thenorth. The mild degradation accounted for only41.35%;The proportion of moderate andsevere degradation occupies22.64%and6.28%.The vegetation degradation got more intense in the period from1990to2000andthe total degradation area increased. Total area increased by110.22×104hm2; moderatedegradation and severe degradation increased by56.07×104hm2and22.41×104hm2onthe basis of1990. From2000to2009, grassland degradation area reduced by32.39×104hm2. The light degradation area increased1.63×104hm2, while moderate and severedegradation area reduced by19.85×104hm2and14.11×104hm2respectively. Theanalysis showed that Bange county was in grassland degradation state from1990to2000; while from2000~2009, Bange county grassland degradation speed graduallyreduce，the overall reverse effect is not significant, grassland degradation situation is stillgrim.(3) Try to improving traditional ecological footprint model and applied it to thequantitative evaluation of grassland ecological security.Traditional ecological footprint through consumption to consider natural systemsprovide, given waste of resources. This line of thinking tend to have certain defects. Forexample, low level of consumption of ecological footprint is small, and with a strongsustainability. In view of this, in this paper, a new method was put based on3“S”technology and the improving method of the traditional ecological footprint model.For the first time alone put a major component of the pure pastoral area ecologicalfootprint,the grass as the research object, replacing consumer ecological footprint withthe productive ecological footprints; Put forward the calculation methods of ecologicalfootprint of space: put the traditional land area per capita demand into use demand perunit area of land productivity, using remote sensing image and CASE calculation netprimary productivity of land instead of using the yield factor calculate grass ecologicalcapacity. And through the spatial and visual function of3“S” technology, implementingthe ecological footprint of visual expression creatively. The improved model can trulyreflect the ecological carrying capacity, ecological deficit and the spatial distribution ofecological security level, compared to traditional model calculation results, spatialcalculation results are more intuitive, more has the reference value.(4) Changes of grassland ecological security situation in time and space in the studyarea. The area of lower ecological security level gradually reduced, the area of higherecological security level increased gradually from1990to2009, it shows that over thepast20years, Bange county ecological safety is becoming worse. From1990to2009,The grassland areas of ecological security grade1is reduced by529200hm2;the ecological security grade2decreased from82.76×104hm2to3.28×104hm2, covers anarea of79.48×104hm2, the proportion decreased from34.94%to1.47%; the ecologicalsecurity grade3decreased from66.89×104hm2to about13.53×104hm2, area decreasedby53.36×104hm2, the proportion decreased from28.46%to6.08%; the ecologicalsecurity grade4increased from28.46×104hm2to63.61×104hm2, area increased by3.81×104hm2, the proportion increased from12.02%to14.51%; the ecological security grade5increased from5.57×104hm2to about122.31×104hm2, area increased by116.53×104hm2,the proportion increased from2.44to54.99%; the ecological security grade6grassland area increased by51.03×104hm2. The improved model evaluation results isconsistent with the traditional ecological footprint evaluation results. Both of which showthat over the past20years Bange county ecological security situation getting worse andworse. Compared with the previous10years, the later10years the low ecologicalsecurity level in the area has a greater reduction, and higher ecological security levelin the area has a greater increasion. That means the ecological safety of Bange county hasa greater reduction in the later10years, compare with the first10years. Also theintensity of coordination between the capacity of ecosystem and human social economicactivity becomes more and more bad, ecological safety degree is more and more bad, andecological economic system is in a state of dangerous. The improved model is moreintuitive and more vividly reflects the ecological security status of the characteristics ofspace and time. A comparison of traditional ecological model and improve ecologicalmodel calculation results, results show that the improvement of the ecological footprintmethod can better reflect the regional actual situation.(5)Analysis of influencing factors on ecological security.Via correlation analysis, five factors(population,per capita GDP, proportion ofagriculture and animal husbandry, intensity of grassland utilization and proportion ofprimary industry)were selected as independent variables.Meanwhile,the amount ofeco-footprint as a dependent variable in the STIRPAT model. Those factors were used inthe regression analysis of this model through partial least squares method.The resultsindicated that the main influencing factors of the Bange county’s eco-footprint arepopulation、per capita GDP and intensity of grassland utilization.Through the greycorrelation analysis, the result showes that correlation degree of these indexes which grassland degradation rate, the primary industry grossa ccount for regional output theproportion, population, animal husbandry output value ccount for agricultural output theproportion, grassland contract amount is bigger. They are the main factors of ecologicalcarrying capacity is less.(6) Research of the protective measures from the grassland degeneration. Based onthe traditional law and technical measures,the ecological compensation and humanemeasures were put forward by a large number of investigations and quantitativeanalysis.The sense of ecological protection should be improved by developing variousmeasures of grassland protection propaganda.The sense of responsibility which is fromherdsmen to grassland should be improved by establishing the system of grasslandprotection and practicable responsibility of the contractor.The herdsmen’s initiativeshould be motivated by establishing ecological compensation and subsidization systemof grassland protection. The prairie law-enforcing supervision should be strengthened bypopularizing the prairie supervisor system construction,increasing input, strengtheningmanagement and enhancing the quality of personnel.Transforming the production modeof pastoral animal husbandry,implementing intensification and large scale production,transforming traditional feeding pattern,enhancing income of herdsmen,popularizinghumanistic concern,are the effective approaches to achieve sustainable development ofthe prairie.