| Vegetation is a kind of autotroph that can carry out photosynthesis,transform inorganic matter into organic matter and live independently.It is the initial producer in ecosystem and determines the morphological structure of an ecosystem.It plays a leading role in terrestrial ecosystem of the earth.Fractional vegetation cover(FVC)is an important index to quantify the growth of regional vegetation,so it is of great practical significance to explore the temporal and spatial dynamics of FVC and its influence factors for environmental quality assessment and ecosystem protection.Based on MOD13Q1 NDVI dataset of Terra satellite from 2001 to 2020,the FVC in Taihang mountainous area was estimated,the spatial distribution and spatiotemporal variation were analyzed,and the stability and evolutionary risk of FVC were discussed.In combination with topography,geomorphic type,soil,land cover type and meteorological data,based on geographic detector model,the influence forces of each factor on the stability and evolution risk of FVC were analyzed.The top three influence factors were selected to analyze the changes of FVC stability and evolution risk within each factor.The main conclusions were as follows.(1)Most areas in Taihang mountainous area had higher FVC,with low FVC in the south and high FVC in the north,and alternate distribution of high and low FVC values in the central region.From 2001 to 2020,the FVC of Taihang mountainous area showed fluctuating growth trend,with average growth rate of 0.0058/a.The lowest FVC was 0.6339 in 2001,and the highest FVC was 0.8100 in 2018.(2)From 2001 to 2020,the area with high FVC in Taihang mountainous area increased from 22.97% to 61.12%,and the area with low FVC decreased from14.83% to 2.81%.In these 20 years,FVC changes showed both increase and decrease spatially,and the improvement was better in the western and central regions,while the improvement was worse in the eastern regions.The area with increase trend of FVC accounted for 84.67%,and the area with decrease trend accounted for 12.97%.The overall FVC in Taihang mountainous area mainly increased.(3)In most areas of Taihang mountainous area,the area with highest FVC stability accounted for 32.63%,the higher stability area accounted for 47.29%,and the lower and lowest FVC stability area accounted for 4.29% and 2.55%,respectively.The regions with poor FVC stability were mainly distributed in the basin areas in the north,west and southwest of Taihang mountainous area,as well as urban built-up areas and their surrounding areas.(4)Hurst index was used to evaluate the persistence of FVC.The closer to 0Hurst index is,the stronger the counter-persistence is;the closer to 1,the stronger the persistence is.The Hurst index of FVC in Taihang mountainous area gradually decreased from northwest to southeast,and the areas with persistent change accounted for 41.27%,mainly distributed in the central and northern parts of Taihang mountainous area with lower altitude.The proportion of counter-persistent change was 57.74%,mainly in the higher altitude area,northeast and southeast area of Taihang mountainous area.The areas with persistent improvement of FVC in the future accounted for 34.84%,distributed in the north,central and southwest of Taihang mountainous area.The areas with persistent degradation were mainly concentrated in the vicinity of urban built-up areas,accounting for 5.69%.The area with potential degradation of FVC accounted for 49.82%,indicating that the overall situation of FVC evolution risk in Taihang mountainous area was not optimistic.(5)The results of geodetector model showed that the stability of FVC in Taihang mountainous area was strongly influenced by land cover type,geomorphy,slope,soil type and sunshine hours,but was less influenced by elevation,relative humidity,air temperature and water vapor pressure,and slope aspect had almost no effect on it.The evolution risk of FVC was strongly influenced by elevation,land cover type,geomorphy and slope,but was less influenced by soil type,sunshine hours,air temperature and water vapor pressure,and the influence of relative humidity,precipitation and slope aspect could be ignored.(6)The top three factors(land cover type,geomorphy type,slope)that influenced the stability of FVC in Taihang mountainous area were selected for further analysis.Among land cover factors,coniferous forest,broad-leaved forest and shrub in Taihang mountainous area showed good stability of FVC,while the FVC of crops,grassland and built-up areas showed poor stability.Among geomorphy factors,the stability of FVC in Taihang mountainous area decreased from plain to platform,and then gradually increased with the increase of topographic relief degree.Among slope factors,the stability of FVC in Taihang mountainous area decreased from the area with slope of 0°? 2.45°to the area of 2.45°? 5.34°,and then gradually increased with the increase of slope.(7)The top three factors(land cover type,geomorphy type,elevation)that influenced the evolution risk of FVC in Taihang mountainous area were selected for further analysis.Among land cover factors,the potential degradation area of FVC in Taihang mountainous area occupied the largest proportion in coniferous forest,broadleaved forest,shrub,grassland and crops,and accounted for more than 50% of the first four types of vegetation.The proportion of continuously degraded areas in builtup areas was the largest among the six land cover types,accounting for 21.93%.Among geomorphy factors,with the increase of geomorphic relief degree,the potential degradation area showed increase trend.Among elevation factors,with the increase of elevation,the area of FVC continuous improvement increased first and then decreased,the potential improvement and persistent degradation areas showed the trend of decrease first and then increase,the potential degradation areas showed fluctuation change of "increase-decrease-increase-decrease". |
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