Study On Dynamic Change Of Vegetation Coverage And Its Driving Mechanism In Guilin Huixian Karst National Wetland Park,Guangxi

Vegetation change monitoring is the premise of ecological restoration and reconstruction.Understanding the past and present state of Fractional Vegetation Cover is the basis for analyzing the law of vegetation change and tracing back to the key influencing factors of vegetation change.Huixian Karst National Wetland Park is the most typical karst wetland park in the middle and low altitude areas of China.Studying the temporal and spatial dynamic change characteristics of vegetation coverage in Huixian National Wetland Park and exploring the driving mechanism of its change are of great significance to understand the current situation of ecological environment of Wetland Park,guide the vegetation restoration and construction of Wetland Park,protect biodiversity and improve the function of wetland ecosystem.This study takes Huixian Karst National Wetland Park as the study area,Based on the data of 8 remote sensing images of 1989(Landsat 5 TM),1994(Landsat 5 TM),1999(Landsat 7 ETM+),2003(Landsat 5 TM),2008(Landsat 5 TM),2013(Landsat 8 OLI),2018(Landsat 8 OLI)and 2021(Gaofen-1),the NDVI index was selected and the dimidiate pixel model was used to estimate the Fractional Vegetation Cover of each image,combined with Unmanned Aerial Vehicle aerial photography,ground sample survey and climate data,based on Arc GIS10.8 software using difference method,transfer matrix method,unary linear regression trend analysis and so on.This paper explores the dynamic characteristics of vegetation coverage in Huixian Karst National Wetland Park from 1989 to 2021,and analyzes the driving mechanism from two aspects of climatic factors and human activities characterized by land use type change by using Mann-Kendall and Spearman's rank correlation coefficient.The results of the study are as follows:1.The change of Fractional Vegetation Cover:(1)General characteristics of Fractional Vegetation Cover:In 1989,1994,1999,2003,2008,2018 and 2021,the range of low Fractional Vegetation Cover was small,and the area with medium Fractional Vegetation Cover or above accounted for the largest proportion of the park area,and its coverage area was above 65%.However,in 2013,the area of medium and above Fractional Vegetation Cover showed the lowest value in recent 32 years.(2)Grade transfer of Fractional Vegetation Cover:Compared with 1989 and 2021,the Fractional Vegetation Cover of Huixian Karst National Wetland Park increased as a whole,and the main change trend was the transfer of low-grade Fractional Vegetation Cover to high-grade Fractional Vegetation Cover,and only a few areas decreased.The growth of vegetation in most areas is good,and the overall level of Fractional Vegetation Cover has been improved.The Fractional Vegetation Cover of low-grade,middle-low grades is mainly transferred out to the high-grade Fractional Vegetation Cover,and the area is about twice the area of other grades degraded and transferred to this grade.The transfer-in and transfer-out areas of medium coverage were roughly the same,the transfer-in area of medium-high and high-grade Fractional Vegetation Cover was significantly larger than the transfer-out area,and the increased area of Fractional Vegetation Cover in Huixian Karst National Wetland Park was greater than the decreased area.(3)Comparison of year difference of Fractional Vegetation Cover:Comparing annual Fractional Vegetation Cover changes in 1994,1999,2003,2008,2013,2018 and 2021 with those in 1989,the results showed that in 1994,1999,2003,2008,2013 and 2018,the Fractional Vegetation Cover of Huixian Karst National Wetland Park showed a large negative change area,and in 2021,the Fractional Vegetation Cover of Huixian Karst National Wetland Park showed a large positive change area.(4)Linear Trend Analysis of Fractional Vegetation Cover Change:From 1989 to 2021,the Fractional Vegetation Cover improvement area of Huixian Karst National Wetland Park was 4.796 km~2,accounting for 70.47%of the wetland park area.Among them,the area with slight improvement accounted for 49.90%,moderate improvement accounted for 13.15%and extreme improvement accounted for 7.42%.Over the past 32 years,the Fractional Vegetation Cover in the wetland park has generally shown a trend of improvement.(5)Spatial variation characteristics of Fractional Vegetation Cover:From a spatial point of view,the Fractional Vegetation Cover in the wetland park shows an increasing trend as a whole,and the areas with improved Fractional Vegetation Cover account for the vast majority of the wetland parks.The obvious improvement areas are mainly near the Mudong Lake Basin,around Longshan Mountain and the northwest and northeast of the wetland park.Only the ancient Guiliu Canal basin near the Xindoumen and the northwest of Mudong Lake and the area near the village near the boundary of the park have a trend of degradation.2.Influencing factors of Fractional Vegetation Cover:(1)Correlation between natural factors and Fractional Vegetation Cover:Both temperature and rainfall are the key natural factors driving the dynamic change of Fractional Vegetation Cover in wetland park,but the driving effect of temperature on Fractional Vegetation Cover is significantly greater than that of rainfall,and temperature is strongly negatively correlated with Fractional Vegetation Cover,while rainfall is strongly positively correlated with Fractional Vegetation Cover.Strong sunshine,simultaneous hydro-thermal and large evaporation,but Fractional Vegetation Cover shows an opposite response to climate factors,which objectively reflects the driving impact of climate on vegetation types in different study areas.(2)Area change of land use type:The area of non-water wetlands and forest and grassland was the largest in 1989;the largest land use types in 2003 and 2013 was cultivated land,which was nearly half of the area of wetland park in 2013;and the area of cultivated land decreased in 2021,forest and grass land has become the main land use types in the wetland park.(3)Transfer of land use types:From 1989 to 2021,cultivated land and water area experienced a trend of first increase and then decrease,construction land area increased slightly,while forest and grass land and non-water wetlands experienced a trend of first decrease and then increase.Comparing the changes in land use types between 1989 and 2021,the largest total changes are in the order of forest and grassland,cultivated land,non-water wetlands,water areas and construction land.Among them,the biggest change is the decrease of non-water wetlands and the increase of water areas,and there is little difference between the incoming and outgoing areas of other land types.(4)Correlation between land use types and Fractional Vegetation Cover:The spearman analysis showed that,except for the change of construction land and forest and grass land,the area change of water area(negative strong correlation),non-water wetlands area(positive strong correlation)and farmland area(negative strong correlation)had the strongest correlation with the change of Fractional Vegetation Cover.Based on the analysis of the causes of the spatio-temporal dynamic change of Fractional Vegetation Cover in Huixian Karst National Wetland Park in the past 32 years,it is found that the Fractional Vegetation Cover of Huixian Karst National Wetland Park shows the alternation of degradation and improvement.Compared with 1989,the Fractional Vegetation Cover in2021 showed an overall improvement trend.The change of Fractional Fractional Vegetation was the result of the combined effects of climate factors and land use,but the direct driving effect of land use change was more obvious.Therefore,human activities are the most important factor driving the Fractional Fractional Vegetation Cover change of Huixian Karst National Wetland Park.We must regulate human activities,mainly natural restoration,supplemented by artificial intervention,and strengthen the protection of vegetation to improve the ecological environment of wetland park.