Fragmentation Process Of Alpine Meadow Landscape In The Yellow River Source Zone And Its Response Mechanism To Two Disturbances

The appearance of bare alpine meadow patches leads to the fragmentation of alpine meadow landscape,and the expansion of bare meadow patches was the main manifestation of the degradation of alpine meadow.The detailed description of alpine meadow landscape spatial indicators will provide very important information for understanding the process of alpine meadow degradation and landscape fragmentation,and provide a basis for effective alpine meadow scientific management.The evolution of alpine meadow landscape pattern was always influenced by natural and human factors.And the driving factors are different at different stages or different scales.In this study,low-altitude ultra-fine resolution unmanned aerial vehicle(UAV)images and 13 satellite images from 1972 to 2019 at the macroscopic county scale were used in the two-factor three-level control experiment at the microscopic sample scale(i.e.,the number of plateau pika and mowing intensity factors were set at three interference levels of high,medium and no interference levels,respectively).Study of the Yellow River Source Zone(YRSZ)of degraded alpine meadow landscape dynamic change,combined with Arc GIS 10.7 software technology,the unmanned aerial vehicle(UAV)imaging and satellite image were interpreted,and the landscape fragmentation index was extracted by the FRAGSTATS 4.2 landscape ecological analysis software.The spatial and temporal dynamic changes of the exposed meadow patch landscape in the study area at different scales and the driving factors causing the landscape fragmentation of the exposed meadow patch were analyzed respectively,and the following research results were obtained:(1)In the degraded alpine meadow at different scales,the number of plateau pika was more important than the grazing intensity to cause the expansion of bare meadow patch and the fragmentation of alpine meadow landscape.(2)At the micro plot scale,the density of plateau pika and mowing intensity had significant correlation effects on the area of bare meadow patch and other landscape fragmentation indexes.The interaction effect of high density plateau pika and heavy mowing had the greatest influence on the fragmentation degree of alpine meadow,followed by the single factor effect of medium density plateau pika,single factor effect of control group and high density plateau pika,and the other three interaction effects,single factor effect of medium mowing and single factor effect of heavy mowing.(3)At the micro plot scale,the total area of bare meadow patches decreased by112.05 m~2 in the plot free of plateau pika disturbance,while the total area of bare meadow patches increased by 126.37 m~2 in the other effect plots.The highest growth rate of bare patch area was 89.02%under high density plateau pika and severe mowing.The single factor effect of plateau pika exceeded the interaction effect of mowing disturbance and plateau pika.The single factor effect of mowing was lower than the interaction effect of plateau pika density disturbance and severe mowing,but higher than the interaction effect of plateau pika density disturbance and moderate mowing.When the mowing intensity increased from moderate to high intensity,the effect of high density plateau pika disturbance(14 plateau pika per plot)on the bare meadow area increased by 5 times.The density of plateau pika had more significant effects on the number,area and proportion of patches than that of mowing,and the influence of mowing disturbance on the fractal,shape,landscape shape,contiguity and nearest neighbor indexes were far greater than that of plateau pika disturbance.(4)In the interaction effect of the two kinds of disturbance at the micro plot scale,the landscape fragmentation degree of the bare meadow patch increased with the increase of the plateau pika population when the mowing intensity was the same.Under the same plateau pika population size,the landscape fragmentation degree increased with the increase of mowing intensity.There was a positive correlation between the number of plateau pika burrow and the bare patch area(R~2=0.538),P<0.01.There was a positive correlation between the number of plateau pika burrow in each community and the proportion of bare patch to landscape area(R~2=0.541),P<0.01.(5)At the macro county scale,the landscape fragmentation index of 13 images of Henan County from 1972 to 2019 shows that its average fragmentation degree was low,with an average of 5.73.The average patch fragmentation of the bare meadow was 3.37,while the average patch fragmentation of the healthy meadow was the lowest,only 0.67.Among the natural disturbance factors,slope aspect has the greatest influence on the area and fragmentation degree of bare meadow patch,followed by slope,terrain and altitude.Among the meteorological factors,the average annual wind speed had the greatest influence on the area and fragmentation degree of the bare meadow patch.(6)Among meteorological factors,there was a positive correlation between the average annual wind speed and the exposed meadow patch(R~2=0.6943,P<0.01),that was,the higher the average annual wind speed,the more serious the degradation of alpine meadow,and the larger the area of the exposed meadow patch.However,there was a negative correlation between landscape fragmentation index and wind speed factor(R~2=0.3921,P>0.05).(7)In altitude factor,landscape fragmentation index(LFI)and distribution in the3201-3300 meters above sea level,4101-4200 m and 4201-4300 m between the meadow patches exposed area was in inverse proportion(R~2=0.5164,R~2=0.6606,R~2=0.6948),and extremely significant difference(P<0.01),and distributed in 3401-3500 meters and 3901-4000 m between bare meadow plaque area was positively proportional relationship(R~2=0.6693,R~2=0.4721),and extremely significant difference(P<0.01).In the aspect factor,the bare meadow patch area on semi-sunny,semi-shady and shady slopes were positively proportional to the total bare patches area(R~2=0.9913;R~2=0.9698;R~2=0.9629),and the difference was extremely significant(P<0.01).Among the slope factors,the bare meadow patch area distributed on gentle slope,beach and steep slope was positively proportional to the total bare patches area(R~2=0.9369;R~2=0.8581;R~2=0.5368),and the difference was extremely significant(P<0.01).