Gradient Variations in Landscape Pattern from Northwest to Southeast in Tangjiahe Nature Reserve, Sichuan Province

Abstract

To explore gradient variations of landscape pattern in Tangjiahe nature reserve,the belt transect(width of 2 km and length of 22 km) was set from northwest to southeast on the remote sensing vegetation image by employing GIS technology.Our results indicate that:(1) as a well-developed vegetation type,the woodland distributes widely in the nature reserve and occupies approximately 91.65% of the total study area.In detail,the evergreen broad-leaved and deciduous broad-leaved mixed forest is considered as background of landscape in the reserve because of biggest distribution area.In contrast,sub-alpine shrub meadow and farmland have lower heterogeneity degree because of small area and simple patch edge.(2) With space change from northwest to southeast,the landscape indices vary in three different ways at the landscape scale: increasing,decreasing and no consistent trend.In general,value of some indices,such as edge density,mean proximity index,landscape shape index and mean patch fractal dimension,maintains a increasing trend along the belt transect,but the value of mean patch size index and mean nearest neighbor distance index decrease obviously.The other indices such as Shannon's diversity index,Shannon's evenness index,largest patch index and interspersion juxtaposition index keep a steady fluctuate.(3) On the other hand,secondary deciduous broad-leaved forest,evergreen broad-leaved and deciduous broad-leaved mixed forest,coniferous and broad-leaved mixed forest and coniferous forest are dominant classes at the patch scale,and have obvious peaks in variation of landscape indices value along belt transect in the reserve.