| The fragile ecological environment of karst mountainous areas in southwest China is easy to form rocky desertification.It is difficult to control and repair rocky desertification.Since the 12 th Five-Year Plan,special control has been initiated for rocky desertification in southwest China,and a series of good results have been achieved.Unreasonable land use will aggravate the situation of rocky desertification and seriously restrict the sustainable development of the region.Based on the theory of landscape ecology,this paper takes Chaoying small watershed in Bijie Salahi Rocky Desertification Comprehensive Control Area as the research area.Using multi-period remote sensing image data,13 landscape indices are selected to calculate.The changes of landscape pattern in the study area in recent 14 years are compared quantitatively and qualitatively from the aspects of landscape area ratio,diversity,evenness,connectivity and fragmentation.This paper analyses the overall changes of landscape pattern in Chaoying small watershed before and after comprehensive control of rocky desertification,compares the changes of landscape pattern in different sub-watersheds and their influencing factors,and puts forward the Countermeasures for spatial optimization of landscape pattern in small watersheds.The following conclusions were drawn:(1)On the scale of patch,cultivated land and shrub land had been the main landscapes of the study area in recent 14 years.However,the dominance degree of cultivated land decreased gradually,and the proportion of its area declined also.In contrast,the dominance degrees of shrub land,woodland,grassland and construction land were on the increase,accounting for an increasing proportion of area.On the scale of landscape,the diversity and evenness of landscapes in the demonstration area had increased in the past 14 years,which indicated that the gap among the proportion of each landscape type was narrowing and the landscape tended to be balanced;the degree of spread and aggregation had decreased,indicating that the landscape distribution tended to be discrete and discontinuous,and the landscape was becoming more and more refined;the fragmentation index had increased,indicating that the fragmentation degree of the landscape was aggravated.In general,the dominance and aggregation of the landscape level had dropped,and the diversity and evenness had increased,which meant the heterogeneity was enhancing.(2)By comparing different subregions,generally speaking,the dominant landscapes in upper,middle and lower reaches of the catchment were still cultivated land and shrub land;in 2010,the indices of diversity and evenness in upstream area was the biggest,however,the middle reaches took the place of it in 2018.The index of fragmentation in the four subregions increased in varying degrees during 2010-2018,indicating that the fragmentation of the landscape was aggravated;the fragmentation of A middle reaches area reached its peak in both two years.In comparison,the fragmentation of the downstream sub-basin was the smallest.From 2010 to 2018,the aggregation index of the four subregions showed a downward trend in general,manifesting that the landscape distribution was discrete and discontinuous,which was consistent with the result of fragmentation index.The aggregation indices of each subarea in 2010 and 2018 showed a characteristic of the following: downstream sub-basin > upstream > midstream B > midstream A.It showed that the downstream sub-basin had the best aggregation and connectivity of patches,and was of the patch combination structure which were the easiest to concentrate and connect.On the contrary,the mid-stream subbasin was the most fragmented and discrete region.(3)The countermeasures of optimizing the landscape spatial pattern of the catchment combined with rocky desertification control were put forward from the view of landscape ecology.Modest-intensity rocky desertification in upstream region could be mainly controlled by enclosing the hills for natural afforestation to strengthen the connectivity of forest land;the slight-modest rocky desertification area in A middle reaches region could be mainly restored by mixed agriculture and forestry as well as planted grass and aquaculture to increase the diversity of landscape pattern;for B middle reaches region,Rosa roxburghii planting could be developed as a leading industry to achieve the coordinated development of ecological and economic benefits;and for non-karst-slight-latent rocky desertification area in downstream area,mulberry breeding and silkworm rearing could be developed to promote regional economic development.(4)The influencing factors of landscape pattern change in the study area were discussed from three aspects: natural factors,rocky desertification control and policy factors.Natural factors were restrictive factors,which determined the overall characteristics of the landscape;rocky desertification control projects were direct driving factors,leading to the sharp decrease of cultivated land area and the increase of forest and grassland area;in addition,policy factors were closely related to and promoted the variation of landscape pattern. |
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