基于分形理论的土地利用时空格局变化——以嘉陵江流域为例

Spatio-temporal pattern change of land use based on fractal theory:Taking Jialing River basin as an example

土地利用影响流域水土流失状况,从分形理论的角度探讨土地利用的时空变化格局,为流域水土保持规划提供科学参考。基于分形理论,计算各土地利用类型分形维数和稳定性指数,分析面积转化情况和空间格局稳定性,阐明土地利用结构变化和演变转换规律。结果表明:1990—2020年间,耕地、草地面积减少,林地、水域、建设用地、未利用地面积增加;整体土地利用类型斑块数减少,平均斑块面积呈现上升趋势;耕地、林地、草地、水域和建设用地分形维数逐年增加,未利用地的分形维数为先减少后增加状态。在此期间,土地利用整体分形维数逐步上升,流域内部自相似性减弱,斑块形状向着不规则状态发展,多边形斑块嵌套结构复杂化,空间结构稳定性减少。

[Background]Land use type is an important indicator to quantitatively predict the degree of soil erosion,which reflects the situation of soil and water loss in the basin to a certain extent.Its change process directly reflects the interaction between human activities and the natural environment.Over the years,scholars have constantly innovated research methods and models to explore the law of land use change.This study discusses the temporal and spatial change pattern of land use from the perspective of fractal theory,and provides scientific reference for future watershed soil and water conservation planning.[Methods]Based on fractal theory,Jialing River basin was selected as the research object.By calculating the land use conversion matrix from 1990 to 2005 and from 2005 to 2020,we calculated the fractal dimension and stability index of the whole basin and different land uses in the third phase,and established a regression model.Further we analyzed the transformation of area and the stability of spatial pattern,and deeply explored the changes of spatial and temporal pattern of land use in 1990,2005 and 2020 to clarify the rules of land use structure change and evolution transformation.[Results]From 1990 to 2020,the area of cultivated land and grassland decreased,and the area of woodland,waters,construction land and unused land increased.The number of patches in the overall land use type decreased,and the average patch area showed an upward trend.The number of patches of the overall land use type showed a downward trend,and the average patch area showed an upward trend.The average patch area of woodland increased the most,11.81 hm 2,and the average patch area of grassland increased the least,0.74 hm 2.The number of patches of cultivated land,woodland,grassland,waters and unused land showed a downward trend,while the number of patches of construction land only showed an upward trend,of which the number of patches of woodland decreased the most,by 591833,and the number of patches of construction land increased the most,by 15130.The fractal dimensions of the overall land use in 1990,2005 and 2020 were 1.4863,1.4972 and 1.5142 respectively,rising gradually.The internal self similarity of the Jialing River basin weakened,and the patch shape developed toward an irregular state.The fractal dimensions of cultivated land,woodland,grassland,waters and construction land increased year by year.The fractal dimensions of unused land decreased first and then increased.The fragmentation of polygon patches of most land use types increased,fragmentation was serious,nesting structures became more complex,and spatial structure stability decreased.[Conclusions]Influenced by the“Changzhi”project and the policy of returning farmland to forests,the land use in the Jialing River region has changed greatly from 1990 to 2020 due to human activities.The overall fractal dimension of land use has gradually increased,the self similarity within the watershed has weakened,the patch shape has developed towards an irregular state,the nested structure of polygon patches has become complex,and the stability of spatial structure has decreased.