Relationship Between Spatial And Temporal Distribution Patterns Of Forests And Environmental Factors In Ganzi Prefecture,Sichuan

The relationship between forest distribution patterns and environmental factors and their formation mechanisms is a hot research topic in physical geography,ecology,and phytogeography.Forests are the mainstay of terrestrial ecosystems,closely related to human ecological well-being and national ecological security,and a strategic resource for promoting the construction of ecological civilization,therefore,it is of great theoretical and practical significance to investigate the spatial and temporal dynamics of forest distribution patterns and their formation mechanisms.Ganzi Tibetan Autonomous Prefecture("Ganzi Prefecture")is located in the heart of the Kang-Dian axis in the northern part of the Hengduan Mountains and is a biodiversity conservation hotspot,climate-sensitive area,and ecologically fragile area of global concern.It is the second largest forest area in China and the main part of the southwestern forest area and is an ideal area for the study of forest spatial distribution pattern formation mechanisms.However,the forests in Ganzi were massively logged and degraded before 1998,and the implementation of forestry ecological projects and conservation policies have brought about great changes.But the forests in Ganzi were massively logged before1998,and the implementation of forestry ecological projects and conservation policies have led to great changes in the forests of the region.However,the spatial and temporal dynamics of forest restoration in the region,the relationship between forest distribution patterns and environmental factors,and their formation mechanisms are not clear until now.This paper took the forests in Ganzi Prefecture,Sichuan Province as the research object,and extracted the forest information in Ganzi Prefecture from 1997 to 2017based on the multi-period Landsat remote sensing images.Using spatial analysis,transfer matrix,landscape pattern index,spatial autocorrelation Moran’s I index,correlation analysis,univariate linear regression,variation partitioning,and spatially constrained multivariate clustering analysis and other methods quantitatively analyzed the spatial and temporal forest distribution patterns in Ganzi Prefecture from 1997 to2017,the relationship between forest distribution patterns and environmental factors,and forestry geological zoning in Ganzi Prefecture,to elucidate the key factors and constraining mechanisms affecting the formation of forest distribution pattern.The aim was to provide important basic data support and a scientific and theoretical basis for forest management,biodiversity conservation,and sustainable development in Ganzi Prefecture.The main results obtained through the research were as follows:(i)The waxing and waning dynamics of each forest type in Ganzi Prefecture and the changing characteristics of its spatial and temporal distribution pattern from 1997to 2017 were clarified.From 1997 to 2017,the total forest area of Ganzi Prefecture showed an increasing trend of"first slow and then strong",with a total increase of6729.95km~2,and the increase rate was 336.50km~2/a.In terms of forest types,the forests of Ganzi Prefecture were dominated by evergreen coniferous forests,accounting for more than 78%of the total forest area of Ganzi Prefecture;in terms of forest dynamic changes,except for the coniferous and broad-leaved mixed forests showed a decreasing trend at a rate of-1.92km~2/a,while other types of forests showed an increasing trend,the evergreen coniferous forest increased the fastest at 275.57km~2/a.The reason for the increase of forests was mainly due to the implementation of forestry ecological engineering and protection policy,and the reason for the decrease of forests was mainly due to deforestation and natural disasters.The characteristics of forest transformation in Ganzi Prefecture were mainly the transformation between evergreen coniferous forest,hard-leaf evergreen broad-leaved forest,and mixed coniferous and broad-leaved forest,and the transfer area was relatively small.In the vertical direction,the forests in Ganzi Prefecture were mainly distributed in the mountain cold temperate zone with an altitude of 3000-3500m and the alpine sub-frigid area with an altitude of 3500-4200m.On the slope,the forests in Ganzi Prefecture were mainly distributed on slopes,steep slopes,and steep slopes;on the slope,the forests in Ganzi Prefecture were mainly distributed on shady semi-shady slopes and semi-sunny slopes.The landscape pattern index showed that the degree of forest fragmentation in Ganzi Prefecture decreased from 1997 to 2017,and the implementation of crucial forestry projects and conservation policies has played a protective role for forests.(ii)The optimal grid sampling scale for the study of the relationship between forest distribution patterns and environmental factors was determined to be 40 km×40 km,on this basis,the relationship between forest distribution patterns and geological and other environmental factors was quantitatively analyzed at the optimal scale,and the combined effects of geological,geographical,and climatic factors on forest distribution patterns were explored,which elucidated the key factors and constraining mechanisms affecting the formation of forest distribution patterns.The results showed that(1)Geological,geographical and climatic factors jointly explain 63.31%of the total variance of forest distribution pattern in Ganzi;the combined effect of environmental factors on forest distribution pattern is shown as climatic factors(50.18%)>geographical factors(44.07%)>geological factors(14.67%);the pure effect(independent explanation)is shown as geographical factors(12.94%)>climatic factors(8.97%)>geological factors(2.12%);the two-two combined effect(combined explanation part)showed geological and climatic factors(63.12%)>geological and geographical factors(56.27%)>geological and climatic factors(52.30%);the interaction effect of the three factors(common explanation part)is higher at 41.21%.(2)Both geological background factors(geological factors and geographic factors)and climatic factors are the key factors limiting the formation of forest distribution patterns.Among them,geological factors are the key factors restricting the forest distribution pattern,geographic factors are the critical surface action factors affecting the formation of the forest distribution pattern,and climatic factors are the most direct environmental factors affecting the expansion of the forest distribution pattern.The geological background factors determine the general framework of forest distribution patterns,and together with climatic factors,they influence the formation of forest distribution patterns.(iii)The geological zoning of forestry based on regional geological background conditions was discussed.The geological background factors were used as the main zoning indicators(lithological diversity,surface cut depth,average elevation,soil diversity),combined with the main climatic factors(average annual temperature)and forest structure indicators(forest diversity)to establish a geological zoning index system for forestry in Ganzi Prefecture.Using the optimal grid scale of 40km×40km as the basic unit of study,the spatially constrained multivariate cluster analysis method was used to carry out forestry geological zoning in Ganzi Prefecture,and the corresponding forestry development direction and regulation strategies were proposed for each zone.The results showed that the geological zoning of forestry in Ganzi Prefecture can be divided into 3 parts:(1)Northern Permian-Triassic,Triassic hilly plateau metamorphic sandstone slate intercalated limestone grass felt soil,black felt soil meadow shrub few forests area,the forestry development in this area should be centered on"forest protection",and the regulation mode of"protection+construction+tending+restoration+prevention and control"should be adopted;(2)South Permian,Triassic alpine mountain valley metamorphic sandstone slate limestone sandstone dark brown soil,brown soil,brown coniferous forest soil shelter forest timber forest economic forest area,the forestry development in this area should be centered on"forest protection,restoration and continuous improvement of forest quality",and the regulation mode of"protection+construction+tending+renewal+prevention and control"should be adopted;(3)Eastern Devonian,Triassic alpine canyon metamorphic sandstone slate Brown soil,dark brown soil,cinnamon soil,brown coniferous forest soil shelter forest economic forest area,the forestry development in this area should be centered on"protecting forests and improving forest quality",and a control mode of"protection+construction+tending+prevention and control"should be adopted.In summary,it can be seen that the formation and maintenance of forest distribution patterns are the results of a combination of environmental factors,and the forests in Ganzi Prefecture showed a continuous increase from 1997 to 2017,with a decrease in forest fragmentation,and the implementation of forestry-related projects and protection policies played a key role in the increase of forests.