| The essence of crop spatial change is agricultural land use change,and reflects the process of agricultural production and utilization of land.The spatiotemporal evolution and response mechanism of crops are the basic contents of agricultural land system research.However,the agricultural land system is huge and complex,and its structure and state also evolve with time,which greatly increases the complexity and research difficulty of agricultural land system.Simplifying the complex agricultural land system into a single crop land space is helpful to reveal the complex relationship of“Human-Nature”complex in the process of agricultural production,deepen the understanding of agricultural land system,and provide an important basis for the adjustment of regional crop planting structure,land space planning and the optimization of agricultural land system.In this study,mathematical analysis,maximum entropy model,Arc GIS technology,spatial econometric model and other methods and tools were used to analyze the temporal and spatial evolution characteristics of citrus production space and its response to the appropriate space in Sichuan Province.The main results are as follows:(1)The suitable areas change of Sichuan citrus was small and showed local spatial adjustment and grade–by–grade conversion in the fluctuation change.(1)Based on the maximum entropy model,the relationship model between citrus suitable distribution and environmental variables in Sichuan Province was established.The areas under ROC curve(AUC)of the model is more than 0.90,and the prediction accuracy is very good.The dominant environmental variables affecting the suitable distribution of citrus in Sichuan Province are elevation,average temperature in July,average annual temperature,duration of≥38℃in summer,average annual air humidity,average air humidity in flowering and fruiting period,slope,annual precipitation,annual temperature range,≥0℃accumulated temperature,annual sunshine hours,average temperature in January,frost free period,≥10℃accumulated temperature and p H.The dominant natural environment variables can be summarized as climate environment variables characterized by light,heat and water.(2)From 1980 to 2015,the suitable areas of citrus in Sichuan changed little and remained stable,and mainly distributed in the hilly region of central Sichuan,Chengdu plain region,and the junction area with the mountain area around the basin.During the study period,the suitable areas overall fluctuated in bimodal pattern,and the suitable areas accumulation decreased by 3.1×10~4ha.In Nanchong,Leshan,Meishan and Luzhou,it is expanding,while in Ziyang,Suining,Dazhou,Neijiang,Yibin and Guang’an,it is shrinking.The expansion and contraction of suitable areas occur alternately in some areas.The moderate suitable areas shows a spatial contraction overall,and shows an evolutionary process of“contraction–expansion–contraction”,with a cumulative decrease of 6.22×10~4ha.The high suitable areas shows a trend of spatial expansion on the whole,and the distribution changes from sporadic dispersion to regional agglomeration.The high suitable areas increase by 3.12×10~4ha accumulatively through the evolutionary process of“expansion-contraction-expansion”.(3)The suitable grades of Sichuan citrus have a change of rise and fall,which mainly occurs between adjacent grades.The two-way conversion of unsuitable grades mainly occurs with low suitable grades.The two-way conversion of low suitable grades mainly occurs between unsuitable grades and moderate suitable grades.The two-way conversion of moderate suitable grades mainly occurs between low suitable grades and unsuitable grades.The two-way conversion of high suitable grades mainly occurs with moderate suitable grades.(2)The spatial agglomeration of citrus production in Sichuan Province was significant,and expanded in fluctuation,and there was a reality of transferring to moderate and low suitable areas.(1)From 1980 to 2015,the citrus production areas in Sichuan Province showed a trend of expansion.The citrus planting area increased rapidly from 3.55×10~4ha to 27.84×10~4ha,and the center of production areas moved to the southwest with the characteristics of“slow-fast-slow”.The time series can be divided into three stages:rapid expansion period(1980-1995),strong shock period(1995-2005)and expansion recovery period(2005-2015).Citrus production areas had significant geographical agglomeration at the county scale,showing a spatial structure of“cold in the west and hot in the east”.As time goes on,the hot spot area gradually shrinks from the mountain area around the basin to the Chengdu plain region and the hilly region of central Sichuan.The Gini coefficient of location has increased from 0.705 to 0.767,and the geographical concentration has increased from 54.75%to 64.02%.(2)For the suitable areas,the response state was weak positive response,and the response index increased from 2.22to 17.40.The citrus production areas were mainly strong negative response and weak positive response.The strong negative response was mainly distributed in the mountains around the basin and Chengdu Plain region,the weak positive response was mainly distributed in the hilly area of central Sichuan,and the strong positive response was scattered.With the expansion of citrus production areas,the response state of production areas and high suitable areas is out of balance,and the response index to high suitable areas decreases from 34.07 to-62.2.Most of citrus production areas have strong negative response,which is mainly distributed in the mountain area around the basin,Chengdu plain region and hilly area in Central Sichuan.The reality that the production areas transferred to moderate suitable area,or even unsuitable areas was existed.(3)The spatial response of citrus production in Sichuan Province is driven by“Natural-Human”factors.Production factors are the key factors,and natural factors are the important factors.(1)The production space of citrus in Sichuan is the result of many factors.The Q values of labor input intensity,fertilizer application intensity,pesticide application intensity and effective irrigation area are more than 0.6,which is the most important factor affecting citrus production areas differentiation in Sichuan.The eight variables,such as slope,elevation,average annual air humidity and annual sunshine hours,are the second,which can explain citrus production areas differentiation,The force is between 0.207 and 0.322.The explanatory power of socio-economic factors such as consumption level,economic support capacity and urbanization level is weak,and their Q values are all less than 0.2.The results show that production factors are the key driving factors of citrus production spatial response in Sichuan,and natural factors are the important driving factors.(2)The interaction of all factors on citrus production space is mainly manifested as two factors enhancement,and there are no independent factors.The factors of production combined with natural factors,market factors and social factors strengthened the influence on the spatial differentiation of Citrus in Sichuan.The interaction of urbanization development,county economic support capacity,consumption level and other factors is mostly nonlinear,which indicates that economic and social development can greatly enhance the impact of other factors on the spatial change of citrus production.(3)Among the natural resources,market factors,production factors,social economy and other factors,the total effect has 15 significant explanatory variables(P<0.1),including 7 natural factors and 8human factors,which indicates that the citrus production space in Sichuan has obvious“Natural-Human”driving characteristics.The total effect of production areas is negatively correlated with elevation,annual precipitation,average temperature in July,annual sunshine hours,annual temperature range,urbanization level,consumption level and technological progress.Every 1%increase of the above variables would reduce citrus area by 0.61%,0.358%,0.844%,1.784%,4.734%,0.398%,2.473%and 0.181%respectively.Production space is positively correlated with the total effect of slope,frost free period,labor input intensity,effective irrigation area,pesticide input intensity,road network density and economic support capacity.With each 1%increase of the above variables,citrus area would increase by 1.270%,1.044%,0.542%,0.172%,0.285%,0.626%and 0.356%respectively.(4)The citrus spatial grid simulation model is suitable for citrus planting control in Sichuan Province,and the plan of positive low growth scene can be used for spatial optimization.(1)Based on the analysis of the response mechanism of production space to natural and human driving factors,the SGSM-Citrus model constructed in this study can better realize the simulation of citrus spatial regulation,which provides a new method for the simulation of crop spatial regulation model.In 2025,the spatial scale of citrus under the four scenes is basically consistent with the predicted scale.The simulation data of the positive low growth scene is 30.7×10~4ha,the positive high growth scene is 36.71×10~4ha,the negative low growth scene is 28.11×10~4ha,and the negative high growth scene is 25.4×10~4ha,and the relative errors with the corresponding scenario are less than 0.05%.(2)In2025,Sichuan citrus production layout should adopt positive low growth scene for spatial regulation.It is mainly distributed in Meishan,Ziyang,Yibin,Nanchong and Neijiang.Bazhong,Guangyuan,Chengdu,Liangshan and other cities and states have irrational expansion,so we should weaken the incentive effect of industrial support,project capital investment and other policy tools on irrational regions in time.In some areas of Panzhihua,Ganzi and Nanchong,due to the unique comparative advantages,such as the light advantage of Panzhihua and the scale advantage of Nanchong,the citrus planting area can be increased moderately.The local government can formulate supporting policies according to the comparative advantages,guide all kinds of social and economic factors to gather in these areas,and promote the sustainable development of citrus industry. |
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