| As an important part of the terrestrial ecosystem in China,the Loess Plateau ecosystem is one of the most fragile ecosystems in the world.Climate change and unsustainable land use practices have led to severe soil erosion and low biodiversity in this region.In order to change this situation,the Chinese government have engaged many ecological measures to increase the coverage of forest and grass on the Loess Plateau.Increase the planting of economic forest trees according to the conditions of this region is an important measure to increase people's income and develop sustainable agriculture.However,as an important economic forest trees in this region,the suitability research of apple is usually limited to counties and cities at present,and there are relatively few attempts based on large-scale simulation,especially the distribution pattern in the future.In order to study the potential cultivation of apples in the Loess Plateau,the potential suitable habitats of apples under two extreme climate scenarios were simulated by analyzing the current situation of land use and apple cultivation on the Loess Plateau with the help of Max Ent model(maximum entropy model).To obtain more accurate simulation results of the suitable area,land use type and the potential distribution of a pathogen with serious effects(Valsa Mali)were setted up to optimize the potential distribution of Apple tree.In this study,the suitable level of the habitats,the contribution of various environmental factors,the area of suitable habitats,the change rate of the habitats and the range shifts of suitable habitats were calculated.The main results are as follows:(1)In the past 20 years,the cultivated area of apple on the Loess Plateau increased year by year,and the proportion increased from 45.05%to 59.71%.At present,the largest land use type on the Loess Plateau is grassland(?40%).Conversions between grassland,mosaic area and bare area was frequently.Till to the end of this century,with current trend of land use change,the grassland area will gradually increase(2.96×10~5 km2),while the area of cropland will gradually decrease(1.51×10~5 km2).Built-up area and bare area are the two land use types with largest area change ratio,while Mosaic area had the largest area change.(2)Climate variables,topographic variables and soil variables had significant effects in affecting the potential distribution of Apples on the Loess Plateau,and the key factors of them were the min temperature of the coldest month,elevation and soil texture.Soil texture had much more contributions on effecting the distribution of apple trees than soil type.At present,the area of moderately suitable habitat(MSH)and highly suitable habitat(HSH)of apple was 7.94×10~4 km~2 and 0.85×10~4 km~2,respectively.Till the end of this century,the area of MSH and HSH was 14.45×10~4km~2 and 3.88×10~4 km~2 under the shared socioeconomic pathways(SSP)1-26,while the area under SSP5-85 was 6.56×10~4 km~2 and 1.03×10~4 km~2.Under two future climate scenarios,the suitability of apple decreased in the south and southeast of the Loess Plateau,while increased in the central and west of the Loess Plateau,which leading to the range of apple suitability moving northwest.Under the SSP5-85 scenario,the suitable range had larger range shifts than that of the SSP1-26 scenario.(3)The simulation results of the potential distribution of V.Mali,a serious pathogen of apple tree,in present and four periods of future showed that both temperature and precipitation had significant effects on the distribution of V.Mali.Min temperature of the coldest month was the dominant environmental varianle effects the distribution of V.Mali,contributed 56.73%of the build of Maxent model.The suitable habitat area of V.Mali increased in different degrees under different climate change conditions.Compared with the present situation,the range of potential suitable habitat shift to northwest in the future,and the distance of the shifts of suitable habitat increased from SSP1-26 to SSP5-85.(4)The distribution of apple tree was optimized by land use and the distribution of V.Mali.The unsuitable type area increased under both scenarios,and the low- suitable area affected by the optimization dramatically.During present-2050s period,the area of lowly and moderately suitable habitats of apple tree was increased under SSP1-26 and SSP5-85 climate scenarios on the Loess Plateau.The SSP5-85 scenario resulted more increase in habitat area than that of SSP1-26 scenario.The suitability range of apple shift to northwest under both climate scenarios.On the Loess Plateau,in the periods of 2030s,2050s,2070s and 2090s,the suitable habitats of apple were still mainly located in Gansu,Shanxi and Shaanxi,and the suitable habitats in Henan decreased dramatically,while the suitable habitats in Ningxia and Inner Mongolia increased dramatically.This study provides a new attempt to study the distribution of an economic forest tree(apple)in a large scale under climate change in the future.This study also provides basement for the cultivation of apple industries on the Loess Plateau and the make-up of relevant policies in the future. |
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