| Land degradation and desertification are severe environmental problems in the arid and semi-arid regions of Northwest China.With the development of the western regions,the fragile ecological environment and the rapid development of economy have generated more prominent contradiction between people and land.Afforestation with eco-economical species has been an ideal choice to ease the contradiction.Since climate is the decisive factor affecting species distribution on macro-scale,the relationship between suitability and climate factors,and the impact of climatic spatial-temporal changes on species distribution have attracted increasing attentions.Within the context of global climate change,understanding the distribution of common eco-economical species and their responses to climate change will contribute to the improvement of afforestation in the arid and semi-arid areas of Northwest China.It is also of great significance to achieve a win-win outcome for improving people’s living standards and improving the ecological environment.A total of 10 tree species(Elaeagnus angustifolia,Nitraria sibirica,Lycium ruthenicum,Tamarix ramosissima,Haloxylon ammodendron,Caragana korshinskii,Calligonum mongolicum,Populus euphratica,Salix cheilophila and Xanthoceras sorbifolia)were selected in this study.Based on occurrence records from herbaria and published literature,and 13 climate factors from BIOCLIM,Holdridge life zone,and Kria index,the potential suitable distribution areas of the 10 species in the present climate scenarios(1950-2000)were simulated,using Max Ent(maximum entropy method)and GIS(geographic information system).Furthermore,the dominant climate factors that affected the distribution of each species were determined,and the relationship between the suitability and climate factors were analyzed.The 2070s(2060-2080)changes of suitable areas of each species under the four representative concentration pathways(RCPs)of greenhouse gases(GHGs)were also predicted.The main results are as follows:(1)The potentially suitable distribution areas of E.angustifolia,N.sibirica,and T.ramosissima are the largest,which span the arid,semi-arid,and semi-humid regions and humid regions with obvious dry seasons.The potential suitable distribution areas of L.ruthenicum,H.ammodendron,C.mongolicum,and P.euphratica are mostly confined to arid regions in Northwest China,while those of X.sorbifolia,S.cheilophila,and C.korshinskii are mostly concentrated in the semi-arid and semi-humid regions of Northwest and Northern China.(2)Humidity index(HI)is the most important factor affecting the suitability of most species,with the contribution rate of 56.1%,53.1%,and 52.3% for C.mongolicum,H.ammodendron,and P.euphratica,respectively,while only 4.7% and 1.0% for C.korshinskii and H.rhamnoide,respectively.Precipitation of wettest month(PWM),annual precipitation(AP),coldness index are important factors as well,among which,the effect of PWM is most significant on L.ruthenicum,while the effect of AP is most significant on X.sorbifolia.(3)Thermal-related climate factors play important roles in affecting the distribution of E.angustifolia and C.korshinskii,while for other species,hydrologyrelated climate factors play more important roles.Species habitat suitability curves in response to hydrology-related factors deviate from normal distribution in right for most species.Those curves in response to thermal-related factors mostly followed Gaussian distribution.(4)E.angustifolia is expected to benefit most from high GHGs emission scenarios(RCP 8.5),with a net increase of 57.5% for its suitable area.The shrink of suitable area of C.korshinskii is expected to be up to 61.4% under low GHGs emission scenarios(RCP 2.6),indicating that the adverse effects of climate changes were larger on C.korshinskii than other species.For almost all species,current suitable areas are expected to shrink under low emission scenarios,while would expand under higher emission scenarios.In addition,with the increase of GHGs emission rates,the shrink tendencies of current suitable areas would change weaker,while the expansion trend will be stronger.(5)The eastern edges of current suitable areas of all species are expected to shrink under the effects of future climate changes.The shrinking rate of different tree species is different.The tree species distributed in the arid regions of Northwest China would own new suitable areas in Tarim basin,Turpan basin and the northern part of the Hexi corridor.For most species,the geographical centriods of suitable ranges are predicted to move west at the speed of 4 ~ 53 km per decade.The movement of most altitudinal centriods are not obvious.The altitudinal centriods are predicted to lower or higher at the speed of 1 ~ 22 m per decade,except for S.cheilophila,whose suitable altitudinal centers are predicted to move upward at the speed of 18 ~ 73 m per decade.The results in this study indicate that the potentially suitable ranges of each species simulated by Max Ent are basically consistent with the investigation data.The response to climate changes are different between tree species due to variable distribution areas and climate scenarios.For most species,the current suitable areas are stable,and can adapt to sustained climate change.Those presently appearing in the arid regions of Northwest China might benefit from the future climate change.In the future,afforestation areas of local tree species,such as E.angustifolia,N.sibirica,and H.ammodendron,can further increase in the Tarim basin,Turpan basin and the northern part of Hexi corridor.This study contributes to better understanding the relationship between the distribution and climate for species in the northwest arid/semi-arid regions,and can provide reference for afforestation measures that adapt to climate change. |
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