Analysis And Prediction Of Factors Affecting The Potential Distribution Of Invasive Alien Plants At Different Spatial Scales In Coastal Wetlands

Global change and species invasion are hot issues in ecological research at present.As a hot area for global change and species invasion,it is very important for coast wetlands to reveal the invasive mechanism of alien species and protect biodiversity of coastal ecosystems.While there are few researches focused on the expansion of alien invasive species in the coastal wetlands and predicting their potential distribution pattern under future climate change and sea level rise.Hence,Spartina alterniflora,a typical intertidal invasive plant,was selected as a case study.Based on the global sensitivity analysis and MaxEnt,at different spatial scales,our paper discussed the interactions among environmental variables and their relative importance,the response of key environmental variables related to the presence of S.alterniflora were studied,as well as the suitable habitats of S.alterniflora and their change under current environmental conditions.Combined the effect separation method based on the four-set Venn diagram,we extracted the pure effect,coupling effect and sharing effect of climate change and sea level rise on the future distribution of S.alterniflora at different spatial scales.Finally,the spatial distribution pattern under different effects was acquired using ArcGIS10.2.The main conclusions can be drawn as follows:(1)There are obvious differences in the environmental variables affecting the distribution of S.alterniflora at different spatial scales.At global scale,Precipitation of driest month(Bio 14),Precipitation of coldest quarter(Bio 19),Max temperature of warmest month(Bio05)are the main environmental variables affecting the distribution of S.alterniflora.At national scale,Max temperature of warmest month(Bio05)is still the most important environmental variable and Soil drainage class(Drainage)becomes the second most important environmental variable.At regional scale,on the northern Chinese coasts,Altitude(Elevation)and Mean diurnal range(Bio02)are the most critical environmental variables that control the distribution of S.alterniflora,while on the southern Chinese coasts,Altitude is the most critical environmental variable.At board scale,climatic variables(especially extreme climatic variables)usually determine the distribution of S.alterniflora.As spatial scales shrink,the relative importance of topography,soil characteristics variables and climatic variables closely relating to species growth(such as Bio02)has begun to stand out from environmental variables.(2)There are obvious differences in interactions among environmental variables and the main environmental variables affecting interactions are also changing at different spatial scales.The interactions among climatic types decrease as the spatial scale shrinks,the interactions among topography types increase as the spatial scale shrinks,the interactions among soil types increase first and then decrease as the spatial scale shrinks.At the global scale,Bio05,Biol4 and Biol9 explain the major interactions among environmental variables.Almost all environmental variables are involved in interactions among environmental variables at the national scale.At the regional scale,whether on the southern coast or the northern coast,Bio02 and Elevation are the main environmental variables affecting interactions.The change of spatial scale and interactions affect the response of S.alterniflora to main environmental variables.Bio05 is more involved in the interactions among variables,thus interactions greatly change the response of S.alterniflora to Bio05 at different spatial scales.There is a significant negative correlation between the presence of S.alterniflora and soil organic carbon(Toc),except at national scale,which means that lower soil organic carbon is more suitable for the growth of S.alterniflora.(3)Under current environmental conditions,the area of suitable habitats of S.alterniflora at global,national and regional scale is 225816 km2,71157 km2 and 56376 km2 respectively.From the global scale to the national scale,the percentage of suitable habitats of S.alterniflora reduces from 47.83%to 15.07%.As the importance of climatic variables is reduced at national scale and the importance of topography and soil characteristic variables is enhanced,it causes a large reduction in habitats.The greatly reduced habitats are mainly distributed in the Liaodong Peninsula,Bohai Bay,Shandong Peninsula and inland in Jiangsu.From national scale to regional scale,the proportion of suitable habitats of S.alterniflora declines from 15.07%to 11.94%.The increased suitable habitats are mainly concentrated in the southern Chinese coast,while the reduced suitable habitats are mainly concentrated in the northern Chinese coast.(4)At different spatial scales,the potential distribution of S.alterniflora is affected not only by the respective pure effects of climate change and sea level rise,but also by coupling effects and sharing effects.At global and national scales,the pure effects of climate change can explain 70.07%and 34.68%of increase in habitats of S.alterniflora respectively,while the pure effects of sea level rise can explain 97.97%and 97.89%of decrease in habitats of S.alterniflora respectively.The increasing habitats caused by the effect of the sea level rise is 53.60%at national scale.Therefore,the effect of sea level rise on the habitats change of S.alterniflora is even higher than that of climate change at board scale.While at regional scale,expect decrease in the habitats on the southern coasts,the change of habitats is mainly caused by the pure effects of climate change(89.26%on the north and 76.36%on the south).The pure effects of sea level rise are low but it can affect the change of habitats through complex interactions with climate change.The coupling and sharing effects mainly promote the increase in habitats on the northern coasts,while on the southern coasts the coupling effects cause the increase in habitats and the sharing effects cause the decrease in habitats.Moreover,although the interactions between the coupling and sharing effects have a low impact on the variation of suitable habitats of S.alterniflora at various scales,their effect cannot be ignored,otherwise the effect of climate change and sea level rise may be underestimated.Our research results suggest that attention should be paid on multiple spatial scales,but also the interactions among variables when estimating the relative importance of explanatory variables for the distribution of invasive species on coastal wetlands.Simultaneously,identifying pure,shared,and coupling effects of climate change and sea level rise for the distribution of S.alterniflora will provide scientific references for assessing the risk of similar coastal species.