The Patterns And Drivers Of Wild Fruit Tree Species Diversity In The Ili Valley Of Xinjiang,China

Useful plants are critical components of biodiversity,supporting important ecosystem services.Wild fruit tree species is an important kind of useful plant in Central Asia,whereas,a systematic assessment of their vulnerability in the face of global change,an in-depth study of their diversity patterns and driving mechanisms,and a comparative study of their response to environmental changes and the diversity maintenance at different life history stages in the Ili Valley are still lacking.This study quantifies the environmental niche threshold suitable for the establishment of wild fruit tree species,reveals the diversity patterns of wild fruit tree species and its driving mechanisms,uncovers the elevational patterns of dominant wild fruit tree species at different growth stages and its limiting factors,and identifies the importance of microhabitat for the existence of wild fruit tree species in the Ili Valley based on field survey,specimen and literature data.The main conclusions included:(1)Elevation,soil pH,and climate factor(mean annual temperature,temperature seasonality,and mean annual precipitation)are among the most important factors driving six wild fruit tree species.Climate and land use changes in the future will cause variations in the degrees and directions of suitable distribution regions of wild fruit tree species.Malus sieversii,Juglans regia,Prunus armeniaca,Crataegus chlorocarpa,Prunus cerasifera and Sorbus tianschanica will move northward to varying degrees,while suitable distribution regions for Prunus armeniaca will move southward.High-intensity(>40%)cropland reclamation of low-elevation region results in a significant decrease in the distribution region of wild fruit tree species.The suitable distribution region for six wild fruit tree species will shift upward,with varying upper limits of elevation.(2)The elevational patterns of species diversity for wild fruit tree species among four mountains in the Ili Valley are inconsistent,a single peak in the Kogirqin,Usun,and Ketmin mountains,with the highest richness at 1300 m,1800 m,and 1400 m,respectively,and a monotonous decrease in the Narati mountains.The minimal temperature of coldest month limits the richness and relative abundance of wild fruit tree species for three mountains(Kogirqin,Usun,and Narati mountains),supporting the Cold Tolerance Hypothesis.Climate and soil factors have different impacts on species diversity of wild fruit tree species.For instance,species diversity of wild fruit tree species is negatively correlated with temperature seasonality in the Kogirqin and Usun mountains,whereas soil organic carbon only extremely significantly(P<0.01)affects species diversity of wild fruit tree species in Kogirqin mountains,which may be related to biogeographical factors of the different mountains,such as the distance from the valley.(3)Intraspecies and interspecies differences were found in the abundance of both adults and seedlings of wild fruit tree species;seedling abundance for Malus sieversii is significantly lower than adult abundance,but there are no significant differences between those of Juglans regia and Prunus armeniaca.The adult abundance of wild fruit tree species has been significantly affected by mean annual temperature,mean annual air moisture,and soil total potassium.For example,the adult abundance for Prunus armeniaca has a extremely significant increased with mean annual temperature(R~2=0.369,P<0.01)and soil total potassium(R~2=0.669,P<0.01).The abundance of seedlings for three wild fruit tree species was significantly affected by soil total nitrogen content.The species richness of woody plants is positively correlated with with the abundance of Malus sieversii and Juglans regia,but negatively correlated with the abundance of seedlings.The basal area of woody plants is negatively correlated with the abundance of Prunus armeniaca,but positively correlated with the abundance of seedlings,which may be related to the adaptive capacity to local environmental conditions of different growth stages of wild fruit tree species.In conclusion,this study selected the representative useful plants of Central Asia as the research objects,quantifies the environmental niche threshold suitable for the establishment of dominant wild fruit tree species at the regional scale,reveals the diversity patterns of wild fruit tree species and its driving mechanisms at the community-level,uncovers the elevational patterns of dominant wild fruit tree species at different growth stages and its limiting factors at the species-level.In 1973,Chang Hsin-shi stated,"The new chapter of wild fruit-tree forest in the history is that humans have significantly entered natural landscapes."In the Anthropocene,this study provides references and scientific information for the conservation and management of wild fruit-tree forest in the Ili Valley of Xinjiang and even the mountains of Central Asia.