The Process Of Herbaceous Plants Migrating Into The Tundra On The West Slope Of Changbai Mountain

Global climate change results in the expansion of plants from lower elevations into higher elevations,which not only threatens the original species at high altitudes,but also changes the composition and structure of plant communities.A typical Asian tundra mountain area is distributed in Changbai Mountain,and the tundra climate has undergone a remarkable change during the past 30 years,resulting the migration of herbaceous plants such as Deyeuxia purpurea and Veratrum oxysepalum,and changing the original vegetation composition and distribution pattern.In order to clarify the process of herbaceous plant migration and trend of vegetation change in the tundra on the west slope of Changbai Mountain,the quadrat survey method was used in this paper,and the plant communities at different altitudes were taken as the main research objects.We surveyed 120 quadrats at 2050?2300m on west slope of Changbai Mountain in 2014,2017 and 2019.This paper studies the characteristics of plant community and the change of vegetation at different altitudes in the tundra on the west slope of Changbai Mountain,and the trend of vegetation change was analyzed,which can provide the basis for predicting the change of tundra vegetation under global warming.The main conclusions of this paper are as follows:(1)The important value status of Deyeuxia purpurea increased from the fifth in2014 to the third in 2017;the important value status of Deyeuxia purpurea did not change from 2017 to 2019,but the important value status of Veratrum oxysepalum rapidly increased from the tenth to the fourth.Therefore,the process of herbaceous plants migrating can be divided into two stages:2014-2017 is the migrating stage of Deyeuxia purpurea,2017-2019 is the migrating stage of Veratrum oxysepalum.Two species of community decreased in the migration stage of Deyeuxia purpurea,while17 species decreased in the migration stage of Veratrum oxysepalum.Among them,the number of shrubs and herbaceous plants in the migration stage of Deyeuxia purpurea decreased by one type,and the number of shrubs and herbaceous plants decreased by 4 types and 13 types in the migration stage of Veratrum oxysepalum.However,the proportion of herbaceous plants increased in the two stages.In the migration stage of Deyeuxia purpurea and the migration stage of Veratrum oxysepalum,the Margalef richness index,Shannon-Wiener index and Pielou evenness index decreased,and Simpson index was increased.The community structure became simpler,and the resource allocation was more uneven.(2)In the migration stage of Deyeuxia purpurea,the important value status of Deyeuxia purpurea gradually decreased along the altitude gradient in 2014 and 2017.The important values are dropped three places(from 3^rd to 6^th)from 2050m to 2300m above sea level in 2004,the same as in 2017(from 2^nd to 5^th).The position of important values of Deyeuxia purpurea at low altitudes in 2014 is equal to that at high altitudes in 2017.In the migration stage of Veratrum oxysepalum,Veratrum oxysepalum is the dominant specie only at low elevations in 2017,but it become the dominant specie at all altitudes in 2019.The relative importance of the important values reduced with a rise elevation,and the important value of Veratrum oxysepalum raised to third at low altitude,the important value of Veratrum oxysepalum has rapidly increase in importance in three years at all altitudes.The Margalef index,the Shannon-Wiener index and the Pielou index increase first and then decrease with the elevation rise.In the migration stage of Deyeuxia purpurea,the peak of the Shannon-Winner index occurs at an altitude of 2150m in 2014,but occurs at 2150m in2017.The altitude at which the peak of the Shannon-Winner index occurs from2150m in 2017 become to 2200m in 2019 during the migration of Veratrum oxysepalum.With the migration stage of Deyeuxia purpurea and Veratrum oxysepalum,the community structure is complicated first and then simplified,and the result also showed that the migration of Deyeuxia purpurea and Veratrum oxysepalum is from low altitude to high altitude.(3)The total niche breadth of Deyeuxia purpurea increased from 1.803 to 1.892in 2014-2017,while the total niche breadth of Deyeuxia purpurea a only changed by0.034 from 2014 to 2017.The total niche breadth of Veratrum oxysepalum from 2017to 2019 increased from 1.148 to 1.872,and the variation range was much larger than that of Deyeuxia purpurea.From 2014 to 2017,the niche overlap value of Deyeuxia purpurea and native shrubs increased significantly,and the variation range at high altitude was greater;from 2017 to 2019,the niche overlap value of Deyeuxia purpurea and native shrubs decreased at low altitude,but still increased at high altitude.From 2017 to 2019,the niche overlap value of Veratrum oxysepalum and native shrubs increased significantly at different altitudes,and the variation range at low altitudes was greater than that at high altitudes.In the migration stage of Deyeuxia purpurea,the distribution range of Deyeuxia purpurea became wider and the competition with native shrubs became more intense,especially in the high altitude area,which indicated that Deyeuxia purpurea migrated from low altitude to high altitude area.In the migration stage of Veratrum oxysepalum,the distribution range of Deyeuxia purpurea decreased,and the competition between Deyeuxia purpurea and native shrubs decreased in the low altitude area,but continued in the high altitude area,which indicated that Deyeuxia purpurea has been stable in the low altitude area,and may continue to migrate the high altitude area.In the future,Veratrum oxysepalum will continue to expand in low altitude areas,and may continue to migrate into high altitude areas.