Research On The Spatial Distribution Pattern Of Plant Communities In Tundra In The West Slope Of Changbai Mountain Besed On Water And Heat Balance

The vegetations in regions with middle and high latitude or high altitude are sensitive to the global climate change,which play an important directive role for the global change.The tundra in Changbai Mountain is very typical in China.Under the background of climate warming,the west slope was affected by the invasion of herbs,such as Deyeuxia angustifolia,showing the trend of meadow vegetation.However the phenomenon occurs less in the Northern and Southern slopes in Changbai Mountain.So we take the west slope with the most serious intrusion by herbs as the study area.Through the monitoring by field experiment,we analyzes the relationship between the distribution pattern of plant communities and environmental factors.We discusses the allocation characteristics of heat and water for plant communities over tundra.Based on the identification of ecological climate to the mainly plant communities over tundra,we resarch the distributions of mainly plant communities under different climate scenarios in the future.The main conclusions are drawn as the follows:(1)The temperature in growing season shows a significant increasing trend(p < 0.05)in the west slope tundra of the Changbai Mountain during the last 57 years.The temperature has the period of oscillation of 3-5 years and 25 years.The abrupt change period of temperature happened in 1996.The accumulated temperatures show significant increase trends in growing season.The precipitation mainly happens in July and August in the growing season,and shows an insignificant decreasing trend.(2)The dominant position of tundra species such as Vaccinium uliginosum and Dryas octopetala has been replaced by the herbs,such as Sanguisorba sitchensis,Sanguisorba tenuifolia and Deyeuxia angustifolia.The species richness and diversity in the west slope shows increase first and then decrease along the altitude,exhibiting a single peak pattern.According to the classification method of TWINSPAN and field survey,we divided the 75 plots into 7 plant communities.We found the water and heat condition are dominant factors determining plant communities distribution,and soil nutrient also plays a certain role.(3)The soil moisture content of Deyeuxia angustifolia is maximum,and that of Vaccinium uliginosum is minimum,and that of Rhododendron chrysanthum is placed in the middle for the growth season.The main influencing factors of soil water content are evapotranspiration,solar radiation and air temperature.The differences of evapotranspiration for three plant communities are small.The evapotranspiration of Rhododendron chrysanthum is maximum(210.5mm),and that of Deyeuxia angustifolia is minimum(191.5mm),and that of Vaccinium uliginosum is placed in the middle(199.7mm).Solar radiation is the main factor affecting the evapotranspiration of plant communities.The fluctuation of surface runoff for the three plant communities is larger,and the differences between them are obvious.The runoff of Deyeuxia angustifolia is maximum,and that of Vaccinium uliginosum is minimum,and that of Rhododendron chrysanthum is placed in the middle.The runoff have significant positive correlations with precipitation and soil water content,negative correlation with evapotranspiration.Runoff is the main expenditure item of precipitation over tundra.(4)The net radiation flux of Vaccinium uliginosum community is higher than that of Rhododendron chrysanthum and Deyeuxia angustifolia communities in growth season.The latent heat flux of Rhododendron chrysanthum is maximum,that of Deyeuxia angustifolia is minimum,and that of Vaccinium uliginosum is placed in the middle.The latent heat flux in the middle growth season is significantly higher than that in the early and late growth season,and that in the late stage is the lowest.The diurnal variation of soil heat flux fluctuates greatly,and shows a continuous decline trend.In the early and middle growth season,the soil heat transfer from the surface to the deep,and the soil is the heat sink,which is opposite in the last stage of growth season.The Bowen ratio of three plant communities all show a U-pattern distribution in the growth season.The average Bowen ratio was 0.69 for Vaccinium uliginosum,0.64 for Rhododendron chrysanthum and 0.66 for Deyeuxia angustifolia,respectively.The latent heat flux is larger than the sensible heat flux.The latent heat flux accounts for the highest proportion of the net radiation flux,and is the main form of energy dissipation for plant communities over tundra,and the soil heat flux is the lowest.(5)We propose the ecological climate identification equations of heat and humidity for dominant tundra plant communities(Rhododendron chrysanthum,Vaccinium uliginosum and Dryas octopetala)and the main invasion plant communities(Sanguisorba sitchensis,Ligularia jamesii and Deyeuxia angustifolia).In different climate scenarios,the suitable distribution area of Rhododendron chrysanthum,Vaccinium uliginosum and Dryas octopetala communities are shrinking,and the upper and lower limits of elevation are rising in 2045.The suitable distribution area of them reduced greatly,the lower limits of elevation for them increase about 75 m.The upper limits of elevation increase about 50 m and 100 m for Rhododendron chrysanthum and Vaccinium uliginosum communities in the RCP8.5 scenario,respectively.The suitable distribution area and upper limit of elevation are increasing for Sanguisorba sitchensis community.Under the RCP8.5 scenario,the suitable distribution area shows maximum increase and upper limit of elevation exhibits maximum raise,about 100 m for Sanguisorba sitchensis community.In the low and middle scenario,the upper limits of altitude for Ligularia jamesii and Deyeuxia angustifolia communities have no significant change,but the distribution area of Deyeuxia angustifolia community increase,that of Ligularia jamesii is opposite.In the high emission scenario,both the suitable distribution areas and upper limits of altitude are increasing,about 50 m and 100 m,respectively.The main conclusions are drown as follows: water and heat are dominant factors determining spatial distribution for tundra plant communities.With the climate warming in the future,the suitable distribution area of herbaceous communities will increase,and upper limit of altitude will continue to rise.The suitable distribution area of shrub communities will decrease,and both the upper and lower limits of altitude will continue to rise.