The Response Of Four Rhododendrons Clone Characteristics And Annual Ring Width On Different Climatic Factors In Qilian Mountains

Global warming has become a major climate problem in today's society.In recent 100 years,the global average surface temperature has risen 0.85°C.It not only has profound influence on ecosystems,but also was a serious threat to human life,production and ecological safety.The climate fluctuation of the Qinghai-Tibet Plateau directly affects climate change in eastern and southwestern China,it was also regulated,advanced and sensitive to climate change in the northern hemisphere and even global climate.However,the high altitude and harsh climate of the Qinghai-Tibet Plateau has become the constraints of tree growth and development,shrubs and bush widely distributed in these areas.It was significant to study the dominant growth characteristics of shrubs in the region,and it was helpful to understand the ecological adaptability of plants to environment and climate change and to implement ecological protection.We studied the clonal growth characteristics and dendrochronology of shrubs of alpine dominant Rhododendron shrubland in eastern Qilian Mountains while searching the environmental factors and ecological characteristics of that.According to the correlation analysis among Rhododendron shrubland annual ring,regional temperature and precipitation,it will provide a theoretical basis for the better vegetation management of countermeasures for future climate change.The highest value of Rhododendron diversity was found at the 3100 m altitude.The results revealed that the bunch of Rhododendron.capitatum,R.thymifolium and R.anthopogonoides decreased,branch and deadwood number of Rhododendron.capitatum plants reduced with the altitude gradient increasing.The specious important values of Potentilla fruticosa,Rhododendron.capitatum and Salix oritrepha were in higher level at the 3050 m altitude.The specious important values of Rhododendron.capitatum and R.thymifolium increased siginificantly.The total coverage of Rhododendron shrubland decreased with the increasing of the altitude gradient.The subcoverage of Rhododendron.capitatum was higher at each altitude gradient.The subcoverage of R.thymifolium was lower at the 3050 m altitude,was higher at the other altitude.The subcoverage of other species reduced while the Rhododendron.capitatum and R.thymifolium height decreased with the altitude gradient increasing.The results showed that the alpine dominant Rhododendron shrubland was a stable population structure in our experimental area,the maximum age of the four species were 63 a,67 a,75 a,67 a respectively,and the average age was 34.73 a?35.33 a?35 a ? 37.08 a years old respectively.The average height,canopy width and radial growth of R.przewalskii were the largest under the same environmental conditions.The height,canopy width,branches and dead wood number and the four Rhododendron shrubland radius have a higher degree of fitting relationship with their age.The height growth of the Rhododendron.capitatum was mainly before 45 to 48 years old,while the radial and canopy growth rate were slow.After 45 to 48 years of age,the radial growth and canopy width were mainly extended and the height growth was tending gradual.The growth of the other three Rhododendron species had the same law as the Rhododendron.capitatum and the age of the growth change was 46-53,40-44,43 years old.The annual ring structures of four Rhododendron shrubs were suitable for the study of dendroclimatology,and the change trend of the four shrubland annual ring was close to climate change in recent years.Narrow wheel years were more consistent with the appearance of wide wheel years.It was proved that the analysis of the relationship between the annual ring and the climate was based on the ring width sequence of four Rhododendron shrubland.There were six main climatic factors affecting the radial growth of Rhododendron shrubland in the region,including growing season average temperature,annual growth average temperature,non-growing season average temperature,growing season and non-growing season average temperature difference,annual precipitation growth,seasonal precipitation.The average season temperature was the most important factor affecting the growth of Rhododendron shrubland.The width of the four Rhododendron rings increased with the average temperature increasing in the growing season,it would decrease when higher than that of the temperature physiological threshold 8.5?,and it was the regional temperature threshold for radial growth of shurbland.The alpine Rhododendron shrubs had still face the challenge under the influence of global warming in the Qilian Mountains of the eastern Qinghai-Tibetan Plateau.The clone growth characteristics of four Rhododendron shrub species were affected by various environmental.The four Rhododendron shrubs rings of alpine regions recorded the change information of history climate and environmental,the age structure of the population was still relatively stable,but it was complex to climate factors such as rising temperatures,so it was a very difficult task to protect and management the Rhododendron shrubs.