The normalized difference vegetation index(NDVI)is used extensively to describe vegetation cover and ecological environment change.The purpose of this study was to contrast the response of different tree species growing in the same habitat to climate change and retrieve past NDVI using tree-ring width data from tree cores collected from the transitional zone of Pinus tabulaeformis and Picea crassifolia in the Luoshan Mountains in the middle arid region of Ningxia.Correlation analysis indicated that radial growth of P.tabulaeformis is more sensitive to precipitation and temperature change than that of P.crassifolia.Natural factors such as water availability and heat at this elevation are more suited to the growth of P.crassifolia,and are more advantageous to its renewal and succession.P.crassifolia is probably the better of the two species for protecting the forest ecosystem and conserving water in the Luoshan desertification area.Ring width of P.crassifolia correlates significantly with average NDVI for April–May(r=0.641,p<0.01),and both of them are influenced positively by precipitation in April–May.The reconstructed NDVI for 1923–2007 shows the relatively low vegetation cover occurred in the 1920s–1930s,the1960s–1970s,and the early 21st century.The reconstructed NDVI better reflected the drought climate in the study area.
As the largest inland lake of China, along with its unique landscape and geographical location, Qinghai Lake has got much atten- tion of the scientists for a long time. The precursors have done substantive researches by using the lake sediment, which deepen our understanding of the climate changes in this region. Although sand dunes and loess sediment are widely distributed around the lake, so far the researches on geochemical elements from aeolian sediment have been less reported. In this paper, we selected a typical aeolian profile on the east of Qinghai Lake. Based on systematic sampling and analysis of seven major geochemical elements, combined with OSL dating and previous researches, this paper discusses climate changes in the Qinghai Lake area since 12.5 ka B.P.. Our conclusions are: (1) Before 12.5 ka B.P., the climate in this region was dry, cold, and accompanied by strong wind-sand activities. (2) During 12.5-11.9 ka B.P., the climate became warm and wet. However, there was an abrupt climate cooling event during 12.2-11.9 ka B.P., which likely corresponded to the Younger Dryas event. (3) During 11.9-8.0 ka B.P., the climate fluctuated greatly and frequently from warm to cold, and three cooling events occurred. (4) During 8.0-2.6 ka B.P., the climate was warm and humid. (5) Since 2.6 ka B.P., similar to the modern climate, the climate was mainly dry and cold.
