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Biodiversity has attracted much attention recently due to its important relationships with ecosystem function under various global warming scenarios. However, an understanding of biodiversity mechanisms requires study over long time scales. Three high-resolution pollen records of Zoige Basin in the eastern Tibetan Plateau are used to reconstruct changes in vegetation diversity during the Holocene, allowing the mechanisms that drove the dynamic to be quantitatively explored. Rarefaction and Hill's indices are used to estimate the diversity richness and evenness based on pollen data. The results show that changes in palynological richness can be divided into five stages: an abnormal change from 10,500 to 9,000 cal bp, an obvious increase from 9,000 to 6,500 cal bp, a decreasing trend from 6,500 to 4,000 cal bp, an increasing trend after 4,000 cal bp until 1,500 cal bp, and a highly fluctuating stage from 1,500 cal bp to the present. Palynological evenness is relatively stable throughout the Holocene except for during a briefly elevated period from ca. 4,000 to 1,500 cal bp. The result of Boosted Regression Tree analysis indicates that climate is the main driving factor and the effect of temperature is stronger than that of precipitation in the study region. However, during ca. 4,000–1,500 cal bp, palynological diversity is primarily affected by vegetation structure, as shown by an increase in palynological evenness, which can in turn be explained by the climate threshold theory. This research provides a long-term, high-resolution reconstruction of palynological diversity which could be used to infer vegetation diversity change in the ecologically sensitive Tibetan Plateau. The results imply that vegetation diversity in the region may increase under global warming if human impacts are not considered. [ABSTRACT FROM AUTHOR]

Temperature profiles provided by the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) global positioning system (GPS) satellite constellation were used to study an eight-year series (2007 to 2015) of gravity wave (GW) potential energy in the stratosphere (18-30 km) around the Tibetan Plateau (TP). We found that with increasing altitude, the GW potential energy ( E ) values in the stratosphere caused by convection decreases. The importance of GWs that are stimulated by topography is enhanced in this area. In the TP, which was considered to lack strong topographical GW activity, clear activity existed in the spring and winter of all studied years. Based on the latitudinal zone of the TP, the distribution of GW potential energy is highly consistent with the elevation of the local topography. The activities of topographical GWs are strongly filtered as they propagate upward to the area of zero speed wind. The analysis indicates that in the TP, clear orographic GW excitation exists and propagates upward to the upper stratosphere, where it is greatly influenced by the wind. [ABSTRACT FROM AUTHOR]