Palaeoaltitudes of fossil sites reconstructed to discuss Yunnan floristic changes

Yunnan is an ideal region to study the impact of tectonics on floristic composition and structure because: (1) the diversity of vegetation types occurring in Yunnan ranges from tropical forest in the south to alpine meadow in the northwest; (2) the complex tectonic history of the province, where modern altitudes range from almost sea level to more than 6000 m above sea level within a distance of approximately 850 km. These marked vegetation and altitude differentiations can enhance the visibility of the changes.

Despite the important relationship between uplift and biodiversity, research in this field lacks a good time and space framework for the uplift. Several studies provided insight into the uplift history of Yunnan, but they all gave relative, instead of absolute, altitude. Dr. Frederic M.B. Jacques of Xishuangbanna Tropical Botanical Garden (XTBG) and his colleagues proposed an original approach: reconstruct absolute palaeoaltitudes of the studied fossil sites in order to discuss Yunnan floristic changes in a strong tectonic context.

The researchers focused on three coeval late Miocene leaf assemblages from Yunnan: Lincang, Xiaolongtan and Xianfeng. First, they reconstructed the geological and tectonic context of the three fossil sites (Lincang, Xiaolongtan and Xianfeng) in terms of palaeoaltitude. They then analyzed the floristic differences between three late Miocene floras of Yunnan. Finally, they looked at possible links between geological patterns and floristic patterns.

The researchers found that Northern Yunnan site was already uplifted, southern sites were not. Yunnan Neogene uplift was diachronous. Vegetation types were already differentiated in Yunnan in Miocene. Vegetation in Yunnan has changed in response to uplift. The uplift of Yunnan during the Neogene shaped the present vegetation: it restricted the tropical taxa to the southernmost areas and induced the expansion of subtropical and warm temperate vegetation.

The uplift framework reconstructed in their study suggested that tectonic context was important in understanding present day biodiversity and the biological characteristics of the component taxa.

The study entitled “Late Miocene southwestern Chinese floristic diversity shaped by the southeastern uplift of the Tibetan Plateau” has been published in Palaeogeography, Palaeoclimatology, Palaeoecology.

Fig. Areal type composition of the three fossil sites. A, Family level; B, genus level.