Pollen-based reconstruction of vegetational and climatic change over the past ~30 ka at Shudu Lake in the Hengduan Mountains of Yunnan, southwestern China

Abstract

The Hengduan Mountains, with a distinct altitudinal differentiation and strong vertical vegetation zonation, occupy an important position in southwestern China as a global hotspot of biodiversity. Pollen analysis of lake sediments sampled along an altitudinal gradient in this region helps us to understand how this vegetation zonation arose and how it has responded to climate change and human impacts through time. Here we present a ~30-ka pollen record and interpret it in terms of vegetational and climatic change from a 310 cm-long core from Shudu Lake, located in the Hengduan Mountains region. Our results suggest that from 30 to 22 cal. ka BP, the vegetation was dominated by steppe/grassland (comprising mainly Artemisia, Poaceae and Polygonaceae) and broad-leaved forest (primarily Quercus, Betula and Castanopsis) in the lake catchment, reflecting a relatively warm, wet climate early in this phase and slightly warmer, drier conditions late in the phase. The period between 22 and 13.9 cal. ka BP was marked by a large expansion of needle- and broad-leaved mixed forest (Pinus, Abies and Quercus) and a decline in the extent of steppe/grassland, indicating warming, drying climatic conditions followed by a cold, wet period. Between 13.9 and 3 cal. ka BP, steppe/grassland expanded and the area covered by needle- and broad-leaved mixed forest reduced, implying a fluctuating climate dominated by warm and humid conditions. After 3 cal. ka BP, the vegetation was characterized by an increase in needle-leaved forest and reduction in steppe/grassland, suggesting warming and drying climate. A synthesis of palynological investigations from this and other sites suggests that the vegetation succession patterns seen along an altitudinal gradient in northwestern Yunnan since the Late Pleistocene are comparable, but that each site has its own characteristics probably due to the influences of altitude, topography, microclimate and human impact.

Fig 1

a. Location of Yunnan in China, b. Location of Shudu Lake and other studied sites in northwestern Yunnan, c. Panoramic view of Shudu Lake (red arrow represents position of core), d. Position of present and previous studied cores at Shudu Lake.

Fig 2. Lithology of the Shudu Lake core and age-depth curve showing rate of sedimentation.

Fig 3. Pollen percentage diagram of major palynomorphs for Shudu Lake surface samples, Yunnan.

Fig 4

Examples of palynomorphs recovered from Shudu Lake core sediments 1. Abies L. 2. Picea Dietr. 3. Pinus L. 4. Tsuga Carr. 5. Polypodiaceae 6. Athyriaceae 7. Hymenophyllaceae 8. Gymnogrammaceae 9. Pteris L. 10. Plantaginaceae 11. Artemisia L. 12. Oleaceae 13. Rosaceae 14. Ericaceae 15. Asteraceae 16. Polygonaceae 17. Betula L. 18. Verbenaceae 19. Ulmus L. 20. Quercus L. 21. Cyperaceae 22. Amaranthaceae 23. Poaceae 24. Salix L. 25. Apiaceae 26. Chenopodiaceae 27. Castanopsis (D. Don) Spach. 28. Fabaceae Scale bar = 50 μm (scale bar A applies to 1–9, scale bar B applies to 10–28).

Fig 5. Pollen percentage diagram for major palynomorphs from Shudu Lake core, Yunnan.

Fig 6. Regional comparison of vegetational succession in northwestern Yunnan.