Spatial variation of modern pollen from surface lake sediments in Yunnan and southwestern Sichuan Province, China

To provide accurate analogues for fossil pollen records from lake cores, we analyzed surface sediments from 42 lakes of Yunnan and southwestern Sichuan Province, China (located between about 1500 and 4600 m elevation) for pollen and spores. The pollen analysis reveals that although large amounts of arboreal pollen, such as Pinus, Picea and Abies, Betula, Juglans, deciduous oaks, evergreen oaks, and Rosaceae, from lower elevations are introduced into sub-alpine and alpine lakes by upslope winds, the pollen assemblages of surface lake sediments among and within different vegetation types can still be distinguished by their pollen spectra and indicator species. For example, Alnus is an indicator of the pollen assemblages of lakes among the Pinus yunnanensis forest-Evergreen broadleaved forest or P. yunnanensis forest-Mixed Pinus and Quercus forest. Tsuga and Ericaceae are indicators of the pollen assemblages of lakes in the Picea and Abies forest or the Picea and Abies forest-Alpine (Rhododendron) shrubland. Little pollen from Picea, Abies, Larix and Tsuga is transported downhill in lake sediments, indicating that lake cores near the lower limit of the Picea and Abies forest more correctly reflect climatic changes than lake cores near the tree line (namely the upper limit of the Picea and Abies forest) when using fossil pollen data. Principal component analysis basically separates surface lake samples below and above 3200 m a.s.l. However, it does not distinctly distinguish between samples from two different vegetation types above 3200 m a.s.l. because percentages of some dominant pollen types, such as Pinus, Picea and Abies, Betula, Juglans, deciduous oaks, evergreen oaks, and Rosaceae, do not markedly change with strong upslope transport.

Research Highlights
► We analyze spatial variation of modern pollen from 42 lakes in southwestern China.
► The pollen records can be distinguished by their spectra and indicator species.
► Pollen records near lower limit of Picea and Abies forest reflect better climate.
► Values of Tsuga and Alnus in fossil pollen records may be used to judge tree line.