Modern pollen distribution in moss samples along an elevational gradient in southeast Tibet

Abstract

Modern pollen distribution and its relationship to vegetation and climate in the lower Yarlung Zangbo River are investigated to provide a reference for paleoenvironmental reconstructions and to improve the understanding of pollen dispersal patterns in mountainous regions. Twenty-eight modern samples collected in moss polsters from 800 and 5400 m a.s.l. are used for palynological analysis. Our results indicate that palynological assemblages and indicator species from moss polsters can reflect the vertical distribution of vegetation belts. Abies, Picea and Pinus pollen from the upper forests and shrub meadow elements (Ericaceae, Cyperaceae and Polygonum) show strong abilities to be transported upward, whereas pollen (e.g. Macaranga, Alnus and Rutaceae) and spore (e.g. Athyrium, Cyatheaceae, Dicranopteris, Pteris) taxa from the lower evergreen forests show weak abilities to be transported upward. An unusual finding is that Tsuga pollen from the lower coniferous forest tends to be transported downslope, probably due to the intense spring rainfall and associated surface runoff in the study area. Due to its potential impact on the geographic range shifts of plants, pollen dispersal may be an additional factor to be considered in studies of vegetation change in the southeastern Tibetan Plateau, such as the projection of Abies or Picea treeline under climate warming. Furthermore, the redundancy analysis shows that precipitation and wind speed are the main factors influencing pollen distribution in the study area.