Uncertain relationships between pollen-based biomes and local vegetation types along altitudinal gradients in the Hengduan Mountains

The Hengduan Mountains (HDM) in southwestern (SW) China, characterized by complex terrain and diverse vegetation types, offer an ideal environment for the reconstruction of paleovegetation and palaeoclimate. Nevertheless, due to the absence of detailed local vegetation investigations corresponding to pollen samples, the comprehension of certain pollen-based paleovegetation results within the region still remains controversy. In this study, we conducted a thorough investigation of 66 vegetation quadrats (700–4700 m a.s.l.) in the HDM, and performed corresponding pollen-based biomes. Results show that 1. pollen-based biomes match local vegetation well in alpine shrublands and meadows (ALSM) and evergreen sclerophyll Quercus forests (ESQF). However, more than half of the cool conifers mixed forest (COMX) was reconstructed as deciduous broadleaved forest (DBLF), because the high proportion of exotic Alnus pollen. Owing to the high proportion of Poaceae resulting from human activities, a small number of evergreen broadleaved forest (EBLF) have been reconstructed into ALSM; 2. The six pollen-based biomes are clearly fewer than the ten investigative vegetation types. This disparity is probably due to the high pollen productivity of high-altitude conifers and the incapability of collecting entomophilous pollen from lowland tropical taxa. Redundancy analysis reaffirms that annual/seasonal climate has a clearly impact on most vegetation types. Nevertheless, DBLF might be more reliant on climatic stability than on the climatic threshold. This study can provide novel data to further clarify the relationship among local vegetation, pollen-based biome, and climate in HDM. Based on this data, the reliability of paleovegetation reconstructions within the region can be improved.