Holocene vegetation characteristics of the southern Loess Plateau in the Weihe River valley in China

The Loess Plateau has a varied topography that creates a mosaic of hydrological and soil microclimatic conditions, and the study of its vegetation characteristics has been controversial. Two loess-palaeosol sequences of Xindian and Beizhuangcun were selected at different topographic units in the Weihe River valley to reconstruct the vegetation history for the Holocene period using high-resolution pollen analysis. Herb plants typically dominated the Xindian region during the Holocene, and sparse-wood grasslands became prominent around 8200-7700 years BP and 5500-4700 years BP. Forest-grassland covered the area between 7700 and 5500 years BP. Sparse-wood grassland dominated the Beizhuangcun region for most of the Holocene. This region contained mixed coniferous and broad-leaved forest dominated by Pinus between 6800 and 5300 years BP. Around 40% of the arboreal pollen indicates that the forest was relatively open with some grasses and shrubs. Therefore, the sparse-wood grasslands and grasslands were the dominant vegetation types in the Weihe River valley, which has the best hydrothermal conditions on the southern margin of the Loess Plateau. The forest in the Weihe valley only became extensively developed in the Holocene Optimum. Topographic units, terrain composition and loess thickness are the important factors controlling the development of this arboreal vegetation, along with temperature and precipitation.