Pollen dispersal and representation of the “Forest Island” within the Chinese desert-loess transitional zone

Abstract

Vegetation reconstruction from fossil pollen records depends on an adequate understanding of the relationship between modern pollen and vegetation. In this study, we present the modern pollen dispersal and representation of the “Forest Island” and its surrounding areas within the Chinese desert-loess transitional zone. Forty-four pollen carpet traps, which imitate the natural pollen sediment process, were collected from the Ningxia Daluoshan Mountain and its surrounding areas along a southeast–northwest transect included five vegetation types. The pollen spectra, spatial distribution patterns of the main pollen types and discriminant analysis of pollen data show that: Pinus Diploxylon-type has high pollen production and good dispersal ability and that the over-represented, with values exceeding the 20% (>100 grains cm−2 year−1) within vegetation dominated by Pinus tabuliformis, below 7% (<39 grains) when Pinus tabuliformis trees are absent. Picea has higher pollen production and a limited pollen dispersal ability via wind-borne dispersal, with values exceeding the 20% (>100 grains) within the spruce forest, decreased abruptly and even disappeared completely outside the forest. Another interesting finding of this study is that Poaceae have higher values and higher pollen production. The modern pollen assemblage of the desert steppe, mountain steppe and Picea crassifolia forest, but especially the desert steppe and mountain steppe, can be separated from each other as follows: (1) desert steppe: Chenopodiaceae–Poaceae pollen assemblage; (2) mountain steppe: Poaceae–Artemisia–Aster type pollen assemblage; and (3) Picea crassifolia forest: Picea–Artemisia–Poaceae pollen assemblage. However, overlap occurs between deciduous broadleaved shrubs and coniferous and broadleaved mixed forests. The very low concentration of deciduous broadleaved shrubs may due to an increased contribution of pine pollen. Our study may facilitate the confident use of fossil pollen data to reconstruct vegetation in the desert-loess transitional zone in China and may be able to be used to correctly interpret fossil pollen records from similar areas.