Climatic and anthropogenic control of surface pollen assemblages in East Asian steppes

Surface pollen samples along moisture and human impact gradients in the steppe zone in East Asia were collected and analyzed to investigate relative control of climatic and anthropogenic factors affecting pollen assemblages. The major pollen taxa are Chenopodiaceae, Artemisia, Gramineae, Polygonum, Compositae, Leguminosae, Pinus and Betula. The pollen assemblages of the meadow steppe zone are dominated by Artemisia, the typical steppe zone by both Artemisia and Chenopodiaceae, and the desert steppe zone by Chenopodiaceae and also Artemisia. The percentage of Chenopodiaceae and the ratio of Chenopodiaceae/Artemisia (C/A) increase from the meadow-steppe zone, through the typical steppe, to the desert-steppe zone. However, there are also great variances of pollen assemblages in each steppe zone. Canonical correspondence analysis showed that annual precipitation has the greatest influence on surface pollen assemblages in the study area, particularly on changes of Artemisia pollen abundance. Severe human disturbance also leads to changes in pollen assemblage, particularly resulting in the increase of Chenopodiaceae percentages. Pollen assemblages are indicative of the relative contributions of climatic and anthropogenic factors to regional vegetation degradation.