Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
doi:10.5194/cp-2017-63
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
03 May 2017
Review status
This discussion paper is under review for the journal Climate of the Past (CP).
Examining bias in pollen-based quantitative climate reconstructions induced by human impact on vegetation
Wei Ding1, Qinghai Xu2, and Pavel E. Tarasov1 1Institute of Geological Sciences, Palaeontology, Free University of Berlin, Berlin, 12249, Germany
2Institute of Nihewan Archaeology, Hebei Normal University, Shijiazhuang, 050024, China
Abstract. Human impact is a well-known confounder in pollen-based quantitative climate reconstructions as most terrestrial ecosystems have been artificially affected to varying degrees. In this paper, we use a human-induced pollen dataset (H-set) and a corresponding natural pollen dataset (N-set) to establish pollen-climate calibration sets for temperate eastern China (TEC). The two calibration sets, taking a Weighted Averaging Partial Least Squares (WA-PLS) approach, are used to reconstruct past climate variables from a fossil record, which is located at the margin of the East Asian Summer Monsoon in north-central China and covers the late glacial–Holocene from 14.7 ka BP (thousand years before AD 1950). Ordination results suggest that mean annual precipitation (Pann) is the main explanatory variable of both pollen composition and percentage distributions in both datasets. The Pann reconstructions, based on the two calibration sets, demonstrate consistently similar patterns and general trends, suggesting a relatively strong climate impact on the regional vegetation and pollen spectra. However, our results also indicate that human impact may obscure climate signals derived from fossil pollen assemblages. In a test with modern climate and pollen data, the Pann influence on pollen distribution decreases in the H-set while the human influence index (HII) rises. Moreover, the relatively strong human impact reduces woody pollen taxa abundances, particularly in the sub-humid forested areas. Consequently, this shifts their model-inferred Pann optima to the arid-end of the gradient compared to Pann tolerances in the natural dataset, and further produces distinct deviations when the total tree pollen percentages are high in the fossil sequence (i.e. about 40 % for the Gonghai area). In summary, the calibration set with human impact used in our experiment can produce a reliable general pattern of past climate, but the human impact on vegetation affects the pollen-climate relationship and biases the pollen-based climate reconstruction.

Citation: Ding, W., Xu, Q., and Tarasov, P. E.: Examining bias in pollen-based quantitative climate reconstructions induced by human impact on vegetation, Clim. Past Discuss., doi:10.5194/cp-2017-63, in review, 2017.
Wei Ding et al.
Wei Ding et al.
Wei Ding et al.

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Short summary
Pollen-based past climate reconstruction for these regions with long-term human occupation is always controversial. We examined the bias induced from human impact on vegetation in climate reconstruction for temperate eastern China by comparing the deviations of the reconstructed results for a fossil record based on two pollen-climate calibration sets. Climatic signals in pollen assemblages is indeed obscured by human impact, however, the extent of bias could be assessed.
Pollen-based past climate reconstruction for these regions with long-term human occupation is...
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