REVEALS-based reconstruction of Holocene vegetation abundance in temperate China: new insights on past human-induced land-cover change for climate modelling

Quantification of the effects of human-induced vegetation-cover change on past (present and future) climate is still a subject of debate. Our understanding of these effects greatly depends on the availability of empirical reconstructions of past anthropogenic vegetation cover. Such reconstructions can be used to evaluate Anthropogenic Land-Cover Change (ALCC) scenarios for the past (such as HYDE and KK), and simulated past vegetation using dynamic vegetation models such as LPJGUESS. In this context, China is an important region given that agriculture started already in early Holocene, and expanded rapidly over large areas throughout the eastern part of the country. Quantitative reconstructions of plant cover based on pollen data has long been a challenge. The REVEALS model (Sugita, 2007) is one of the approaches for quantitative reconstruction of past plant cover that has been applied, tested, and validated in many regions of the world over the last years. Relative pollen productivity (RPP) of plant taxa is a key parameter required for REVEALS applications. A synthesis of all RPP estimates available in temperate China is published in Li et al. (2018). These RPPs were used with pollen records from lakes and bogs to produce REVEALS-based estimates of Holocene regional vegetation-cover change in temperate China. In order to interpret the REVEALS reconstructions in terms of climate or anthropogenic land-cover change, we compared the REVEALS estimates of vegetation-cover change with existing palaeoclimatic data and archaeological evidences on human history and past land-use change. We also compared the REVEALS estimates with fractions of plant functional types simulated by LPJGUESS and ALCC scenarios from HYDE and KK.

The results suggest that the REVEALS-based values of plant cover strongly differ from the pollen percentages and provide new insights on past changes in plant composition and vegetation dynamics over the Holocene. Human-induced deforestation is highest in eastern China with 3 major phases at ca. 5500, 3000 and 2000 calibrated years before present. Disentangling human-induced from climate-induced pollen-based open-land cover remains a challenge. However,  thorough comparison of the REVEALS reconstructions with historical and archaeological information on settlement and land-use history, and with palaeoclimate reconstructions provide important clues to the question. This study is a contribution to PAGES LandCover6k.

References: Li et al., 2018. Front Plant Sci; Sugita, 2007. Holocene.