Anthropogenic and climatic impacts on surface pollen assemblages along a precipitation gradient in north‐eastern China

Abstract

Aim To understand the scenarios of 'anthropogenic biomes' that integrate human and ecological systems, we need to explore the impacts of climate and human disturbance on vegetation in the past and present. Interactions among surface pollen, modern vegetation and human activities along climate and land-use gradients are tested to evaluate the natural and anthropogenic forces shaping the modern vegetation, and hence to aid the reconstruction of vegetation and climate in the past. This in turn will help with future predictions.Location The North-east China Transect (NECT) in north-eastern China. MethodsWe analysed 33 surface pollen samples and 213 quadrats across four vegetation zones along the moisture/land-use gradients of the NECT. Detrended correspondence analysis (DCA) and redundancy analysis (RDA) of 52 pollen taxa and three environmental variables were used to distinguish anthropogenic and climatic factors that affect surface pollen assemblages along the NECT. ResultsThe 33 surface samples are divided into four pollen zones (forest, meadow steppe, typical steppe and desert steppe) corresponding to major vegetation types in the NECT. Variations in pollen ratios of fern/herb (F/H), Artemisia/ Chenopodiaceae (A/C) and arboreal pollen/non-arboreal pollen (AP/NAP) represent the vegetation and precipitation gradient along the NECT. DCA and RDA analyses suggest that surface pollen assemblages are significantly influenced by the precipitation gradient. Changes in the abundance of Chenopodiaceae pollen are related to both human activities and precipitation.Main conclusions Surface pollen assemblages, fossil pollen records, archaeological evidence and historical documents in northern China show that a large increase of Chenopodiaceae pollen indicates human-caused vegetation degradation in sandy habitats. The A/C ratio is a good indicator of climatic aridity, but should be used in conjunction with multiple proxies of human activities and climate change in the pollen-based reconstruction of anthropogenic biomes.

Modern pollen assemblages from surface lake sediments in northwestern China and their importance as indicators of vegetation and climate

“…The studied sites were located in variety of vegetation zones, including desert, steppe, meadow and forest. The vegetation type of each site was assigned according to field investigation and regional vegetation literatures (ISTXCAS and IBCAS, 1978;Wu, 1980;Zhang, 2007). Mean annual temperature (MAT) and mean annual precipitation (MAP) of studied sites referred to the Earth Systems Modelling Results of Bristol Research Initiative for the Dynamic Global Environment (http://www.…”

“…Studies of pollen assemblages of topsoils (Liu et al, 1999;Zhang et al, 2010;Zhao et al, 2012a) suggested that high AP/NAP ratios were always found in forest zones and zones with forest patches in northern and northwestern China. The investigation of the pollen assemblages of surface lake sediments in the eastern Tibetan Plateau indicated that a much higher AP/NAP ratio occurred in the patchy forested areas (Herzschuh, 2007).…”

“…The Artemisia/Chenopodiaceae (A/C) ratio has been fre-quently used to indicate humidity change in northern and western China (e.g., Liu et al, 1999;Herzschuh, 2007;Zhao et al, 2007;Zhang et al, 2010;Zhao and Li, 2013), after El-moslimany (1990) found that it is a good humidity indicator in the Middle East. Recently, Zhao et al (2012b) reviewed the reliability of the A/C ratio as humidity indicator in the arid region of China.…”

“…The ecosystem of this region is fragile and very sensitive to climatic changes (Zhang et al, 2000). Generally, four vegetation types are distributed in the arid region of northwestern China (ISTXCAS and IBCAS, 1978;Wu, 1980;Zhang, 2007). Desert is the major vegetation type of this region and is mainly dominated by xerophilous taxa such as Chenopodiaceae (Anabasis, Ceratoides, Eurotia, Haloxylon, Kalidium, Kochia, Nanophyton, Salsola, Suaeda, Sympegma), Zygophyllaceae (Nitraria, Tetraena, Zygophyllum), Tamaricaceae (Reaumuria, Tamarix), Ephedraceae (Ephedra), Polygonaceae (Atraphaxis, Calligonum, Gymnocarpos), Fabaceae (Ammopiptathus, Caragana), and Asteraceae (Artemisia, Ajania).…”

“…Numerous studies (e.g., Wright et al, 1967;Gaillard et al, 1992;Sugita, 1994;Cour et al, 1999;Davis, 2000;Shen et al, 2006;Ma et al, 2008;Zhao and Herzschuh, 2009;Herzschuh et al, 2010;Lu et al, 2011;Fall, 2012;Zheng et al, 2013;Tian et al, 2014) have been conducted to understand the relationship of modern pollen assemblages with contemporary vegetation and climate. Modern pollen assemblages are mainly collected from airborne pollen collectors (e.g., Cour et al, 1999;Giesecke et al, 2010), moss polsters (e.g., Hicks and Birks, 1996;Mazier et al, 2006), topsoils (e.g., Xu et al, 2009;Zhang et al, 2010) and surface lake sediments (e.g., Herzschuh, 2007;Seppa et al, 2004). However, the four types of pollen traps always yield different pollen assemblages even if they are collected from the same site (e.g., Fall, 1992;Wilmshurt and McGlone, 2005a;Lisitsyna et al, 2012;).…”