How prehistoric humans use plant resources to adapt to environmental change: A case study in the western Chinese Loess Plateau during Qijia Period

Abstract

Fossilized charcoals can document how prehistoric humans used wood resources. Here, we present a quantitative result of charcoal fossil records, compiled with archaeobotanical data of Qijia Culture (4.3–3.8 cal. kyr BP) in the western Chinese Loess Plateau, to study how prehistoric people used plant resources and adapted to their environment. The charcoal records showed that Quercus, Ulmus, Pyrus, Acer, Picea, Prunus, and Bambusoideae were abundant during the Qijia Period, implying a warmer and wetter environment at that time. It also clearly showed that Qijia people had a strong preference to select woods in their daily life. Quercus was the most favorable wood, and thus, it was found in all samples. Many fruit trees planted in the Chinese Loess Plateau today were found in charcoal records. These fruit trees were, during the Qijia Period, at least in the process of being domesticated. Qijia people expanded the scope of using plant resources, and many new crops appeared during that time. These results provide a new insight into economic management and human adaption strategies in the Neolithic Age.

Keywords

adaption climate change fossil charcoal fruit trees Qijia Culture western Chinese Loess Plateau

Introduction

Human culture and its relationship with environment have interested paleoclimatic and archaeological researchers for centuries. However, most studies focus on the impact of environmental changes on human societies (e.g. Haug et al., 2003; Hodell et al., 1995; Nunez et al., 2002; Polyak and Asmerom, 2001), ignoring the human beings’ subjective responses. Moreover, the previous studies paid attention to the grasses (e.g. An et al., 2010; Barton et al., 2009; Liu et al., 2004), ignoring the woods. In recent years, scholars are increasingly concerned with origin and diffusion of crops (e.g. Li et al., 2009; Lu et al., 2009). But how prehistoric people use wood resources, such as fruit trees, is still poorly known, especially in China. Despite the fact that the knowledge of this process is essential for our understanding of how human beings adapt to environment, the study on domestication of fruit trees has been hampered by limited data.

As the cradle of Chinese drought-adaptive millet agriculture, the Chinese Loess Plateau should be scrutinized to find how prehistoric people use plant resources. In that sense, the western Chinese Loess Plateau (WLP) deserves more attention because its semiarid life-supporting ecosystem is sensitive to environmental change. Pollen studies show that environmental conditions transited from wet and warm mid-Holocene to dry and cool late Holocene when Qijia Culture (4.3–3.8 cal. kyr BP) flourished in the WLP (An et al., 2003, 2005; Zhao et al., 2010). The Qijia Period, the final stage of wet and warm mid-Holocene, was on the threshold of upcoming big changes, and so it is scientifically rewarding to study how people used plants and adapted to environmental changes at that moment.

Fossil charcoal from archaeological sites, the product of the incomplete use of fire by humans, is always used to reconstruct regional vegetation history (e.g. Cui et al., 2002; Shackleton and Prins, 1992) and to evaluate human activities (e.g. Dufraisse, 2006; Li et al., 2009, 2012). But little is known about whether prehistoric people had a preference to select wood in their daily life and how fruit trees had been used in the Chinese Loess Plateau. Here, we present a study from the WLP based on fossilized charcoal records from the Qijia Culture and other archaeobotanical data to show how prehistoric humans used plant resources, including fruit trees, to adapt to environmental change. In this paper, we focus on botanical data; zoological data are not discussed here.

Regional setting

Today, the mean annual temperature ranges from 6°C to 10°C, and the mean annual precipitation is between 300 and 500 mm in the WLP. This area is hilly with dispersed and sporadic woodlands. The vegetation is temperate steppe (Geography Department and the Map Press, 1984).

Archaeological studies indicate that rain-fed agriculture began to take place in the early to mid-Holocene, and millet dominated agriculture at least during 5 cal. kyr BP (An et al., 2010; Barton et al., 2009; Li et al., 2007). Furthermore, the Qijia Culture, based on millet agriculture, was distributed all over WLP during 4.3–3.8 cal. kyr BP (An et al., 2010; Jia et al., 2012). Meanwhile, charred wheat and barley seeds were also found in many Qijia sites in the WLP (Wu, 1997; Zhao, 2009), and even Oryza was found in a Qijia site (Zhou et al., 2011).

The typical Qijia Culture sites are mainly distributed around the upper Yellow River region as well as its tributaries in the WLP. Sand inclusion reddish-brown pottery and muddy red pottery with basket veins, rope veins, and addition veins are the most distinct features of Qijia Culture pottery. There are thousands of Qijia Culture sites located in the WLP, and we selected four sites in the core area of Qijia Culture to study (sites 5, 6, 7, and 8 in Figure 1).

Figure 1.

Location of the study area and sites mentioned in the text. (1) Lajia, (2) Buziping, (3) Lixian, (4) Qinan (Dadiwan), (5) Daping, (6) Gaozhuang, (7) Qiaocun, and (8) Jiangjiazui.

Daping (35°15′48″N, 106°04′13″E; 1923 m a.s.l.) is located in the Yangjiaping village, Zhuanglang County, on a terrace of a small river. Ash pits accompanied with typical Qijia Culture pottery and houses were found in the site during our field survey in August 2012.

Gaozhuang (35°14′59″N, 106°04′20″E; 1704 m a.s.l.) is located on a terrace in the Gaozhuang village, Zhuanglang County. Pottery of Qijia Culture, ash pits, and bones were found during our investigation in August 2012.

Qiaocun (35°9′N, 107°30′E; 1318 m a.s.l.) is located in the Beizhuang village, Lingtai County. Typical Qijia Culture pottery, ash pits, and tombs were exposed. The site was excavated in 1978. We investigated this site in May 2011.

Jiangjiazui (35°2′N, 107°26′E; 1012 m a.s.l.) is located in the Niangou village, Lingtai County. The site covers an area of about 15,000 m², and culture layers are 1–4 m thick. Sand inclusion, reddish-brown pottery, muddy red pottery, and gray pottery shards with basket veins, rope veins, and addition veins were collected during the archaeological survey. We investigated this site in May 2011.

Methods

Collection of environmental archaeological samples followed two principles: first, pits, houses, vaults, and other archaeological sites selected should have clear stratigraphies and second, in the case of the absence of a clear stratigraphic unit, a single cultural layer should be selected. Then, samples were recovered from these units/layers about 10–20 litter of sediment: three samples from the Daping site (DP1, DP2, DP3) and Jiangjiazui site (JJZ1, JJZ2, JJZ3); two samples from Gaozhuang site (GZ1, GZ2) and Qiaocun site (QC1, QC2). In this study, all samples were collected from ash pits accompanied with typical Qijia Cultural pottery and houses. Ash pits are primarily used as a receptacle for ash removed from a hearth or fire pits.

Charcoals were collected by flotation using sieves to collect the light fractions. After drying and sorting, all samples were prepared with a razor blade to produce fresh, clean surface presenting transverse, radial, and tangential section. Then, samples were examined under a 5×, 10×, 20×, and 50× metallurgical microscope. The taxa were identified, referring to China Timber Atlas (Chen et al., 1992) and China’s Major Timber Structure (Yao, 1988). Furthermore, a typical sample of each type was photographed under a scanning electron microscope (SEM) to enhance identification. For samples of fragments fewer than 100, each piece was identified and a minimum of 100 fragments were identified for samples of fragments more than 100. Then, the percentage of a certain species in the total fragments and the frequency of samples containing certain taxa were calculated.

Results

A total of 708 pieces of charcoal were identified from the samples, and 30 different taxa were also identified (Figure 2). The most abundant taxa were Quercus, Ulmus, Pyrus, Acer, Picea, Prunus, and Bambusoideae. Quercus was present in all samples. Pyrus, Prunus, Ostrya, Acer, and Bambusoideae appeared in many samples. Picea was present only in two samples.

Figure 2.

Abundance ratio of fossil charcoal in the study area. Location of sites is shown in Figure 1.

Quercus, Ulmus, Pyrus, Acer, Picea, Prunus, and Bambusoideae make up over 80% of the charcoal fossil assemblage in most samples (Figure 2). Therefore, they are assumed to have been the main source of firewood of prehistoric people. Ziziphus, Cotoneaster, Catalpa, Acanthopanax, Toona, Aesculus, Cercidiphyllum japonicum, and Padus are low and occasionally appear in the samples.

Discussion

The charcoal assemblage in Qijia Culture sites includes warm temperature taxa, such as Picea, Acer, and Bambusoideae, indicating that the woodland types were mixed with the conifer–broadleaved forest during that time. This also suggests that the climate was warmer and wetter than it is currently. This is generally consistent with the findings of pollen studies (An et al., 2003; Zhao et al., 2010): in long-term trend, the climate turned to dry and cool from mid-Holocene to late Holocene in the WLP, but it was still warmer and wetter than the present time during the Qijia Period. Hence, the Qijia Period is the final stage of wet and warm mid-Holocene in the WLP.

In archaeological sites, charcoal is always the product of the human use of fire for pottery or in daily life. Therefore, the charcoal assemblage not only reflects what kind of firewood was available around archaeological sites, but also reflects what kind of woods humans preferred to use. Case studies show that the activity range of prehistoric farmers was limited to approximately 1-h walking distance (Qin et al., 2010), so it is reasonable to assume that the charcoal fossil at the archaeological site reflects nearby woodland composition and human-selective usage on these woodlands.

Quercus appears in all samples and keeps high percentage in the charcoal records, most likely reflecting a wide distribution of Quercus in the WLP. More important, it reflects that Quercus was a favorable plant to Qijia people since pollen assemblage showed that Quercus was not the most abundant wood at that time (An et al., 2003; Zhao et al., 2010). Actually, Quercus was widely used in constructing houses and sacrificial sites during the Neolithic Age in the study area (Lang, 2002). It is clear that prehistoric humans had a strong preference to use wood in their daily life.

Meanwhile, there are many fruit trees appearing in charcoal records, such as Pyrus, Prunus, Ziziphus, and Padus. The common features of these trees are that they produce nutrient nuts or fruits. In fact, these fruit trees were used by inhabitants in the study area early than the Qijia Period (Li et al., 2012), but the percentage of these fruit trees in the Qijia Period increased compared with the previous stages, implying that Qijia people used more fruit trees. Interestingly, Pyrus, Prunus, Ziziphus, and Padus are still main fruit trees in the Chinese Loess Plateau nowadays (Zhao, 1994).

We are still unsure whether these fruit trees are wild or domesticated. But the fruit tree charcoals demonstrate the same characters as the modern fruit trees (Figure 3). Domesticated species evolved through the management of their wild progenitors, thus identification of predomestication cultivation or management of phenotypically wild species is required to provide the crucial link between gathering wild fruit trees and cultivating domesticated species. Archaeological data suggest that cultivated fruit trees existed in the Loess Plateau for at least 3200 years (Sun, 2010). Increased percentage of fruit trees during the Qijia Period implies that more attention was paid to these trees compared with the previous periods. Since the process of plant domestication generally lasts a long time (Cornille et al., 2012; Erickson et al., 2005; Hillman et al., 2001; Tanno and Willcox, 2006), these fruit trees during the Qijia Period were at least in the process of being domesticated.

Figure 3.

Fossil charcoals of fruit trees and their comparison with modern fruit trees. Upper: SEM pictures of fossil charcoal of fruit trees. Lower: optical microscope (OM) pictures of modern fruit trees (vessels in SEM pictures are black, whereas white in OM pictures). (a1) Ziziphus and (a2) Ziziphus jujube Mill.; (b1) Padus and (b2) Prunus padus L.; (c1) Pyrus and (c2) Pyrus calleryana Dcne; and (d1) Prunus and (d2) Prunus salicina Lindl.

This means that Qijia people expanded the scope of using plant resources, similar to flotation results of plant seeds (Figure 4). Our previous studies and others’ studies showed that many kinds of herbs were used by prehistoric people (An et al., 2010; Jia et al., 2012; Li et al., 2007). Although foxtail millet (Setaria italica) and common millet (Panicum miliaceum) dominated agriculture in Qijia Culture, many herbs, such as Cannabis sativa, Leguminosae, Glycine soja, Panicoideae, and Chenopodiaceae, are found in many archaeological sites, implying diversity in the use of plant resources. For example, Panicoideae is a common weed, but C. sativa can be used possibly for oil or as a raw material in textile industries. Except weeds, some of these herbs can produce edible seeds or useful tissues, indicating that they have been important resources. Why the Qijia people still try to find other food resources after intensive agriculture has been established in the WLP?

Figure 4.

The results of flotation in the study area: Lajia (The Team Study on Agriculture, 2011), Buziping (Jia et al., 2012), Qinan and Lixian (An et al., 2010), and Qiaocun (Zhou et al., 2011).

The earliest common millet remains in the WLP date to 7.8–7.3 cal. kyr BP (An et al., 2010; Barton et al., 2009; Liu et al., 2004). However, in northern China, rain-fed intensive agriculture first developed during the Yangshao Period in Shaanxi and Henan provinces (Gong, 2001; Li, 1979; Zheng, 1996) and then spread across the Loess Plateau (Li, 1998, 2009; Wu, 1982; Zhang et al., 2010). Consequently, the rapid development of agriculture in the WLP occurred after 5.9 cal. kyr BP (An et al., 2010; Barton et al., 2009). The first large-scale cultural expansion during the Neolithic Period in the WLP occurred during the late-Yangshao Period (5.5–5 cal. kyr BP) and Majiayao Period (5.3–4.3 cal. kyr BP; An et al., 2005, 2010; Barton et al., 2009).

During Majiayao Culture, millet dominated agriculture (An et al., 2010; Jia et al., 2012). Remains of crops of Majiayao Culture, including foxtail millet and broomcorn millet were found at many sites (An et al., 2010; Jia et al., 2012). Unlike the millet agriculture during the Majiayao Period, the features of agriculture during the Qijia Period were much different; many new crops appeared at that time. For example, charred wheat and barley seeds were found in many Qijia sites in the WLP (Wu, 1997; Zhao, 2009), even Oryza was found in the Qiaocun site (Zhou et al., 2011), suggesting that subsistence strategies of Qijia people had changed to a broad plant resource, including more crops and wild plants (such as C. sativa, Leguminosae, G. soja, Panicoideae, and Chenopodiaceae; Figure 4), when the climate turned to dry and cool in the long-term. Furthermore, barley became a staple crop after the Qijia Period in the western edge of WLP (Institute of Archaeology et al., 2004), most possibly because barley rather than other crops adapted to the dry and cool climate conditions. This subsistence strategy was adopted by human beings facing dry and cool climate and intensified cultural exchange. This is a veiled criticism of modern agriculture since modern agriculture depended more and more on few crops. Overreliance on few crops might weaken our choice in the face of climate change.

Conclusion

The fossil charcoal records from the Qijia Culture sites indicate that the climate was warmer and wetter than the present time in the WLP during 4.3–3.8 cal. kyr BP.

Qijia people had a strong bias to use woods in their daily life. Quercus was the most favorable wood and was found in all samples. Most common fruit trees that are found today in the Chinese Loess Plateau were found in charcoal records. The fruit trees during the Qijia Period were at least in the process of being domesticated.

Comprehensive archaeobotanical results show that the features of agriculture during the Qijia Period were much different from the previous periods; many new crops appeared in that time. Qijia people expanded the scope of using plant resources. Our findings suggest that diversification of economy is the way Qijia people adapted to climate change.

Footnotes

Funding

This work was funded by National Natural Science Foundation of China (41071051) and 2013BAK08B02.

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