Agricultural Transformations and Their Influential Factors Revealed by Archaeobotanical Evidence in Holocene Jiangsu Province, Eastern China

The development and adoption of agriculture has been investigated for decades, and remains a central topic within archaeology. However, most previous studies focus on the crop’s domestication centers, leading to gaps in knowledge, particularly in transitional zones between these centers. This paper reviews published archaeobotanical evidence and historical documents to reconstruct the trajectory of agricultural systems in Holocene Jiangsu Province. Comparing these new results to paleoclimate information, historical documents, and archaeological data enables us to better understand the underlying influences of past agricultural development. Our results indicate that a warm and wet climate may have promoted ancient peoples to first settle in Jiangsu between 8,500 and 6,000 BP and adopt rice farming. The continuous warm and wet climate may have facilitated the rapid development and expansion of rice agriculture, ultimately contributing to large-scale human settlement in 6,000–4,000 BP in Jiangsu Province. Between 4,000 and 2,300 BP during a cooler and drier climate millet agriculture diffused southward, facilitating a mixed rice and millet agricultural system. This mixed farming supported a continuesd widespread settlement and population growth in Jiangsu. After 2,300 BP, political instability in north China resulted in further southeastward migration, advanced planting technology was brought about to south China, facilitating highly developed agricultural systems and rapid population expansion in Jiangsu. Population growth led to the establishment of Jiangnan as the regional economic center, where people chose high-yielding rice and wheat rather than millet.


INTRODUCTION
The transition to entrenched agricultural systems is a critical topic relevant to modern economics, politics, international security, and climate change and adaptation. Environmental factors such as climate, landform, hydrology, and soil are critical variables impacting changing agricultural systems (Zhang et al., 2014;Chen et al., 2015;Ren et al., 2016;Wang et al., 2017;Liao et al., 2019). Climactic change is regarded as a key factor for prehistoric agriculture changes and cultural evolution (e.g., Dalfes et al., 1997;Bawden and Reycraft, 2002;Staubwasser et al., 2003;An et al., 2005;Jia et al., 2013, Jia et al., 2016Dong et al., 2019, Dong et al., 2021. It is argued that a warm and humid climate was critical in promoting the large-scale development of millet farming on the Loess Plateau after 6,000 BP Sheng et al., 2018;Dong et al., 2019). While a cold and dry climate supported the widespread cultivation of barley and wheat in the Hexi Corridor and northeast Tibetan Plateau around 4,000 BP (Chen et al., 2015;Zhou et al., 2016;Li and Dong, 2018). Other researchers have argued that geomorphic and hydrological conditions constrained agricultural systems . Wang et al. (2017) posit that two modes of farming existed along the middle reaches of the Yellow River Basin during the Peiligang period (8,500-7,000 BP): millet-based agriculture in hilly areas and mixed rice-millet farming on the plains. In addition to human innovation and adaptation, cultural and political factors played pivotal roles in subsistence systems (Kearns, 2010;Zhang et al., 2015;Pei et al., 2019), as did people's preference for certain crops change agricultural systems (Zhou et al., 2016;Xhauflair et al., 2017;Overton and Barry, 2018). To anticipate potential future agricultural risks, it is necessary to understand the many complex variables impacting changing ancient agricultural systems, particularly in transitional areas between regions.
The widespread adoption of agriculture is regarded as one of the most significant events in human history (Zohary et al., 2012;Barker and Goucher, 2015). Around 10,000 BP, crops were almost simultaneously domesticated in six discrete centers across the world (Mannion, 1999;Lev-Yadun et al., 2000;Zohary and Hopf, 2000;Diamond and Bellwood, 2003;Nakamura, 2010;Price and Bar-Yosef, 2011). This strategy has improved the ability of human beings to adapt to their surrounding environment, increasing worldwide population dramatically (Gignoux et al., 2011). Newly domesticated crops spread from centers of domestication alongside Neolithic peoples, initiating agricultural production in new areas (Gignoux et al., 2011). Many scholars have conducted studies of agricultural exchanges between centers of domestication, including the spread of wheat and barley from Western Asia to China, and of millet from the Yellow River basin to Western Asia (Sherratt, 2006;Frachetti et al., 2010;d'Alpoim Guedes, 2011;Jones et al., 2011;Spengler et al., 2014;Jones et al., 2016;Stevens et al., 2016;Dong et al., 2017Liu et al., 2019;Dai et al., 2021). However, the spread of agricultural systems is often ignored in the transitional areas between adjacent centers of domestication. This is likely due to the complexity and difficulty of understanding the relationships within these processes.
In East Asia, millets and rice were domesticated in the Yellow River Basin and the mid-lower reaches of the Yangtze river around 10,000 BP, changing human lifeways and subsistence in these two areas, then spreading (Fuller et al., 2009;Lu et al., 2009;Zhao Y., 2011, Qin, 2012Zhao, 2014;Yang et al., 2012). Located in the center of Eastern China, Jiangsu Province lies between a center of dry-land agriculture, Shandong Province to the north and a center of rice agriculture, Zhejiang Province to the south (Fuller et al., 2009;Crawford et al., 2016;Jin et al., 2016;Zhao, 2020). Therefore, Jiangsu Province is a transitional area where the north dry-land agriculture spread southward and the southern wet rice agriculture spread northward. However, the changing impact of these agricultural systems on local people's subsistence strategies in Jiangsu remain unclear. Sporadic archaeobotanical data indicates that rice farming first appeared in Jiangsu Province around 8,500 BP (Lin et al., 2014;Qiu et al., 2018), with millet farming introduced around 6,000 BP (Cheng et al., 2020), and wheat and soybean identified after 4,000 BP (Wu et al., 2019). These studies indicate the timeline and potential routes of millet and rice agriculture into Jiangsu Province, but have not paid much attention to the transformations in agricultural systems after their introduction. Further complicating our understanding is that Jiangsu is densely covered with lakes and rivers, with a variety of landforms, with a complex and changeable ecology.
To address these complications, this paper reconstructs the trajectories of agricultural systems in Holocene Jiangsu through published prehistoric archaeobotanical data and historical agricultural records. In addition, paleoclimate information, historical documents, and other archaeological data influences on agricultural change in Jiangsu Province are also explored. This study contributes to our understanding of changes in areas of converging agricultural systems and human adaptation within those ecologically diverse regions.

Regional Settings and Data Sources
Jiangsu Province (30°45'-35°20' N, 116°18'-121°57' E) is located in the center of Eastern China between Shandong Province in the north and Zhejiang Province in the south ( Figure 1). Its total land area is 10.72 × 10 4 km, accounting for 1.12% of China's total. The primary landforms include low hills, alluvial plains, and water areas. Easily traversable flat terrain spans most of the plains area of Jiangsu Province, providing convenient communication and access between the north and south of the province. The Yangtze River runs across the south of Jiangsu, while the Huai River runs through central Jiangsu. These two rivers divide Jiangsu into three areas, from north to south: the northern Jiangsu Plain, the Jianghuai area and the southern Jiangsu area (Zhou and Han, 2008;Zhao Z., 2011). There are significant environmental differences between the southern Jiangsu area and the northern Jiangsu Plain, with the Jianghuai region transitioning between them. The climate of Jiangsu province is impacted by a transitional monsoon climate, and is split between a subtropical humid monsoon climate in the south and warm temperate humid monsoon climate in the north (Jiang et al., 2006;Xia et al., 2015). The average annual precipitation in Jiangsu Province is 660-1,617 mm (Xu, 2016), and the average annual Frontiers in Earth Science | www.frontiersin.org June 2021 | Volume 9 | Article 661684 2 temperature is 13-14°C in the north, 14-15°C in the Jianghuai, and 15-16 C in the south. The principle modern crops in the region are rice, wheat, corn, and potatoes, and the main livestock are pigs, cattle, and sheep.
Forty-five published archaeobotanical records from Jiangsu are presented here, including macrobotanical seeds, phytoliths, and starch grains samples. Information from twenty historical documents about crops in Jiangsu are summarized and presented. For the presented chronology, we used direct radiocarbon dating on macrobotanical crop remains when available, followed by carbonized charcoal from the related contexts. Four relative chronological intervals were selected based on artifact assemblage and are combined with prehistorical archaeological culture and historical periods: 8,500-6,000, 6,000-4,000, 4,000-2,300 BP, and <2,300 BP. The locations of these sites are shown in Figure 1, and detailed information can be obtained from published archives ( Table 1 and Supplementary Table S1).

RESULTS AND DISCUSSION
The History of Agricultural Processes in Holocene Jiangsu Province Based on previous archaeobotanical studies, rice farming appeared around 8,500 BP in Jiangsu Province. Starch grains and phytoliths of rice were identified from the Shunshanji and Hanjing sites, respectively, from the Shunshanji Culture (8,500-7,000 BP) in Suqian, northern Jiangsu Plain Qiu et al., 2018). Charred rice was also recovered at the Shunshanji and Hanjing sites, and directly radiocarbon dated to 7,869 ± 74 and 8,284 ± 88 cal yr BP, respectively, (Lin et al., 2014;National Museum of China et al., 2018). While rice remains were identified from thirteen Majiabang cultural (7,000-6,000 BP) sites in southern Jiangsu ( Figure 1; Table 1). Rice agriculture was clearly present in Jiangsu Province around 8,500-6,000, however, there are differences in the timing of appearance. Rice farming appeared earlier on the northern Jiangsu plains than in southern Jiangsu (Table 1; Figure 1). It must be emphasized that it is very possible that rice management was a supplement to a primarily hunting and gathering economy. For example, the ubiquity and proportion of wild plant remains such as Coix lacryma-jobi and Trichosanthes kirilowii dominate the microfossil assemblages (phytoliths and starch grains) at the Shunshanji and Hanjing sites Wu et al., 2017a;Qiu et al., 2018). Further wild plant remains such as Euryale ferox and water chestnut account for more than 80% of the macrofossil remains (charred seeds) in the Longqiuzhuang site in Gaoyou (Tang and Zhang, 1996;Tang, 1999;Wang, 1999), 93.33% in the Jiangli site in Kunshan (Qiu et al., 2013), and 71.6% in the Yangjia site in Wuxi (Qiu et al., 2016). While rice was planted by people in Jiangsu Province between 8,500 and 6,000 BP, it was likely a supplementary component of hunting and gathering subsistence.
Rice agriculture was established and developed rapidly between 6,000 and 4,000 BP. The number of archaeological  Phase Ⅲ (4,000-2300 BP)  Figure 1). Systematic archaeobotanical work demonstrates that charred rice dominates the macrobotanical seed assemblages between 6,000 and 4,000 BP. For example, the proportion of rice grains increases from 20% in 7,000-6,300 BP to 80% in 6,300-5,500 BP at the Longqiuchuang site, while proportions of the Euryale ferox and water caltrop fell from more than 80% to around 20% (Tang, 1999;Tang and Zhang, 1996;Wang, 1999). Next, the number of rice grains was also much higher than that of other weeds in the subsequent Liangzhu period (5,300-4,000 BP), including the Jiangzhuang site in Taizhou (Wu et al., 2019), Jiangli site in Wuxi (Qiu et al., 2013;Qiu Z. W. et al., 2014), and Zhumucun site in Kunshan . Extensive cultivation of rice was also confirmed by excavated rice paddy fields at many Liangzhu period sites, including the Tenghualuo site in Lianyungang (Lin and Zhang, 2005), the Jiangli site in Wuxi (Qiu et al., 2013;Qiu Z. W. et al., 2014), the Zhumucun and Chuodun sites in Kunshan (Cao et al., 2007;, the Chenghu site in Suzhou (Fuller, 2011;Qin, 2011), and the Luotuodun site in Yixin (Lin et al., 2003). During this time, millet farming also spread southeastward from the Haidai or Central Plains culture area to the northern Jiangsu Plain. 19 carbonized foxtail millets, 17 carbonized broomcorn millets, and 407 carbonized rice seeds were identified at the Wanbei site in Shuyang during the Dawenkou period (6,000-4,600 BP) (Cheng et al., 2020). However, millet agriculture seems to be blocked by the Huai River as there are no millet remains in the Jianghuai and southern Jiangsu area. We conclude that between 6,000 and 4,000 BP rice agriculture developed rapidly and was firmly established in Jiangsu Province, while millet agriculture was introduced on the northern Jiangsu plain.
Millet farming began to expand southward to the Jianghuai and southern Jiangsu areas between 4,000 and 2,300 BP. Simultaneously wheat crops originating in western Asia were introduced to southern China. Between 4,000 and 2,300 BP a mixed agricultural system had formed in Jiangsu Province including the integrated farming of millets, rice, wheat, barley, and soybean. Charred foxtail millet, broomcorn millet, wheat, rice, and soybean seeds were found together in the Shang and Zhou cultural layers (3,600-2,256 BP) at Miaotaizi site in Xuzhou (Wu et al., 2021, in press). Charred foxtail millet, broomcorn millet, rice, wheat, and barley were also unearthed from the Shang cultural layers (3,600-3,046 BP) at Wanbei site in Shuyang (Cheng et al., 2020). The co-existence of foxtail millet, broomcorn millet, wheat, rice, and soybean were also recovered from the Hushu culture layer (3,600-2,400 BP) at Dingjiacun site in Zhengjiang (Wu et al., 2017b). Notably, in  Frontiers in Earth Science | www.frontiersin.org June 2021 | Volume 9 | Article 661684 spite of the integration, the most ubiquitous crops were different at these three sites. The ratio and ubiquity of crop remains reveal that foxtail millet, rice, and wheat were the dominant crops in the Miaotaizi site, Wanbei site, and Dingjiacun site, respectively, (Wu et al., 2017b;Cheng et al., 2020;Wu et al., 2021, in press). Agricultural systems shifted in Jiangsu Province once more after 2300 BP. Due to little archaeobotanical research covering this period (Li et al., 2006;Wu et al., 2021, in press), we draw on historical documents to inform agricultural systems during the imperial period. Particular crops were often recorded by multiple historic documents in the region, indicating that it was widespread and common. The Chinese character "稻" (rice plant body) and "米" (rice caryopsis) were recorded in many Jiangsu historical documents, such as the "Shi Ji, Huo Zhi Biography", "Records of the Three Kingdoms, Wei shu", "Jiang Nan Cui Geng Ke Dao Bian" etc ( Table 1; Supplementary Table S1). These records indicate that rice was common in Jiangsu Province from the  to Qing (AD 1636-AD 1912) dynasties ( Table 1).The Chinese character "麦" (wheat) was also recorded in many historical documents in Jiangsu, such as the "Song Shu, Biography of Emperor Xiaowu", "Song History, Monograph on Food and Currency", "Tao Shan Ji" etc ( Table 1; Supplementary Table  S1), suggesting that wheat was also commonly found in Jiangsu Province. Millet and soybean had withdrawn from much of Jiangsu Province, and only were planted in some relatively dry areas in Jiangnan, Zhejiang, Jinghu and similar areas, recorded by the "Song History, Monograph on Food and Currency". From this evidence, after 2,300 BP people were primarily engaged in the production of rice and wheat after in Jiangsu, and millet and soybeans only planted sporadically in some drylands.
In summary, rice farming first emerged in Jiangsu Province around 8,500 BP, and dominated subsistence strategies between 6,000 and 4,000 BP. With the introduction of millet, mixed agriculture was practiced between 4,000 and 2,300 BP, including rice, millet, wheat and soybean. Agricultural practices shifted after 2,300 BP, when rice and wheat were predominately grown, while sporadic millet agriculture remained in a few dry areas. It is worth noting that the existence of differences in subsistence from the north and south of the Huai River. Rice agriculture emerged around 8,500 BP in the north of the Huai River, which was 1,500 years earlier than its appearance south of the Huai River. Millet was introduced north of the Huai River between 6,000 and 4,000 BP, and was introduced with wheat south of the Huai River only between 4,000 and 2,300 BP. After 2,300 BP, a mixed cropping pattern continued north of the Huai River in Jiangsu Province including rice, foxtail millet, broomcorn millet, wheat, and soybean, while millet farming disappeared. South of the Huai river, rice, and wheat agriculture remained the dominant agricultural subsistence.

Influential Factors on Human Settlement and Agricultural Systems in Holocene in Jiangsu Province
The beginning of plant domestication is often argued to be related to the warm climate transformations of the early Holocene (Zeder, 2008;Willcox et al., 2009;d'Alpoim Guedes and Bocinsky, 2018). Similarly, the emergence of agriculture is also often argued to be a result of a warm climate during the Holocene Optimum (Richerson et al., 2001;Feynman and Ruzmaikin, 2007;Atahan et al., 2008). Many previous paleoclimate studies indicated that a warmer and wetter climate was present between 8,500 and 4,000 BP in the lower Yangtze River (Wang et al., 1996;Qu et al., 2000;Wang and Gong, 2000;Hori et al., 2001;Tao et al., 2006;Atahan et al., 2008;Chen et al., 2009;Ma et al., 2009;Qiu et al., 2020). The emergence of rice farming likely benefited from the warm climate between 8,500 and 6,000 BP in its original centers of domestication. A recent study showed that the increase of rice pollen in the Tai Lake Basin may be related to the emergence of rice agriculture during the warm and wet climate between 8,500 and 6,000 BP (Qiu et al., 2020). Similarly, the warm and wet climate potentially supported the emergence and adoption of rice farming in Jiangsu between 8,500 and 6,000 BP, with increasing food production facilitating a growing population. In this time people settled far from the current coastline of Yellow Sea (Figure 2A) owing to the amount of land covered by the sea during this period (Li et al., 2008;Li et al., 2009).
Formal agriculture was established in China by 6,500-6,000 BP, likely benefiting from the warm and wet Holocene Optimum (Fuller et al., 2009;Zhao Y., 2011;Qin, 2012;Zhao, 2014). The favorable climate conditions likely promoted the adoption of agriculture with a resulting population expansion in northern China in this time. The population expansion on the Central Plains of China is likely mirrored, the migration and expansion of the Yangshao culture southeastward . Southeastward migration brought millet farming to the northern Jiangsu plain, verified by archaeobotanical evidence (36 charred millets) at Wanbei site in Shuyang County during the Dawenkou period (6,000-4,600 BP) (Cheng et al., 2020). Therefore, the warm and wet climate promoted the establishment of rice agriculture in Jiangsu between 6,000 and 4,000 BP, and indirectly facilitated the development of millet agriculture on the northern Jiangsu plain. Some scholars have argued that the marine regression process increased available land for human activities in the Liangzhu cultural period. This would further encourage rapid development and establishment of rice agriculture in Jiangsu Province Zhang, 2005;Li et al., 2008. The establishment of agricultural systems likely led to populations increasing in Jiangsu Province during 6,000-4,000 BP, where the number of archaeological sites increased from 86 in 8,500-6,000 BP to 213 in 6,000-4,000 BP (Figures 2A,B).
Around 4,200 BP, the "Holocene Event 3", an extreme cold and dry climate event, commenced, impacting climate across the world (Bond et al., 1993;Bond et al., 2001;DeMenocal, 2001). This event has been argued to lead to the demise of some ancient states, such as the Akkad Empire and the Harappa civilization (Weiss et al., 1993;Kerr, 1998;Cullen et al., 2000;Staubwasser et al., 2003). This event also played a significant impact on the transformation of civilization in China Liu, 2001, Wu andLiu, 2004;Sun et al., 2019), and is argued to have led to significant culture change and transformations of subsistence strategies in China Liu, 2001, Wu andLiu, 2004;Wang, 2004;Chen et al., 2015; Frontiers in Earth Science | www.frontiersin.org June 2021 | Volume 9 | Article 661684 2016). In particular, the collapse of the Liangzhu Culture is considered a result of this event in southeastern China (Stanley et al., 1999;Li et al., 2010;Sun et al., 2019). This climate event potentially caused southward human migration, bringing millet and wheat dry-land farming to Jiangsu Province. During this time mixed agriculture was prevalent in Jiangsu Province, verified by the archaeobotanical evidence from the Miaotaizi site in Xuzhou (Wu et al., 2021, in press), the Wanbei site in Suqian (Cheng et al., 2020), the Datongpu site in Yancheng (Liu et al., 2021; Under review) and the Dingjiacun site in Zhenjiang (Wu et al., 2017b) (Table 1). Mixed agriculture potentially increased food production, and indirectly improved the human ability to respond the environmental risks. Concurrent with these changes between 4,000 and 2,300 BP is the transition in Chinese societies from the late Neolithic, to Bronze Age, and to the Iron Age. This transformation is confirmed by bronze-iron implements obtained from the archaeological excavation in various cemeteries during 4,000-2,300 BP in Jiangsu Province (Liao, 1982;Liang, 1986;Wu, 2011). Productivity and grain production were greatly improved by the widespread utilization of bronze-iron implements. Therefore, mixed agriculture and the revolutionary implements jointly increased food resources in Jiangsu Province, leading to widespread population growth between 4,000 and 2,300 BP, illustrated by multiple archaeological sites (616) ( Figure 2C). Human settlement peaked after 2,300 BP in Jiangsu Province ( Figure 2D). According to the "Zizhi Tongjian", "Xin Tang Shu", and "Song Shi", the increasing population was considered a result of the shifting of the provincial economic center from the Central Plain to the Jiangnan area (southern Jiangsu) (Zheng, 2003;Cheng, 2004). Over time recurrent wars in northern China led to a large scale of migration southward, such as the Yongjia rebellion (AD 311), the rebellion of An Lushan (AD 757), and the Jingkang rebellion (AD 1127) Sun and Liu, 2011;You, 2018). Some scholars further argue that two cold climatic events compelled human Frontiers in Earth Science | www.frontiersin.org June 2021 | Volume 9 | Article 661684 migration southward from northern China during the Tang Dynasty (AD 710-750 and AD 780-860) (Fang, 1989;Man, 2009;Ge et al., 2014). With the human migration southward, revolutionary tools and technology were introduced into southern China. A variety of advanced agricultural tools such as "lóu ch e" (a sowing tool), two advanced crop planting techniques such as "lí-pá-lóu" (a kind of soil preparation technology) and "s ou zhòng fǎ" (a sowing technology) (Min, 1986;Zeng, 2005;Wang et al., 2019). According to the "Leisi Jing," the advanced farming tools and techniques were introduced from the northern China into the southern Jiangsu Province during the late Tang dynasty, and led to people discarding extensive farming practices, leading to the era of intensive farming. With the introduction of new tools and technologies, larger areas of land were cultivated in southern China, leading to agricultural production increasing and a doubling of income. According to the Xin Tang Shu, Song Shi, Nung Sang Chi Yao, and Agricultural Administration book, the government also carried out a series of policies to increase agricultural production in south China, such as draining lakes, building terraces, and "wéi tián" (low-lying paddy fields surrounded with dikes). The state's economic center gradually shifted to the Jiangnan Area (southern Jiangsu area) after the dredging on Beijing-Hangzhou Grand Canal in the Sui-Dynasty (AD 581-AD 618). With an increasing population, crops with higher productive yields were preferred in Jiangsu Province after 2,300 BP, such as rice and wheat, while millet and other crops were gradually abandoned owing to their relatively low yield. In summary, the warm and wet climate encouraged the emergence of rice agriculture after 8,500 BP, facilitating human settlement in Jiangsu Province. Between 6,000 and 4,000 BP rice agriculture was firmly established, encouraged by the continuous warm and humid climate and marine regression process, and ultimately contributing to large-scale human settlement in Jiangsu. Millet agriculture was also brought into northern Jiangsu plains in this time. This is indirectly attributed to the warm and humid climate conditions in northern China, increasing food production supported by a favorable climate led to greater population growth and migration. Dry-farming was introduced into Jiangsu after 4,000 BP, which was likely the result of human migration southeastward from northern China from the "Holocene event 3". Mixed agriculture and the revolutionary implements jointly increased food production in Jiangsu Province, leading to higher population increases between 4,000 and 2,300 BP. After 2,300 BP, frequent wars in northern China caused large migrations southward to Jiangsu Province, facilitating the introduction of new agricultural tools and farming innovations into southern China. Rice and wheat replaced millet as the principle crops owing to their low yield in southern China. These transformations led to the enhancement of agricultural productivity and yield in southern China, ultimately shifting the national economic center southward.

CONCLUSION
Rice agriculture first appeared in Jiangsu Province around 8,500 BP, and was firmly established between 6,000 and 4,000 BP. Millet agriculture was brought to the northern Jiangsu plain around 6,000 BP, with millet and wheat introduced into southern Jiangsu after 4,000 BP. After 2,300 BP, millet agriculture disappears from Jiangsu Province, while a mixed rice and wheat agricultural system remained.
The warm and wet climate promoted the emergence of rice agriculture and settlement after 8,500 BP in Jiangsu Province. Benefiting from a continually warm and wet climate between 6,000 and 4,000 BP, rice agriculture was firmly established and spread rapidly, supporting greater human settlement in Jiangsu Province. The introduction of millet after 6,000 BP to the northern Jiangsu plain may also be a result of the southward migration of northern people caused by the warm and wet climate. Between 4,000 and 2,300 BP, a mixed agricultural system formed in Jiangsu Province due to the introduction of dry farming from northern China. Meanwhile, the introduction of bronze and iron farming tools improved human productivity and expanded the scale of human settlement. In the end, the new agricultural tools and farming techniques were brought southward after 2,300 BP, and led to the overall increase of the agricultural productive yield in the South, and finally promoted the scale of human settlement to the peak.
In addition, the difference of agricultural patterns was simple and rough in several different geographical units owing to the lack of systematic archaeobotanical research in Jiangsu Province. With further long term systematic archaeobotanical work, our understanding of these long-term transformations will be enriched.