Before the emergence of agriculture and permanent settlement, seasonal variations in precipitation and temperature challenged the survival of ancient people in higher-latitude areas in the northern region of China. China’s vast territory is described as the Three Steps or the Three Gradient Terrains based on the average altitude from west to east and the relief amplitude (Guan et al., 2020). The first gradient terrain is the Qinghai–Tibetan Plateau. The second gradient terrain includes the Inner Mongolian Plateau, Xinjiang Autonomous Region, Yunnan–Guizhou Plateau, Loess Plateau, and Sichuan Basin. The third gradient terrain comprises plains and hills below 500 m above the sea level (Guan et al., 2020). Most Paleolithic–Neolithic sites are found on the second- and third-gradient terrain where the environment is suitable for animal–plant domestication, permanent occupation, and human survival. Figure 1 shows the geographical location of the Pigeon Mountain site, which is in Northwest China, characterized by an arid and semi-arid climate.

The Pigeon Mountain site (QG) is located in northwest of Qingtongxia City, Ningxia Hui Autonomous Region, China. It is composed of 15 localities. In the literature, the site is either referred to as “Pigeon Mountain Loc. 10” or it is Chinese pinyin equivalent, i.e., “Gezishan Loc. 10” (Zhang et al., 2022). In the 1990s, QG3 and QG4 were excavated by a joint team of Chinese and American scholars. Evidence of microblades, grindstones, and flakes had been yielded (Elston et al., 1997). These remains provide valuable insights into the subsistence patterns of those who lived there during these periods. The ¹⁴C age indicates that it is a Mesolithic period site less commonly discovered in the arid region. Meanwhile, the site is situated in a transition zone between the northwest desert and the Loess Plateau, with a presently mid-temperate continental climate and proximity to the edge of the East Asian monsoon climate zone (Madsen et al., 1996). The mean annual temperature and precipitation are approximately 8.5°C and 260 mm, respectively. The frost-free period is 176 days, the annual sunshine is 2,955 h, and the temperature difference between day and night is significant (Madsen et al., 1996).

The locality 10 of the Pigeon Mountain site (known as QG10, N38°03′33.1″, E105°50′30.3″, altitude ca. 1,200 m) is located on the foothills of the Helan Mountains and the southeast edge of the Tengger Desert, which is about 20 km from Qingtongxia City, Ningxia Hui Autonomous Region, China (Madsen et al., 1996). It is the most important locality in the site complex because of its rich discoveries. QG10 was discovered in the 1990s. However, just sporadic artifacts were collected at that time. In 2013, the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (IVPP-CAS), and the Ningxia Institute of Cultural Relics and Archaeology launched a new investigation in this region. Two new localities were discovered: QG14 and QG15 (Guo et al., 2019). From 2014 to 2017, a formal excavation was conducted at QG10. The new excavation of QG10 unearthed multiple sets of archaeological data with a well-stratigraphic context. This work provides a reliable chronological framework for site research and an opportunity to explore ancient humans’ technological adaptation, resource utilization, and environmental adaptation behavior in the desert fringe area. Latest 14C dating display the excavated area covers c. 200 m² and reaches a depth of c. 3.5 m (Madsen et al., 1998). The map in Figure 2 shows the QG10 stratigraphic sequence comprising five geological layers from 1 on the top to 5 at the bottom.

Three archaeological horizons were identified in layers 2, 3, and 4 separately. They were named CL1 in Layer2, CL2 in Layer3, and CL3 in Layer4. CL3 yielded the richest archaeological assemblage, including architectural structures, hearth, grinding discs, grinding rods, typical amphibians, Helan pointed implements, animal skeletons, macro-remains, micro-remains, and small ornaments made of ostrich egg skins, especially animal skeletons, macro-remains, micro-remains, fire ponds, architectural structures, and others remains indicating that ancient humans exploited more diverse food resources, widening their recipe, closely related to the Broad Spectrum Revolution and society complexities increased.

A total of 361 starch grains and a small amount of plant organ debris were found in 19 stone artifacts from CL2 and CL3. The starch grains include Triticeae, Panicoideae, possibly Fagopyrum, beans (Fabaceae), acorns (Quercus), possibly Typha, Dioscorea or Fritillaria, underground storage organs of other plants, lotus seed and a small number of unidentifiable starch granules and broken granules. Among them, grasses occupy an absolute advantage, while legumes, nuts, and tubers account for a smaller proportion (Guan et al., 2020). More than 2,000 animal remains were unearthed from CL3. In decreasing order of the identified specimens, animal skeletons are represented by Lepus sp., Equus przewalskyi, Procapra przewalskii, Vulpes sp., and Cervids (Zhang et al., 2022).

The proportion of Tamarix spp. in the Pigeon Mountain site is very high, which is the most widely distributed regional vegetation. The plants of Tamariaceae are all xerophytes, indicating that the climate is arid. The ubiquity of Agriophyllum squarrosum is also very high. Agriophyllum squarrosum is an annual summer and autumn plant that rarely develops in drought years. The appearance of the large number of Agriophyllum squarrosum indicates significant precipitation in summer. In addition, Corispermum declinatum, Kochia scoparia, and Salsola collina are also annual plants that develop in summer and autumn. According to the climatic characteristics of this study area, the rainfall season is conceived in summer. In the terrestrial ecosystem, the microenvironment plays a fundamental role in plant species’ growth, germination, mortality, and reproduction (Cao et al., 2009). This role is essential because of the direct and indirect influence on essential processes such as nutrient cycles, evapotranspiration, and photosynthesis (Figures 7A–C). The changes in the vegetation composition and structure due to human activities and natural disturbances alter local conditions (Gehlhausen).

As Corispermum declinatum, Kochia scoparia, and Agriophyllum squarrosum show changes based on the environment, it demonstrates how the interaction of biotic and abiotic factors influences the microenvironment. This means that a change in the microenvironment influences the ecosystem and structural processes (Behera). Among the changes observed at the Pigeon Mountain site, the changes in the ecosystem are increased air and soil pressure, solar radiation levels, and decreased relative humidity, soil moisture, and vapor pressure. The Pigeon Mountain site has provided an exciting system for analyzing the relationship between variations in plant composition and structure and the microenvironment. This shows that the ecosystem has specific environmental conditions for plants to grow despite the climatic conditions. The topography of the Pigeon Mountain Site shows that the most common species found are mainly flowery plants such as Artemisia sieversiana. The number of plant species in the region shows the variation in environmental conditions based on the topography, moisture, and degree of disturbances.

Plants are essential to our well-being and they are included in people’s food, religions, cultures, and medicines. The vital component of plants results in plant species’ coevolution and domestication (Guo and Li, 2014). The archaeological practices to identify ancient practices ensure that indigenous plants do not become extinct because of environmental changes and human adaptation to modern plantation. Ancient people of the Pigeon Mountain site strengthened their utilization of herbal plants for a long time. The use of plant resources by ancient ancestors mainly includes two aspects: wooden tools and edible resources (Guo and Li, 2014). Wooden tools are commonly used for building materials, firewood, and tool-making. At the same time, edible resources focused on collecting seeds, fruits, roots, stems, and leaves of various plants. Almost all the remains of carbonized seeds unearthed in and around the archaeological site remain in the Pigeon Mountain site appearance (Cao et al., 2009). The ancient ancestors of the Pigeon Mountain site used fire frequently, and firewood resources, such as Tamarix spp., Myricaria spp., Tetraena mongolia, Zygophyllum spp., and Caragana korshinskii, were abundantly found. Therefore, the occupants of the Pigeon Mountain site did not have to collect the stems of herbs for fuel.

The community-staggered zone is also named the ecological or ecological transition zone. The environmental conditions of the community-staggered zone are relatively complex, which can provide growth conditions for plants of different ecological types, even species unique to the staggered region (Cao et al., 2009). The QG10 is located in a transitional area from grassland to the desert. It is also a community-interlaced area, providing conditions for human development and selecting a wider variety of food resources.

Related theories, such as the optimal foraging theory (Smith, 1983; Pyke, 1984; Yi et al., 2013), Niche construction theory (Odling-Smee, 1988; Smith, 2011), and adaptation cycle theory, all explain the adjustment of the survival strategies of ancient humans to a specific period, such as the transition from a hunter–gatherer economy to an agricultural economy. According to the cost and return rate in development and utilization, natural resources can be divided into different grades. Ancient humans always preferred natural resources at higher rates of return. However, when specific high-return resources were scarce or difficult to obtain due to climate change or over-exploitation of specific resources, ancient humans had to include natural resources with relatively low returns to expand food sources (Piperno and Pearsall, 1998). Among all kinds of natural resources, the return rate of plant resources is usually lower than animal resources (Piperno, 2011). Therefore, ancient humans likely used animal resources first and then various plant resources.

Even the animal bones unearthed at QG10 are the highest (Zhang et al., 2019). The number of plant remains obtained by flotation and residue analysis is exceptionally abundant, which may indicate adaptions made by the ancestors of the QG10 in exploiting natural resources. Herb-seed plants, such as Agriophyllum squarrosum and Artemisia sieversiana, are primarily annual plants with solid recovery ability, which can meet the needs of the continuous utilization of ancient humans. In addition, grass-seed plants are productive and can be stored; this can also help the Pigeon Mountain site populations get through the harsh condition and food-scarce winter. In summary, grass-seed plants have been strengthened in the selection and utilization at the Pigeon Mountain site, indicating the ancient humans’ adaption strategy to the living environment.

The current research and various relic phenomena and relics unearthed can provide valuable information about ancient ancestors’ survival and adaptation ability in arid areas. First, grinding tools such as stone grinding discs and grinding rods were unearthed at Locality 10 (Guo et al., 2017). The residue analysis identified many starches of grasses, tubers, and other plant types on the surface (Guan et al., 2020). The existence of the ancestors’ grinding behavior indicates that plant processing and utilization frequency were improved and strongly dependent on plant resources. Second, the suspected column–hole remains found in Layer4 are characterized by uniform horizontal distribution, strip-like, similar inner diameters, and similar internal contents. They contain much large amounts of Tamarindaceae charcoal, indicating the possibility of early attempts to build huts at the Pigeon Mountain site, though it still needs further discussion. The rich relic phenomenon and the continuous distribution of the culture layer indicate that ancient humans lived in this area for a long time. In addition, plenty of fire remains were found on the site, including many fire ponds with clear structures, indicating the ancestors of the site had behaviors such as heating and even cooking animal and plant resources and adapted to changes in the environment.

In the QG10, Agriophyllum squarrosum dominated the unearthed plants in number and ubiquity. Thus, the seeds of Agriophyllum squarrosum seem to be one of the most important food sources for the ancient people at the Pigeon Mountain site. However, according to textual research studies, there is no cultivation tradition of Agriophyllum squarrosum in China or other countries. In our observation, seeds unearthed in the Pigeon Mountain site did not show domestication characteristics, so further research is needed.

The dried seeds of Artemisia sieversiana can be ground into Artemisia powder, which is sticky when exposed to water. When kneaded with flour and water, the Artemisia powder can refine the flour and be kneaded into the soft and flexible dough to make Artemisia seed noodles. The seeds of Artemisia sieversiana could improve the digestion in humans. Therefore, we speculate that the ancestors of the Pigeon Mountain site used the seeds of Artemisia sieversiana to bind the powder made by other seeds (or fruits) and then ate them. Among the plant food resources unearthed from the Pigeon Mountain site, the resources that can be ground into powder include Agriophyllum squarrosum and Elaeagnus angustifolia. In addition, the tender leaves of Artemisia sieversiana are edible, and Artemisia sieversiana seeds were used as a source of oil by ancient ancestors.