The Tibetan Plateau, known as the "Third Pole," presents extreme challenges for human habitation due to its high altitude, cold temperatures, hyper-aridity, and unpredictable weather. Despite these harsh conditions, Tibetans developed sophisticated agro-pastoral systems thousands of years ago. This study aims to understand the evolution of these survival strategies and their relationship with climate change, particularly drought. Previous research focusing on lower altitudes has shown the importance of cold-tolerant crops like barley and wheat in enabling human adaptation. However, high-altitude regions (>3500 m a.s.l.), comprising 85% of the TP, remain less understood. While archaeological findings suggest the presence of agro-pastoral systems during the late Holocene, information on the evolutionary process and the role of climate change is limited and fragmented. This study utilizes high-resolution microfossil records from lake sediments to provide a continuous and detailed history of arable agriculture and pastoralism on the STP, allowing for a more comprehensive understanding of human adaptation to this challenging environment over the past 3600 years. The focus is on reconstructing subsistence strategies (agriculture and pastoralism) and their link to climate change, providing insights into human resilience in the face of environmental pressures in the high-altitude regions of the Tibetan Plateau.

Existing research highlights the introduction of cold-tolerant barley and wheat as crucial for human adaptation to the harsher plateau climate after ~3600 cal yr BP, leading to permanent settlements in the northeastern TP (Chen et al., 2015). However, evidence from higher-altitude regions remains scarce. Archaeological investigations in high-altitude areas provide evidence of agro-pastoral systems during the late Holocene (Wang et al., 2023; Lu et al., 2021; Tang et al., 2023), with studies indicating a transition to barley-dominated agriculture around 3000 years ago at the Bangga site (Tang et al., 2021). Zooarchaeological, paleoproteomic, and lipid residue evidence points to the emergence of pastoralism in higher-elevation regions around 3500-3000 years ago (Tang et al., 2023; Zhang et al., 2023). Genetic studies suggest yak domestication 7300 years ago (Qiu et al., 2015). However, inconsistencies exist, and continuous detailed information on agricultural and pastoral developments from these scattered records is lacking. Studies using microfossil evidence from other regions (Andes, Nile delta, northern China) show the utility of pollen, fungal spores, and charcoal in reconstructing agro-pastoral history and its relationship with climate change (Akesson et al., 2020; Nascimento et al., 2020; Zhao et al., 2022; Huang et al., 2021; Wei et al., 2021). This study builds upon this prior research by providing a high-resolution, continuous record from the STP.

This study used a 142-cm long sediment core (AR-02) obtained from Angrenjin Co, a closed lake on the southern Tibetan Plateau (STP) at 4306 m a.s.l. The core was dated using eight radiocarbon dates, supplemented by 210Pb and 137Cs profiles, and paleomagnetic secular variation (PSV) data. The age-depth model spans approximately 3600 years. 142 samples from the core were analyzed for pollen (Poaceae >40 µm and Stellera), fungal spores (Sporormiella-type, Coniochaeta sp., Glomus-type, Gelasinospora sp.), and charcoal particles >100 µm. Standard acid-alkali treatments were employed, and Lycopodium spores were added for concentration calculations. Microscope analysis (Leica DM 750 at ×400 magnification) was used to identify and count microfossils and charcoal. Stratigraphically constrained cluster analysis (CONISS) was applied to the data. The microfossil data was categorized into four indicator groups: (1) Cereal indicators (Poaceae >40 µm and the ratio of cereal-type Poaceae to total Poaceae), (2) Grazing indicators (Stellera and coprophilous fungal spores), (3) Erosion indicator (Glomus-type), and (4) Fire indicators (Gelasinospora sp. and charcoal >100 µm). Generalized additive models (GAMs) were used to analyze regional paleoclimate data (pollen, geochemical elements, grain size from Angrenjin Co, Paru Co, and Nam Co) and reconstruct summer precipitation and mean annual air temperature.

Analysis of the Angrenjin Co core revealed two distinct zones: Zone 1 (3600–1800 cal yr BP) shows abundant cereal pollen (Poaceae >40 µm) and a high ratio of cereal-type Poaceae to total Poaceae, indicating dominant arable agriculture with low-level pastoralism (low Sporormiella-type spores and Stellera). Zone 2 (1800 cal yr BP to present) is characterized by a sharp decrease in cereal pollen, a low ratio of cereal-type Poaceae to total Poaceae, and a significant increase in grazing indicators (Sporormiella-type spores and Stellera), indicating a shift to intensified pastoralism with reduced arable agriculture. The increase in fire indicators (Gelasinospora sp. and charcoal) in Zone 2 suggests more frequent local fires, likely linked to the increased availability of animal dung as fuel. Comparison with regional paleoclimatic records shows that the shift in subsistence strategies coincides with a period of drought intensification, characterized by reduced monsoon rainfall and increased evaporation after 1800 cal yr BP. Zooarchaeological evidence from other high-altitude sites supports these findings, showing a low proportion of domesticated animals in Zone 1 and a high proportion in Zone 2. The study indicates a shift from predominantly arable agriculture supplemented by low-intensity pastoralism (3600–1800 cal yr BP) to a strategy emphasizing intensified pastoralism with reduced-level arable agriculture (1800 cal yr BP to present).

The findings strongly suggest that the observed shift in subsistence strategies on the STP was an adaptive response to the intensified drought conditions after 1800 cal yr BP. The decline in arable agriculture likely reflects the reduced soil moisture and crop yields due to lower rainfall and increased evaporation, forcing the population to rely more heavily on pastoralism, which is more resilient to arid conditions. The increased use of animal dung as fuel in Zone 2 underscores the adaptation to fuel scarcity in high-altitude environments. The results highlight the flexibility and resilience of high-altitude human populations in adapting to significant climatic shifts. The shift to a predominantly pastoralist economy may have also facilitated westward expansion of populations from the southern plateau.

This study provides a detailed reconstruction of human subsistence strategies on the southern Tibetan Plateau over the past 3600 years using high-resolution microfossil data. The findings reveal a significant shift from arable agriculture to intensified pastoralism in response to intensifying drought conditions. This adaptation demonstrates the remarkable resilience of human populations in this high-altitude environment. Future research could focus on further exploring the social and cultural dimensions of this transition, including examining potential migrations and interactions with neighboring populations, and expanding the analysis to encompass a wider geographic area of the plateau to better understand the regional patterns of adaptation.

The study primarily focuses on a single location (Angrenjin Co). While the regional paleoclimate data provides context, the findings might not fully represent the diversity of adaptation strategies across the entire southern Tibetan Plateau. Further research involving multiple sites and a wider range of proxies would be valuable for enhancing the generalizability of the findings. The reliance on microfossil proxies has limitations; it offers indirect evidence of human activity, and further integration with direct archaeological evidence is needed for a comprehensive understanding of the human-environment interaction.