Abstract
The development of adaptive survival strategies is crucial for human occupation of the high-altitude areas of the Tibetan Plateau (TP). However, the history of this adaptation and its driving mechanisms are poorly understood. We used records of pollen, coprophilous fungal spores, and charcoal from a well-dated, high-resolution lake sediment core from the Southern Tibetan Plateau (STP) to investigate the history of high-altitude survival strategies, including arable agriculture and pastoralism, spanning the past 3600 years. The results revealed that survival strategies were dominated by arable agriculture, supplemented by pastoralism, from ~3600 to 1800 cal yr BP. However, after 1800 cal yr BP, this strategy shifted to low-level arable agriculture with intensified pastoralism. Comparison of our findings with regional paleoclimatic and archaeological records revealed that this transformation was an adaptive response to drought intensification. This adaptive resilience was a key aspect of human occupation of the high-altitude regions of the TP during the late Holocene.
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Introduction
The Tibetan Plateau (TP), Earth’s “Third Pole”, has an average elevation of more than 4000 m above sea level (m a.s.l.)1,2. It is characterized by cold temperatures, hyper-drought, and capricious weather, resulting in resource scarcity in most of its high-altitude areas, which limit human occupation. Therefore, establishing strategies to obtain adequate living resources in this harsh environment is a major challenge for its inhabitants3,4,5,6. Remarkably, despite the harsh climate and environmental changes, Tibetans developed a productive arable agricultural and pastoral system on the plateau several thousand years ago3,6,7,8,9. However, we know very little about how these adaptive survival strategies evolved to form the modern plateau economy, based primarily on pastoralism, supplemented by arable agriculture. In particular, the relationship between this process and climate change remains unclear.
In recent years, great efforts have been made to address the above issues. Previous research has shown that the introduction of cold-tolerant barley and wheat played a critical role in enabling human adaptation to the increasingly harsher plateau climate after ~3600 cal yr BP7. This adaptation eventually led to the establishment of permanent human settlements on the northeastern TP7. However, the evidence for this process is limited to lower altitude regions (<3500 m a.s.l.) on the northeastern TP, and minimal evidence is available from the higher elevation regions (>3500 m a.s.l.) that comprise ~85% of the land area of the TP5,10. Recent archeological investigations in high-altitude regions of the TP have provided compelling evidence of well-adapted agro-pastoral systems during the late Holocene5,6,8,9,11,12,13. Around 3,000 years ago, the Bangga site (3715 m a.s.l.), on the central TP, underwent a transition from a mixed-cropping to a barley-dominated arable system. Although this change was influenced by both climatic and social factors, the evolutionary process behind the development of pastoralism remains unclear14. In contrast, previously published zooarchaeological, paleoproteomic, and lipid residue evidence suggests that pastoralism had emerged in higher-elevation regions some ~3500–3000 years ago5,6,12. Furthermore, genetic studies indicate that yaks were domesticated on the TP some 7300 years ago15. These findings are inconsistent; moreover, it is difficult to obtain continuous and detailed information about successive agricultural and pastoral developments from these scattered archeological records. Hence, our understanding of the historical development of arable agriculture and pastoralism in the high-altitude regions of the TP and their relationship with climate change remains limited.
Fortunately, the microfossil evidence preserved in sediments enables us to obtain a continuous and detailed history of the development of arable agriculture and pastoralism in different regions16,17,18,19,20,21,22,23. Records of Sporormiella-type fungal spores and crop pollen in the Andes have provided information about the adaptation of agro-pastoral activity to climate change16,17. Additionally, a recent record of coprophilous fungal spores and crop pollen in Nile delta sediments indicated an early transition from pastoralism to agriculture some 7000 years ago; this adaptive shift coincided with a change from arid to wet conditions18. Besides, a sedimentary record of Sporormiella-type spores and the pollen of crop plants from northern China revealed that shifts in animal herding and cultivation practices were influenced by a drying climate23. Similarly, Sporormiella-type records from northern China indicated the rapid intensification of pastoralism after ∼3600 cal yr BP, which may have been related to climate change19. Furthermore, a record of coprophilous fungal spores from the northeastern TP indicated a major increase in grazing activity during ~2600–2200 cal yr BP, likely in response to climatic deterioration and/or social factors20,24. To conclude, accurately-dated, high-resolution records of pollen, fungal spores, and charcoal from lake sediments can help us to reconstruct the history of arable agriculture and pastoralism and their potential climatic linkage on the southern TP.
In this study we obtained high-resolution records of pollen, coprophilous fungal spores, and charcoal from a precisely-dated lake sediment core from the STP (Fig. 1). Our aims were to determine the history of high-altitude human survival strategies, including both arable agriculture and pastoralism, over the past 3600 years.
A Referenced archeological sites: 1. Kyamo (KM, >3600 m a.s.l.)6; 2. Khog Gzung (KG, 3920 m a.s.l.)13; 3. Qugong (QG, 3700 m a.s.l.)9,32; 4. Changguogou (CGG, 3570 m a.s.l.)11; 5. Chaxiutang (CXT, 4589 m a.s.l.)37; 6. Bangga (BG, 3715 m a.s.l.)8; 7. Bangtangbu (BTB, 3620 m a.s.l.)34. Sites where barley remains have been found are shown by green circles. Referenced paleoclimatic sites: 8. Nam Co46; 9. Paru Co45 and Angrenjin Co42,43,44,47. The brown shading in the upper right indicates the ___location of the Tibetan Plateau. The extent of the study area is indicated by the black dashed rectangle, and the solid arrow indicates the modern Indian summer monsoon (ISM) direction. B Distribution of modern cultivated land and pastoral land on the STP90.
Results
Eight environmental indicators were identified in the Angrenjin Co core: two pollen taxa (Poaceae >40 μm and Stellera); four fungal spore types (Sporormiella-type, Coniochaeta sp., Glomus-type, Gelasinospora sp.); and charcoal particles >100 μm. Among them, Poaceae >40 μm (range of 0–157 grains/g, and mean of 40 grains/g, and the same convention below) and Sporormiella-type coprophilous fungal spores (0–346 spores/g, 117 spores /g) are dominant (Fig. 2). Additionally, Coniochaeta sp. (0–65 spores/g, 13 spores/g), Glomus-type (0–1073 spores/g, 361 spores/g), and charcoal >100 μm (0–132 particles/g, 10 particles/g) are represented. The microfossil diagram is divided into two zones based on CONISS results and the concentrations of Poaceae >40 μm pollen and Sporormiella-type spores, and they are described below (Fig. 2).
Zone 1 (3600–1800 cal yr BP) has abundant cereal pollen: Poaceae >40 μm (mean: 54 grains/g), with a high ratio of cereal-type Poaceae to total Poaceae. The representation of grazing indicators is very low; they include Stellera (mean: 5 grains/g, and the same convention below), Sporormiella-type (37 spores/g), and Coniochaeta sp. (3 spores/g). The erosion indicator Glomus-type is present (332 spores/g), and the numbers of fire indicators are low, with the sporadic occurrence of Gelasinospora sp. and charcoal >100 μm (2 particles/g) (Fig. 2).
Zone 2 (1800 cal yr BP to the present) is characterized by abrupt decreases in cereal pollen, with the mean of Poaceae >40 μm decreasing from 54 grains/g to 32 grains/g, and a low ratio of cereal-type Poaceae to total Poaceae. In contrast, the grazing indicators increase rapidly, including Stellera (8 grains/g), Sporormiella-type (157 spores/g), and Coniochaeta sp. (18 spores/g). The mean of the erosion indicator Glomus-type is 376 spores/g. Additionally, the fire indicators increase substantially, with the frequent occurrence of Gelasinospora sp. and charcoal >100 μm (14 particles/g) (Fig. 2).
Discussion
Evolution of arable agriculture and pastoralism on the STP
The evolution of arable agriculture and pastoralism on the TP is much debated in studies of human development and adaptation to extreme environmental conditions4,7,10,25,26. Archeological evidence demonstrates that stable arable agriculture and/or pastoral systems were established on the TP during the late Holocene7,10,25. However, the further evolution of arable agriculture and pastoralism after their initial appearance, especially in the high-altitude regions above 3500 m, is less clear. However, our multi-proxy records from Angrenjin Co provide insights into these issues (Figs. 2 and 3).
(a) Concentrations of coprophilous fungal spores (grazing indicator) from Angrenjin Co (this study); (b) Age distribution of zooarchaeological sites in the high-altitude areas of the STP (the brown pie charts represent the proportion of domesticated animal remains among total animal remains) (Supplementary Table 2), BG (E–P) is the Bangga site (early phase), and the sites correspond to those in Fig. 1A; (c) Stellera concentrations from Angrenjin Co42; (d) Age distribution of archeological sites with cereals in the high-altitude areas of the STP (Supplementary Table 2) (site locations are shown in Fig. 1A; (e) The ratio of cereal-type Poaceae to total Poaceae, and (f) Poaceae >40 μm concentration (cereal indicators) from Angrenjin Co (this study); (g) Glomus-type concentrations (erosion indicator) from Angrenjin Co (this study); (h) Gelasinospora sp. distribution and charcoal >100 μm concentration (fire indicators) from Angrenjin Co (this study); (i) Pollen PCA1 sample scores from Angrenjin Co42; (j) Geochemical PCA1 sample scores from Angrenjin Co43; (k) Reconstructed summer precipitation anomaly (mm/day) from Angrenjin Co44; (l) Grain size PCA1 sample scores from Paru Co45; (m) Median grain size (μm) from Nam Co46; (n) Reconstructed mean annual air temperature (°C)47. All climate proxies are fitted with Generalized additive models (GAMs). The shaded bands are 95% confidence intervals.
During the first stage (3600–1800 cal yr BP), the low concentration of pastoral indicators indicates a period of low grazing activity in the Angrenjin Co basin (Fig. 3a, c). Similar indications of low-intensity pastoralism are provided by comparable records from the southern and central TP21,27,28. In contrast, the abundance of cereal pollen suggests intensified cultivation around Angrenjin Co and its surroundings (Fig. 3e, f). Additionally, the persistent presence of erosion indicators reveals the continuity of varying levels of human activity in the study area, likely related to arable agriculture or pastoralism (Fig. 3g). However, the low concentrations of fire indicators suggests that local fire events around Angrenjin Co were infrequent (Fig. 3h), possibly due to the limited availability of primary fuel sources in this high-altitude region24,29,30,31. In summary, during 3600–1800 cal yr BP our microfossil and charcoal records suggest that human subsistence around Angrenjin Co was primarily based on arable agriculture, supplemented by pastoralism, while local fire events were at a low level (Fig. 3).
Archeological evidence from the high-altitude regions of the STP supports this subsistence model of arable agriculture, supplemented by pastoralism, during 3600–1800 cal yr BP6,8,9,13,32,33,34. The earliest remains of domesticated yak (Bos grunniens) were discovered at the Qugong site on the STP, indicating that large herbivores were exploited at least 3600 years ago32. Additionally, the remains of domesticated yaks (Bos grunniens), sheep (Ovis aries) or goats (Capra hircus), cattle (Bos taurus), and dogs (Canis familiaris), as well as of wild animals, have been discovered at contemporary archeological sites on the STP6,8,13,32 (Supplementary Table 2). Nonetheless, the proportion of domesticated animals was low, indicating that animal herding was relatively limited during this period: for example, the proportion of domesticated animals was only 23% at the Khog Gzung site6 (Fig. 3b). This low proportion is consistent with the low concentration of grazing indicators at Angrenjin Co (Fig. 3a, b).
However, recent evidence from paleoproteomics and lipid residues indicates that dairy products derived from domesticated animals were used by high-altitude populations on the TP at least 3500–3000 years ago. This utilization has important implications for the successful colonization of high-altitude regions by human communities5,12. Nevertheless, it is worth noting that reliable evidence for milk proteins remains scarce in the STP5, which suggests that the consumption of dairy products may have been less important than arable agriculture during this phase.
Overall, our findings reveal that a low-intensity pastoral economy was established at an early stage in the high-altitude regions of the STP. However, the dominance of an arable agricultural economy is indicated by the abundance of cereal indicators from Angrenjin Co during this period, which is supported by independent archeological evidence (Fig. 3d). For example, abundant crop plant remains (e.g., barley, wheat, millet), and stone knives, sickles, and grinding stones were excavated at contemporary archeological sites on the STP, providing direct evidence of the cultivation and processing of crop plants8,9,11,13,33,34 (Supplementary Table 2). The cereal indicators from Angrenjin Co suggest that the intensity of arable agriculture peaked at ~2000 cal yr BP and declined rapidly after ~1800 cal yr BP (Fig. 3e, f). This pattern is consistent with archaeobotanical evidence, including the summed probability distribution of radiocarbon dates from the Southeast TP, which indicates that intensive arable agriculture was practiced from ~2000 cal yr BP, but that it declined rapidly after ~1800 cal yr BP35. Therefore, based on the available evidence for arable agriculture and pastoralism in the high-altitude regions of the STP, we conclude that subsistence strategies during 3600–1800 cal yr BP were dominated by the cultivation of crop plants supplemented by animal herding.
During the second stage (1800 cal yr BP to the present), the increased representation of grazing indicators suggests the significant intensification of pastoralism around Angrenjin Co, compared to the first stage (Fig. 3a). Higher concentrations of Sporormiella-type spores, indicating the regional development of pastoralism, were observed on the central and northeastern TP at this time19,20,24,28,36. Notably, the reduced pollen representation of Poaceae >40 μm, together with the low ratio of cereal-type Poaceae to total Poaceae during this interval, suggest the decline of arable agriculture in the Angrenjin Co area and its surroundings (Fig. 3e, f). Additionally, the continuous occurrence of erosion indicator at Angrenjin Co indicates the continuity of human activities around Angrenjin Co (Fig. 3g), while the increasing representation of fire indicators suggests more frequent local fire events, possibly related to the improved fuel availability despite the general fuel scarcity in high-altitude regions (Fig. 3h).
Previous studies have highlighted the use of animal dung as fuel, a strategy adopted by early populations which has persisted among the modern-day inhabitants to cope with the harsh environmental conditions of high-altitude regions24,29,30,31. This strategy is supported by the close association between grazing indicators and fire indicators at Angrenjin Co (Fig. 3a, h). It is reasonable to infer that the use of animal dung as fuel was a common practice in the high-altitude regions of the STP since at least 1800 cal yr BP. Hence, the temporal changes in the concentrations of grazing indicators, cereal cultivation indicators, and fire indicators suggest the significant intensification of animal herding which became dominant, while arable agriculture decreased. The increase in local fire events likely resulted from intensified pastoralism, which in turn produced increased quantities of combustible animal dung during this stage.
This pastoralism-based economy on the southern TP at this time is supported by zooarchaeological evidence from other high-altitude areas of the TP, where domesticated animals comprised a high proportion of the animal remains6,37. For instance, at the KM site, domesticated animals comprised 100% of total animal remains6, while at the CXT site they comprised 73%37 (Fig. 3b). In contrast, archeological evidence of cultivation is scarce, possibly due to insufficient archeological excavations (Fig. 3d). Alternatively it may reflect an extremely low level of arable agricultural activity during this stage38.
Based on the above evidence, the subsistence strategies in the high-altitude regions of the STP can be subdivided into two phases. During the first phase (3,600–1,800 cal yr BP), the subsistence strategy was predominantly cultivation, supplemented by animal herding (Fig. 4A). During the second phase (1,800 cal yr BP to the present) there was a shift towards intensive pastoralism, accompanied by low-level cultivation (Fig. 4B).
A Weaker grazing activity, stronger farming activity and decreased local fire activity during a relatively wet climatic phase with low evaporation (3600–1800 cal year BP); B Stronger grazing activity, weaker arable farming activity and increased local fire occurrence during a drier climatic phase with higher evaporation (after 1800 cal year BP). Credit: livestock and fire icons, Huaban.com.
Adaptation of subsistence strategies on the STP to climate change
In the previous section, we documented two distinct stages of subsistence strategies on the STP (Fig. 3). A transformation of human subsistence patterns in the high-altitude regions of the STP occurred at ~1800 cal yr BP (Fig. 4), which raises intriguing questions about adaptive responses to environmental change. For example, climate change, including variations in both temperature and precipitation, has emerged as a critical factor influencing the adaptive evolution of human subsistence strategies on the TP during the late Holocene4,7,14,39,40,41.
We compared our multi-proxy records from Angrenjin Co with regional paleoclimate records processed with GAMs (Fig. 3). Previous records of pollen, geochemical elements, and grain size from Angrenjin Co have revealed a relatively wet climatic interval42,43,44, which is supported by GAMs records from Paru Co and Nam Co, spanning the first stage at Angrenjin Co (Fig. 3i–m)45,46. Despite local differences between records there was a trend towards drier conditions after 1800 cal yr BP (Fig. 3i–m). For instance, a weaker monsoon and intensified drought during the second stage at Angrenjin Co have been demonstrated at this and other sites42,43,44,45,46. Furthermore, an interval of enhanced mean annual air temperature is evident (Fig. 3n)47. Interestingly, the period of intensified drought after 1800 cal yr BP is temporally correlative with a subsistence shift observed in high-altitudes regions of the STP (Fig. 3). This relationship suggests that the shift in subsistence strategies was an adaptive response to regional climate change, specifically increased drought. The causes of the drought are linked to two regional climatic factors: the primary factor is the reduction in monsoon rainfall on the STP, causing the seasonal precipitation to fall below the minimum requirement (378 mm) for barley growth in high-altitude areas48,49; and the secondary factor is increased evaporation due to rising temperatures47, which further hindered arable agricultural development in this region.
Previous studies have highlighted the role of aridity as a significant factor driving the expansion of pastoralism due to its greater adaptability compared to arable agriculture. Animal herding may be economically more productive than cultivation during dry intervals6,18,38,50,51. Therefore, we propose that relatively high-intensity arable agriculture developed on suitable land during the preceding warm and wet climatic stage, such as in northern China23,52, while low-intensity pastoralism became the dominant subsistence strategy in the surrounding mountainous areas of the high-altitude STP (Fig. 4A). As drought intensified and the air temperature increased, reduced precipitation and increased regional evaporation led to decreased soil moisture, reducing the potential for cultivation. Reduced crop yields may have failed to sustain the human population during the subsequent drought stage, forcing the local population to expand into the surrounding mountains and develop animal herding strategies38,40. Thus, after 1,800 cal yr BP, the subsistence strategies of high-intensity pastoralism and low-level arable agriculture were developed to mitigate the effects of aridification and increased environmental pressures on the human population (Fig. 4B)38. Additionally, this shift in subsistence strategy may have facilitated the westward expansion of multiple prehistoric STP populations from the southern plateau from ~1800 cal yr BP53. Overall, our findings suggest that the human population of the high-altitude regions of the STP was able to develop resilience in the face of climatic deterioration during the late Holocene. Moreover, this adaptation has persisted in this region up to the present-day.
Conclusion
We have obtained well-dated, high-resolution records of pollen, coprophilous fungal spores, and charcoal from the sediments of Angrenjin Co, in the high-altitude region of the STP. These records enabled us to reconstruct the evolution of regional subsistence strategies over the past 3600 years. Low concentrations of coprophilous fungal spores and the abundant pollen of crop plants during ~3600–1800 cal yr BP suggest that subsistence in the high-altitude STP was dominated by arable agriculture, supplemented by relatively low-level pastoralism. However, increases in coprophilous fungal spores and decreases in cereal-type pollen after 1,800 cal yr BP indicate the intensification of pastoralism and a much lower level of arable agriculture. Regional paleoclimatic records corroborate this shift in subsistence patterns and show that it coincided with a phase of intense drought. This temporal correlation suggests that the shift in subsistence strategies on the high-altitude STP was an adaptive response to the pressures exerted by increasing aridity. Moreover, we suggest that this adaptive transformation provided the basis for the modern economy of the high-altitude regions of the STP.
Materials and methods
Study site
Angrenjin Co (29°17′–29°20′N, 87°9′–87°13′E, 4306 m a.s.l.) is a closed lake on the southern TP, with a watershed area of 194 km²54. This area has a semi-arid alpine climate and it is ecologically sensitive and vulnerable to global climate change. The mean annual precipitation is ~300 mm, more than 90% of which falls between June and September. The recorded mean annual temperature from 1977 to 2015 was ~7.1 °C (Supplementary Fig. 2B). Around 82% of the water vapor entering the region comes from the Bay of Bengal and the Arabian Sea, driven mainly by the Indian summer monsoon (Supplementary Fig. 2A). The vegetation surrounding Angrenjin Co is dominated by alpine steppe and alpine meadow55. This area is adjacent to the center of the agro-pastoral zone on the TP, in and around the Yarlung Zangbo River valley, which attracted early human settlement and where agro-pastoralism has a long history56,57 (Fig. 1B). High-altitude barley (Hordeum vulgare), rapeseed (Brassica rapa), and wheat (Triticum aestivum) are cultivated on well-watered alluvial fans around the lake margins and in the valley areas56,58. Additionally, yaks (Bos grunniens), sheep (Ovis aries), and goats (Capra hircus) are the main livestock species in the Angrenjin Co basin56. Thus, Angrenjin Co is a potentially important site for documenting the adaptive evolutionary process and possible climatic drivers of arable agriculture and pastoralism on the STP.
Sediment sampling and chronology
A 142 cm–long gravity core (AR-02) was obtained at a water depth of ~14 m from near the center of Angrenjin Co in October 2011. The sediments are composed of gray silt (142–80 cm), interbedded black and gray silt layers (80–50 cm), and black silt (50–0 cm) (Supplementary Fig. 1). Owing to the absence of macroscopic plant remains in the sediments, eight radiocarbon dates were obtained from the bulk organic fraction, conducted by Beta Analytic (Florida, USA). These dates were calibrated using the IntCal20 calibration curve59 with Oxcal 4.4.160. Additionally, to refine the age model, we obtained 210Pb and 137Cs profiles from the uppermost 40 cm of the core, measured at 1-cm intervals, with the 210Pb ages calculated using the CRS model61. Additionally, the paleomagnetic secular variation (PSV) record from Angrenjin Co was compared with a well-dated PSV record from East Asia (EA PSV)62, and with the results from a global geomagnetic field model (Pfm9k.1a)63 (Supplementary Fig. 2). The eight 14C-dates, validated by independent 210Pb-137Cs and PSV dating, combined with Bacon age–modeling64, indicate that the core spans the past ~3,600 years (Supplementary Fig. 2). The detailed age-depth model is presented in our previous study65.
Pollen, fungal spores, and charcoal analysis
A total of 142 samples from core AR-02 (0–142 cm) were used for analyses of pollen42 and fungal spores and charcoal (this study). All samples were prepared using the standard acid-alkali treatment66. Lycopodium spores (27,560 spores per tablet) were added to each sample to calculate the concentrations of microfossils and charcoal particles. The sample residues were passed through a 7-μm mesh with ultrasonic agitation to concentrate the pollen, fungal spores, and charcoal particles. Fungal spores were identified with reference to published fungal spore plates and descriptions20,67,68,69,70,71,72. Pollen, fungal spores, and charcoal particles were counted using a Leica DM 750 microscope at ×400 magnification. The pollen, fungal spores, and charcoal records were analyzed using stratigraphically constrained cluster analysis CONISS (Fig. 2). Tilia 3.0173 was used to process and plot the data. Specifically, we counted the numbers of Poaceae pollen grains with diameters > 40 μm, fungal spores, and charcoal particles >100 μm. Stellera pollen grains were identified as described in a previous investigation42.
To facilitate interpretation and discussion, pollen, fungal spores, and charcoal records (Fig. 2) are classified into four groups based on their specific ecological implications, following recent studies:
-
(1)
Cereal indicators: Poaceae >40 μm is a reliable indicator of the development of arable agriculture74,75,76,77. Poaceae (>40 μm) is well represented in modern agricultural land in the arid areas of northwest China, and changes in its abundance in sedimentary records reflect changes in the intensity of prehistoric cultivation77. Additionally, given the influence of the pollen productivities of the other pollen taxa, we chose the ratio of cereal-type Poaceae to total Poaceae as another indicator of arable agriculture. Thus, we adopted the comprehensive approach of quantifying the abundances of Poaceae >40 μm and the ratio of cereal-type Poaceae to total Poaceae to capture detailed information about changes in arable activity (Supplementary Fig. 4 and Fig. 2).
-
(2)
Grazing indicators: Ecological studies on the TP have indicated that the abundance of Stellera in pollen records is an indicator of the intensity of animal grazing21,27,78. Additionally, the abundance of coprophilous fungal spores in sedimentary records has been shown to be a reliable proxy of changes in the population of large herbivores79,80 and grazing intensity19,20,23,24,36,51,67,72. Hence, in this study we determined the abundance of coprophilous fungal spores, including Sporormiella-type and Coniochaeta sp.70,71 (Supplementary Fig. 4).
-
(3)
Erosion indicator: These include Glomus-type fungal bodies and cells. Glomus is the largest genus of arbuscular mycorrhizal fungi, commonly associated with certain host plants, and their presence is an indirect indicator of soil erosion67,70,81 (Supplementary Fig. 4).
-
(4)
Fire indicators: Gelasinospora sp. thrives predominantly on burnt substrates, with fire acting as a stimulus for spore germination or heat inducing the fungus to produce fruiting bodies68,82. Hence, Gelasinospora sp. is a useful indicator of local fires in paleoecological studies83,84. Additionally, the abundance of larger charcoal particles (>100 μm) is an indicator of the intensity of local fire activity20,85,86.
Generalized additive models
Generalized additive models (GAMs) are used to estimate significant changes in trend in regional climate time-series. GAMs can model non-linear relationships between time and a response variable, and it can accommodate the irregularities in sample spacing and resolution typical in paleoecological time-series87. We used the restricted maximum likelihood (REML) method to fit the smoothed GAMs, which has been used to identify trends within climate time-series87. GAMs were performed using the mgcv package in R88,89.
Data availability
The abundance of selected pollen types, fungal spores, and charcoal particles from Angrenjin Co on the southern Tibetan Plateau in this study are freely available online (https://doi.org/10.6084/m9.figshare.26962855).
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Acknowledgements
This study was supported by the National Key Research and Development Program of China (2022YFF0801502), the Strategic Priority Research Program (Category B) of Chinese Academy of Sciences (XDB0710000), and the National Natural Science Foundation of China (42071103, T2192952, 42471175, 42202217, 42242104). We sincerely thank Prof. Zhaoyan Gu, Guoqiang Chu, Luo Wang, Chunsheng Jin, and Drs Quan Li and Yong Ge for their kind assistance in data analysis, and in the field and laboratory; and Dr. Jan Bloemendal for editing this manuscript; We thank Dr. Zhe Sun for help with providing the data. This research contributes to the DiverseK (a working group of PAGES) initiative. We acknowledge the use of the “Refrigeration storage for high value sediment samples” facility at Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences.
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Deke Xu, Houyuan Lu and Naiqin Wu conceived and designed the study; Hao Li wrote the first draft; Deke Xu and Houyuan Lu revised the manuscript; Hao Li identified and analyzed the microfossil and charcoal data and performed the data analysis; Deke Xu constructed the age-depth model; Chang Li, Anning Cui, Xinxin Zuo, Yajie Dong and Can Wang conducted the fieldwork and collected the samples; and Deke Xu, Hao Li and Anning Cui prepared the samples. All authors discussed the results and provided input to the manuscript.
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Communications Earth and Environment thanks Kangyou Huang, John Dodson and the anonymous reviewers for their contribution to the peer review of this work. Primary Handling Editors: Jiaoyang Ruan and Joe Aslin. A peer review file is available.
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Li, H., Xu, D., Li, C. et al. 3,600 years of human adaptation to drought intensification on the southern Tibetan Plateau. Commun Earth Environ 5, 579 (2024). https://doi.org/10.1038/s43247-024-01745-5
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DOI: https://doi.org/10.1038/s43247-024-01745-5