Journal Pre-proofs Late Holocene vegetation responses to climate change and human impact on the central Tibetan Plateau Qingfeng Ma, Liping Zhu, Junbo Wang, Jianting Ju, Yong Wang, Xinmiao Lü, Thomas Kasper, Torsten Haberzettl PII: DOI: Reference:
S0048-9697(19)35362-8 https://doi.org/10.1016/j.scitotenv.2019.135370 STOTEN 135370
To appear in:
Science of the Total Environment
Received Date: Revised Date: Accepted Date:
6 August 2019 1 November 2019 1 November 2019
Please cite this article as: Q. Ma, L. Zhu, J. Wang, J. Ju, Y. Wang, X. Lü, T. Kasper, T. Haberzettl, Late Holocene vegetation responses to climate change and human impact on the central Tibetan Plateau, Science of the Total Environment (2019), doi: https://doi.org/10.1016/j.scitotenv.2019.135370
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© 2019 Published by Elsevier B.V.
Late Holocene vegetation responses to climate change and human impact on the
central Tibetan Plateau
Qingfeng Ma,1 Liping Zhu,1,2,3* Junbo Wang,1,2, Jianting Ju,1 Yong Wang,4 Xinmiao L ü ,1,2
Thomas Kasper5 and Torsten Haberzettl6
Tibetan Plateau Research (ITP), Chinese Academy of Sciences, Beijing 100101, China
Laboratory of Tibetan Environment Changes and Land Surface Processes (TEL), Institute of
Center for Excellence in Tibetan Plateau Earth System, Beijing 100101, China of Chinese Academy of Sciences, Beijing 100049, China
Basin, School of Geography and Tourism, Anhui Normal University, Wuhu 241002, China
Laboratory of Earth Surface Processes and Regional Response in the Yangtze-Huaihe River
Geography, Institute of Geography, Friedrich-Schiller-University Jena, 07743 Jena,
Geography, Institute of Geography and Geology, University of Greifswald, 17489
16 17 18 19 20 21 22 23 1
Understanding long-term environmental changes under natural and anthropic forces is helpful for
facilitating sustainable development.
Tibetan Plateau to investigate the impacts of climate and human activities on alpine vegetation
during the late Holocene, based on a 162-cm-long lacustrine sediment core collected from Tangra
Yumco. Palynology, charcoal and minerogenic input reveal variations of climate and human
activity during the past 3400 cal yr BP. Our results show that alpine steppe dominated by
Artemisia, Cyperaceae and Poaceae was present in the Tangra Yumco area during the entire
covered period. Only minor human activities are visible between 3400 and 2300 as well as from
1700 to 400 cal yr BP, when vegetation was mainly influenced by climate. Although human
activities (presence/grazing) became more intensive between 2300 and 1700 cal yr BP
corresponding to the Zhang Zhung Kingdom, vegetation change is still mainly affected by a more
arid climate. Strongest human influence on vegetation was found after 400 cal yr BP, when
vegetation composition was altered by farming and grazing activities. Our records indicate human
activities did not have significant impacts on alpine environment until the past few centuries at
Tangra Yumco on the central Tibetan Plateau.
Here we present a sedimentary record from the central
Pollen analysis, climate reconstruction, human-indicator taxa, late Holocene, Tangra Yumco
Knowledge of long-term environmental changes is helpful for facilitating sustainable development
(Mercuri and Florenzano, 2019). The understanding of human impacts on shaping the landscapes
in the present and past is crucial (Mercuri and Florenzano, 2019; Mercuri and Sadori, 2014). For 2
this aim, studies focusing on long-term human impacts based on environmental data by using
various approaches have been carried out in different parts of the world, such as Central and South
America (Flagg, 2018; Peri et al., 2018), Europe (Luelmo-Lautenschlaeger et al., 2018;
Florenzano, 2019) and China (Liu et al., 2018; Xu et al., 2018). Human production and life are
largely based on plants (Mercuri et al., 2018) and in turn cause the variations in the plant species
composition and vegetation cover. Changes in vegetation cover, either due to climate variability or
human impact, can influence on climate through feedback mechanisms by altering land surfaces
themselves and the entire energy budget of an area (Shen et al., 2015; Chen et al., 2013; Zhang et
al., 2013). Therefore, reconstructing environmental change sequence formed under natural and
anthropic forces is essential for future predictions and sustainable development.
Generally, it is a challenge to distinguish human impacts from the effects of climate change
(Kouli et al., 2018; Kramer et al., 2010; Zhang et al., 2010). Palynology provides an appropriate
method to analyze vegetation dynamics and changes in the assemblages as response to climatic or
anthropogenic effects (Edwards et al., 2017; Zhang et al., 2010; Li et al., 2008; Liu et al., 2008).
Hitherto, numerous studies have detected human impacts on vegetation since the mid to late
Holocene based on palynological data. In the Mediterranean region, for example, human impact is
difficult to detect in pollen spectra during the early Holocene, probably because human activity
did not affect regional pattern of vegetation (Mercuri and Sadori, 2014). During the mid and late
Holocene, however, both climate and human activities have been the key factors on determining
vegetation changes (Mercuri and Sadori, 2014; Hoelzmann et al., 2001; Oldfield et al., 2003;
Zolitschka et al., 2003). In the South America, Flantua et al. (2016) recently discussed evidence
for human land use and provided an overview seen as important in separating climatically from 3
anthropogenically driven vegetation change, based on 60 vegetation (pollen) records from across
the region. They found that human impacts were present in most records during the last 2000
years by using a wide range of indicators (e.g. appearance of introduced taxa, deforestation, crops
and indicator of overgrazing).
An “indicator species approach” is often used to trace human activity in palynological
records. Indicators for human activity include deforestation (loss of tree taxa), appearance of
introduced taxa (e.g. Olea, Juglans, Castanea, Eucalyptus, Pinus, Rumex), crop taxa (e.g. cereal
pollen), presence/elevated abundance of species known as possible disturbance taxa (e.g. Cecropia,
Chenopodiaceae, Humulus, Plantago)(Kouli et al., 2018; Mercuri et al., 2013; Flantua et al., 2016;
Wischnewski et al., 2011). Furthermore, several studies form Europe summed some plant taxa to
develop the indexes for human indicators (Kouli, 2015; Mercuri et al., 2013; Mazier et al., 2009).
However, there are different human indicator taxa in different region. For example, cereal pollen
grains are often found in fossil records from farming areas, while they are not relevant in the
pastoral areas, such as most parts of the Tibetan Plateau (TP) (Ma et al., 2019; Li et al., 2019).
Another challenge is the ambiguous interpretation of certain pollen types, e.g., high abundance of
Chenopodiaceae may either reflect a decrease in moisture (Ma et al., 2017a, b; Zhang et al., 2012)
or stronger human disturbance (Miehe et al., 2014; Zhang et al., 2010) in these semiarid to arid
regions. Thus, such data have to be interpreted with great care, especially when studying records
from areas where these taxa are used to trace human activity.
A further valuable proxy to determine human impact on a landscape, via the interpretation of
human induced fire, is charcoal, which is produced by an incomplete burning of plants (Miao et al.,
2019; Xiao et al., 2017; Zhang et al., 2010; Bowman et al., 2009; Patterson et al., 1987). Sharp 4
increases in microcharcoal concentration in palaeoenvironmental records have been used to
indicate regional fire occurrence caused naturally by aridification or intentionally by strong
human-related burning activities. Microcharcoal records from fossil records can provide the
opportunity to explore climate change and human activity in the past (Miao et al., 2019; Jaffé et al.,
Human activities have profound impacts on the environment, not only in the low altitudes but
also in the high altitudes. In the Alps, for example, Gilck and Poschlod (2019) found that alpine
farming began in the Bronze Age (2200-800 BC) in different parts and high-altitude pasture use
began from 4500 BC, by reviewing the archaeological, linguistic and archaeobotanical studies. On
the TP, palynological studies also detected human influence on vegetation since the mid-late
Holocene (Herzschuh et al., 2014; Miehe et al., 2014; Wischnewski et al., 2014, 2011; Kramer et
al., 2010; Miehe et al., 2009; Schlütz and Lehmkuhl, 2009). However, some studies did not detect
human impacts, even on the eastern TP (Li et al., 2019; Shen et al., 2006). Furthermore, most of
these studies targeted sites on the eastern TP, while records from the central and western parts are
quite rare. This scarcity might be explained by either inappropriate palynological indices for
human activities, or by only a minor signal of human activity in this high altitude region on the
central-western TP. Therefore, more studies from the TP are needed to understand human
influence on the environment.
For the central TP, one of the most and best investigated archives for environmental change
is Tangra Yumco. This lake is one of the cultural centers of the ancient Zhang Zhung kingdom
(Bellezza, 2008; Zhang and Shi, 2016), which spans approximately the period of 2300-1300 cal yr
BP (Zhang and Shi, 2016). There has frequent human activities, which was proved by founds of 5
stone tools, a megalith assemblage, abandoned buildings and fields as well as irrigation channels
(Miehe et al., 2014). Further, studies on peat and lake sediments, as well as paleo-shorelines and
beach ridges revealed that Tangra Yumco has experienced distinctive Holocene climate-related
lake level changes (Wang et al., 2017a; Ahlborn et al., 2016; Rades et al., 2015, 2013) with a
decreasing trend of moisture availability since the Mid-Holocene (Ma et al., 2019; Ahlborn et al.,
2017). Based on a sediment core from a recessional lake terrace at 4700 m a.s.l., 160 m above the
present lake level of Tangra Yumco, Miehe et al. (2014) found out that Artemisia steppe
dominated and human influence increased during the Holocene.
In this study, we present a late Holocene palynological and charcoal record from the deepest
part of Tangra Yumco. These data are combined with other paleohydrological records and the
minerogenic input from Tangra Yumco, which was previously presented as a small part of a
composite record spanning the past 17500 cal yr BP from Tangra Yumco (Ahlborn et al., 2017).
By applying this multi-proxy approach, the main aim is to disentangle the climate and human
influence on the alpine vegetation during the late Holocene.
Tangra Yumco (30°45’-31º22’ N, 86°23’-86°49’ E; Fig. 1) is located at the northern flank of the
Gangdise Mountain. Its basin belongs to a north-south trending graben (Cao et al., 2009). The
western mountain range has peaks up to 6132 m a.s.l. (Institute of geography, 1990). Tangra
Yumco has no outflow but is fed by two major rivers, which drain into the lake from the west and
southeast. Quaternary deposits are widely distributed on the lake shore (Wang et al., 2017b). Well
preserved Holocene palaeo-shorelines occur up to ~185 m above the recent lake level of 4545 m
a.s.l. (Rades et al., 2013), while poorly preserved palaeo-shorelines going back to the Pleistocene 6
are exposed up to >260 m (Kong et al., 2011). It is one of the largest and deepest lakes on the TP
with an area of 835.3 km2 (Wang et al., 2017b) and a maximum depth of 230 m (Wang et al.,
2017b; Haberzettl et al., 2015). The climate of this lake basin is mainly influenced by the Indian
Summer Monsoon (ISM) (Miehe et al., 2014). The mean annual temperature is 0-2 ℃ and mean
annual precipitation is 200-250 mm, dominated by the summer rainfall (Institute of Geography,
Alpine steppe and meadow are the two major vegetation types in the basin. Alpine steppe
mainly occupies the catchment area at altitudes below 4900 m a.s.l., dominated by Stipa purpurea
along with Orinus thoroldii, Artemisia wellbyi, A. stracheyi, S. basiplumosa. Alpine meadow
mainly consisting of Kobresia pygmaea and Festuca ovina occurs at altitudes of 4900-5300 m a.s.l.
Sparse alpine vegetation mainly exists above 5300 m a.s.l., consisting of Saussurea spp., Ajania
purpurea, Rhodiola, Saxifraga (Miehe et al., 2014; Tibetan Investigation Group, 1988). Crops
(barley, rape and turnip) can be found at small areas of farmland near the villages to the north and
northeast of Tangra Yumco (Fig. 1b).
Figure 1. Study site. (a) Location of Tangra Yumco (red circle) and comparison sites referenced in the text
(dark circles): 1. Nam Co (Kasper et al., 2012), 2. Basomtso (Li et al., 2017), 3. Lake Naleng (Kramer et al.,
2010), 4. Lake Dongerwuka (Wischnewski et al., 2014), 5. Lake Ximen (Herzschuh et al., 2014). (b)
Sampling site of Core TAN 10/4.
Materials and methods
Based on a seismic survey (Akita et al., 2015; Wang et al., 2010), the 162-cm-long gravity core 7
TAN 10/4 (31°15.15’ N, 86°43.37’ E; Fig. 1b) was taken at 223 m water depth in the northern part
of the lake. The core location was chosen because it was expected to be well suited to capture
anthropogenic impact, as the short distance to villages and farmlands and the steep morphology of
the lake basin make it easy for crop pollen and charcoal from human burning activities to be
transported there (Fig. 1b).
An age-depth model for core TAN10/4 was developed by Henkel et al. (2016). The original
length of core TAN10/4 was 162 cm. Event-related deposits were excluded from the cores, which
were regarded as reworked material of single events. Event layers were identified by their
lithology, magnetic susceptibility, grain size, water content and Ti content (Akita et al., 2015;
Henkel et al., 2016). Finally, a sediment profile with an event corrected total length of 130 cm was
created. Event corrected composite depth (ECCD) was used hereafter. Six radiocarbon ages
(including one age of wood) for core TAN 10/4 were obtained (Henkel et al., 2016). The age of a
modern water plant (2070±40 BP) was used for reservoir correction (Henkel et al., 2016), which is
in the same range as the ages of the sediment-water interface and surface lake sediments (Wang et
al., 2017b; Haberzettl et al., 2015). Some outliers of ages were excluded from the chronology,
which were thought too old in comparison to nearby ages in stratigraphic order and alter the
sedimentation rate without any corresponding changes in the lithology (Haberzettl et al., 2015;
Henkel et al., 2016; Ahlborn et al., 2017). Therefore, the chronology was established by a linear
interpolation between youngest median ages in stratigraphic order (Fig. 2). Optically stimulated
luminescence (OSL) ages of core TAN 10/4 yielded an age offset of approximately 2000 years
compared to the uncorrected radiocarbon ages (Long et al., 2015). Furthermore, the paleomagnetic
secular variation (PSV) record of the past 3400 cal yr BP in this core based on the age-depth 8
model above is in good agreement with the Lake Baikal record, PSV stack for East Asia, as well
as with the predictions of geomagnetic field models (Henkel et al., 2016; Haberzettl et al., 2015).
These results support the chronology and the assumption of a constant reservoir effect. For this
study, 29 samples were subsampled for palynological analysis, each of which had a volume of 4-6
Chronology of core TAN 10/4 as published in Henkel et al. (2016).
Table 1. Radiocarbon ages for core TAN 10/4 as published in Henkel et al. (2016) and Haberzettl et al.
Pollen samples were treated with 10% HCl, 10% NaOH, 40% HF and acetolysis treatments
and sieved over a 7 μm mesh to remove clay-sized particles. Pollen samples were counted under a
Zeiss light microscope at 400x magnification. Pollen identifications followed regional guidelines
from the appropriate references (Wang et al., 1995; Xi and Ning, 1994). More than 300 terrestrial
pollen grains per sample were counted. Pollen taxa with percentages > 0.5% in at least two sample
were used in the pollen diagram and ordination analysis. Spores of Sporormiella, Glomus and
charred particles >10 μm were counted in each sample. Sporormiella and Glomus are presented as
percentages based on a pollen sum. Charcoal values are presented as concentration (particles/ml).
Pollen zonation of core TAN 10/4 is based on the constrained incremental sum of squares
(CONISS) cluster analysis in the Tilia program (Grimm, 2004). A principal component analysis
(PCA) was used to study the variation in biological assemblages (Birks, 1995). To stabilize
variances and to optimize the ‘‘signal to noise’’ ratio in the data set, a square root transformation 9
was applied to the pollen percentage data prior to the PCA. Previous studies revealed that there
were no trees in the late Holocene on the central TP (Ma et al., 2014; Miehe et al., 2014).
Therefore, arboreal pollens in the fossil should be transported long distances by air masses from
forested region. We thereby deducted the arboreal pollen types from pollen assemblages and
analyzed the principal of pollen types of shrubs and herbs. These analyses were made using the
Canoco software program (ter Braak and Smilauer, 2002; ter Braak, 1988).
Semi-quantitative K-values from Core TAN10/4 were obtained using an ITRAX XRF core
scanner at 0.2 mm resolution. Details on the scanner settings and statistic data treatment are given
elsewhere (Ahlborn et al., 2017; Henkel et al., 2016). For a better visualization of trends in the record,
the data were smoothed using the LOWESS at the span of 0.1.
Palynological record of core TAN 10/4
Pollen percentages and concentrations of 26 taxa (abuandance > 0.5% in at least two sample) are
shown in Fig. 3 and Fig. S1. The pollen record is dominated by herb types, especially Artemisia,
Cyperaceae and Poaceae. Other herb types mainly include Chenopodiaceae, Brassicaceae,
Lamiaceae, Ranunculaceae, Fabaceae, Saxifraga, Caryophyllaceae, Polygonum, Crassulaceae, and
Urtica. Tree and shrub pollen types are dominated by Pinus, Betula, Quercus-evergreen, Picea,
Tsuga, Ephedra, and Rosaceae. The pollen percentage diagram of core TAN 10/4 can be divided
into three zones, based on the CONISS cluster analysis (Fig. 3).
plotted on the age scale. Pollen taxa with relatively low percentages have been magnified five times.
Pollen percentage diagram of the selected taxa，spores and charcoal concentration from TAN 10/4
In Zone 1 (127-65 cm, 3440-1700 cal yr BP), herb assemblages are characterized by high
Artemisia (mean 50.9%) and Cyperaceae (23.2%). Chenopodiaceae (1.2%) pollen percentages
were lowest for the entire core. Also the major tree pollen taxa, Pinus (3.4%) and
Quercus-evergreen (1.1%) are highest of the entire record (Fig. 3). Charcoal concentration is 1631
grains/ml on average. Glomus (1.0%) and Sporormiella (1.8%) are low. This zone could be
divided into two subzones: Subzone 1a (3440-2300 cal yr BP) and Subzone 1b (2300-1700 cal yr
BP). Compared with the Subzone 1a, pollen assemblages of Subzone 1b are characterized by low
Pinus percentage and highest Cyperaceae percentage. Charcoal is higher than in Subzone 1a.
In Zone 2 (65-23 cm, 1700-400 cal yr BP), Artemisia percentage (60.1%) shows the highest
values in the whole record. Cyperaceae (20.9%), Pinus (2.8%) and Quercus-evergreen (0.1%) are
lower than in Zone 1. Charcoal concentration decreases to 1247 grains/ml. Glomus (1.3%) and
Sporormiella (2.1%) have no significant changes.
Zone 3 (23-0 cm, 400 cal yr BP-present) is characterized by high percentages of Brassicaceae
(1.6-12.8%, mean 5.5%) and a rapidly decreasing trend of Artemisia. Cyperaceae decreases to
13.7% at 150 cal yr BP, and increases thereafter to the initial value. Urtica and Chenopodiaceae
show distinctly higher values than Zone 2. Other taxa, such as Polygonum, Poaceae and Pinus,
increases only slightly. Charcoal concentrations, Glomus and Sporormiella rapidly increase in this
period. The transition from Zone 2 to 3 is the most intensive change in the entire record.
Ordination of pollen assemblages
PCA results show that the first two principal components capture 52.9% (PC 1: 38%, PC 2: 14.9%)
of the total variance in the pollen data (Fig. 4). PC 1 mainly exhibits high negative values for
Brassicaceae, Chenopodiaceae and Urtica, and high positive values for Artemisia, Ephedra and 11
Cyperaceae. PC 2 mainly separates steppe and desert taxa (Artemisia, Chenopodiaceae,
Caryophyllaceae, Ephedra) from meadow taxa (Cyperaceae, Lamiaceae, Saxifraga, Rosaceae).
PCA result for pollen percentage data from Core TAN 10/4.
The K record of core TAN 10/4 was previously presented as a small part of a composite
record spanning the past 17500 cal yr BP from Tangra Yumco (Ahlborn et al., 2017). As no
details are visible in this composite record, K values of TAN 10/4 are presented in detail in the
follows. From 3300 to 2300 cal yr BP, the record shows high K values (Fig. 5). During 2300 and
2000 cal yr BP, the K content decreases and is stable thereafter until 1800 cal yr BP. Between
1800 and 1300 cal yr BP, values are slightly elevated whereas until 700 cal yr BP the signal is
rather stable. Subsequently, the lowest values of the entire sequence are reached at around 400 cal
yr BP. After that, K shows a rapid increasing trend towards recent times.
Proxies for changes in climate and human activity
For Tangra Yumco, K has been shown to be highly positive correlated to Fe, Ti and Rb since
17500 cal yr BP (Ahlborn et al., 2017). As reported in other paleoenvironmental studies based on
lake sediments from the TP, these elements usually reflect the allochthonous, minerogenic input
into lakes (Xu et al., 2019; Gyawali et al., 2019; Kasper et al., 2015, 2012). This input is
considered to be related to surface runoff resulting from precipitation in the catchment brought by
the ISM on the central TP (Kasper et al., 2015, 2012). As the representative for minerogenic input,
K is thus used to indicate the intensity of the ISM in this study. 12
According to our field investigation, the Tangra Yumco basin hosts the world’s highest
altitude agriculture of barley, rape and turnip. Although these farmland areas are small in the
northern and northeastern part of the basin (Fig. 1b), our sediment record contains high
percentages of the related pollen taxa. The significantly high percentages of Brassicaceae in the
upper part of the record are very likely caused by farming of crops (rape/turnip). Urtica is found in
wasterlands around settlements and grazing areas (Miehe et al., 2014), which can be an indicator
for human activity.
Chenopodiaceae is one common herbaceous type found in samples from steppe and desert
zones (Ma et al., 2017a; Zhang et al., 2012; Zhang et al., 2010). On regional scale,
Chenopodiaceae percentages rise along with increasing aridity (Ma et al., 2017a, b; Zhang et al.,
2012; Zhang et al., 2010). However, human disturbance can also lead to an increase in
Chenopodiaceae percentage in steppe regions (Miehe et al., 2014; Zhang et al., 2010; Liu et al.,
2006). Thus, changes in Chenopodiaceae percentage can be related to both human activities and
climate change, which is needed to be separated through further analysis combined with other
proxies. As K indicates more precipitation in the area since 400 cal yr BP, high Chenopodiaceae
percentages in this period are interpreted as vegetation degradation under the impact of human
Fossil charcoal records from lake sediments can provide information about the fire history
and its relationship to changing climate and vegetation (Xiao et al., 2017; Miao et al., 2016;
Rimmer et al., 2015; Gavin et al., 2007). Microcharcoal concentrations are mainly controlled by
climate on long time scales (Miao et al., 2019, 2016; Xiao et al., 2017), and by a combination
action of climate and human disturbances during the late Holocene (Xiao et al., 2017). As this 13
study focuses on the late Holocene, high microcharcoal concentrations are used to indicate more
intense human activities or aridification. However, the first two axes of PCA can be used to
distinguish between human or climate-induced fires. PC 1 (Fig. 4) distinguishes human-indicator
taxa (e.g., Brassicaceae and Urtica) from natural vegetation types (Artemisia and Cyperaceae).
Therefore, PC 1 is interpreted as an indicator for human activity. PC 1 shows low values when it is
related to intensive human activity and vice versa. PC 2 separates regional steppe and desert taxa
from meadow taxa. Thus, PC 2 can be served as a moisture indicator. PC 2 shows positive values
related to humid conditions and negative values related to arid conditions.
Figure 5. Charcoal, Brassicaceae, spores (Sporormiella and Glomus), PC 1, PC 2 and K data for Tangra
Yumco compared with lake level record of the lake (Wang et al., 2017a) and paleoclimate records in the
ISM-dominated region: Basomtso (Li et al., 2017), Nam Co (Kasper et al., 2012) and Arabian Sea (Anderson
et al., 2002).
Late Holocene variations in climate and human activity
The pollen record is dominated by Artemisia, Cyperaceae and Poaceae in the entire sequence (Fig.
3), which indicates that Artemisia steppe dominated the Tangra Yumco basin during the past 3400
cal yr BP.
Between 3400 and 2300 cal yr BP, the lowest charcoal concentration and high PC 2 values
reflect a relatively humid environment. This is supported by the minerogenic input, which
indicates more precipitation caused by a strong ISM (Fig. 5). Contemporaneous high values in PC
1 and low Sporormiella values reveal only minor human activities and low grazing intensity (Fig. 14
by a sedimentary record from Nam Co (Kasper et al., 2012).
For the same period, humid conditions with an intense ISM on the central TP is also proved
From 2300 to 1700 cal yr BP, climate shows a significant drying trend indicated by
decreasing values in PC 2. This is also proved by decreasing K content, which coincides with the
paleohydrological record from Nam Co on the central TP (Fig. 5, Kasper et al., 2012). Human
activities became a little stronger in this period, reflected by the decreases in PC 1. This phase
corresponds to the Zhang Zhung kingdom period (Huo, 1997), when the Tangra Yumco basin has
evolved to one of the centers of the ancient kingdom (Zhang and Shi, 2016). However, our pollen
record does not show intense agricultural activities at that time. Slight increases in Sporormiella
revealed the occurrence of grazing influence. Therefore, relatively high charcoal concentrations
and Chenopodiaceae percentages is suggested to result partly from human disturbance but mostly
from the region due to a weakening in the ISM.
Between 1700 and 400 cal yr BP, climate gets more arid reflected by decreasing values in PC
2, which is supported by low minerogenic input into the lake. A reduced minerogenic input into
Nam Co and a lower lake level support the aridity on the central TP (Kasper et al., 2012). In this
period, human activities became weaker reflected by high PC 1 values and low charcoal
Since 400 cal yr BP, increasing PC 2 values indicate moister conditions in the lake basin.
Increases in lake level of Tangra Yumco in recent centuries inferred from a record of n-alkanes
also indicate a more humid environment (Wang et al., 2017a). Similar tendencies towards moister
conditions can be observed in other sediment records from TP (Fig. 5), such as at Nam Co (Kasper
et al., 2012) and Lake Basomtso (Li et al., 2017). This is also reported in the fossil record from 15
Arabian Sea (Anderson et al., 2002). Increasing Globigerina bulloides abundance during the past
four centuries from the Arabian Sea (Fig. 5) revealed that monsoon wind strength increased
(Anderson et al., 2002). Enhanced ISM can bring more moisture into the Tangra Yumco basin and
thus make its environment to be more humid. During this period, strongest human activities are
reflected by sharply decreasing PC 1 values. Higher minerogenic input (increasing K content) and
Glomus peaks reflected the strong erosion probably due to the combined action of increasing
moisture condition and strong human impacts. High Sporormiella abundance indicates the
strongest grazing influence in the whole record. Extremely high percentages of Brassicaceae are
probably due to rape and/or turnip cultivation in the basin. Brassicaceae percentage also showed a
peak of > 10% in another study in the basin (Miehe et al., 2014), which is in good agreement with
our results. According to these data, it is suggested the agriculture was becoming more important
in the Tangra Yumco catchment after 400 cal yr BP. Due to the Feudal Serf System in Tibet and
progress of agricultural production technology during the Ming and Qing Dynasties, the extent of
cultivated land expanded from the Mid-Brahmaputra River and Three-River area in southern and
eastern Tibet to the more central region (Wang and Chen, 2014). This might correspond to the
relatively higher Brassicaceae percentages at Tangra Yumco core in this period, indicating that
farming became a wide spread phenomenon on the TP during this time. Remarkable high values
of charcoal concentration, Urtica, Chenopodiaceae percentage also indicate increasing intensity of
human impact on the natural environment, with moister conditions.
Human influence on vegetation on the TP and its significance for paleoclimate reconstructions
Recent studies reveal that human impact expanded on the TP at least since the mid-late Holocene. 16
Chen et al. (2015) reported archaeological evidences from the northeastern TP to indicate that the
first villages were established by 5200 cal yr BP and a novel agropastoral economy facilitated
year-round living at higher altitudes since 3600 cal yr BP. Several palynological studies (Table 2)
also indicated that human activities have a significant impact on vegetation of the TP during the
mid-late Holocene (Herzschuh et al., 2014; Wischnewski et al., 2011; Kramer et al., 2010; Schlütz
and Lehmkuhl, 2009). In the Lake Naleng basin, Kramer et al. (2010) indicated that more rapid
forest retreat after 3400 cal yr BP was probably promoted by human activities, and that grazing
probably increased from 3400 to 2000 cal yr BP and after 1300 cal yr BP. Similar finding was
described in the record of Lake Ximen, which reflected human influence expanded from 3000 cal
yr BP indicated by higher Potentilla-type and Quercus values (Herzschuh et al., 2014). At Lake
Muge, Ni et al. (2019) also held that the large increases of Pinus percentage in pollen spectra
during 3500-2300 cal yr BP was related to human activities. However, peat records from
Nianbaoyeze Shan pointed out that human impact can trace back to 6000 cal yr BP. This
discrepancy of pollen records from the eastern TP may be due to the use of various geological
archives. Compared with peat record, the lake pollen record with much larger pollen source area
reflects the vegetation change beyond a local scale (Herzschuh et al., 2014). Records covering the
last few centuries indicated signs of human impact increasing visible (Wischnewski et al., 2011,
2014). These records are from the eastern TP with a relative appropriate environment for human
life and agricultural production due to its high mountain canyon topography. However for the
central TP at high altitudes where hostile natural environment prevents human surviving, the
previous record from the lake terrace of Tangra Yumco reflected human impacts become stronger
since 1800 cal yr BP (Miehe et al., 2014). Our results showed low human influence indicated by a 17
slight increase in charcoal and Sporormiella during 2300-1700 cal yr BP. Human influence on
plant cover may be variable but not detectable in the lake record with large pollen source area
(Mercuri et al., 2019). However, vegetation change in Tangra Yumco basin was considered to be
mainly forced by climate based on low values of human-indicator taxa in our record. At Tangra
Yumco, there were no significant human impacts on alpine vegetation composition until 400 cal
yr BP. Thereafter, human activities (e.g., farming and grazing) changed the local vegetation
composition, characterized by the rapid increases in Brassicaceae, Urtica, Chenopodiaceae and
Sporormiella percentage in the fossil palynological spectra of Tangra Yumco. Thus, more related
studies are needed to detect the scope and intensity of human impact on alpine environment.
Table 2. Palynological records for human impact on vegetation on the Tibetan Plateau.
In the regions with strong human impacts on vegetation, paleoclimate reconstructions based
on pollen data will be biased due to the marked increase in human influence (Li et al., 2014;
Miehe et al., 2009). However despite the human impacts, alpine vegetation on the TP is generally
thought to be mainly controlled by climate (Ma et al., 2017a; Herzschuh et al., 2010; Song et al.,
2004; Ni, 2000). For example, Herzschuh et al. (2010) proposed that human impact did not blur
the general regional signals revealed by the pollen spectra from lake sediments on the central and
eastern TP. Similar results were obtained from a study of the relationships amongst modern pollen
assemblages, vegetation, climate and human activity on the central-western TP (Ma et al., 2017a).
Our pollen results revealed that there were no particularly large vegetation changes since 3400 cal
yr BP, with a persistent alpine steppe dominated by Artemisia, Cyperaceae and Poaceae. However,
the record occasionally captures the information of human disturbance to local vegetation 18
(increases in Brassicaceae, Urtica and Chenopodiaceae) to some extent on the central TP and also
suggests the need for palaeoenvironmental renconstructions to take into account human impacts.
The sedimentary record of Tangra Yumco on the central TP reflects impacts of climate and human
disturbance on alpine vegetation since 3400 cal yr BP. Minor human activities and a relatively
humid environment were detected between 3400 and 2300 cal yr BP. Vegetation change was
mainly affected by climate during this interval. From 2300 to 1700 cal yr BP, human activity
became only imperceptibly stronger and climate showed a significant drying trend. Vegetation
change was partly influenced by human disturbance but mostly by aridification. Between 1700
and 400 cal yr BP, human activities became weaker and climate got a bit drier than the previous
period. During this time, human activity had no marked impact on vegetation. Since 400 cal yr BP,
strongest human activities in the basin are observed and climate tended to be moister. Human
activities (e.g., rape farming and grazing) caused the increases in Brassicaceae, Chenopodiaceae
Urtica and Sporormiella. Our results recommend that human influence needs to be taken into
account in pollen-based climate reconstructions and sustainable development, even in remote
regions such as the Tibetan Plateau.
We are grateful for the funding from the National Natural Science Foundation of China (grant
number 41831177, 41501223), the CAS Strategic Priority Research Program (grant number
XDA20020100), MOST Project (grant number 2018YFB05050000), the 13th Five-year 19
Information Plan of Chinese Academy of Sciences (grant number XXH13505-06), CAS Field
Work Monitoring Stations Project (grant number KFJ-SW-YW038) and DFG priority program
1372 (grant number MA 1308/23-1, MA 1308/23-2, MA 1308/23-3). We thank Ping Peng,
Ruimin Yang, Xing Hu, Jifeng Zhang, Xiao Lin for their participation in the fieldwork. We are
grateful to Gerhard Daut, Heike Schneider, Karoline Henkel and Marieke Ahlborn for their
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682 683 684 685 686 687
Impacts of climate and human activities on alpine vegetation are investigated.
688 689 690 691 692
Charcoal and human-indicator pollen taxa are used to reflect human activity.
Strongest human influence on vegetation is found after 400 cal yr BP.
radiocarbon age (BP)
modern water plant
693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708
Table 1. Radiocarbon ages for core TAN 10/4 as published in Henkel et al. (2016) and Haberzettl et al. (2015).
709 710 711
Palynological records for human impact on vegetation on the Tibetan Plateau.
of human impact
3400-0 cal yr BP
Kramer et al.,
cal yr BP
3500-2300 cal yr
Ni et al., 2019
Increases in grazing-taxa (i.e.
Apiaceae, Liliaceae) and taxa likely
More rapid forest decline; Apperance of Sanguisorba, Rumex and Apiaceae
Higher Potentilla-type and Quercus
Increases in grazing taxa (i.e.
3000-0 cal yr BP
6000-0 cal yr BP
Senecio-type, Saussurea-type, Matricaria-type, Rheum, Rumex-type)
Increase in Pinus
introduced through human cultivation (i.e. Humulus, Fabaceae) Lake
Increases in Potentilla-type,
Appearance of Plantago, high
1800-0 cal kyr
Miehe et al.,
values of Cercophora-type,
Dongerwuka Lake terrace
713 714 715 716 717