Invited review articleName and scale matter: Clarifying the geography of Tibetan Plateau and adjacent mountain regions
Introduction
Accurate terminology is a vital prerequisite for efficient communication, synthesis, and generalization of knowledge across multiple disciplines of science. To harmonize the usage of terms, international organizations or mechanisms have been set up to unify and standardize the use of terms in taxonomy (International Committee for Phytolith Taxonomy, 2019; Ride et al., 1999; Turland et al., 2018), astronomy (IAU, 2022), genetics (INSDC, 2022), phytosociology (Theurillat et al., 2021) and chemistry (IUPAC, 2022), and have also been proposed for ecology (Herrando-Pérez et al., 2014) and biogeography (Ebach et al., 2008). Nevertheless, ambiguous and confused use of terms persists in many fields, for example causing problems early in the development of ecology (Tansley, 1935), and - in many other disciplines even today (e.g., Amador-Cruz et al., 2021; Dabiri and Blaschke, 2019; Kotze et al., 2020).
Geographical (place) names are fundamental to geography, and have existed since early in human history (Aurousseau, 1957), yet in comparison with terms in other disciplines, both the names and borders of geographical regions are frequently complicated and often controversial, due to their convoluted history and political sensitivity, a classic example being that of Karakoram in the 1930s (Burrard, 1929; Close et al., 1930; Mason, 1938). Despite recurring efforts to address standardization (Aurousseau, 1957; UNGEGN, 2006; Whitney, 1888), problems of polyonymy (multiple names for one place) remain rife, creating problems of communication and the possibility of accidental duplication of effort.
Equally important is precise geographical scale, specifically the spatial extent of a named region (Dabiri and Blaschke, 2019; Lam and Quattrochi, 1992; Wu and Li, 2009), which is defined and determined by boundaries (Fletcher and Fortin, 2018). However, the scale and boundary designation of named regions vary across, and even within, fields of research. For example, most previous ecological studies have focused on sub-regional scales (ca. 106 km2) (Estes et al., 2018; Pearson and Dawson, 2003) and the majority do not clearly report relevant spatial extent parameters (Dungan et al., 2002; Estes et al., 2018), even when they cover a well-defined area. Such inconsistencies between studies concerning the geographical scale of a given area inevitably hinder communication and generalization across and within disciplines. For example, the regional spatial extent of some very well-known and important areas, like the Tibetan Plateau and adjacent mountain regions, remain poorly defined in current literature, making it hard to compare studies about them on topics such as geological history and dynamics, biodiversity, climate, and water cycle changes.
The Tibetan Plateau, together with surrounding mountain regions (i.e. the Himalaya, the Hengduan Mountains and Mountains of Central Asia), collectively form the world's highest and most expansive upland area (Fig. 1, also see Fig. 5, Fig. 6 in results). The only term currently in use for these regions combined is ‘High Mountain Asia’, but this term is both grammatically awkward and somewhat misleading (see discussion), and hence the term ‘Pan-Tibetan Highlands’ is here proposed to replace it. The topography of this region varies considerably, owing to a complex history of geological events stretching back well into the early Mesozoic (Deng and Ding, 2015; Spicer et al., 2021b; Wang et al., 2014). Although most of the region is often loosely referred to as a ‘plateau’ due to its relatively high elevation (>4000 m above sea level), a true plateau should show low relative relief and more shallowly sloping ground compared with mountains. Therefore, from a geological and topographic perspective, the term ‘plateau’ as applied to this broader region is an oversimplification and incorrect.
This region is the source of ten major Asian rivers (see Fig. 6), which support the livelihoods of more than one billion people living in and around it. The Pan-Tibetan Highlands harbors parts of three of the world's 36 biodiversity hotspots (i.e., the Himalaya, Mountains of Southwest China, and Mountains of Central Asia) (CEPF, 2022; Mittermeier et al., 2004) (Fig. 1, also see Fig. 5). In recent decades, the Pan-Tibetan Highlands has experienced significant climate warming (Kraaijenbrink et al., 2021), which has caused extensive shrinkage of glaciers (Bhattacharya et al., 2021), formation and expansion of lakes (Chen et al., 2021) and considerable browning of vegetation (Liu et al., 2021). The region has attracted immense scientific and public interest worldwide, especially in the past 30 years or so, with relevant regional names generating >66,000 hits within Web of Science on December 31st, 2021 (Fig. 2a). However, there are inconsistencies between sources concerning the regions' geographical attributes, e.g. the stated area and elevation of the Tibetan Plateau can vary from 5.5 × 105 km2 to 2.57 × 106 km2 and 4000 m to 5400 m among different publications (Table S1, q.v. for references).
Subregions of the Pan-Tibetan Highlands suffer from issues of polyonymy. For example, Qinghai-Tibet Plateau, Qinghai-Tibetan Plateau, Tibet Plateau, Qinghai-Xizang Plateau and at least ten other names have been used for the Tibetan Plateau region in scientific literature (Fig. 3; Tables S2, S3). Similarly, singular and pluralized forms for both ‘Himalaya(s)’ and ‘Hengduan Mountain(s)’ are used interchangeably both in scientific literature and general communication. In the worst cases, various names for the same region are used within a single study. In recent decades, the use of variant names has remained prevalent, with no convergence towards a single agreed-upon name for any of these three regions (Fig. 3).
A second, more significant problem concerns differing opinions regarding the geographical scale of the Tibetan Plateau and adjacent mountain regions. Definitive delimitations for the boundaries of the Pan-Tibetan Highlands and component parts are lacking from most of publications (Böhner, 1994, Böhner, 2006; Hirabayashi et al., 2010), but more concise range sizes for the region were recently proposed in glaciology and climate change work (Bolch et al., 2019; Dehecq et al., 2019; Lalande et al., 2021; Wang et al., 2020). However, there remain considerable differences in boundary definitions among studies. Moreover, defined boundaries as there may be discipline-specific, and may therefore have little applicability in other disciplines (e.g. geography, geology and biology).
Early attempts to define the extent of the Tibetan Plateau (Chen et al., 1996; Li, 1987b; Zhang et al., 2002), Himalaya (Hughes, 1866; Le Fort, 1975; White, 1838) and Hengduan Mountains (Li, 1987a) were all constrained by the available data and technologies. The stated extent of the Tibetan Plateau varies across more recent studies, with a lack of clear criteria for boundary definitions (Pang et al., 2022; Shen et al., 2011; Zhang et al., 2013; Zhou and Zhang, 2021) (Fig. 1a); the same applies to the Himalaya (Bolch et al., 2012; Körner et al., 2017; Rana et al., 2019), Hengduan Mountains (Körner et al., 2017; Li, 1987a; Wang et al., 2018b) and Mountains of Central Asia (CEPF, 2022; Foggin et al., 2021; Mittermeier et al., 2004) (Fig. 1b-d). Zhang et al. (2014) used geographic information system (GIS) and digital elevation models (DEMs) to define the Tibetan Plateau, but in this case, political boundaries prevented a full, natural definition of the region. Such delimitation was recently revised by the same team(Zhang et al., 2021), with the newly determined Tibetan Plateau including the Himalaya, Hengduan Mountains and part of Mountains of Central Asia. Using the clear criterion of relative relief alone, Körner et al. (2017) defined a very small Tibetan Plateau (7.72 × 105 km2) (Table S4). More recently, a sensu stricto Tibetan Plateau, which excludes the Himalaya and Hengduan Mountains and treats each as a separate region, was adopted in some biogeographical analyses (Ding et al., 2020; Liang et al., 2018; Wu et al., 2022; Xing and Ree, 2017), but still without sufficient empiricism or scientific rationale to define the boundaries. In addition, it is far from clear whether the Hindu Kush, Karakoram and Pamir Mountains to the west make up part of the ‘plateau’ in some usages. Although they are of similar topography to the Hengduan Mountains, and the names used often feature in geological literature (e.g., Frey et al., 2014; Jain et al., 2020; Mason, 1938), they are seldom mentioned in some disciplines like biogeography. Overall, the boundary of the Tibetan Plateau and adjacent mountains has never been consistently nor accurately defined. These large-scale geographical inconsistencies among studies impede meaningful comparisons, and exchange of information across disciplines, ultimately hampering further scientific exploration and understanding of these regions.
The availability of DEMs and GIS technology makes it possible to map landforms using quantitative models and computer visualization (Smith and Clark, 2005). Google Earth (Google Inc., Menlo Park, California, USA) now provides three-dimensional terrain modeling, and the quality and resolution of Earth DEMs (e.g. Shuttle Radar Topography Mission (SRTM) (Farr et al., 2007) and EarthEnv-DEM90 (Robinson et al., 2014)) are improving (Florinsky, 2016). Furthermore, digitization (e.g. digital libraries) has made possible the unrestricted searching of scientific literature regardless of its location in the world (Candela et al., 2012), even going as far back as the 17th century.
Here, we take advantage of these recent advances in software and available data, combining a historical retrospective meta-analysis with GIS spatial analysis approaches, to progress towards a consensus nomenclature and a clear, meaningful, and well-defined demarcation of the Tibetan Plateau and its three adjacent mountain regions. The specific objectives were to (1) determine the most appropriate and valid names for the Tibetan Plateau, Himalaya, Hengduan Mountains, Mountains of Central Asia and all four regions together; (2) define the spatial extent and boundaries of the four regions, separately and combined, taking into account their distinct geological histories, and update their topographic characteristics; and (3) report on the spatial pattern of protected areas and vascular plant diversity using the newly defined boundaries. These outcomes will facilitate consistency in how the region is named and defined, allowing greater co-operation across disciplines, thus enhancing reproducibility in future work.
Section snippets
Literature survey
By 1st March 2022, we conducted a literature search using the ‘Advanced Search’ option in Web of Science (Clarivate, London, UK), entering the search terms ‘Pan-Tibetan Highlands’ ‘Tibetan Plateau’, ‘Himalaya’, ‘Hengduan Mountains’, ‘Mountains of Central Asia’ and their synonyms or similar terms (see Table S3 for specific search terms and query strings). We did not include individual mountain systems within these regions such as Tian Shan, nor regional names that do not match a particular
Nomenclature
A total of 66,218 papers were retrieved from Web of Science (Fig. 2a). Of these, ‘Tibetan Plateau’, ‘Himalaya’ and ‘Hengduan Mountains’ together with their synonyms (Tables 1, S3) were used in 38,125 (58%), 25,503 (39%), and 1454 (2%) works, respectively, while the remaining terms (‘High Mountain Asia’, ‘Mountains of Central Asia’, ‘Roof of the World’, ‘Hindu-Kush Himalaya’, ‘Sino-Himalaya’, ‘Himalaya-Hengduan Mountains’, ‘Mountains of Southwest China’, ‘Pan Himalaya’ and others) together were
A common name for the Tibetan Plateau and adjacent mountain regions
Geographical names provide the most basic geographical reference system, acting as a unifying factor to functionally connect and align discussion and research across disciplines. Therefore, to avoid confusion and misunderstanding, it is important to adopt a unique name that is consistently and accurately applied. However, variations in the form of a name often occur when names are transferred from their native language into English, and further variations may be produced during a long history
Concluding remarks
Our study provides an integrated framework, from which standardized names and boundaries are proposed, defining the Tibetan Plateau, Himalaya, Hengduan Mountains, Mountains of Central Asia and the Pan-Tibetan Highlands. If these names and boundaries are widely adopted, they will greatly aid cross-disciplinary synthesis and discussions of the environmental status of these regions. While some boundaries we assign are somewhat arbitrary, local geology and topography provide no better options in
Data availability
The GIS dataset generated in this study was deposited at Zenodo (doi:https://doi.org/10.5281/zenodo.6432940) (Liu and Zhu, 2022). The dataset includes the boundaries of the Pan-Tibetan Highlands, Third Pole, Tibetan Plateau, Himalaya, Hengduan Mountains and the Mountains of Central Asia; and the position of cratons, terranes and other geological structures mapped in this study.
Author contributions
JL, LMG and DZL obtained funding, conceived, and designed research; JL, GFZ, ZYW and YHL collected and analyzed the data; JL wrote the first draft of the manuscript with critical input from RM and RAS, then subsequent input from WWM, ZYW, DEB, LMG, JP, TSY, JC, HW, LMG and DZL, and all authors contributed to revisions.
Declaration of Competing Interest
The authors have no competing interests.
Acknowledgements
We are grateful to Mr. Xue-Wen Liu, Mr. Tao Liu, Dr. Kai Chen, Miss Wang-Ting Wang for field investigation and data analysis. We thank Prof. Jed O Kaplan and three anonymous reviewers for critical and insightful comments and suggestions. We also thank professors Yin An, Dai Erfu, Zhang Guoqing, Peter Cawood, Tobias Bolch, Marc Foggin, Zhang Huiping, Yu Lupeng, Alice Hughes, Jürgen Böhner and Michael Taylor for suggestions and providing GIS files. This study was supported by the Strategic
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