Ethnobotany of the Himalayas: The Nepal, Bhutanese, and Tibetan Himalayas

Abstract

Plant use in the Nepal Himalaya, recorded in the 6500-year-old text of the Rigveda, ranks among the earliest uses of medicinal plants (Malla and Shakya 1984). Another early account, the Saushrut Nighantu, is perhaps the oldest Nepali medicinal plant book, which was produced during the rule of the Great King Mandev in the fifth century, and records the uses of 278 Nepalese medicinal plants (Subedi and Tiwari 2000; Gewali and Awale 2008). Later compendia of herbal pharmacopoeias such as Chandra Nighantu and Nepali Nighantu published in the nineteenth and twentieth centuries, respectively, described 750 plants and 971 articles (IUCN Nepal 2004).

The Nepal Himalaya

Plant use in the Nepal Himalaya, recorded in the 6500-year-old text of the Rigveda, ranks among the earliest uses of medicinal plants (Malla and Shakya 1984). Another early account, the Saushrut Nighantu, is perhaps the oldest Nepali medicinal plant book, which was produced during the rule of the Great King Mandev in the fifth century, and records the uses of 278 Nepalese medicinal plants (Subedi and Tiwari 2000; Gewali and Awale 2008). Later compendia of herbal pharmacopoeias such as Chandra Nighantu and Nepali Nighantu published in the nineteenth and twentieth centuries, respectively, described 750 plants and 971 articles (IUCN Nepal 2004).

During 1802–1803, a French botanist Francis Buchanan-Hamilton who visited Nepal was the first foreigner to catalogue the useful plants of this country. Later the books Prodromus Florae Nepalensis by D. Don in 1825 and Tentamen Florae Nepalensis by N. Wallich were noteworthy in presenting the records of useful plants of Nepal. Due to its geographical location and the isolationist policies of its Rana rulers, Nepal remained inaccessible to much of the outside world and became known as a “land of mystery.” After the Anglo-Nepalese war (1814–1816), the government made slight concessions and allowed a few British botanists to visit Kathmandu, but the area remained mostly off limits to outsiders (Bhatt 1964). The inaccessibility of Nepal to foreigners was well versed by Hooker (1855) and Heim and Gansser (1939). The situation changed in 1950 when the Rana rule came to an end. While the collection of plants for different purposes dated back to centuries, the research on medicinal and food plants from eastern Nepal by ML Banerji in 1955 (Banerji 1955) was considered to be the first publication on Nepal’s ethnobotany. Since then, many researchers have studied the medicinal and edible wild plants of Nepal. The seminal early works on medicinal plants of Nepal come from BD Pandey (1964), PR Pande (1964), Devkota (1968), and Malla and Shakya (1984), while the paper by Singh (1968) on wild food plants was also influential to the field (Rajbhandary and Winkler 2015).

There have been approximately 1000 ethnobotanical studies carried out in Nepal: mostly about medicinal plants. A review of 822 publications made between 1968 and 2014 done by Rajbhandary and Winkler (2015) revealed that 44% of published studies were associated with ethnomedicine and 23% with ethnobotany. Another review by Ghimire (2008) reported that 53% studies were related to inventory and use of medicinal plants. There are other review studies on ethnobotany in Nepal such as Rajbhandari (2001), Shrestha et al. (2004), and Kunwar and Bussmann (2008); however, none is attempted to analyze the spatial coverage of ethnobotanical studies in Nepal. Recently, a few accounts ventured into describing the ethnobotany at spatial scales. Kunwar et al. (2020) documented the ethnobotany of Paris polyphylla Sm. from 51 districts, and Charmakar et al. (2020) reported that of Valeriana jatamansi Jones from 55 districts out of 77 districts in Nepal.

Medicinal plants have long been collected and used in Nepal and are mostly from the wild. There are a large number of policies on sustainable harvesting of medicinal plants, but they are not strictly implemented. As a result, many high-value medicinal plants, on which local livelihoods depend, are depleting. Sustainable management of medicinal plants with commercial potential and their effective integration in development plans is urgently needed to improve local livelihoods and the national economy. Similarly, studies focusing on applied and conservation ethnobotany are of urgent need, as most of the ethnobotanical studies carried out to date are traditional, only documenting the knowledge and inventory of the resources (Figs. 1 and 2).

Fig. 1

Alpine ecosystem, Manang. (Photo Krishna R Bhattarai)

Fig. 2

Shey Phoksundo National Park, Dolpa, November, 2006. (Photo Ripu Kunwar)

Physiography

Nepal’s geological history has given rise to the country’s complex biogeography reinforced by its location at the crossroads of two biogeographic realms: Palearctic in the north and Paleotropic in the south (Udvardy 1975). It is a small landlocked country which lies along the slopes of the Himalayan mountain between China and India between 80° 04′–88° 12′ E and 26° 22′–30° 27′ N. Being laid at the lap of the lofty Himalayas, the country has the largest elevational gradient in the world (Li and Feng 2015), extending from tropical alluvial plains as low as 59 m above sea level (m asl) in the lowland Tarai to the world’s highest summit Mt. Everest (8848 m) in a distance of only 150–200 km (Hagen 1969). Thus, Nepal’s terrain is extremely complex with steep geographical gradients.

Broadly, the country is divided into three longitudinal zones (East 80° 04′–83°, Central 83°–86°30′, and West 86°30′–88°12′) (Stearn 1960). Vertically, there are distinct five eco-physiographical regions: the Himalayas (23% of total area and above 5000 m), High Mountains (20% of total area, between 3000 and 5000 m), the Middle Mountains (30% of total area, between 1000 and 3000 m), Siwalik Hills (12.8% of total area, between 500 and 1000 m asl), and the flat lowlands of Tarai (13.7% of total area, up to 500 m asl), representing nival, alpine, temperate, subtropical, and tropical bioclimate, respectively (Dobremez 1976; LRMP 1986; IUCN 2000). There are 71 mountains of over 6000 m in Nepal among which Mt. Everest, Mt. Kangchenjunga, Mt. Lhotse, and Mt. Makalu are the world’s first, third, fourth, and fifth highest peaks, respectively. You will behold the magnificent vista of these snow-capped mountains at the northern part of the country (Figs. 3 and 4).

Fig. 3

Physiographic map of Nepal. (Photo Bhagawat Rimal)

Fig. 4

Range of hills and mountains, taken from Bipyakatal, Baitadi. (Photo Ripu Kunwar)

Geo-ecology

All the mountains within the nival zone, above 5000 m, are covered with perpetual snow and treeless vegetation and are characterized by Precambrian metamorphosed gneisses, mica schist, limestone, and shale of different ages (Pariyar 2008). This biome includes some dry inner-Himalayan valleys and arid plateaus in Mustang, Manang, and Dolpa districts (NBSAP 2014). There are over 400 plant species recorded from above 5000 m of the Everest region (Miehe 1989). The highest recorded flowering plant Ermania himalayensis (Cambess.) O.E. Schulz (Brassicaceae) is found at around 6000 m (Bhuju et al. 2007). Saussurea gnaphalodes (Royle ex DC.) Sch. Bip. (Asteraceae), Lepidostemon everestianus Al-Shehbaz (Brassicaceae), Arenaria bryophylla Fernald (Caryophyllaceae), and Androsace khumbuensis Dentant (Primulaceae) are found up to elevations of 6400 m on the northern and southern slopes of Mt. Everest (Dentant 2018), the highest recorded elevation of any living plants in the world.

The High Mountains Zone (3000–5000 m) is characterized by biologically diverse summer grazing pastures ranging from luxuriant natural conifer and mixed forests in some locations (Aryal et al. 2014). The soils can be characterized by phyllite, schist, gneiss, and quartzite of different ages. The Middle Mountain (also known as Mid-Hills) is characterized by a great variety of terrain types and intensive farming on hillside terraces between 1000 and 3000 m. This region has the greatest diversity of ecosystems and species in Nepal (BPP 1995). It covers 2.25 million hectares of forest, about 38% of the country’s total forest cover (DFRS 2015), and contains several fertile and densely populated valleys, including Kathmandu and Pokhara. It is a highly populated (38% of total population) region and borders the lowland Tarai (41%) (CBS 2011).

The Siwalik zone, the southernmost Himalayan foothills, is characterized by steep hills of unstable geomorphology. These hills are primarily semi-consolidated tertiary sandstone, siltstone, shale, and conglomerate. The Siwalik is the youngest mountain range in the Himalayas (Dahal et al. 2010) and extends across four countries including Pakistan, India, Nepal, and Bhutan (Taral et al. 2018). In Nepal, the Siwalik spreads from east to west across 36 different districts and covers 12.78% of Nepal’s area, of which 72.56% are forests (DFRS 2015). A fossilized tooth of a Ramapithecus, an extinct group of primates, found in 1980 at the bank of Tinau river (Butwal), Siwalik Hills, dated as the second oldest in the world at 9.0–9.5 million years (Munthe et al. 1983), which connotes prehistoric habitation of the western Nepal (Pradhan 1998). A group of early settlers (Aryans) advanced into the western parts of Nepal in 1100 AD (Chaturvedi and Singh 1986) is considered one of the early accounts of human civilization and forest and plant exploitation in Nepal (Shrestha 2001; Kunwar et al. 2019) (Figs. 5 and 6).

Fig. 5

Churia-Siwalik Hills, youngest hills in the Himalayas, taken from Motahaldu, Dadeldhura. (Photo Ripu Kunwar)

Fig. 6

Women carrying Murraya koenigii (Asare) for processing, Baitada, Kanchanpur. (Photo Ripu Kunwar)

Lowland Tarai comprises of a narrow belt of fertile flat land with recent and post Pleistocene alluvial deposits (Carson et al. 1986) in the southernmost part of the country up to 500 m (NBSAP 2014). It is considered as a rice bowl of the country (Gauchan and Pandey 2011). The fertile alluvial lands in Tarai and riverbanks in the Mid-Hills are highly suitable for mixed farming of rice, millet, maize, wheat, as well as other cash crops and dairy products and different forest practices. Dense broad-leaved Shorea robusta (Sal) forest and riverine Dalbergia sissoo-Acacia catechu forests support the lush biodiversity of the area and boast large number of charismatic animals including tiger (Panthera tigris), one-horned rhinoceros (Rhinoceros unicornis), etc. which are found only in South Asia and Southeast Asia (Jnawali et al. 2011) (Figs. 7 and 8).

Fig. 7

Endangered Ailurus fulgens (red panda) at Polangpati, Langtang National Park, Nepal. (Photo Hari P Sharma)

Fig. 8

Mussaenda macrophylla and butterfly, Pokhara-5, Kaski, Nepal. (Photo Mira Dhakal)

Water Resources

The Himalayas, also known as the “third pole” or the “water tower of Asia,” is the most glaciated area in the world outside of the Polar Regions, with vast stocks of fresh water in the forms of snow and ice. Nepal’s glaciers, snow, and ice-melt waters feed more than 6000 rivers including rivulets and tributaries across the country (WECS 2011). The major perennial river systems in Nepal are Mahakali, Karnali, Gandaki, and Koshi rivers, all of which originate from the Himalayas. All of Nepal’s rivers flow into the Ganges, a river of great cultural and religious significance and the most populous river basin in the world. These river systems contain water resources with tremendous potential for productive ecosystems, hydropower, and irrigation development. Nepal is rich in hydro-resources, with one of the highest per capita hydropower potentials in the world. The estimated theoretical power potential is approximately 83,000 MW. However, the economically feasible potential has been evaluated at approximately 43,000 MW (Adhikari 2006). All these river systems harbor 42 globally threatened species (CSUWN 2009) with over 25% of the country’s total flora (Kunwar et al. 2015).

Climate

Nepal exhibits a wide range of climatic conditions varying from tropical at southern lowland to alpine/arctic in the north due to its topographic extremes. The climate is predominantly influenced by three major factors: altitude, monsoon, and western disturbances (GoN 2014). The year in Nepal is characterized by four distinct seasons, namely, the pre-monsoon (March–May), monsoon (June–September), post-monsoon (October–November), and winter (December–February) (WECS 2011). Nepal receives average annual rainfall of around 1600 mm, but this number varies widely by region. The southern flanks of the Himalayas, such as Pokhara, receive the highest amount of rainfall (3345 mm), while the rain shadow areas of Dolpa and Mustang receive less than 10% of that amount (295 mm). Total annual rainfall increases with altitude up to approximately 3000 m and then diminishes at higher elevations (MoSTE 2014). The high-altitude regions of Nepal are most sensitive to climate change and have been warming the most quickly (WWF 2005).

Climate vulnerability indices have shown that Nepal is one of the most climate-vulnerable countries worldwide (Maplecroft 2011; Christensen et al. 2013; Kreft et al. 2015). According to Nepal Climate Vulnerability Study Team (NCVST), the mean annual temperatures could increase by a mean of 1.4 °C (with a range of 0.5 °C–2.0 °C) by the 2030s, rising to an increase of 4.7 °C (3.0 °C–6.3 °C) by the 2090s. Cities are warming faster than the surrounding outskirts (Baidya et al. 2007). In this same time period, precipitation levels are expected to change dramatically. Some reports posture that they may decline by 34% or rise by 22% by the 2030s, decline by 36% or rise by 67% by the 2060s, and decline by 43% or rise by 80% by the 2090s (NCVST 2009). It is also generally expected that there will be an increase in interannual variability in monsoon rainfall and an increase in the occurrence of extreme (or heavy) rainfall events (Christensen et al. 2013). Between 1990 and 2014, approximately 3.4 million Nepalese were affected by floods, droughts, and landslides (MoE 2010b). It is estimated that more than 1.9 million people are highly vulnerable to climate change, while 10 million are at increasing risk due to climate impacts (MoE 2010a). Mean annual temperatures and precipitation are expected to change in Nepal over the remainder of this century. The country is also vulnerable to seasonal foods, drought, and landslides (WECS 2011) and seismic and developmental disasters (Klein et al. 2019) (Figs. 9, 10, and 11).

Fig. 9

Drying chilis on house floor, Pahada, Dolpa, 1750 m. (Photo Ripu Kunwar)

Fig. 10

Local people harvesting buckwheat, Kagbeni, Mustang. (Photo Nipesh Dhaka Adhikari)

Fig. 11

Drying rice on house floor, Jhyari, Rara National Park, Mugu, 2800 m. (Photo Ripu Kunwar)

Biodiversity

Aided by diverse terrain and topography, Nepal’s variety of climatic conditions has spurred the evolution of unique flora, fauna, livelihoods, and cultures across the country. This cornucopia of endemic features aid in creating a diversity of rich and unique ecosystems and human-nature interactions (Maraseni et al. 2006). The country possesses about 0.1% of the Earth’s terrestrial land, but it harbors about 2% share of the world’s biodiversity and ranks 25th position in terms of species richness (Bhuju et al. 2007). The feature is associated with the dense tropical monsoon forests of the Tarai, deciduous and coniferous forests of the Mid-Hills and, and subalpine and alpine pastures and rugged/arid landscape of the Himalayan range. The rugged topography has created geographic isolation and numerous ecological niches to which different ethnic groups have adapted (Manzardo 1977) and high-value medicinal plants are refuged (Subedi 2006).

There are a large variety of forest types and different ecosystems across the different landscapes of Nepal (Dobremez 1976; Stainton 1972). This includes more than 10,630 plant and 3000 wildlife species living in 118 different ecosystem types, 75 vegetation types, and 35 forest types (NBSAP 2014). There are over 6500 species of flowering plants (Press et al. 2000; DPR 2001; Ghimire 2008; Kunwar et al. 2010; MoFSC 2014; Shrestha and Bajracharya 2019; Shrestha 2020) including over 2300 useful and medicinal plant species (Baral and Kurmi 2006; Rokaya et al. 2010; Kunwar et al. 2018). Useful plants along with non-timber forest products (NTFPs) from Nepal have a total export value of over US$ 700 million annually and account for 11% of the country’s total exports (DPR 2001). This number is only 40–50% of the NTFPs harvested, since approximately the same amount is either consumed within households or sold in local markets without ever being recorded.

Of 312 endemic flowering plants in Nepal (Rajbhandari and Rai 2017), about 63% are from the high mountains, and 38% are from the Mid-Hills (Press et al. 2000). Indicator species such as the Indian horse chestnut (Aesculus indica (Wall. ex Cambess.) Hook.) and Deodar cedar (Cedrus deodara (Roxb. ex D. Don) G. Don) are predominantly found in the west, while broad-leaved evergreen (Castanopsis hystrix Miq.) and the Sikkim larch (Larix griffithiana) are predominantly found in eastern and central Nepal (Bhuju et al. 2007). The plant family with the largest number of species are Orchidaceae (450 species) followed by Asteraceae (395 species), Poaceae (366 species), Fabaceae (304 species), and Cyperaceae (191 species) (Miehe et al. 2015). Medicinal plants are an integral part of indigenous medical systems and livelihoods and have long been collected, consumed, and conserved by indigenous populations, leading to a wealth of accumulated indigenous knowledge (Singh et al. 1979) (Figs. 12, 13, and 14).

Fig. 12

Paris polyphylla (Satuwa) flower bud, Daman, Makawanpur. (Photo Giridhar Amatya)

Fig. 13

Mucuna pruriens (Kauso) pods, Parigaon, Kanchanpur. (Photo Prem Budha and Ripu Kunwar)

Fig. 14

Debregeasia salicifolia (Tusare) fruits, Chatiwon, Doti. (Photo Giridhar Amatya)

Population, Ethnicity, and Religion

Nepal is inhabited by 30 million people and has an annual growth rate of 1.32% per year between 2001 and 2011. Socioculturally, the country has over 125 ethnic groups and castes, including Chepang, Raute, etc., and 123 languages (CBS 2012). The Raute are the last nomadic people of Nepal (Fortier 2009). Nepali language, derived from Sanskrit, is the national and official language of the country. Over 80% of Nepalese are Hindus and about 10% are Buddhists. Hindu mythology considers the Himalayas to be the home of the gods. Three principal Hindu deities, Brahma (the creator), Vishnu (the caretaker), and Shiva (the destroyer), are worshipped equally. Pashupatinath, a large Shiva temple in Kathmandu, is one of the holiest sites in Nepal and attracts Hindu pilgrims all over the world. Similarly, being the birthplace of Lord Buddha, Nepal is an international pilgrimage site to the Buddhist all over the world. Buddhists visit Lumbini – the birthplace located some 300 km south west of Kathmandu. Hindus consider Buddha as one of the incarnations of Lord Vishnu and worship him.

Socioeconomy

About 70% of the population lives in rural, mountainous areas and the Mid-Hills region; both zones characterized with a fragile and remote physiography and low economic productivity (Abington 1992; CBS 2011). Limited access foments the regional disparities in development and discrepancies in income and education between rural and urban area. Nepal’s Human Development Index (0.579) and Gender Inequality Index put the country in the medium human development category (UNDP 2019). The Government of Nepal put forward an ambitious goal of graduating from the least developed country (LDC) status by 2022 (GoN 2013) (Figs. 15, 16, 17, and 18).

Fig. 15

Buddhist flag at Swayambhu, Kathmandu. (Photo Yagya Adhikari)

Fig. 16

A woman in traditional attire, Sundamunda village, Khar, Darchula. (Photo Yadav Uprety)

Fig. 17

Women collecting hey grass during famine in winter, Dhap, Darchula. (Photo Ripu Kunwar)

Fig. 18

Nomadic Raute tribe, Khanikhola, Dailekh. (Photo Nipesh Dhaka Adhikari)

Nepal’s economy, strongly backed up by agriculture and remittances from working abroad, is growing but varies greatly year to year (GoN 2014). The economy is also dependent on the use of natural resources, including farmed areas, pastures, and forests. Agriculture including forestry and fishery remains the country’s principal economic activity. Majority of the population are subsistence farmers and grow paddy, wheat, maize, millet, barley, vegetables, and potato. Rice and wheat are the two main crops grown in the Tarai region along with other cash crops such as sugarcane, jute, cotton, and mangoes. Animals such as cow, buffalo, and goats are reared by most of the households, while some households also keep chickens and pigs (Figs. 19, 20, 21, and 22).

Fig. 19

Terrace cultivation, Nayagaun, Kavre, with mountain range of Mt. Gaurishankar and Jugal. (Photo Bijaya Khadka)

Fig. 20

Agroforestry and primitive round house, Astam, Kaski. (Photo Ripu Kunwar)

Fig. 21

A rural village livelihood in the Mid-Hills, Gurja Khani, Myagdi. (Photo Ripu Kunwar)

Fig. 22

Transhumance and pastoral life, Budhi, Darchula. (Photo Ripu Kunwar)

At higher altitudes, agro-pastoralism prevails and yaks and sheep are reared, and the number a person owns symbolizes their family’s wealth. Moreover, the mountains and rivers of the Himalayas are valued as sacred sites, and the alpine meadows, pastures, and forests are treasured for transhumance, livestock grazing, and collecting of high-value medicinal plants like Himalayan caterpillar fungus, Ophiocordyceps sinensis (Berk.) G.H. Sung; Himalayan yew, Taxus contorta Griff.; and love apple, Paris polyphylla Sm. (Kunwar et al. 2020). Many of the plants are collected and used for cultural practices, livelihood and primary health care under theoretical and practical traditional knowledge, and mores and beliefs of surrounding health, illness, and sociocultural values and because of limited access to other healthcare options (Kunwar et al. 2013). Plants collected for socioeconomic gain, cultural heritage, and drug development (Farnsworth and Morris 1976), are now been threatened due to local peoples’ changing perceptions (Bhattarai 1992; Bussmann and Sharon 2006; Byg et al. 2010). Some medicinal plants are severely threatened, as changing climatic gradients, land-use patterns, and socioeconomic and cultural changes force plant species to either adapt, move, or perish (Parmesan and Yohe 2002; Alves and Rosa 2007; Cameron 2010) (Figs. 23 and 24).

Fig. 23

Mule train transporting goods, Rara National Park, Mugu, April 2011. (Photo Ramesh Basnet)

Fig. 24

Sky islands, the mountain at foreground is a reservoir of medicinal plants, Hilsa, Humla, 3200 m. (Photo Dipesh Pyakurel)

Forest exploitation was severe before the 1970s (Robbe 1954; Ekholm 1975) because the government forests were considered open commodity and harvesting of NTFPs and medicinal plants was free or could be done with the payment of a nominal fee (Chaudhary et al. 2017). Forest management structures such as community forests, beginning in late 1970s, and local (indigenous) participatory forest management initiatives are meant to control the degradation of government-managed forests, but the loss has remained substantial (Kunwar et al. 2019). As a result, the country is successful in restoring forests that cover about 43% of the land area (DFRS 2015). The community forestry in Nepal has often been hailed and reported as one of the successful forestry programs in South Asia (Karki et al. 2017). Community forestry covers 40% of the total forest cover of the country, providing immediate goods and services to marginalized and disadvantaged communities of rural and remote areas of the country (Bhattarai et al. 2019). In its Master Plan of Forestry Sector, Nepal has identified 61% of the total forests of the country that have potential for community forestry and provide the possibility for rural communities to be engaged in NTFP-based enterprise activities while maintaining the overall forest health for generations to come (Subedi and Tiwari 2000). However, these forests are coming under existential threats from invasive species and changing land-use patterns and climate change (Figs. 25 and 26).

Fig. 25

Schima-Castanopsis forest, Godawari, Lalitpur. (Photo Yagya Adhikari)

Fig. 26

Rhododendron-Quercus forest, Sigas, Baitadi. (Photo Ripu Kunwar)

Way Forward

There are few studies that explore the opportunities generated by ethnobotany to aid in cultivating sustainable use of forest resources and complement local livelihoods and the national economy. This book, Mountain Ethnobotany in Nepal, is a co-created project among botanists, foresters, environmentalists, naturalists, and pharmacists of Nepal and abroad to share opportunities and knowledge that will contribute to the advancement of sustainable conservation and development in the country. We hope policy-makers will become increasingly aware of the critical role of traditional knowledge, ethnobotany, and medicinal plants of Nepal can play in building the resilience and adaptive capacities of the country’s population and economy against the challenges of climate change, socio-acculturation, and land-use change. Understanding the function of mountain ethnobotany and appreciating its important services will enhance our ability to guide policies on conservation and sustainable management of flora resources. This communication will hopefully strengthen the network of botanists, foresters, ethnobiologists, environmentalists, anthropologists, forest managers, and cultural heritage policy-makers working to developing strategies that might lead in the future to increased recognition, preservation, and renewal of traditional practices in Nepal. And we hope it will help you, the reader, better appreciate the scope of ethnobotany and its role in the conservation of ecosystems through the harmony of human-nature interactions.

The Eastern Himalaya: Bhutan and Tibet

Of the 34 biodiversity hotspots in the world, the Eastern Himalayan range is one of the richest with nearly 750,000 sq. km area covering Nepal, Bhutan, the Indian states of West Bengal, Sikkim, Assam and Arunachal Pradesh, southeast Tibet (China), and northern Myanmar. The region is in the limelight as a part of crisis ecoregions, biodiversity hotspots, endemic bird areas, megadiverse countries, and the Global 200 Ecoregions. This area is geologically young and shows high altitudinal variation resulting in the formation of the tallest alluvial grasslands among the world and subtropical broadleaf forest in the foothills to temperate broadleaf forest in the Mid-Hills, conifer forest in the higher hills, and alpine meadows above the tree line. The Indo-Burma hotspot itself is home to 7000 endemic plants and has 1.9% of the world’s total endemic vertebrates. More than 7000 plants species have been recorded from the region, which alone consists of many endemic and endangered flora and fauna (Banerjee and Bandopadhyay 2016) (Fig. 27).

Fig. 27

Main Central-Eastern Himalayan Range with Mt. Everest. (Photo R.W. Bussmann & N.Y. Paniagua-Zambrana)

During the Quaternary period, the Tibetan Plateau underwent the greatest changes of any region in the world. Since the Neogene, a series of enormous and drastic geologic and climatic events has occurred. The Indian plate collided with the Eurasian plate; the highest mountain and plateau region in the world arose from the ancient sea, the Tethys Sea, which was forced far to the west; atmospheric circulations changed their routes, and some new systems were formed; and mountain glaciers progressed and withdrew repeatedly. As a result of these changes, large-scale movement and exchange took place in the floras and vegetations on the Plateau. After passing through this period of harsh natural selection and evolution, some of the specialized young plateau vegetation types emerged, for instance, the high-cold desert, steppe, and meadow. But there remain some ancient forest vegetation types which have been reestablished somewhat to the south. In particular, the vegetational gradient or zonal system now peculiar to the Plateau developed (Chang 1981).

Climate

The climate of the Eastern Himalaya is extremely diverse. This variation in climatic conditions and average temperature is maintained by two main factors – the vast differences in altitude and influence of the North Indian monsoons. Mountain peaks are permafrost, and lower valley regions are cool in summer owing to the high-altitude terrain. In the far northern part of the kingdom, the weather is cold during winter. In the central areas of the country, the climate is cooler, changing to deciduous and temperate forests with warm summers and cool, dry winters. While the Tibetan Plateau and the peak regions are cool to cold, southern Bhutan has a hot, humid, subtropical climate, static the whole year. The Indian summer monsoon stays from late June to late September and is mostly limited to the southern border areas of Bhutan, resulting in heavy rain and high humidity in the region. They bring 60–90% of total rainfall of the western region. Annual precipitation varies extensively in different areas of the country. The northern border area and Tibet get about 40 mm of precipitation per year, which is mainly snow. In the temperate central regions, a yearly average of 1000 mm precipitation occurs, whereas 7800 mm/year precipitation is registered in the humid, subtropical south, resulting in thick tropical forests and savannas (Banerjee and Bandopadhyay 2016).

The latitudinal differences in solar radiation and temperature are basic determinants of the plateau vegetation zones in Tibet. Although the enormous height of the Plateau may tend to diminish the latitudinal temperature differences, the relief (which is higher in the northwest and lower in the southeast) compounds the effects of the latitudinal gradient of heat. Therefore, on the southern slope, there are tropical and subtropical mountain forests; in the central part, mesothermal steppe and desert vegetation prevail; and there are high-cold steppes and deserts in the north. The main ridge of the Great Himalaya provides the northern limit of tropical mountains. In the east, the Himalayas extends to 29° north latitude. This is almost the northernmost limit of the tropical zone on earth. The extensive mountains, which protect the area to the south from cold air masses that move across interior Asia, permit this northward extension of the Tropics. The limit between mesothermal and high-cold climate or vegetation corresponds approximately to the mean July isotherm of 9 °C in the west and 11 °C in the east. South of this limit on the Plateau, or in the mountains below it, temperate vegetation occurs in mesothermal or meso-microthermal forest, steppe, or desert. North of this limit on the Plateau, or above it on the mountains, the vegetation changes to alpine meadow, low scrub, high-cold steppe, or desert types. However, moisture affects the plateau vegetation even more strongly than temperature. Precipitation decreases from southeast to northwest and provides a moisture gradient from humid and subhumid to semiarid and arid corresponding to a vegetational gradation from forest and meadow to steppe and desert. The gradients of temperature and precipitation interact to form seven plateau vegetation zones, of which five are plateau zones. These are the humid­hot tropical montane forest zone on the southern slope of the Himalayas, the moist-warm subtropical montane forest zone in southeastern Tibet, the moist-cryophilic high-cold meadow and low scrub of eastern Tibet and western Sichuan, the arid mesothermal montane steppe and shrubland zones in the Tsangpo River Valley of southern Tibet, the arid and cryophilic high-cold steppe zone of Chiangtang (northern Tibet) and western Qinghai, the arid and mesothermal montane desert zone of western Ali, and the very arid and cryophilic high-cold desert zone of northwestern Tibet. Among these the boundary between the moist meadow and forest zones and the semiarid steppe zone corresponds approximately to the annual isohyet of 400 mm in the north and of 500 mm in the Tsangpo River Valley. The aridity index at this limit is about 1.0. The limit between the semiarid steppe zone and very arid desert zone corresponds approximately to the 100 mm isohyet and an aridity index of 3.5.

The particular features of the atmospheric circulation above the Plateau have a major effect on these climatic conditions. With the uplift of the mountains during the Quaternary, the Tibetan Plateau became a “hot island” in the troposphere, impeding atmospheric circulations and bringing about significant changes in climate and vegetation both on the Plateau and in surrounding areas. The uplift disrupted the planetary wind system resulting from the Earth’s rotation and changed atmospheric circulation resulting from the temperature effects caused by the heating of the Plateau. Anomalous patterns thus caused are the Tibetan Highland which forms at high elevations on the Plateau; the Mongolian-Siberian anticyclone, which develops to the north in the winter; and the summer Southwest Monsoon in the south. The climate of the Plateau, then, is largely controlled by a strong high-pressure center with continental climate characteristics. It is also strongly influenced by two other major circulations: the tropical maritime Southwest Monsoon coming from the Indian Ocean which drenches the southeastern part of Tibet in the summer but rapidly weakens toward the inner reaches of the Plateau and the westerlies which control the climate of the Plateau during the winter (Chang 1981).

The southeastern mountains of Tibet, including the southern slopes of the Eastern Himalaya and the southern part of the Traverse Mountain Ranges (Hengduan Mountains), face the humid Southwest Monsoon in summer and receive abundant rainfall. Even in winter, there is a warm and moist region of convergence with low pressure and high precipitation. Due to the protection afforded by the northern mountains and the Plateau, the influences of the dry west wind and northern cold current are minimal. The humid Southwest Monsoon may extend along valleys of the Tsangpo River and the Three Rivers (Nu, Lancang, and Jinsha) into the southeastern part of the Plateau. Luxuriant montane forest vegetation grows in those parts of Tibet which are influenced by the humid maritime monsoon. Forest vegetation occurs in peripheral valleys and on the southern slopes of the Plateau, but it is never found on the level of the Plateau itself with its cold continental climate (Chang 1981).

Ecoregions

The Eastern Himalaya is among the 234 globally outstanding ecoregions of the world, according to a comprehensive analysis of global biodiversity by the World Wildlife Fund. Bhutan is also an exclusive biodiversity hotspot in the world where forest coverage has increased to 72% of the country’s total area. It has six major agro-ecological zones equivalent to certain altitudinal ranges and climatic environments: alpine, cool temperate, warm temperate, dry subtropical, humid subtropical, and wet subtropical. The country is gifted with large forest coverage of 70.46% of the total land area. Bhutan is also unique for its conservation policy and its varied altitudinal and climatic range. The country can be broadly divided into the following three zones: (i) alpine zone (4000 m and above, Fig. 28) with no forest cover, (ii) temperate zone (2000–4000 m) with conifer or broadleaf forests (Figs. 29 and 30), and (iii) subtropical zone (150–2000 m) with tropical/subtropical environment. The forest types include fir, mixed conifer, blue pine forest, chir pine, broadleaf with conifer, highland hardwood, lowland hardwood, and tropical lowland forests (Banerjee and Bandopadhyay 2016) (Figs. 28, 29, and 30).

Fig. 28

Alpine lake, Nepal. (Photo R.E. Hart)

Fig. 29

Coniferous forest zone, Bumthang, Bhutan. (Photo R.W. Bussmann & N.Y. Paniagua-Zambrana)

Fig. 30

Over-aged coniferous forest, Bhutan. (Photo R.W. Bussmann & N.Y. Paniagua-Zambrana)

The vegetation of the Tibetan Plateau also cannot be considered to belong to the mountain vertical zonal vegetation. The Plateau vegetation shows the following characteristics in zonation, ecological conditions, and vegetation physiognomies which are very different from the general mountain vegetation. The vegetation zones on the mountains surrounding the Plateau fit into the mountain vertical zonal scheme, yet the main zonal differences in the vegetation on the Plateau are not caused by differences in elevation but by horizontal gradients in moisture and temperature conditions. Nevertheless, the altitudinal variations do introduce further modifications. The widths of the vegetation zones on the Plateau are much greater than those of mountain vegetation zones. Mountain vertical vegetation zones are known for their narrow width, rapid transition, extensive fragmentation, and complex interdigitation of their vegetation types. These characteristics are due to the complex relief of mountains. The vegetation zones on the Plateau are horizontally extensive; they are usually several hundred kilometers wide. They also have more internal continuity and uniformity and more gradual transitions than mountain vegetation zones. In these respects, at least, the zonation of plateau vegetation is similar to the usual horizontal lowland vegetational zonation (Chang 1981).

Vegetation and Flora

The region includes the mountain forests along the southeastern periphery of Tibet and the southern slopes of the Himalayas. To the east, it contacts the subtropical montane forests in western Sichuan and northern Yunnan. To the west, it connects with the tropical montane forests of Bhutan, Sikkim, Nepal, and western India on the southern slopes of the Himalayas. Wherever there are high mountains and gorges in the area, they are watered by the Southwest Monsoon. The major components of the vegetation are the Indo-Malayan floral element and the Sino-Himalayan floral element of Eastern Asia. If the main ridge of the Himalayas is viewed as a limit between tropical and subtropical zones, then this region may be divided into two montane forest zones (Chang 1981).

Tropical Montane Forest Zone of the Himalayan Southern Slope

The southern slope of the Eastern Himalaya faces the Southwest Monsoon and receives abundant rainfall. Its annual rainfall generally exceeds 2500 mm. The mean annual temperature on the lower mountains exceeds 20 °C. Although there is a relatively dry season of 2–3 months (during which monthly rainfall is less than 100 mm), the area is always fog-bound in these months which keeps the air moist. The range in elevation in this narrow area is more than 7000 m (from 200 to 7765 m). Consequently, one of the most complex and perfect systems of mountain vertical vegetation zones on earth has developed on its slopes, with tropical montane rain forest in the basal zone. The vertical vegetation zonal spectrum is as follows.

The tropical lower montane rain forest and semi­evergreen forest zone includes the lower mountains and hills, below 1100 m, in the Eastern Himalaya. The luxuriant tropical rain forest in the valleys consists mainly of Dipterocarpus turbinatus, Mesua ferrea, Canarium resiniferum, Artocarpus chaplasha, Tetrameles nudiflora, Dillenia indica, and Talauma phelocarpa. Most of these are evergreen trees belonging to the Indo-Malayan floral element. Some of them have prominent tropical characteristics such as plank buttresses on roots and cauliflory. Lianas (Dendrocalamus hamiltonii, Calamus spp.) and epiphytes are abundant in these forests. Usually Bambusa pallida is found in the understory, and Pandanus furcatus is present in gaps. On the slopes of the lower mountains, 600–1000 m, there are tropical montane semi-evergreen forests mainly consisting of semi-deciduous gigantic trees, such as Dysoxylum gobara, Terminalia myriocarpa, and Altingia excelsa, and luxuriant lower tropical evergreen trees (e.g., Beilschmiedia, Cinnamomum). Lianas and epiphytes are also abundant (Chang 1981).

The montane evergreen broadleaf forest zone lies at elevations between 1100 and 2200 m and can be divided into upper and lower parts. The lower subzone is dominated by Castanopsis hystrix and C. indica and is mixed with many tropical evergreen broadleaf trees, such as Machilus, Machilia, Cinnamomum, and Phoebe, belonging to the Lauraceae, and Magnolia, Engelhardtia spicata, and Schima wallichii. The forests of the upper subzone consist mainly of Quercus lamellosa, Quercus glauca var. gracilis, and Lithocarpus xylocarpus. In addition to some further species of evergreen broadleaf trees, deciduous trees are increasingly common. These include Acer spp., Alnus nepalensis, Mallotus nepalensis, Carpinus viminea, and the arborescent Rhododendron. The zone of the montane evergreen broadleaf forest is very humid, with annual rainfall that may exceed 3000 mm. Trunks of trees and the ground are often fully covered by thick mosses. It can be called a “mossy forest,” but it differs from the low “elfin” forests and the mossy forests in other tropical mountains in its much taller trees (Chang 1981).

The montane mixed coniferous and broadleaf forest zone is between 2200 and 2800 m and is dominated by Tsuga dumosa, which sometimes mixes with Quercus pachyphylla and Quercus lamellosa to form mixed evergreens, coniferous, and broadleaf forests. Also present are Taxus baccata, Magnolia campbellii, Acer campbellii, Acer pectinatum, and Rhododendron spp. Arundinaria griffithii often is present in the understory, and ferns are very abundant in ground herbaceous layers (Fig. 27).

The upper montane dark coniferous forest is located between 2800 and 3600 (up to 3900) m. The climate is wet, cold, and always foggy. The vegetation is dominated by Abies delavayi var. motuoensis and has a large amount of Rhododendron spp. and Sinarundinaria as understory. Larix griffithii often is present on open ground and Betula utilis “krummholz” at the upper forest line. The subalpine Rhododendron shrubland and meadow zone is situated between 3600 (3900) and 4000 (4200) m and transition from forests to the alpine zone. The luxuriant subalpine shrubland consists especially of Rhododendron campanulatum, Rhododendron barbatum, Rhododendron lepidotum, and others, with deciduous shrubs such as Salix, Rosa, Cotoneaster, Viburnum, and Lonicera, and interspersed luxuriant forb meadows (Chang 1981).

The alpine scrub and meadow zone is between 4000 (4200) and 4600 m. The alpine dense scrub consists of lower Rhododendron setosum and Rhododendron nivale. The alpine meadow contains abundant species of colorful forbs. Most of them belong to the Sino-Himalayan floral element. Because the seasonal changes are great, and in the winter there is a thick snow deposit on the alpine zone of the Himalayas, the alpine vegetation there does not have tropical characteristics and belongs to subtropical or temperate types. West of Bhutan, the climate of the Himalayas becomes progressively drier, and there is a well-developed arid season. The tropical monsoon forest consists of deciduous Shorea robusta instead of the tropical rain forest on the lower hills. In the upper montane coniferous zone, the more drought-resistant Picea smithiana and Larix griffithii occur. In the alpine zone, the eastern Himalayan forb meadow is replaced by a Kobresia meadow (Chang 1981).

Subtropical Montane Coniferous Forest Zone of Southeastern Tibet

The zone includes mountains and valleys along the middle reaches of the Tsangpo (Brahmaputra) River, its tributaries (Niyan, Yegongqu, and Polong-Tsangpo), and three eastern rivers (Nu, Lancang, and Jinsha). These rivers cut deeply into the southeastern part of the Plateau. The humid Southwest Monsoon passes through their valleys and penetrates into this corner of the Plateau. The dense forest vegetation is distributed correspondingly on the valley slopes. The rainfall is obviously less than that on the southern slopes of the Himalayas, varying between 500 and 1000 mm. Northward along the upper rivers onto the inner part of the Plateau, the forest vegetation becomes sparse and vanishes as a consequence of decreasing moisture. The lowest elevation in this area is above 2000 m, and the basic topography is of mountains and valleys (the Plateau has been strongly eroded, and only fragments of the original surface remain). The vegetation belongs to the montane vertical-zoned types.

Subtropical evergreen broadleaf forests, which are distributed widely along the eastern periphery of the Plateau (Western Sichuan and Northern Yunnan), occur in only a very limited region in Tibet: the Tongmai Valley to the north of the great curvature of the Tsangpo River which is reached by humid and hot air currents and supports subtropical evergreen broadleaf forests between 2000 and 2500 m. These forests consist mainly of oaks (Quercus incana and Quercus gilliana) and contain abundant subtropical Eastern Asian floral elements. Because the elevation of most valleys in this region exceeds 2500 m, the subtropical broadleaf zone usually is not present here (Chang 1981).

From 2500 to 3200 m, there is a lower montane mixed coniferous and broadleaf forest zone or coniferous forest zone. On southern slopes, it is composed of forests of Pinus densa, Quercus aquifolioides, or mixed forest of both species. Forests of Pinus armandii exist where it is more humid. On northern slopes, forests composed mainly of Picea balfouriana (in the eastern part) or Picea likiangensis var. linzhiensis (in the western part) extend from 2500 to 3200 m. Usually this is the basic subzone of the upper montane dark coniferous forest zone. The biomass of this spruce forest is immense. The height of trees may be more than 60 m, and the timber volume can reach over 1500 m³/ha. Under spruce forest canopies, there is abundant undergrowth: Enkianthus deflexus, Lindera cercidifolia, Litsea cubeba, Acer campbellii, Rhus succedanea, Deutzia corymbosa, Rhododendron spp., and Sinarundinaria spathiflora. The moss layer is very well developed (Chang 1981).

From 3200 to 4000 m or somewhat higher, there is a dark-colored coniferous forest zone consisting of Abies delavayi (in the eastern part, Fig. 31) or Abies spectabilis (in the western part). The most common undergrowth species are Rhododendron houlstani, Rhododendron przewalskii, Sorbus spp., Rosa omeiensis, Lonicera succata, Deutzia corymbosa, and Sinarundinaria spathiflora. Most of these undergrowth and herb species in the coniferous forests belong to Eastern Asian floral elements (Sino-Himalayan element). Some boreal elements (Vaccinium spp., Bergenia, Chamaenerion angustifolium, Circaea alpina, Fragaria vesca, Polygonum viviparum, Thalictrum alpinum, especially, and some mosses) appear in the upper montane forest regions, and the subtropical evergreen broadleaf forest floral element dominates in the lower montane regions (Chang 1981) (Fig. 31).

Fig. 31

Mixed Abies-Rhododendron forest, Yunnan, China. (Photo R.E. Hart)

In the northern part of this forest region, the climate becomes drier and colder. In the upper part, particularly on southern slopes, the forests are often composed of Juniperus tibetica and Juniperus convallium. Their upper limits reach 4300 or even 4600 m. On the western edge of this region where the forest vegetation changes gradually to steppe, the humid dark coniferous forest zone disappears, and a sparse coniferous forest of Cupressus gigantea is present and merges into steppe vegetation (Chang 1981).

The transitional alpine vegetation above treeline is low Rhododendron scrub (Rhododendron ramosissimum, Rhododendron nivale, Rhododendron anthopogon) on northern slopes and Cassiope fastigiata scrub on southern slopes. The alpine meadow which consists mainly of Kobresia angusta and Kobresia pygmaea occupies higher areas above the scrub vegetation. Some alpine herbs are often present in the meadow, among them Polygonum viviparum, Anaphalis nepalensis, Gentiana spp., Meconopsis horridula, Oxygraphis polypetala, and Thalictrum alpinum. In the hot and dry valleys of the Three Rivers, the coniferous forest vegetation is distributed only on upper slopes, whereas the valley bottoms are occupied by xeric thorny scrub which consists mainly of Sophora vicinijolia and Elsholtzia capituligera, sometimes with cacti (introduced Opuntia) (Chang 1981).

The High-Cold Vegetation Region

The extensive plateau between the Himalayan and Kunlun Mountain ranges has relatively low mountains, platform plateaus, and lake and valley basins. The elevation of the main plateau level is about 500 m in the southeast and over 5000 m in the northwest. Some valleys in the south may extend down to approximately 3000 m. The Plateau is controlled by the Westerlies in the winter half of the year and has an arid, cold, and continental climate. From east to west, with increasing drought, the high-cold meadow, steppe, and desert vegetation occur in sequence. The flora of the eastern meadow zones is dominated by Tibetan endemic species and Sino­Himalayan elements. The flora of the central and western steppe and desert zones is dominated by Central Asiatic (Tethys) elements and Tibetan endemic species (Chang 1981).

Naqü (Eastern Tibet) High-Cold Meadow and Scrub Plateau Zone

The elevation of the Plateau in eastern Tibet is approximately 4000–4500 m. Although the landscape is more eroded here than in western Tibet, it remains a prominent and relatively complete plateau plain. The climate is cold and somewhat moist. The annual mean temperature is between −3.0 °C and 0 °C. The mean temperature of the warmest month is 8–10 (12)°C and the frostless season from 20 to 100 days. The annual rainfall is 400–700 mm. There are thunderstorms with hailstones in the summer and relatively abundant snow accumulation in the winter and spring. Judged by its vertical zones, vegetation of this Plateau zone seems much like an extension of the upper part of the preceding mountain forest zonation onto the Plateau. In the valleys of its southeastern part, fragmentary coniferous forests persist. On the Plateau proper, there is extensive high-cold meadow which consists mainly of low-growing Kobresia pygmaea and Kobresia humilis, usually associated with Polygonum sphaerostachyum and other forbs, including Thalictrum alpinum, Anaphalis xylorrhiza, Leontopodium pusillum, Carex atrata var. glacialis, Meconopsis horridula, Polygonum viviparum, Potentilla stenophylla, Pedicularis, and Gentiana, and cushion plants such as Arenaria musciformis and Androsace tapete. High-cold evergreen sclerophyllous scrubs, composed of microphyllous Rhododendron cephalanthus and Rhododendron setosum on northern slopes, and deciduous shrubs of Salix spp., Potentilla fruticosa, and Caragana jubata in valleys or on southern slopes are always found in conjunction with the high-cold meadow. In level areas and swampy valleys, there occur high-cold swampy meadows with a mound-like growth form of Kobresia littledalei. Westward, as the climate becomes drier, the importance of mesic forbs decreases gradually, leaving almost pure Kobresia meadow. Finally, some steppe species appear in the community, and the Rhododendron scrub disappears to be replaced by Juniperus spp. on the inner Plateau (Chang 1981).

The high-cold Kobresia meadows differ in floristic composition, community structure, and other ecological features from the humid dicotyledonous alpine meadows of the Alps or other moist-temperate mountains and the alpine tundra of higher latitudes. This vegetation is referred to as Tibetan high-cold meadow. It has evolved under drier and harsher high mountain and plateau conditions with continental climates. By its ecological features and phytogeographic situation, Kobresia meadows appear to be a transitional or intermediate type between cryo-mesic alpine meadow and cryo-xeric high-cold steppe. They develop a compact tussock physiognomy and have a series of typical mesic meadow species, but its dominant, Kobresia, has xeromorphic characteristics and contains some xeric steppe species. In fact, the Kobresia meadow zone is situated between the humid alpine meadow and mountain forest vegetation zone in the east and the arid high-cold steppe plateau zone in the west. The range of Kobresia meadow is mainly the Tibetan Plateau and its surrounding mountain regions such as the Pamir, Kunlun, Tian Shan, Qilian, Altai, Hangai, and Traverse Mountains, northward to the Ural and Caucasus. Most species of Kobresia belong to Sino­Himalayan elements endemic to Tibet and Central Asia (Chang 1981).

Tsangpo (Upper Brahmaputra) Valley Xeric Shrubland and Steppe Plateau Zone

The Tsangpo Valley, located between the northern piedmont of the Himalayas and Nyenchen Tanglha and Gangdisi Mountains, is a subduction zone at the margin of two continental plates. It extends east-west through the south section of the Plateau. Its altitude increases westward from 3500 m to 4500 m. Because of the rain shadow effect of the Himalayas, annual precipitation is generally between 300 and 500 mm and decreases gradually. Above about 4400 m, the slope vegetation changes from mesothermal steppe to high-cold steppe which is dominated by Stipa purpurea. The shrubland vegetation of Potentilla fruticosa, Lonicera tibetica (in the east), and Caragana versicolor (in the west) occurs widely in this range in conjunction with the steppe communities. On the southern slopes of the Gangdisi and Nyenchen Tanglha ranges, there are extensive Juniperus shrubland communities in the steppe zone (Chang 1981).

From 4600 to 5400 m in the east and 5000 to 5600 m in the west, the mountains and plateaus are occupied by high-cold meadow and cushion plant vegetation. These are composed mainly of Kobresia pygmaea and the cushion plants Arenaria musciformis, Androsace tapete, and Oxytropis chiliophylla. The Kobresia meadow usually occupies relatively flat or gentle, stable slopes with rather well-developed soil. On the steep or rocky slopes, there is sparse cushion plant vegetation. The latter extends down into the lower steppe zone and forms a special cushion plant­steppe vegetation type there (Chang 1981).

Above 5400 (5600) m and to approximately 6000 m, there is a subnival zone where sparse alpine forbs (Saussurea, Saxifraga, Gentiana, Draba, Braya, Androsace, Potentilla) grow in rock fractures and on slopes of rock debris. The surfaces of rocks are covered with lichens (e.g., Rhizocarpon geographicum, Glypholecia scabra, Caloplaca elegans, Parmelia conspersa). The nival zone begins between 5800 and 6200 m. Along the western edge of the valley steppe region, in the Pulan Valley and the basin of Mafamutso and Langaktso lakes, the climate and vegetation tend toward desert. Mountain desert-steppe vegetation consisting of Stipa glareosa and Ceratoides latam occurs there and is characteristic of the transition from steppe plateau zone to desert plateau zone (Chang 1981).

Chiangtang (Northern Tibet) High-Cold Steppe Plateau Zone

Chiangtang extends between the Gangdisi, Nyenchen Tanglha, and Kunlun ranges. It is a whole plate which uplifted at the end of the Tertiary and is a landform consisting of a plateau basin of gently undulating plains with abundant scattered lakes. The level of the plateau rises gradually from 4500 m in the south to 5200 m in the north. The climate is cold, arid, and quite windy. The mean annual temperature ranges between −2 °C and 0 °C; the mean temperature of the warmest month ranges between 6 °C and 10 (12)°C. During 6–7 months, the mean temperatures remain below 0 °C. The temperature is much lower northward, and continuous permafrost is widespread. The diurnal and annual temperature ranges are very high. The annual precipitation varies between 100 and 300 mm concentrated in the summer and decreasing from southeast to northwest (Chang 1981).

The most extensive vegetation zone on the plateau is the steppe of Stipa purpurea, the center of distribution for which is the Chiangtang Plateau. The typical high-cold steppe community of purple feathergrass is rather sparse, with plant coverage never more than 20%. Usually there are some cushion plants (Arenaria musciformis, Androsace tapete, Thylacospermum rupifragum) in the community. On different parts of the Chiangtang Plateau, the high-cold steppe of purple feathergrass shows some prominent ecological differentiation. Along the east and southeast periphery of Chiangtang, there is a transitional section between the high-cold meadow zone and the high­cold steppe zone. There, Kobresia pygmaea and some mesic forbs occur in the steppe communities, and the plant cover in general is somewhat more complete. Northward, since the altitude increases, the climate becomes colder and drier, and the vegetation gradually changes to high-cold desert; Carex moorcroftii becomes more important with increasing altitude. Finally, the high-cold desert­steppe of Carex moorcroftii and Ceratoides compacta is dominant in the northernmost part of Chiangtang. Conversely, in the southern part of Chiangtang, since the climate is a little warmer and moister, some mesothermal plant elements (e.g., Orinus thoroldii, Pennisetum flaccidum, Artemisia wellbyi, the shrub Caragana vmicolor) are present. Westward, as the climate becomes drier and warmer, in large lake basins are found steppes of Stipa glareosa (of the desert-steppe flora of Central Asia) and Stipa subsessiliflora var. basiplumosa. Here, the steppe vegetation is transitional toward desert. However, the plain and the lower mountains of the Plateau are still dominated by the steppe vegetation of purple feathergrass (Chang 1981).

Western Ali Mountain Desert Plateau Zone

On the western edge of Tibet, between the northwestern Himalaya and Karakoram ranges, there is a series of mountains and valleys called the Ali region. The elevation of the valleys is 3000 m in the south and 4300 m in the north. This region experiences the driest climate in Tibet. The center of the summer thermal low of Tibet is located here, and this is also the hottest region on the Plateau. The July mean temperature is 15 °C but may be as low as −10 °C in the winter. The annual precipitation is no more than 50–75 mm. The aridity is in the range of 3.4–6, with a drought period of between 5 and 6 months during the growing season. Therefore, this region has a cold temperate steppe-desert or desert climate (Chang 1981).

The plateau zonal vegetation is a desert community which consists of suffrutescent Ceratoides latens (Tethys flora), Ajania fruticulosa (Central Asiatic flora), and the endemic perennial Christoka crassifolia. The driest core of desert is in the Bangong Mountains and the Chiangchenmo Mountains which surround Bangong Tso and Spangul Tso in the northwestern part of the region. This is a region of rocky desert with almost no vegetation; there is only a very sparse growth of Ceratoides latens. Above 4500 m, some feathergrasses (Stipa glareosa, Stipa subsessiliflora, Stipa breviflora) enter the desert community with Ceratoides latens, changing the vegetation to steppe-desert, and this community extends up to 5200 m on Mount Chiangchenmo. This may be the world’s highest desert. In south Ali, the climate is a little more humid. The Shiquanhe (lndus) River Valley, Ge’erqu River Valley, Xiangquanhe (Sutlej) River Valley, and the surrounding lower mountains are occupied by mountain steppe-desert vegetation which consists mainly of Ceratoides latens, Ajania fruticulosa, Stipa glareosa, and some xeric shrubs (Ephedra gerardiana and Caragana versicolor). The desert community develops vigorously there because of relatively abundant snowfall in the winter and the spring. Some ephemeral plants (Tauscheria lasiocarpa, Koelpinia linearis) are present in the desert (Chang 1981).

In the southwestern comer of Ali, where the Xiangquanhe Valley falls to 2900 m, the climate is warmer. Some Mediterranean subtropical elements, such as Colutea arborescens, are present there. The dominants of the desert vegetation are species with more Tethystic and Central Asiatic affinities such as Artemisia salsoloides, Artemisia sacrorum, Scorzonera, Ceratoides latens, Capparis spinosa, Kochia, Polygonum paronychioides, and Stipa stapfii. These reflect a change toward the subtropical desert in the Kashmir Valley. The vertical zonation of mountain vegetation in western Ali has a spectrum of desert types, too. The structure of the vertical zones is as follows: desert or steppe-desert zone (basic zone), giving way to steppe zone, giving way to high-cold cushion plant vegetation zone, finally yielding to the subnival zone (Chang 1981).

The mountain steppe zone can be divided into two or three subzones. The lower one is a desert-steppe subzone, which is mainly composed of Stipa glareosa and Ceratoides latens, the former being the dominant. The intermediate subzone exists only in southern mountains of the area and is formed by the conjunction of mountain shrublands (consisting of Caragana versicolor) and steppe communities (the dominants are Stipa glareosa, Stipa breviflora, and Stipa purpurea). The upper subzone is a high-cold steppe subzone which consists of Stipa purpurea and Carex moorcroftii. North of about latitude 33° in Ali, the shrubland of Caragana versicolor disappears, leaving the steppe zone with only the two other subzones (Chang 1981). The high mountains of Ali usually lack alpine meadows except for some isolated patches under moist conditions. The typical high mountain vegetation there is of sparse cushion plants, mainly Arenaria musciformis and Thylacospermum caespitosum. The upper vegetation line reaches almost to 5600 or 5700 m. The upper limit of the agricultural cultivation is also very high. On the southern slopes of the Karakoram Range at latitude 34°, bare barley is grown to 4780 m and can be harvested in most years (Chang 1981).

Northwestern Tibetan High-Cold Desert Plateau Zone

The northwestern part of the Chiangtang Plateau is located between the Kunlun and Karakoram ranges. The elevation of the Plateau and lake basins is over 5000 m. Here is the coldest and driest climate of the Plateau. The mean annual temperature is about −8 to −1 0 °C. There are 9–10 months in which the mean monthly temperature is lower than 0 °C, with no frostless season in the year. Even in the warmest part of the year, there are heavy frosts every night, and an extensive permafrost horizon generally exists there. The annual and diurnal temperature ranges are rather high. The mean annual precipitation is only 20–50 mm, all in frozen forms. Eastward, the precipitation is somewhat greater, about 100–150 mm. The wind is very strong and frequent (Chang 1981). Because of the extremely severe ecological conditions and the shorter history of vegetation development after the uplift of the Plateau, the vegetation is very sparse and rather poor in species. Usually one is presented with a vast expanse of plateau gravel or Gobi without plants or many bare rocky slopes and hilltops. The plateau zonal vegetation is sparse high-cold desert, which has evolved during the time since the Plateau was uplifted. It is composed of cryophytic-xeric cushion-like nano-suffruticose Ceratoides compacta. These plants exist on debris or gravel slopes and especially on vast ancient lake plains formed by lake sediments. The soil contains high concentrations of salt and has permafrost. The salt in the soil may be due to the evaporation of an ancient salt lake, coupled with the low precipitation which causes continual salt accumulation (Chang 1981).

Very low temperatures, very short or non-existent growing season, severe drought, high wind, and barren, rocky, and salty soil are typical ecological conditions for the high-cold desert plateau zone. The plant coverage of a high-cold desert community of Ceratoides compacta usually is never more than 8% and often as little as 1–2%. Companion species are very few (Pegeophyton scapiflorum, Hedinia tibetica). The only woody plant in the high­cold desert zone is Myricaria hedinii, which grows along riverbeds. Its branches and trunks are entirely underground, and only its branchlets with small leaves are exposed on the ground surface. This plant forms a dense cushion, no more than 1 cm above the ground (Chang 1981). Eastward from longitude 80° on the Plateau, the high­cold desert vegetation prevails. The wide lake plain is occupied by high-cold desert of Ceratoides compacta, but the piedmont slopes and steppes are covered by high-cold desert-steppe which is dominated by Carex moorcroftii with some Ceratoides compacta. The vegetation on the mountainsides on both sides of the lake plain is more vigorous than on the plain itself. This may be caused by a persistent temperature inversion. The structure of the vertical zonal spectrum is very simple. Above the basic vegetation zone of high-cold desert and desert-steppe, there is a narrow zone of high-cold steppe consisting of Carex moorcroftii. Its vertical range is not wider than 200 m and its upper limit is at 5300 m. Above this, a subnival zone with some sparse alpine herbs (such as Saussurea gnaphalodes, Melandrium apetalum, and cushion plants) is found. The snowline lies between 6000 and 6200 m (Chang 1981).