Plants by Elevation Belt of Nepal: Vertical Vegetation Zones

Nepal rises from the Terai plains near 60 metres (m) above sea level to Sagarmatha (Mount Everest) at 8,849 m within a horizontal distance of barely 200 kilometres. Because air cools by roughly 6 degrees Celsius for every 1,000 m gained, this steep climb compresses the plant zones of an entire continent into a single mountain flank. A traveller walking uphill from Chitwan to the Everest base area passes, in a few days, through vegetation that elsewhere would be spread from India to the Arctic.

Two forces control which plants grow where: temperature, which falls with height, and moisture, which is delivered by the summer monsoon and drops sharply from the wet eastern hills to the drier far-west and the rain-shadow valleys behind the main Himalaya. Aspect (whether a slope faces the sun or the shade) and soil add finer detail. Together these produce a predictable stacking of vegetation belts that botanists call altitudinal or vertical zonation.

The classic framework comes from J.D.A. Stainton's 'Forests of Nepal' (1972 AD) and Jean-Francois Dobremez's mapping of the same decade, later refined by Nepal's forest agencies. Dobremez recognised four regional belts, eleven bioclimatic zones, about 35 forest types and 75 vegetation types across the country. For everyday study, however, five broad elevation belts capture the pattern, and this page describes the signature trees, shrubs and herbs of each.

The lowest belt covers the Terai plains, the Bhabar gravel apron and the Churia (Siwalik) foothills, roughly below 1,000 m, though Sal can climb to about 1,200-1,500 m on warm lower slopes. Its signature tree is Sal (Shorea robusta, sakhuwa), a tall hardwood that forms extensive, near-pure stands and is Nepal's most economically important timber species. Associated trees include Asna/saj (Terminalia species), karma (Adina cordifolia), bel (Aegle marmelos) and several Albizia species.

Along rivers and freshly deposited sand the forest changes character. Pioneer riverine stands of khair (Acacia catechu) and sissoo (Dalbergia sissoo) colonise gravel bars, while moister patches carry semi-evergreen species. Grasslands of tall elephant grass (Saccharum, Themeda and Narenga) fill floodplains and old river courses, forming the famous phanta habitats of Bardiya and Shuklaphanta.

This belt is warm and wet enough to be species-rich in trees but is not where Nepal's medicinal-herb wealth peaks. Its economic role lies in timber (Sal, khair, sissoo), fuelwood and grazing, and in providing habitat for lowland wildlife. Because it is the most accessible and fertile belt, it has also been the most cleared for farming and settlement.

The subtropical belt clothes the lower midhills. On moist, north- and east-facing slopes of eastern and central Nepal it is dominated by the Schima-Castanopsis forest: chilaune (Schima wallichii) and katus (Castanopsis indica, a chestnut-relative), typically between about 1,000 and 1,700 m. This mixed broadleaf forest is one of the most widespread and heavily used forest types in the hills, supplying fodder, leaf litter and firewood to farming communities.

On drier ground, on south-facing slopes, and increasingly toward western Nepal, the broadleaf forest gives way to Chir pine (Pinus roxburghii, rani salla or khote salla), which is generally dominant between about 900 and 2,000 m. This resin-rich pine tolerates poor soils and fire, and its open, needle-carpeted stands look and feel very different from the humid katus-chilaune woods. The east-wet, west-dry contrast is a defining feature of this belt: where the east has broadleaf forest, the drier west often has pine.

Alnus nepalensis (utis, Nepalese alder) is a fast-growing pioneer that lines gullies, landslides and stream banks throughout this belt, fixing nitrogen and stabilising slopes. The subtropical belt also marks the lower edge of Nepal's great medicinal-plant richness, and studies of medicinal and aromatic plants find that species richness rises steeply through the lower hills before peaking in the belts above.

In the temperate midhills and lower high-hills, evergreen broadleaf forests take over, dominated by oaks (Quercus) and rhododendrons. Characteristic oaks include Quercus lamellosa, Quercus semecarpifolia (khasru) and, at lower edges, Quercus leucotrichophora (banjh). These gnarled, moss-draped oak forests hold moisture and anchor the steep slopes on which they grow.

Rhododendron becomes the emblem of this belt. Lali gurans (Rhododendron arboreum), Nepal's national flower, forms whole hillsides that blaze red and pink in spring; higher and cooler stands add other rhododendron species as a dense understorey. On moist north- and west-facing slopes of central and eastern Nepal, an upper temperate mixed broadleaf forest carries maples (Acer species), Tsuga dumosa (east Himalayan hemlock) and rich epiphyte and orchid growth.

This belt and the subalpine one above it are the heartland of Nepal's herbal wealth. Two prized understorey shrubs of the moist temperate and subalpine forests are lokta (Daphne bholua and Daphne papyracea), whose bark is beaten into the durable handmade Lokta paper used for government records and ritual texts, and allo (Girardinia diversifolia, Himalayan nettle), whose fibre is woven into cloth in the eastern and central hills.

Above about 3,000 m the forest thins into the subalpine belt, the last belt with true trees. Its defining conifer is Himalayan silver fir (Abies spectabilis, gobre salla), often growing with blue pine (Pinus wallichiana) and, in the drier west, spruce (Picea smithiana). Beneath and beside the firs grow dense thickets of shrub rhododendrons and, near streams and in the far north, Himalayan birch (Betula utilis, bhojpatra), whose papery bark was historically used to write manuscripts.

At the very top of the belt the trees dwindle to a stunted, twisted growth form called krummholz. Around 3,900-4,000 m a zone of gnarled Rhododendron campanulatum and Himalayan birch marks the tree line, above which upright forest cannot survive. Junipers (Juniperus species, dhupi) form aromatic scrub here and are burnt as incense in Buddhist and Hindu rituals across the high country.

The subalpine belt supports a large share of Nepal's endemic plants and many high-value medicinal species, and it is the doorway to the alpine herb zone above. Cool, moist and short-summered, it is the belt where forest gives way to open country and where the collection of Himalayan herbs becomes a mainstay of local livelihoods.

Above the tree line lies the alpine belt, a treeless world of low shrubs, cushion plants, grasses and sedges that runs from roughly 4,000 m to the permanent snow line near 5,000-5,500 m. Dwarf rhododendrons (Rhododendron anthopogon, R. setosum, R. lepidotum), shrubby cinquefoil (Potentilla fruticosa) and cushion-forming herbs give way upslope to open alpine meadows dominated by sedges (Kobresia, Carex) and alpine grasses. Above about 5,000 m only lichens, mosses and a few hardy flowering plants cling on in the nival zone.

This is Nepal's celebrated alpine medicinal-herb zone. Yarsagumba (Ophiocordyceps sinensis) - the 'caterpillar fungus' that is a fungus infecting moth larvae, not a plant - is harvested from alpine meadows at roughly 3,500-5,000 m in districts such as Dolpa, Rukum, Darchula and Manang, and is among the most valuable natural products collected in Nepal. Growing in the same high country are kutki (Neopicrorhiza scrophulariiflora), jatamansi or spikenard (Nardostachys jatamansi, recorded up to about 5,000 m), and chiraito (Swertia chirayita) on the belt's lower edge.

Although the alpine belt has fewer total plant species than the warmer belts below, it holds a disproportionate share of Nepal's commercially traded and endangered herbs. Modelling of medicinal and aromatic plants places their richest hotspots high in the mountains, with the largest predicted concentration between about 4,000 and 4,500 m - which is exactly why herb collection is central to the mountain economy and why over-harvesting of yarsagumba, jatamansi and kutki is a serious conservation concern.

Species richness is not spread evenly up the mountain. Overall flowering-plant diversity is highest in the warm, wet lower and middle belts, and Nepal harbours a little more than 6,000 flowering-plant species (of which about 312 are endemic) despite occupying only about 0.1 percent of Earth's land area. For medicinal and aromatic plants specifically, richness tends to rise through the hills and remain high across the temperate-to-alpine band, so the herbs that matter most to the economy are concentrated in the upper belts even though the total number of species is greatest lower down.

The belts also shift with geography. Because the east is wetter than the west, each belt sits a little lower and is more broadleaf-dominated in the east, while the drier west favours pines, junipers and steppe-like vegetation and pushes belts upward. Behind the high peaks, trans-Himalayan valleys such as Mustang and Upper Dolpa lie in rain shadow and carry sparse, cold-desert vegetation quite unlike the green midhills.

Understanding these belts is the backbone of Nepali geography and botany study and of practical conservation. Nepal's protected-area system deliberately spans the belts - from Chitwan's tropical Sal forest to Sagarmatha and Shey-Phoksundo's alpine zones - so that the full vertical sequence of vegetation, and the herbs and wildlife tied to each band, are safeguarded together.