18.104.22.168 Lowlands (Terai and Siwalik Hills, below 1,000m)
The biological diversity contained in the Terai and Siwalik Hills (lowlands) ecosystems are of international importance both in view of the number of globally threatened species of wildlife and flora as well as the diversity of ecosystems contained within the area (BPP 1995f). The Terai is heavily populated, resulting in serious pressures on forest resources. The lowlands are mostly dominated by Sal (Shorea robusta), tropical deciduous riverine forest, and tropical evergreen forest. Sal forests have suffered greatly from lopping and felling of trees by local villagers in eastern and central Nepal, but it still form some magnificent stands of tall trees in western Nepal.
Recognising the great significance of the biodiversity of the lowlands, HMGN established five protected areas in the Terai and Siwalik Hills. These are: Koshi Tappu Wildlife Reserve, Parsa Wildlife Reserve, Royal Chitwan National Park, Royal Bardia National Park and Royal Suklaphanta Wildlife Reserve. While the Terai ecosystems are well represented within these protected areas, coverage of the Siwalik Hill ecosystems is less comprehensive (Maskey 1996). Out of 23 ecosystems described by Dobremez in the lowlands, 15 are included in the current protected areas of Nepal (Table 2.4). Unfortunately, biological resources outside these protected areas are under great pressure from exploitation and the conversion of forests to farmland.
Table 2.4 Ecosystems identified by Dobremez (1970), and their representation in protected
TOTAL NUMBER OF ECOSYSTEMS
NUMBER IN PROTECTED AREAS
Source: modified from BPP (1995i) by Maskey (1996)
Dobremez (1996) presented an altitudinal distribution of flora in central Nepal. He categorised biogeographical domains into 11 levels of vegetation at altitude differences of 500m. The Biodiversity Profiles Project (BPP 1995f) lists 1,885 species of angiosperms, 61 species of bryophytes and 81 species of pteridophytes from the Terai and Siwalik Hills (Table 2.5).
Table 2.5 Number of species of flora and fauna occurring in each physiographic zone
TERAI & SIWALIK HILLS <1,000m
> 2,000 * (38.70%)
648 (77.8 0%)
Source: BPP (1995f). * Approximate figure. Species of flora and fauna may occur in more
than one physiographic zone, and therefore the percentages (of the total number of species
of each group found in Nepal) do not necessarily add up.
Most of the exploratory work on the flora of Nepal has been done in the Mid-hills Mountains, and the current number of floral species in the Terai and Siwalik Hills may change significantly with more surveys. The faunal diversity in the different ecological zones is not well categorised, however, faunal diversity is high in the Terai and Siwalik Hills (BPP 1995f). The Biodiversity Profiles Project lists 648 bird species, 111 of them confined species, in the Terai and Siwalik Hills (out of 833 bird species found in Nepal). The lowland fauna is more endangered than the Mid-hills or Mountain fauna (Table 2.6) because of greater human activity in the lowlands (Terai and Siwalik Hills).
22.214.171.124 Mid-hills (1,000-3,000m)
The Mid-hills have the greatest ecosystem diversity as well as species diversity in Nepal. This is due to the great variety of terrain and the occurrence of subtropical to temperate flora and fauna in this zone. Nearly 32% of the forests in Nepal occur in the Mid-hills, and the zone includes 52 types of ecosystems. Dobremez (1996) listed the highest number of angiosperms in the Mid-hills, particularly between 2,000-2,500m in altitude. The Biodiversity Profiles Project (BPP 1995f) lists 3,364 species of angiosperms, 493 species of bryophytes, 272 species of pteridophytes and 16 species of gymnosperms in the Mid-hills. Furthermore, 557 species of butterflies, 76 species of fishes, 29 species of amphibians, 56 species of reptiles, 691 species of birds and 110 species of mammals are listed in the Mid-hills.
Table 2.6 Number of threatened species of fauna according to physiographic zone
Source: BPP (1995f, g, h). Species may occur in more than one physiographic zone, and therefore
the percentages (of the total number of species of each group found in Nepal) do not necessarily add up.
126.96.36.199 Highlands (above 3,000m)
The Nepal highlands are the meeting place of two major geographical regions of the world - the Palaearctic region to the north and the Indo-Malayan region to the south. There are 38 major ecosystems found in the highlands. Recognising the significance of these ecosystems, HMGN established seven protected areas in the highland mountains (and three protected areas spanning the Mid-hills and highlands), covering 78.52% (20,939km2) of total protected areas. These protected areas represent 30 of the 38 ecosystems of the highlands (Table 2.4).
The highlands are relatively less diverse in flora or fauna than the Mid-hills and lowlands because of the adverse environmental conditions. However, they are characterised by a large number of endemic species. They comprise around one third of the total forest cover of Nepal, representing birch, oak, rhododendron, juniper, fir, cedar, larch, and spruce forests. About 420 phanerogamic species have been recorded above 5,000m on both sides of the Himalayan range in the Everest region (Miehe 1989).
2.3.2 ECOSYSTEMS DIVERSITY
188.8.131.52 Forest ecosystems
Forests play a vital role in maintaining ecological balance and economic development. Pristine forests are also a major attraction for foreign tourists. Major energy sources, animal fodder and timber are all found in the forest environment. Forest catchments are the main sources of water used for hydroelectric power, irrigation, and domestic/household consumption. Rural people are very dependent on many non-timber forest products (NTFPs) for their subsistence needs.
Forest types Nepal has a very diverse flora with 35 forest types, as classified by Stainton (1972). These forest types are categorized into ten major groups - tropical, subtropical broad-leaved, subtropical conifer, lower temperate broad-leaved, lower temperate mixed broad-leaved, upper temperate broad-leaved, upper temperate mixed broad-leaved, temperate coniferous, sub-alpine and alpine scrub forests. In addition, there are some patches of plantation forest. The habitats and characteristics of the major forest types within these groups are briefly described below:
(1) Tropical forest (below 1,000m): This forest type is predominantly composed of Shorea robusta in the southern parts of Nepal. Acacia catechu/Dalbergia sissoo forests replace Shorea robusta forests along streams and rivers. There are other riverine forests with mainly evergreen species such as Michelia champaca or deciduous species such as Bombax ceiba. Shorea robusta forests are replaced by Terminalia/Anogeissus forests in the foothills of western Nepal.
(2) Subtropical broad-leaved forest (1,000-2,000m): Schima wallichii/Castanopsis indica forests are found in central and eastern Nepal. Riverine forests of Cedrela/Albizia occur along large rivers such as the Arun on subtropical foothills. Alnus nepalensis forests are widespread along streams and in moist places.
(3) Subtropical pine forest (1,000-2,200m): Pinus roxburghii forests occur particularly on the south-facing slopes of the Mid-hills and Siwalik Hills in western and central Nepal.
(4) Lower temperate broad-leaved forest: This forest type occurs between 2,000-2,700m in the west and 1,700-2,400m in the east. Alnus nitida, Castanopsis tribuloides/C. hystrix, Lithocarpus pachyphylla, and several species of Quercus forests thrive in the Mid-hills. Among them, Alnus nitida forests are confined to the riverbanks of the Mugu Karnali, at 2,130-2,440m. Quercus leucotrichophora/Q. lanuginosa forests and Q. floribunda forests occur mostly in west Nepal, whereas Q. lamellosa forests are widespread in central and eastern Nepal. Lithocarpus pachyphylla forests occur in eastern Nepal.
(5) Lower temperate mixed broad-leaved forest (1,700-2,200m): This type of forest is confined to north and west-facing slopes. In many places, prominent tree species of this forest type belong to the Lauraceae family.
(6) Upper temperate broad-leaved forest (2,200-3,000m): Quercus semecarpifolia forests are widespread in central and eastern Nepal on south-facing slopes but it are absent in heavy rainfall areas such as the upper Arun and Tamur valleys and the hills lying north of Pokhara.
(7) Upper temperate mixed broad-leaved forest (2,500-3,500m): This forest type occurs in central and eastern Nepal, mainly on north and west-facing slopes. Acer and Rhododendron species are prominent throughout this altitude range. However, Aesculus/Juglans/Acer forests are mostly confined to western Nepal.
(8) Temperate coniferous forest (2,000-3,000m): Pinus wallichiana, Cedrus deodara, Cupressus torulosa, Tsuga dumosa and Abies pindrow forests characterise the temperate conifer forest type. However, many of the above species also thrive above 3,000m. Pinus wallichiana is an aggressive coloniser and is found in temperate parts of Nepal, extending to 3,700m. Cedrus deodara, Picea smithiana, Juniperus indica and Abies pindrow forests occur in the western Himalayas. The valley of the upper Bheri River demarcates the eastern boundary for Cedrus deodara. Larix himalaica forests only occur in the Langtang and Buri Gandaki valleys of Nepal, preferring moraine habitats. Larix griffithiana is an eastern Himalayan larch species and extends to 3,940m. Both, Cupressus torulosa forests and Tsuga dumosa forests are widespread throughout Nepal between 2,130-3,340m.
(9) Sub-alpine forest (3,000-4,100m): Abies spectabilis, Betula utilis, and Rhododendron forests occur in subalpine zones, the latter in very wet sites.
(10) Alpine scrub (above 4,100m): Juniper-Rhododendron associations include Juniperus recurva, J. indica, J. communis, Rhododendron anthopogon, and R. lepidotum associated with Ephedra gerardiana, and Hippophae tibetana in inner valleys. Caragana versicolor, Lonicera spinosa, Rosa sericea and Sophora moocroftiana, amongst others, occur north of the Dhaulagiri-Annapurna massif. Alpine meadows, locally called 'Kharka', are subjected to grazing during the summer and rainy seasons. Perpetual snow occurs above 5,200m, and mosses and lichens are found in scattered locations. Stellaria decumbens and Parrya lanuginosa have been recorded at an elevation of about 6,100m, but beyond 6,000m, in the Arctic desert/nival zone, even mosses and do not survive.