SPECIES MAINTENANCE IN DYNAMIC LANDSCAPE OF THE CHURIYA, EASTERN NEPALネパールシワリク山地の植生の生態学的研究 動的景相域（ランドスケープ）における生物種管理

Authors著者名

D. Bhujuブジュ・ディネス¹⁾, P. Yonzonヨンゾン・プロラド²⁾

Summary要約

The Churiya hills are the youngest and southernmost mountain chain of the Himalaya. They conjoin two ecological regimes the tropical in the south and temperate in the north. In Nepal, the Churiya Hills cover 12.7% of the total land area and contribute to 25.8% of the forest cover of the country. As the human encroachment continues to increase, the fragile landscape of Churiya is in danger. However, ecological information on Nepal Churiya is almost non-existent. The present study covering the Churiya of eastern Nepal is an initiation of creating ecological data base of Nepal Churiya. The study dwells on six major areas: (i) GIS analysis of change in landuse pattern between 1958 and 1992, (ii) floristic composition, forest structure and regeneration, (iii) tree species association at various altitudes, (iv) local knowledge on plant uses among the resident ethnic groups, (v) distribution of butterflies, and (vi) baseline information on birds.

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シワリク地区は、ヒマラヤ山脈の最南域に位置する。地史的には最も若い山域である。ここは、南から熱帯、北から温帯と二つの生態域の結節域でもある。シワリク高地はネパールの国土の12.7%、森林面積の25.8%を占めている。現在、土地開発が増加し続ける状況の中で、シワリク地区の自然環境の分断化が深刻化している。しかし、これまで、ネパール、シワリク地区の生態学的情報は極めて少なかった。この調査研究は、東ネパールのシワリク地区の生態学的基礎情報の収集を主たる目的としつつ、以下の6つのテーマについて詳しく研究された。(1)GISによる1958年と1992年の土地利用状況の比較、(2)植物相および森林の構造と更新、(3)様々な標高域における樹種構成、(4)地域民族の植物利用、(5)チョウ類の分布、(6)鳥類相のベースライン調査。

（推薦者：中村 俊彦　訳）

INDEX

• BACKGROUND
• METHODOLOGY
• RESULTS
• ACKNOWLEDGMENT
• REFERENCES

BACKGROUND

The Churiya comprise the youngest and the southernmost mountain chain of the Himalayan system (Bhatt 1977, Hagen 1998) and conjoin two distinct ecological regimes: the tropical environs of Gangetic plains in the south and the temperate mountains which extend to the alpine in the north (Fig. 1). Also known as the Siwaliks, the Churiya consist of Tertiary unconsolidated and highly erodible fluviatile sediments ranging from relatively fine-grained gray wackes in the south (Lower Siwalik), through soft of clay (Middle Siwalik) to very coarse sands and conglomerates (Upper Siwalik) in the north (Carson 1985). The Churiya Hills extend from Afganisthan to Assam with an average summit of less than 1,500 m asl and the width varying from 8 to 50 km.

The Churiya rocks are rich in vertebrate fossil contents. Churiya's unearthed fossils of later Tertiary have provided basis for much of our present knowledge of the evolution of Asian flora and fauna (Itihara et al. 1972). Major fossil fauna includes primates, carnivores, ungulates, elephants, rodents, birds, reptiles and fish. The primate collection from the Churiya formations includes a number of genera of Anthropoids. A comparative study indicates that the animals of that period were the immediate ancestors of the present-day species. Furthermore, the variety that existed then was greater than what exists today.

In Nepal (area: 147,181 km²), the Churiya Hills cover 12.7% of the total land area and contribute to 25.8% of the forest cover of the country (LRMP 1978). Churiya's hardwood component (Shorea robusta and Terminalia spp) is the highest in the country which comprises 37.% of the total (HMGN 1988). The existing protected network does not encompass the Churiya Hills but at least two protected areas in the south, Chitwan and Bardia, are bordered with the Hills. At some places the Churiya Hills could also make biological corridor such as between Bardia and Shukla Phanta in the far-western Nepal.

There is a growing concern on rapid deterioration of the Churiya Hills in Nepal. As the human encroachment continues to increase, the fragile landscape of Churiya is in danger. However, ecological information on Churiya Hills of Nepal is almost non-existence, except a few studies conducted in support of development activities. The present study, conducted in eastern Nepal, covered the Churiya Hills between Mechi and Saptakoshi. The study included six major areas, viz. (i) change in land-use pattern in 1958, 1978 and 1992, (ii) floristic composition, forest structure and regeneration, (iii) tree species association, (iv) local knowledge on plant use, (v) distribution of butterflies, and (vi) baseline information on bird species.

METHODOLOGY

Study area

The study area is a part of the Churiya in east Nepal (26°40'N-27°53'N, 87°08'E-88°11'E) extending 105 km from the Mechi River (Nepal's eastern border) to the Saptakoshi River covering a total area of 779.24 km²(width: 500 m - 20 km; elevation: 115-1,300 m) (Fig. 2). There were 390 villages (settlements) under 37 Village Development Committees of the five districts: Jhapa (32.9 km²), Morang (211.3 km²) and Sunsari (89.4 km²) districts and Ilam (443.9 km²) and Dhankuta (1.8 km²) districts.

Sampling methods

For GIS (Geographic Information System) analysis, three time-series maps of 1958 (scale 1:63,360; Govt. of India 1961), 1978 (scale 1:50,000; LRMP/HMGN 1986) and 1992 (scale 1:25000; HMGN/FINNIDA 1996) were digitized using ArcInfo 3.52 and Arcview 3.2. Land-use categories were agriculture, forest, shrub, grazing, barren, and sand/gravel. Information were also assessed for urban area, swamp, tea/coffee plantation, orchard and infrastructure such as canals.

Sampling plots for field data collection were ascertained using geographical grids on 1992 map using random table of Rohlf and Sokal (1969). In the field the grids were located with the help of Global Positioning System. There were altogether 35 geographic reference points (sampling grids). Field surveys were completed between January - April, 2000.

Vegetation samplings were done in quadrates, each grid based site comprised of two large quadrates (25m x 25m) representing two different slopes where applicable. For shrub stratum, each such quadrate had two sub-quadrates of 5m x 5m, and four small quadrates of 1m x 1m for ground vegetation. Sampling parameters included height, DBH, coverage, seedling and sapling density of plant species. Beside, noting site condition, soil samples were collected from the study plots. Recorded plants were identified at species level where possible and specimen were confirmed at the National Herbarium, Godavari (KATH). Nomenclature follows Press et al (2000).

Occurrence of bird and butterfly were recorded en-route to the sampling plots. Ethnobotanical information were gathered from the nearest village/settlements of the sampling plots for which rapid ethno-botanical appraisal (Martin 1995) was applied. Vegetation data were also collected from 64 selected points in an elevational difference of 100 m en-route to the sampling grids which ranged from 200-800 m.

RESULTS

Landuse pattern

GIS analysis of the recent map 1992 showed that the major land in the Churiya in the eastern Nepal was occupied by the forests with an area of 477.28 km² covering 61.25% of the total area (779.24 km²) and the agriculture land was 221.71 km² (28.45%). Sand and gravel covered nearly 6.0% indicating the presence of a large network of rivers and streams. Shrub and grazing land occupied 1.5% each, and the rest land-use including urban area made 1.5%. Both the forests and agriculture lands varied in similar pattern in their altitudinal distribution which were high in lower elevation (＜ 300 m) and decreased gradually in the higher elevation showing an interrelationship between the forests and agricultural practices in Nepal. (Fig. 3).

Analysis showed that the forest cover has decreased by over 25% in less than 35 years. In 1958, the total area of the forests in the Churiya was 631.6 km² sharing 81.0% of the total area. By 1978, it decreased by 10% or an area equivalent to 63.5 km². In 1992, it further deteriorated and the forests shrunk to a total area of 477.2 km². During the same period, the agriculture land had increased by more than 120%, i.e. from a total area of 101.8 km² in 1958 to 221.7 km² in 1992. Also, increment in agriculture land was high comparatively between 1978-1992 than 1958-1978. While the highest gain was for agriculture with 127.1 km² or 56% of the total changed area, and a marginal change for urban area with a gain less than 0.1% of the total changed area. Similarly, grazing land and shrub land had increased during the period at the expense of forests. On the other hand, there was a little gain (48.9 km²) for the forests which included some forms of plantations (Table 1).

Floristic composition and forest structure

Over 265 vascular plant species, belonging to 85 families and 178 genera, were recorded from the study sites. Family Leguminosae included the highest number of species (25 spp.) which included rare/threatened tree species like Dalbergia latifloia and Acacia catechu, and endemic species Ormosia glauca. Other families comprising high number of species were Gramineae (16 spp.), Compositae (12 spp.) and Euphorbiaceae (10 spp.). By habit, tree and sub-tree species comprised the highest composition with 45% of the total species, followed by Herbs (22%), Shrubs (20%), Liana (10%) and Fern (3%).

Out of 16 plants of Nepal included in CITES, three species (Cyatheacea sp., Cycas pectinata and Rauvolfia serpentina) were found in the studies area of Churiya. A total of 36 individuals of C. pectinata were observed which were found growing mostly in the Schima and/or Shorea forests in association with Phoenix sp. and/or Pandanus fascicularis. Similarly, 19 individuals of Cyathea sp. were also noted. The recorded individuals of both species were growing near streams and in the eastern sites in the altitudinal range of 300-750 m. Seven rare and/or endangered species identified by IUCN, and several species of specific scientific interest were also noted.

The forests of Churiya in eastern Nepal were estimated with a basal area (BA) of 37.28 m² ha^-1 and a density of 786.5 n ha^-1. The predominant tree species at canopy stratum (height >10 m) were Shorea robusta (relative basal area: 44.0%), Terminalia alata (RBA: 6.8%), Lagerstroemia parviflora (5.0%), and Adina cordifolia (5.0%). Mean DBH (diameter at breast height) of these species was 26.4 cm, though a few S. robusta had a maximum DBH of 124.0 cm. The dominant species presented a sporadic type of size-class distribution indicating the variation in sample plots and/or presence of species with different age groups. Beside these species, the most frequently occurring (Freq. >40%) trees were Semecarpus anacardium, Albizia lebbeck, Syzygium cumini, and Schima wallichii. S. wallichii was observed up to 300 m, a lowest record of its occurrence which could be attributed to the moister environs of eastern Nepal. (Fig. 4, Table 2).

The understory stratum (Ht. ＜4 m), had species like Colebrookea oppositifolia (Freq. 32.9%), Eupatorium spp. (Freq. ＞22%), Leea sp. (Freq. 18.6%), Maesa montana (Freq. 17.1%), and Boehmeria platyphylla (Freq. 15.7%). The highest density, however, was that of Clerodendrum viscosum with 2940 n ha^-1. Eupatorium sp., C. oppositifolia, and Phoenix sylvestris, a tree species but occurring in the understory in the study site (Average Ht. 1.3 m), shared comparatively a high basal area, each having RBA over 3.0%. The ground stratum was poorly developed with a coverage of 15.4% in average which can be attributed to prevailing dry season during the investigation and wide spread over-grazing. The most abundant species by frequency of occurrence were Oplismenus sp. (Freq. 23.46%), Capillipedium assimile (Freq. 16.54%), and Sida cordata (Freq. 10.38%). By relative dominance, C. assimile, Arundinella nepalensis, Oplismenus sp., Ageratum conyzoides and Carex cruciata were most prevalent in the area.

Tree Species association

A dendrogram from similarity analysis based on RBA and floristic composition categorized the study site into seven groups with varying diversity index. The major groups were that of dominated by Shorea robusta, Terminalia alata, Lagerstroemia parviflora, Adina cordifolia, Schima wallichii and Bombax ceiba. The pre-dominant species was S. robusta in the studied site indicating its higher germination percentage, higher adaptability and higher rate of survivorship. The species was recorded as dominant species in 24 sites (37.5% of the total), and co-dominant in at least 11 sites. However, as also shown by the dendrogram, S. robusta appeared along with other dominant and/or co-dominant trees in those sites (Table 3).

Out of 64 sampling sites, S. robusta was found associated with one or more species in 49 sites, and was growing with 46 types of tree species in total. While L. parviflora and T. alata had an association with 44 and 42 types of species. S. robusta showed the highest association with all dominant species; with T. alata 42.2% frequency, with L. parviflora 35.9%, with S. anacardium 32.8%, with S. wallichii 21.9%, and with A. cordifolia 20.3%. A high association was also seen between T. alata and L. parviflora (28.1%). On the other hand, S. wallichii showed lesser association frequency (＜10%) except with the S. robusta. Among the dominant species, S. robusta had the widest distribution range and occurred from 200-800 m altitudes, while S. wallichii was basically a midhill element mostly distributed above 500 m.

Local knowledge and ethnic groups

The present study documented 82 species of medicinal plants and 76 wild edible plants. Altogether 30 types of diseases were found to be treated by phyto-therapy using the reported 82 plant species in the Churiya of east Nepal. Azadirachta indica (Neem) was reported to be used for the highest number (10) of diseases as antiseptic, analgesic, antispasmodic and antipyretic. The species was found also effective to cure diabetes, gastric, snake bite and fever due to typhoid, malaria, pneumonia. Three species, viz. Phyllanthus emblica (Amala), Aegle marmelos (Bel), and Phlogacanthus thyrsiflorus (Chuwa) were reported to be used for six different diseases. Similarly, Rauvolfia serpentina (Chandmaruwa), Butea minor (Bholetro) and Terminalia bellerica (Barro) were also found for multi-uses treating at least six different types of complaints and disorders.

Among the four major ethnic groups interviewed, Limbu reported a total of 64 medicinal plants (78.1% of the total plants reported for medicinal purposes) while Bahun-Chhetri informed 55 such species (67.1% of the total). Similarly, Rai and Magar informed 43 and 37 species respectively (Fig. 5). In average, each individual belonging to Limbu, Rai and Magar was familiar with less than four species of medicinal plants, while each individual belonging to Bahun-Chhetri was familiar with more than five such plants. The Limbus were the pioneering and still dominant inhabitants of the Churiya in East Nepal. Bahun and Chhetris, dominating social Hindu class have given them access to better their education. They had knowledge on Ayurved and other Hindu literature which contain a wealth of knowledge on plants and plant uses.

Distribution of butterflies

Altogether 35 species belonging to 28 genera and 8 families were enumerated from the present study site of the Churiya of eastern Nepal (Table 4). The documented species comprised 5.3% of the total species of butterflies known to Nepal. Genus Precis was found to be the most common with its four species, while Athyma, Danaus, Delias and Elymnias were also common in this part; the rest were single species genus. Figure 2 shows that the majority of recorded species come from Nymphalidae family which comprised 34.3% followed by Lycaenidae (20.0%), Pieridae (14.3%) and Satyridae (11.4%).

Considering seasonal change, the species richness of butterfly was found to increase from winter to spring season. Out of 35 species collected, 15 species (42.85%) were found in winter season and the rest in spring. A significant correlation was found between the species richness and the months indicating that the abundance of butterfly was positively affected by approaching warmer days and availability of more food that is the nectar. Similarly, the species richness of butterfly in the Churiya of east Nepal gradually increased up to 500 m, then it decreased. This tendency corresponds with the area of shrub-land in the studied area indicating the habitat preferences of the butterflies. However, the habitat loss is adversely affecting the butterfly diversity in Nepal.

Baseline information on birds

A total of 150 bird species were recorded totaling 2,374 birds during the field study. From the observed data, it was inferred that a species/time curve is of interest because it not only indicates species richness per unit time investment but also ascertains whether time investment in the field was adequate. Of the 255 observation, birds were predominantly observed either in forests (38%) or in farm lands (31%). Additional 24 observations were not included in the analysis as birds were seen flying out of a given habitat type. Majority of the birds were found in agriculture fields, especially at the edge of cultivation or degraded shrubberies.

All observed bird species were grouped into four categories to determine their status: endangered (E), vulnerable (V), rare and common. The first two categories (E and V) constitute 4% of the total specie (Table 5). Of the observed bird species, giant hornbill (Buceros bicornis), pale blue flycatcher (Muscicapa unicolor), and long-tailed broadbill (Psarisomus dalhousiae) are endangered. Species that are vulnerable were crow-billed drongo (Dicrurus annectans), pintail green pigeon (Treron apicauda) and large necklaced laughing-thrush (Garrulax pectoralis). The orange-breasted green pigeon (Treron bicincta) was considered rare. Some six habitat sites where all endangered and vulnerable species were found, were considered important for birds and these sites need to be monitored to check if these species continue to exist in such adverse settings.

ACKNOWLEDGMENT

The study was supported by Pro Natura Fund (Nature Conservation Society of Japan) to the first author. GIS facility and GPS were made available by the Resources Himalaya, Kathmandu. Sincerest thanks are to Dr T. Nakamura of Natural History Museum and Institute, Chiba and Prof. Dr M. Ohsawa of University of Tokyo for their kind cooperation.

All GIS work was conducted by Bidur Baidya. Giri Joshi and Bhesh oli did floristic survey. Daya Bhusal conducted butterfly survey. Gokarna Khanal conducted bird survey. We thank them all.

REFERENCES

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