Species maintenance in a dynamic landscape:Ecology of the Churiya (Siwaliks) in Nepal Himalayasネパールシワリク山地の生態学的研究:動的景相域における生物種維持管理

Authors著者名

Dinesh R.Bhujuディネス・ラジ・ブジュ, Pralad B.Yonzonプララッド・ヨンゾン

Affiliations著者所属

  1. Resources Himalaya

ABSTRACT要約

The ecological study of Churiya Hills was extended in central Nepal (area:5,475 km2) with grant support of Pro Natura Fund in 2002. The study, aimed at identifying key areas of the Churiya in conservation at larger landscape perspective, assessed time-series change in land use pattern in 1958, 1978 and 1992 using GIS. Field visits were guided by geographic projection grids, and accumulated information on biodiversity including forest structure and regeneration, tree species association, local knowledge on plant uses and bird distribution. It was found that the forests and agriculture area covered 74% and 8% of the total area respectively in 1958. In 1978, the forests decreased to 68%, while the agriculture land increased to 22%. The deterioration, however, did not worsen later. Perhaps, the protected areas and community forests (established after 1970s) contributed in ecological stability of the area. The forests of Churiya in central Nepal were estimated with a basal area of 33m2/ha and a density of 774n/ha, dominated by tree species such as: Shorea robusta, Terminalia alata, and Lagerstroemia parviflora. However, 78 out of 83 sampling plots contained cut stumps and/or lopped stems that shared nearly 20% of the total stems. S. robusta showed highest association with all dominant species and the association varied in different altitudinal ranges. 103 local residents were consulted to record the indigenous knowledge on plant uses. A total of 151 plant species were found used by the local people for medicinal and other purposes. During the field survey, a total of 170 species of birds were recorded representing 40 families. Strunidae was recorded as the largest family with 713 birds, and Laridae and Upupidae with only 2 species.


2002年度プロ・ナトゥーラ・ファンドの助成を受け、チュリヤ丘陵(シワリク山地)の生態学的研究の調査範囲をネパール中部(面積5,475km2)に拡大した。本研究は、広域な景観生態学的見地からチュリヤ丘陵における保全上重要な地域を特定することを目的とし、1958、1978、1992の各年のGISデータベースを用いて土地利用パターンの経時的変化を調べた。また、地形図上のメッシュを単位とした現地踏査を行い、森林の構造と更新、高木層の種組成、現地住民における有用植物の知識、鳥類の分布といった生物多様性に関わる情報を収集した。1958年には森林と耕作地の面積比率がそれぞれ74%と8%であったが、1978年には森林が68%に減少し、逆に耕作地は22%に増加していた。しかし、こうした環境の悪化はその後進行していない。おそらく、1970年代以降に設定された保護地域や村落共有林(community forests)が地域の生態学的安定性に寄与しているものと考えられる。ネパール中部のチュリヤ丘陵の森林は基底面積比が33m2/ha、幹密度が774/haと見積もられ、Shorea robusta(サラノキ;フタバガキ科サラノキ属)、Terminalia alata(シクンシ科モモタマナ属)、Lagerstroemia parviflora(ミソハギ科サルスベリ属)などが優占していた。しかし、83カ所中78の調査地点で切り株や刈り込まれた幹がみつかり、その頻度は総幹数の20%近くに達した。全ての優占種と最も高い頻度で共存するのはS. robustaであったが、群落の組成は標高帯によって異なっていた。現地住民103人から土着の植物の利用方法についての情報が得られ、合計151種の植物が薬用その他の目的に用いられていた。現地踏査の際に記録された鳥類は40科170種にのぼった。最も多かったのはムクドリ科で713個体が確認され、カモメ科、ヤツガシラ科はそれぞれ2種しか記録されなかった。

(推薦者:尾崎煙雄)

1. BACKGROUND

The Himalayas constitute the youngest and highest mountain chain on the Earth stretching over 3,000km. Its extremities which include topography and climatic features, have contributed to a rich biodiversity. But, biodiversity as such is not evenly distributed because the Nepal Himalayas within a width of over 150km, is comprised of 5 principle mountain ranges (Hagen 1961, LRMP 1986): 1) Himalayas, 2) High Mountains, 3) Mid Hills, 4) Churiya (Siwaliks) and 5) Lowland Terai. However, the Churiya have been over-shadowed in Nepal both in terms of biodiversity conservation and sustainable development as there is a major on-going move since the last 50 years to conserve the Himalayas.

The Churiya, a ravine landscape and the youngest mountain range in the Himalayas, extend from the Indus River in Pakistan to the Bramhaputra River in India (Jhingran 1981). The Churiya, also known as the Siwaliks, make the southernmost chain of the Himalayas and bridge the Gangetic subtropics in the south and the temperate forests in the north. Geologically, the Churiya consist of Tertiary unconsolidated fluviatile sediments range from relatively fine-grained gray wackes in the south (lower Churiya), through soft clay (middle Churiya) to very coarse sands and conglomerates (upper Churiya) in the north (Hagen 1961, Carson 1985). As Churiya is affected by soil erosion due to flash floods and landslides, it is estimated that the erosion rate ranges between 780 ~ 20,000 tones/km2/yr depending upon land use type (Mishra and Bista 1998).

The Churiya are equally rich in paleontology. Several Churiya fossils of later Tertiary have provided a basis for much of our present knowledge on the evolution of the Asian flora and fauna (Itihara et al.1972). The fauna obtained is particularly rich in vertebrates and includes a wide variety of groups including primates, carnivores, ungulates, elephants, rodents, birds, reptiles and fish that were the immediate ancestors of the present-day species (Sah et al. 1993). Living fossil plants such as Tree fern (Cyathea sp.) has also been reported from the Churiya of east Nepal (Bhuju and Yonzon 2000).

2. BIODIVERSITY ISSUES

There is a growing concern about the Churiya in Nepal whose sphere of influence are realistic for 3 robust reasons: 1) Once, contiguous Terai forests have fragmented beyond restoration; 2) Protected areas and their buffer zones are inadequate in large-scale conservation; and 3) Rapid deterioration of the Churiya needs to be addressed properly as they are the only land bridge for biodiversity conservation.

Of all the 5 physiographic zones in Nepal, Churiya has the highest percent forest cover (76%) and least percent area (13%) (area:19,134km2; forest cover:14,450km2), (LRMP 1986). Churiya's hardwood component (Shorea robusta and Terminalia spp.) is the highest in Nepal which comprised 37% of the total. However, for many policy makers, the Churiya have been more of an impression of dynamic geology and infertile dry land. Considering natural resources and other biological phenomena, they are neither stark and magnificent as the high mountain ranges nor they have the impressive subtropical flora and fauna. Given the low water table, high erodibility, sparse wildlife with absence of charismatic species and low productivity of the land, Churiya in the past, had little to offer against the backdrop of Terai, Mid Hills and the High Mountains. With the 45-years old hubbub of priorities elsewhere under the 9 different 5-year plans, the Churiya have been, obviously, a case of nation's neglect.

Primeval forests used to cover the Churiya, and they were practically uninhabited. That is no longer true now. Today, the Terai along with Churiya, supports 46.7% of the total population of Nepal (CBS 1995). In eastern Nepal, 400 settlements, mostly new, were observed in a small area of 779km2 (Bhuju and Yonzon 2000). The increased human encroachment and their associated disturbances such as livestock grazing and tree-felling have made the fragile landscape vulnerable.

In most of the classical schemes, life zone ecology of Nepal is described through distinct horizontal belts running parallel from west to east (Troup 1926, Stainton 1972, Numata 1983, LRMP 1986). However, some 118 distinct vegetation of western and eastern types that prevail in the country, a few interpretations have included phytogeographic descriptions by longitudinal divisions as well (Stearn 1960, Dobremez 1972, Ohsawa et al. 1986). The increasing elevation of Churiya from east (1,300m) to west (over 1,800m) is complemented by the corresponding rise of Terai plain from 90m average elevation in the east to 180m in western Nepal (Gurung 1989).

Baseline information to grasp 'hotspots' and 'bottlenecks' are vital to biological conservation and societal intervention for economic upliftment. However, gathering ecological information in the Churiya for its sustainable development, have had never been the first choice, except for a few ancillary surveys in support of other development activities. For example, a bibliography (ICIMOD 1996) clearly confirms this deduction as less than 4% of all published papers on Nepal's biodiversity, is attributed to the Churiya.

3. ECOLOGICAL DISCOURSE

In 1999, a 6-year ecological framework to evaluate the Nepal Churiya was conceptualized with a prospect of developing comprehensive ecological database to aid development processes that will not impair Churiya's environment and its ecological integrity (Bhuju 2000). However, international institutions were not found keen to support the scheme. Thanks to the support fund of Pro Natura Foundation-Japan and The Nature Conservation Society of Japan (PNF-NACSJ), 2 phases of the study has been completed covering the Churiya of eastern Nepal (length:103km; area:780km2) and central Nepal (length:235km; area:5,447km2). The study has assessed changes in land use pattern since 1958 to evaluate the impact of human encroachment and to identify the potential role of the Churiya forest in the context of landscape level conservation. The results of the study are compiled in 5 specific topics: 1) Land use pattern and its changes, 2) Floristic composition, structure and regeneration, 3) Tree species association, 4) Indigenous knowledge of local people on plants uses, and 5) Baseline information on the birds.

4. STUDY AREA

The present study area is extended between the latitudes of 27゜06' N to 27゜55' N and longitudes of 85゜12' E to 85゜30' E. It covers the Churiya range of central Nepal between the Bagmati River at Karmaiya in the east and Kanchan River near Butwal in the west. The length of the study area is about 235km from east to west and the width varies between 4km and 45km north to south. The Churiya demarcation is based on the geological map (Topographic Survey Branch, Department of Survey, HMGN 1984).

The land use change was determined with the help of GIS of 1958, 1978 and 1992 supported by ground truthing. The forest structure including regeneration and tree species association were evaluated by plot sampling while the local knowledge on plant use is assessed through interviews with traditional healers and local people. In addition, the distribution of birds was recorded by direct observation.

5. SAMPLING METHODS AND FIELD VISITS

The systematic sampling method described in the ecological study of the eastern Churiya (phase-I) (Yonzon et al. 2000) was followed for the present field survey. Field visits by principal investigator accompanied by 3 research associates and 2 local guides were completed in 2 phases beginning during February and March 2000. The study site was sub-divided into geographical mesh (grids) of latitude and longitudes. Reference plots (sampling grids) were ascertained with longitudinal variables by using random numbers and tables (Rohlf and Sokal 1969). In the field, the reference plots were located with the help of Global Positioning System (GPS 315 Magellan, USA).

In the study area, a total of 207 reference sites (grid points) were ascertained. Of the total sites, 155 were forest land and 52 were settlement or agriculture land. In the field, 83 reference sites of forest land were visited and sampled while 65 points were not accessible because of national park and/or steep terrain. Also, visit to some sites was not possible because of civil armed conflict. Beside these reference points, samplings were done in 132 spots en-route at every 100m elevational difference to determine tree species association.

Each reference site (grid) comprised one large quadrate of 25m×25m size for canopy and sub-canopy stratum, 2 sub-quadrates of 5m×5m for shrub stratum, and 4 small quadrates of 1m×1m for ground stratum. Sampling parameters included height, dbh, coverage, seedling and sapling density of plant species. Altitude, aspect, steepness, and any disturbance presence were also noted for each plot. At different altitudes en-route, canopy trees (>8 m) were identified and their dbh and height were noted.

Local knowledge on plant uses was collected by interviews with resident people who live near the reference sites. Distribution of birds was recorded in each sampling site and also en-route.

Figure1 Geographic reference Points (sampling sites) in the Churiya, central Nepal

Figure1 Geographic reference Points (sampling sites) in the Churiya, central Nepal

Table1 General Survey records of the sampling sites in the Churiya forests of central Nepal

6. RESULTS

(1) Landuse pattern and changes

GIS analysis of recent land use (1992) showed that nearly 2,000 settlements were scattered over the study area of about 5,475km2. Beside the East West Highway, Kanti Rajmarg, Narayangadh-Mugling and Tribhuvan Rajpath all connecting Kathmandu also pass through the Churiya. Hetauda, Narayangadh, Butwal are major business centers in the study area developed after 1960s. Beeshajari (a Ramsar site) and Satyawoti were 2 prominent wetlands in the area. The study area includes several important river systems and their valleys such as Narayani, Bagmati, Rapti (eastern), Arungkhola and Tinau.

Table 2 shows the change in land use in 1958, 1978 and 1992. Forest cover was the major characteristics of the Churiya in central Nepal. In 1958, the forest covered 74.11% of the total area. The 1958 data does not include 2 maps covering 6.79% of the area, which would further add the forested area. The forest area decreased by less than 6% in 1978 which did not further decline in 1992. Perhaps, the establishment of Royal Chitwan National Park (est. 1973; area: 932km2) and Parsa Wildlife Reserve (est. 1984; area: 499km2) are the key areas for ecological stability in the Churiya. The establishment of community forest in the buffer zone of the protected areas is expected to increase the forests. However, during the same period of 1958 and 1978, the agriculture land increased by 3 times (7.58%-22.40%).

Table2 Land use changes in three time series maps of 1958, 1978 and 1992 in the Churiya of Central Nepal

Table2 Land use changes in three time series maps of 1958, 1978 and 1992 in the Churiya of Central Nepal

Figure2 Land use pattern 1958 in the Churiya, central Nepal

Figure2 Land use pattern 1958 in the Churiya, central Nepal

Figure3 Land use pattern 1978 in the Churiya, central Nepal

Figure3 Land use pattern 1978 in the Churiya, central Nepal

Figure4 Land use pattern 1992 in the Churiya, central Nepal

Figure4 Land use pattern 1992 in the Churiya, central Nepal

A prominent observation in land use change was an increment of the patches. In 1958, a total of 178 patches of forests and 694 patches of agricultural land were observed. In 1992, the forest patches increased to 602 indicating a discrete fragmentation of the intact forests mainly for agriculture and human settlements. Similarly, the grasslands distinctly seen in 1958 near the Beeshazari lake were found converted into human settlements in 1978. The grasslands provided suitable habitat for the One-horned Rhinos (Rhinoceros unicornis), an endangered mammal listed in CITES appendix-I. In 1958, the grasslands covered an area of 286.59km2 (5.26% of the total area) which decreased to 119.88km2 in 1978, and further to 91km2 in 1992.

(2) Floristic composition and forest structure

Over 230 vascular plant species belonging to 90 families and 168 genera were recorded from the 83 sampling plots of the study area. Family Leguminosae included the highest number of species which included rare/threatened tree species like Dalbergia latifolia and Acacia catechu. Other families comprising high number of species were Compositae (13 species), and Moraceae (8 species). Thus, the study area in the Churiya had 41.7% of the total families and 11.0% of the total genera of the country. By habit, tree and sub-tree comprised the highest composition with 41% of the total species, followed by herbs (26%), shrubs (23%), climbers (15%).

Table3 Structural parameters of Churiya forests in central Nepal

The central part of Nepal conjoins the moister east and drier west zones of the country. Some of the vegetation types found in the present study reflect this fact. Natural patches of Pinus roxburghii, reportedly to occur in the hills above 900m, were recorded at the low level of 450m on the southern slopes in the Churiyamai of Hetauda. Similarly, as we move towards the west, Anogeissus latifolius were recorded instead of Lagerstroemia parviflora.

The forests of Churiya in central Nepal were estimated with a basal area (BA) of 33.1m2/ha and a density of 773.5n/ha. The predominant tree species at canopy stratum (height >10m) were Shorea robusta (relative basal area: 48.8%; relative density: 42.0%), Terminalia alata(RBA: 12.4%, RD: 4.2%), and Lagerstroemia parviflora(RBA: 3.2%, RD: 4.8%). These species also showed high frequency of occurrence. Out of 83 sampling plots, S. robusta occurred in 73 plots, T. alata in 51 plots, and L. parviflora in 49 plots. Beside these, Semecarpus anacardium also occurred quite frequently (freq. 53%).

The mean DBH (diameter at breast height) of S. robusta was 17.4cm, though at a few plots it had a maximum DBH of 105cm. As also indicated by the diameter class distribution, S. robusta had a large number of small size (DBH class 5~10cm) individuals specifically in the regenerating forests maintained by community forest users' groups. Similarly, T. alata had a mean DBH of 30.3cm and a maximum DBH of 145cm. The highest size was that of Ficus religiousa, a religious tree in the region, with a diameter size of 180cm. Both the protected areas and the community forests maintained by users' groups contained a good stock of trees and/or regenerating population. However, 78 out of 83 sampling plots contained cut stumps and/or lopped stems, mainly that of S. robusta (in 64 plots). The mean dbh size of cut stumps of S. robusta was 18.3cm (std dev: 12.3), an appropriate size for its timber use. The cut stumps shared 19.7% of the total stems of 5,006 trees and sub-trees (height: >4m) counted in the sampled plots.

The most common understory species in the study area was Phoenix humilis with the frequency of occurrence of 63.9%. The other common species were Clerodendrum viscosum (43.4%), Woodfordia fruticosa (43.4%), Mallotus philippensis (34.9%), Pogostemon benghalensis (34.9%), and Inula cappa (24.1). Eupatorium sp. occurred nearly in 50% of the plots indicating its invading capability in the forests and open areas as well. The ground coverage (<1m) was less than 20% in average, though some 15 sampling plots had over 70% ground coverage. The most common species in the ground stratum with frequency of occurrence >20% were Oplismenus sp., Flemingia sp., Crassocephalum crepidioides, Ageratum conizoides, and Cheilanthes arbomarginata. The poor record of the herb species could be because of the dry winter season of the survey.

(3) Tree species association

Over 68 tree species with a total basal area of 1,418,035cm2 were recorded from 139 sites en-route to the reference sites. Shorea robusta occurred at the highest frequency (80.58%) followed by Terminalia alata (65.47%), Lagerstroemia parviflora (39.57%), Semecarpus anacardium (31.65%), Schima wallichii (18.71%), Syzygium sp. (17.99%), and Adina cordifolia (17.99%). In Species association, S. robusta was found associated with one or more species in 110 sites, and was growing with 57 types of tree species in total. T. alata and L. parviflora had an association with 53 and 42 types of tree species in 91 and 55 sites, respectively. Table 4 shows that S. robusta showed highest association with all dominant species except with L. parviflora. But L. parviflora showed higher association with T. alata (37.86%) than S. robusta (32.86%).

Table4 Tree species association (%) in the Churiya hills of central Nepal

Table4 Tree species association (%) in the Churiya hills of central Nepal

It was found that the association between Shorea robusta varied with other major tree species in different altitudinal ranges. The association of S. robusta with Lagerstroemia parviflora and Schima wallichii gradually decreased with the increased altitudes while it did not show such change with others such as Terminalia alata, Semecarpus anacardium, and Adina cordifolia. This could be attributed partly to the distribution range of the species. Similarly, at some lower tropical Sal (S. robusta) forests in dry hills, Pinus roxburghii was found associated with S. robusta, and others. Similarly, Acacia catechu, a rivereine tree species of tropical zone, was also recorded on the hill ridge (Gaidatarsir, plot 19, ref. a1; Alt. 650m) associated with L. parviflora, S. robusta, and T. alata. Quercus floribunda, reportedly a species of high altitudes was also noted below 1,400m in association with Castanopis indica, C. tribuloides, S. wallichii, and Eurya accuminta at Pangre area (plot 43, ref. l16).

(4) Indigenous Knowledge

To record the indigenous knowledge on plant uses, 103 local residents (58 male and 45 female) were interviewed. The interviewee included 3 major ethnic group of the area, viz. Magar (30.1%), Tamang (20.4%), Bahun-Chhetri (20.4%), and also some minority indigenous groups such as Chepang and Kachhade. The Chepangs are elusive community living in remote hills of Chitwan, away from the modern life-style. The age of the interviewees varied from 16 to 72 years old. Local healers were consulted where possible. In total, 151 plant species belonging to over 65 different family were found to be used by the local people. Beside medicinal use, the plants were also had food, fodder, timber, and cultural values among the studied ethnic groups. The plants have been used to cure more than 63 different diseases including fever, diarrhea and dysentery, diabetes, fractured bones, cough and cold, cuts and menstrual disorder. The most and frequently used medicinal plants for specific ailments among the studied groups were: Terminalia bellirica, T. chebula, Porana sp., Azadirachta indica, Pogostemon benghalensis, Phyllanthus emblica, Woodfordia fruticosa, Viscum album, Cuscuta reflexa and Asparagus racemosus.

Several developmental programs are being undertaken by various national and international agencies in the area. However, they do not include programs to document ethno-botanical information from the tribal groups. The knowledge is mostly conveyed verbally from one generation to other. The allopathic practice with easily accessible medicines is gradually replacing the knowledge even in the remote mountain areas. It is feared that the knowledge may lost forever before its proper documentation and scientific study.

Table5 Ethnic groups consulted in the Churiya of central Nepal

Table5 Ethnic groups consulted in the Churiya of central Nepal

Table6 Most common plant species used by local people in the Churiya of central Nepal

Table6 Most common plant species used by local people in the Churiya of central Nepal

(5) Bird Distribution

A bird survey was conducted from mid February till March 2003 in the Churiya of central Nepal covering Narayani and Lumbini zones. The sites include Chitwan and Lumbini which provide habitats for winter migratory birds. A total 186.5 man-hours were spent in 63 survey sites. The survey areas covered different habitat types such as; sal (Shorea robusta) forest, mixed forest, bushes, grassland, highways, agriculture land, river as well as lake.

A total of 170 species birds were recorded from the study area representing 40 families. Strunidae was recorded as the largest family with 713 birds and Laridae and Upupidae with only 2 birds. Common myna, Acridotheres tristis was observed as the most common bird species of that region totaling altogether of 441 numbers of birds. More species could have been found but limited time and large survey areas were 2 most limiting factors that constrained the survey. Highest number of birds, irrespective of species richness and diversity, were seen in agriculture land, sal forest and mixed forests (Figure 5).

Figure5 Observed bird numbers. in different land use / habitat types

Figure5 Observed bird numbers. in different land use / habitat types

7. CONCLUSION

The study has assessed changes in land use pattern since 1958 to evaluate the impact of human encroachment and to identify the potential role of the Churiya forest in the context of landscape level conservation. Although the Churiya in central Nepal have wide spread human settlements and associated disturbances, some forest sites (beside the protected areas) still appear to be the remnants of what they looked like some 30 years back. Over 60% of the sampled sites contained more than 25 trees (400n/ha) and with basal area (of >20m2/ha) at canopy and sub-canopy stratum (height >4m). Given the resilience of the Churiya, these sites are reservoir of hope for species recolonization linking not only the protected areas but also the Terai forests of the south with that of Mahabharat in the north.

ACKNOWLEDGEMENTS

The study was a part of the initiative taken up by the Resources Himalayas in preparing an ecological database on Nepal Churiya. The present research study, covers the Churiya of central Nepal, was supported by Pro Natura Fund. Cooperation extended by Mr. Kemurio Ozaki, Natural History Museum and Institute, Chiba is highly appreciated.

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