Life Zone Ecology of the Bhutan Himalaya

LIFE ZONE ECOLOGY OF THE BHUTAN HIMALAYA

Edited by

M. OHSAWA

Laboratory of Ecology, Chiba University

1987 Scanned from original by ISRIC - World Soil Information, as ICSU World Data Centre for Soils. The purpose is to make a safe depository for endangered documents and to make the accrued information available for consultation, following Fair Use Guidelines. Every effort is taken to respect Copyright of the materials within the archives where the identification of the Copyright holder is clear and, where feasible, to contact the originators. For questions please contact soil.isrictawur.nl indicating the item reference number concerned.

Life Zone Ecology of the Bhutan Himalaya Published March 1987

Editor: Dr. M. Ohsawa, Associate Professor of Ecology Laboratory of Ecology, Faculty of Science, Chiba University 1-33, Yayoicho, Chiba 260, Japan

Published with The financial support of the Grant-in-Aid for Scientific Research(Grant-in- Aid for Overseas Scientific Survey) of the Ministry of Education, Science and Culture of Japan. Project No. 60041009 and 61043007. CORRECTION 193 16-17 "To the contrary" should read "On the contrary". OHSAWA, M. VEGETATION ZONES IN THE BHUTAN HIMALAYA ITINERARY Page Line Fig. 2: in climate diagram below left, place name 312 6 "24: Dali( 1 500m;U:30)" should read "SHRBHANG" should read "SARBHANG". "24.: Nagor(7:45)-Dali(1500m;14:30)".

16-17 "Abies densa (in 52 plots) and Quercus griffithii (4.8)" should read: Abies densa (in 48 plots) and Quercus griffithii (46). Fig. 5: legend line 3, "upper(shaded) or lower limit" should read "upper or lower(shaded) limit".

19 Fig. 2: a box showing vertical range but missing species name should read "Bamboo".

37 25-26 "at around 1900 m on Mount Kerinci, Sumatra" should read "at around 1900 m".

58 Fig. 15: in the figure "CAINPÜR" should read "CHAINPUR".

60 Photo 25: legend line 3, "for trunk" should read "trunk for".

NÜMATA, M. VEGETATION, PLANT INDUSTRY AND NATURE CONSERVATION IN BHUTAN 139 Photo 6: legend line 2, "marked ree" should read "marked tree".

OKAZAKI, M. SOILS OF THE BHUTAN HIMALAYA

151 4 "amongthem" should read "among them". 157 Photo 5: legend "Umshelb" should read "Umshalbi".

159 15 "5-6 + 0.47" should read "5.6 + 0.47".

23 "us/cm" should read "us/cm". 27 "Alpinemeadow" should read "Alpine meadow".

32 "organiccarbon" should read "organic carbon".

EGUCHI, T. TOPOGRAPHIC FEATURES IN THE CENTRAL PART OF THE BHUTAN HIMALAYA

192 26 "many" should read "mainly".

1 CONTRIBUTORS

EGUCHI, Takashi Department of Geography, Faculty of Science, University of Tokyo, Hongo, Tokyo 113, Japan

NUMATA, Makoto Shukutoku University, Daiganji, Chiba 280, Japan

OHSAWA, Masahiko Laboratory of Ecology, Faculty of Science, Chiba University, Yayoicho, Chiba 260, Japan

OKAZAKI, Masanori Laboratory of Soil and Aquatic Environment, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183, Japan

TSUCHIDA, Katsuyoshi Laboratory of Nature Conservation, Faculty of Liberal Arts, Shinshu University, Matsumoto, 390, Japan PREFACE

This is a preliminary report of our nature trekking in Bhutan, in 1985. Some of our members, Numata and Ohsawa had visited Bhutan in 1984, and were impressed very much with its nature. In 1985, the following five members visited Bhutan to observe the nature of Bhutan on a wide scale. The members and their main field of study are as follows: Dr. M. Ohsawa, Leader, -Forest ecology Dr. M. Numata, -Weed and grassland ecology Dr. K. Tsuchida, -Grassland ecology Dr. M. Okazaki, -Soil science Dr. T. Eguchi, -Climatology Since 1963, Chiba University has been carrying out Himalayan studies in East Nepal under the leadership of Prof. Emeritus M. Numata. Four expeditions in 1963, 1971, 1977, and 1981, were all concentrated in East Nepal. The temperate vegetation of East Nepal is very similar to that of Japan as is understood by the fact that both of the regions are in the same floristic region, the Sino-Japanese region. Bhutan lies between East Nepal and Japan and if the distance also has some meaning to the similarity, Bhutanese vegetation may have more similarities with Japanese vegetation. Moreover the nature of Bhutan is still well preserved and we are able to obtain proper information about Himalayan vegetation. We are greatly indebted to the VIPs of Bhutan, Lyonpo Sangye Penjor, Dasho late Lam Penjor, Dasho C. Dorji, Dasho K. Letho, Dasho Dorji Tenzing, Dasho Tseten Dorji, and Dasho, K. Nishioka for their valuable advice and help with our trekking. Also to Mr. Jigme Tshultim of Bhutan Tourism Corporation and his staff who helped us very much in many ways. We also thank to Y. Imaeda and T. Tsugawa who also helped us very much at Thimphu. We have a strong desire to cooporate with the Bhutanese people to study and conserve the last and most valuable Himalayan nature in Bhutan. I hope that this will promote future cooperation between the peoples of Bhutan and Japan.

March 1987 Masahiko Ohsawa CONTENTS

Preface Part I. VEGETATION AND CONSERVATION

Vegetation Zones in the Bhutan Himalaya, by Masahiko Ohsawa j Grassland Vegetation and Succession in Central Bhutan, by Katsuyoshi Tsuchida 73 Observations of Farmlands and Pastures in Central Bhutan, by Makoto Numata 1 17 Vegetation, Plant Industry and Nature Conservation in Bhutan, by Makoto Numata 133 Part II. SOILS AND TOPOGRAPHY Soils of the Bhutan Himalaya, by Masanori Okazaki 145 Topographic Features in the Central Part of the Bhutan Himalayas, by Takashi Eguchi 185 Part III. CLIMATE Synoptic Analysis of Temperature, Precipitation and Moisture Conditions in the Bhutan Himalayas, by Takashi Eguchi 209 Synoptic- and Meso-analysis of Climatic Conditions in Bhutan

from September through November in 1985, by Takashi Eguchi 249

Part IV. MISCELLANEOUS

List of Plants collected in Bhutan, by Katsutoshi Tsuchida 281 Itinerary 305 Part I

VEGETATION AND CONSERVATION M.Ohsawa(ed.), Life Zone Ecology of the Bhutan Himalaya.1987. Chiba University.

VEGETATION ZONES IN THE BHUTAN HIMALAYA

M. OHSAWA

Laboratory of Ecology, Faculty of Science, Chiba University, Chiba 260, Japan

ABSTRACT

The vegetation zones in the Bhutan Himalaya are studied based on 363 plot data collected by plot sampling methods along the trekking route ranging from 100 to 5200 m in altitude. About 90 dominant and co-dominant trees were identified in all the forest plots. The three groups of dominant trees having different habitat requirements, i.e., mesic, xeric, and scree or ravine trees, are distinguished. The mesic dominants show a clear segregation of distribution along altitudes, and are the climax dominants of respective zone. The xeric dominants are extrazonal in their distribution, and scree or ravine species are sporadic. Vegetation zones can be divided into six zones (five forest and one scrub) on the basis of higher frequency of distribution limits at certain altitudes. Floristic similarities of the dominant species composition in every 200 m altitudinal segments also show six clusters of forest types from lower to higher altitude; Tetrameles- Pterospermum-Phoebe type, Schima-Lithocarpus-Castanopsis type, Castanopsis-Quercus-Acer type, Tsuga-Picea type, and Abies type, and above forest limit, Rhododendron scrub type. These six zones correspond to the following climatic zones: tropical, subtropical, warm-temperate, cool-temperate, subarctic (cold-temperate, subalpine), and arctic (alpine) zone. The principal pattern of zonation is equivalent to that of East Nepal.

-1- The six zones are further grouped into two pan-zones; i.e., 1) tropical pan-zone, including tropical, subtropical, and warm- temperate zones, and 2) temperate pan-zone, including cool- temperate, subarctic (cold-temperate), and arctic (alpine) zones. The boundary between two pan-zones at 2500 m corresponds to that of two floristic regions, Paleotropis and Holarctis, on the southern slopes of the Himalaya. In the Bhutan Himalaya, these two floristic regions are represented by contrasting life forms of principal dominants, i.e., evergreen broad-leaved trees in tropical pan-zone and conifers in temperate pan-zone. Within the temperate pan-zone, the equivalent forest zones between Himalaya and Japan are distributed under the similar temperature conditions. But within tropical pan-zone, the similar temperature conditions between the Himalaya and Japan, flourish in different zonal forests. The vegetation in the dry valleys is a binding route for some common species both east and west of the Himalaya.

INTRODUCTION

The Bhutan Himalaya is the main part of the East Himalaya, which span ca. 700 km from Mount Namcha Barwa to the Tista river in Sikkim (Mani, 1973). The topography is composed of rather simple slopes facing south dissected deeply by seven big rivers flowing south, and in the middle part of these rivers, dry valleys are developed at different al- tiudinal ranges by valley. The land is covered by dense natural forests amounting to 64 % of the total land area (47000 sq. km). The percentage is similar to that of Japan, but the qualities of the forests are different in many respects. For example natural and semi-natural forests comprise more than 99 % of the total forested area of Bhutan (C. Dorji, 1983), while that of Japan is about 30 % of the forested area. Undoubtedly, such forest resources in Bhutan are valuable not simply as timber but through their vital functions of maintaining natural environment and human welfare. As has been discussed by many researchers since the pioneering

-2- work by Hooker (1906), the Himalaya itself is the transitional region, between tropical and temperate region of the northern hemisphere, and between dry west and humid east of the south slope of the Himalaya (Schweinfurth, 1957; Troll, 1967; de Laubenfels, 1975; Meusel, 1971; Meusel and Schubert, 1971; Ohsawa et al., 1986; Ohsawa, 1987). Most of these discussions are based on research made in the Himalaya westward from Sikkim, except some research of the Assam Himalaya done by Indian scientists including some previous researches by British colonials. In the Nepal Himalaya, the transition zone of vegetation between tropical and temperate zone on the south slopes is heavily disturbed by cultivation or degradation by human activities, and it is rather difficult to investigate the boundary of vegetation between tropical and temperate zones. However, the forests of those parts are still continuous in some parts of Bhutan. There is an urgent need for study of the structure and dynamics of these transition zones in natural state in the Bhutan Himalaya. Another point is that dry valleys in the Bhutan Himalaya are well developed and are in the middle portion of such dry valleys which extend from the dry West Himalaya to the Heng tuan shang valley, Yun- nan in the East. The vegetation of dry valleys in Bhutan may give some insights into gradatiónal changes of xeric type vegetation from west to east in South Asia. Moreover Bhutanese vegetation has many similarities with those of Assam and S.W. China including Yunnan and Sichuan, where the diversification of modern plants is most intensive, and réfugia for epibiotics are most concentrated. The influences of the present flora in this cen- ter may be observed more strongly in the Bhutan Himalaya than the rest of the Himalaya in the west of Bhutan. This characteristic situation of Bhutanese nature has brought greater diversity in its vegetation. And intensive study of Bhutanese vegetation may give us a clearer picture of the structure and diversification of the Eurasian vegetation. The objective of this study is to know the basic pattern of altitudinal zonation of vegetation in the Bhutan Himalaya mentioned above in a broader view. This is only a preliminary overview of Bhutanese vegetation zonation, because identification of specimens is still incomplete. Further analysis of the collected data will be made. I would like to thank many people in Bhutan, especially Lyonpo

-3- Sänge Penjor, Dasho late Lam Penjor, Dasho C. Dorji, Dasho K. Letho, Dasho Dorji Tenzing, Dasho Tseten Dorji, and Dasho K. Nishioka for their valuable advice and help in our nature trekking. Mr. Jigme Tshultim and his staff also helped our trip in the field. I am greatly indebted to the people of Bhutan, without those kind cooperation and help, we would not have been able to achieve anything.

STUDY AREA

Bhutan lies on the southern slopes of the Himalaya ranging approximately between latitudes 26.45 and 28.10 north and longitudes 88.45 and 92.10 east. Altitudinal ranges are from around 100 m at Indian border to more than 7500 m at Tibetan border. Field survey was conducted in Western and Central Bhutan. The study area ranged from the lowest altitude at Manas, 140 m a.s.l. near Assam to the highest at Gophu La, 5320 m near Tibet, including such places as Nikkachu, Tampeytso, Tsochena, Duersachu, Jakar, Mongar, Nagor, Panbang, Pangtang, Tshaidang, Dagphey, Shemgang, Kurutang, Punakha, Thimphu and Paro (Fig. 1). One of the characteristic features of Bhutanese vegetation is the occurrence of dry valleys along big rivers. Below the forest limit, two kinds of dry valleys which differ in altitudinal ranges and therefore having different vegetation, could be identified: upper dry valley at around 2500 m and lower dry valleys at around 1000 m (cf. Fig. 8). Available climatic data on several sites in Bhutan were illustrated by using the method of climate diagram of Wal- ter et al. (1975) (Fig. 2). Of the six sites, Wangdiphodrang and Mongar have a rather long dry season of six to seven months. These pattern of climate diagram correspond well to those of the dry monsoon forest types in India (Walter, 1973). However, most of the mountain slopes are rather humid with ample rainfall, though there is little available climatic data so far for these sites.

FIELD METHODS

As many natural or semi-natural plant communities as possible were

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Fig. 2. Topography of Bhutan and Walter's climate diagram at six locations in Bhutan. sampled along our trekking route. In total 363 plots were sampled for studying the distribution of natural or semi-natural forests along altitudinal and humidity gradients in the study area including some scrub communities above the forest limit. The plant community types were characterized by their dominant species and were named as the dominance type. Most of the field measurements were carried out by a method of reconaissance survey of vegetation ("the survey method", Oh- sawa et al., 1986). This is a method of quick sampling of a homogeneous vegetation unit (dynamic unit, Ohsawa, 1981) having the same causal factors of community formation, and is suitable for grasping the whole scale pattern and structure of vegetation in a wide area like the Bhutan Himalaya as a whole. The habitat conditions were recorded in the following items at each sampling site: plot number, date, locality, altitude, exposure, inclination, plot size, areal extent of the vegetation type, topography, and miscellaneous records of habitat conditions, such as disturbances, natural or human. At each sampling site, after filling the above proforma for site description, tree inventory of various accuracy levels was conducted according to available time for survey and the conditions of the community. At the most accurate level, all trees in a certain area (e.g., 400 sq. m) were measured in DBH (diameter at breast height), in H (tree height), the position of the trees was mapped and then crown projection map was prepared. Then the ground vegetation was recorded in its dominant species with H (height) and C (coverage) measurements. If the time available was insufficient, survey was made by measuring DBH of the canopy trees (more than 10 trees), or by counting the number of trees when the DBH showed not much difference in an area determined ar- bitrarily. In some cases only the dominance percentages of trees were determined by ocular observations. In all these cases, dominance of trees was calculated in the laboratory as a percentage against total abundance of all species. Besides the survey method sampling of forests, altitudinal distribution of forest trees was recorded at as many sites as possible to grasp the altitudinal distribution of each trees. Altitude of each site was measured by using two altimeter (Thommen, Type 2000). Field recordings of altitude were done by using two altimeters and the readings were checked with map readings. Figure

-7- 3 shows the linear regression of altimeter readings to map readings of altitude. Fairly constant deviations of altimeter readings from the map readings (82 m) due to wrong setting of altimeter at Thimphu. Therefore the following records of altitude were done by adjusting map readings. Field survey was conducted from September to November, 1985. Nomenclature follows mainly Hara et al. (1978, 1979, 1982) and Grierson and Long (1984, 1983). However, for identification of specimens, the following floras were consulted: Hooker (1872-1897, Indian reprint, 1973), Hara (1966, 1971), Ohashi (1975), Institute of Botany, Academia Sinica (1972-1976), Institute of Botany, Kunming (1979, 1983), and Wu (1986).

VERTICAL DISTRIBUTION OF FOREST TYPES

The 363 forest plots were sampled in altitudinal ranges of 102 to 5142 m in Western and Central Bhutan (Fig. 4, a complete list of plots is given in Appendix 1). There were 91 dominant tree species sharing these plots. The most frequent was Abies densa (in 52 plots) and Quer- cus griffithii (48). Table 1 indicates dominant species in an order of their frequency among the 363 plots with their distribution ranges. The species with higher frequency may be commoner dominants in the area studied. These dominants can be divided into three groups according to their habitat preferences, i.e., 1) mesic species, 2) xeric species, and 3) species which grow on scree slopes or ravines. The species included in a mesic group are the dominant trees of the so-called climatic climax forest at respective altitudes and are, from higher to lower altitudes, the shrubby species in alpine zone, and below forest limit, Juniperus recurva, Juniperus squamata, Abies densa, Tsuga dumosa, Picea spinulosa, Acer campbellii, Quercus lamellosa, Litsea elongata, Castanopsis hystrix, Quercus semiserrata, Schima wallichii, Castanop- sis tribuloides, Lithocarpus elegans, Engelhardtia spicata, Quercus glauca, Castanopsis indica, Phoebe cathia, Terminalia myriocarpa, Tetrameles nudiflora, and Phoebe hainesiana. These species can be grouped into six according to their altitudinal distribution as will be analysed in detail in the next section (cf. Figs. 6 & 7). The xeric group is composed of species found in dry valleys and/or Table 1. Distribution ranges of dominant species in an order of the value of frequency among 363 plots.

DOMINANT SPECIES FREQUENCY MAXIMUM ALT.MINIMUM ALT. DIFF RI in Abies densa 48 4032 2982 1050 Bombax malabaricum 3 722 182 540 Q. griff ithii 46 2482 722 1760 Pterospermum acerifolium 3 722 102 620 Pinus roxburght i 35 1882 722 1160 Bauhinia purpurea 3 352 162 190 Tsuga 33 3322 2382 940 Oalbergia cultrata 3 182 102 80 Schima wall ichii 31 2072 1002 1070 Sorbus foliolosa 2 4232 3952 280 C. tribuloides 25 2072 252 1820 Spiraea canescens 2 4212 4132 80 P. vallichii 22 3482 2362 1120 Cupressus" corneyana 2 3402 3082 320 L ithocarpus elegans 18 2262 862 1400 Larix grfffithiana 2 3362 3242 120 Picea spinulosa . 16 3462 2592 890 Litsea elongata 2 2452 2232 220 Q. semecarpifolia 16 3122 2212 910 Q. semiserrata 2 2262 1892 370 Q. lanata 15 2482 1372 1110 Neocinnamomum caudatum 2 1282 1172 110 Q. lamellosa 13 2532 2002 530 Erythrina 2 1222 1132 90 C. hystrix 13 2352 1822 530 Albizzia 2 1172 1152 20 Engelhardtia spicata 13 1882 1132 750 Potent ilia biflora 1 4932 4932 0 Juniperus recurva 11 4372 3402 970 Lonicera obovata 1 4622 4622 0 Q. glauca 11 1682 852 830 Hyricaria rosea 1 4462 4462 0 Rh. setosum 10 4802 4302 500 Cotoneaster microphyUa 1 4232 4232 0 Acer campbellii 10 3142 2062 1080 Rlbes orientale 1 4212 4212 0 Rh. anthopogon 9 4882 4252 630 Acer pectinat urn 1 3362 3362 0 Rh. campanulatum 9 4332 4002 380 Hydrangea heteromalla 1 3362 3362 0 C indica 9 1632 . 252 1380 Magnolia campbellii 1 2872 2872 0 Rh. nivale 8 5142 4302 840 Taxus baccata subsp. wallichii 1 2872 2872 0 Bamboo 8 1172 222 950 Cornus 1 2762 2762 0 8etula utilis 7 3472 3112 360 Ilex macropoda 1 2762 2762 0 Rh. arboreum 7 2962 1562 1400 Jug lance 1 2212 2212 0 Q. semiserrata 7 2872 2232 640 Prunus cornusa 1 2212 2212 0 Lyonia ovalifolia 7 2082 1462 620 Persea rubusta 1 1932 1932 0 Duabanga sonneratioides 7 832 252 580 Neolitsea foliosa 1 1932 1932 0 Juniperus squama ta 6 4932 3972 960 Carpinus 1 1882 1882 0 Terminaüa myriocarpa 6 1082 212 870 Elaeocarpus 1 1852 1852 0 Tetrameles nudiflora 6 722 102 620 Ilaesa chisia 1 1832 1832 0 Potent ilia fruticosa 5 4932 4462 470 Melastoma 1 1832 1832 0 Rh. Lepidotum 5 4632 4132 500 Rhus javanica 1 1832 1832 0 Alnus nepalensis 5 2192 1392 800 Bassya butyracea 1 1222 1222 0 Betula alnoides 5 1152 882 270 Unknovn 1 1222 1222 0 Berber is 4 4932 4222 710 Callicarpa arborea 1 1172 1172 0 Salix 4 4232 2762 1470 Sloanea sterculiaceus 1 1032 1032 0 Persea clarkeana 4 2552 2282 270 Ficus 1 1012 1012 0 exbucklandia populnea 4 2022 1882 140 Acer oblongum 1 882 882 0 Lithocarpus fenestratus 4 1982 1222 760 Mallotus phillipinensis 1 852 852 0 Astragallus candolleanus 3 4932 . 4702 230 Teroiinthia paniculata 1 722 722 0 Juniperus indica 3 4082 3932 150 Bakkarin shin 1 182 182 0 Populus ciliata 3 2862 2682 180 Sap i uni insigne 1 182 182 0 Lauraceae sp. 3 2262 2002 260 Lagerstroemia parviflora 1 162 162 0 Acer sterculiaceum 3 1452 1162 290 Phoebe hainesiana 1 162 162 0 Phoebe cathia 3 1242 1032 210 6000

5000

4 000 -.

3000 CO O S 1 1 Q 2000 OS O I 1000 MA P

1000 2000 3000 4000 5000 6000

ALTIMETER READINGS, m

Fig. 3. Regression between altimeter readings in the fields and map readings of altitude. The regression equation was Y = 1.01 X + 82 (r=1.00). Plot No.

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Fig. 4. Trekking route (broken line) and locations of some sampling sites. on ridges, such as Quercus semecarpi folia, Q. griffithii, Pinus wallichii, Pinus^ roxburghii, and Q. lanata, and there are many other shrubby species such as Cotoneaster microphylla, Woodfordia fruticosa, Terminthia paniculata, Phyllanthus emblica, and Jasminum officinale which dominate in the dry valleys. Most of them are wide-ranging species having altitudinal ranges of more than 1000 m except Quercus semecarpifolia which has a range of 660 m. The xeric species can be grouped into three, i.e., 1) cool-temperate group such as Pinus wallichii and Quercus semecarpifolia 2) subtropical to warm-temperate group such as Quercus griffithii and Q^ lanata, and 3) subtropical group such as Pinus roxburghii and the shrubs mentioned above except Cotoneaster microphylla. The species in the group found on scree slopes or ravines are, Larix griffithii, Alnus nepalensis, Acer sterculiaceus, Bamboo, Betula alnoides, and Duabanga sonneratioides. Some dominant species have a very wide altitudinal range, e.g., Quercus griffithii in a range of 1760 m, Lithocarpus elegans 1400 m, Rhododendron arboreum 1400 m, Castanopsis tribuloides 1040 m, C^ indica 1380 m, Pinus roxburghii 1160 m, Pinus wallichii 1120 m, Quercus lanata 1110 m, Schima wallichii, 1070 m, etc. Table 1). Most of these wide-ranging species belong to the xeric group. Some of these trees also have wide distribution in the other part of the Himalaya. Cowan (1929) reported that Schima wallichii has also a very wide distribution range of 1800 m in the Kalimpong area. According to our observations in East Nepal, pioneer and serai trees, such as Alnus nepalensis (2000 m), Rhododendron arboreum (2400 m), and Betula alnoides (2200 m), have a generally wide ranging distribution, but some climax trees such as, Cas- tanopsis tribuloides (1920 m), Schima wallichii (1700 m) also show a wide distribution.

SEGREGATION OF ZONES BASED ON FOREST DISTRIBUTION

Figure 5 illustrates the distribution ranges of the dominant species. The arrangement of dominant species is in an order of maximum altitude from the highest in the left to right of the figure. The distinction between mesic, xeric, and scree or ravine species was made by differen- tiating each line. The histogram in the right side of the figure indicates

-12- I -ei- I I I A L T I I U D E I Rhododendron Juniperus squamata 4 Potentilla fruticosa . Berberfs sp Astragallus candolleanus Rhododendron anthopogon » *~->. >- I Rhododendron setosum »*t-. 1- Rhododendron lepidotum » 1 11 —< Rhododendron campanula t um %, ,, n» Juniperus recurva »,,.,, , Juniperus indica Abies densa Pinus wallichii I ^* Picea spinulosa Betula utilis Cupressus corneyana O=O Larix griffithii Tsuga dumosa Acer canpbellii I ' • nt-i m -t--n-# Quercus semecarpifolia I — • Rhododendron arboreun t-n—. • Quercus semiserrata | i O Magnol ia camp be Uil • Taxus baccata subsp. uallichiana 1 O O Populus ciliata • Persea clarkeana i—(—• Quercus lamellosa I 3 et S 2 I--O Quercus griffithii —• Quercus 1 ana ta = 2. 3 —• Litsea elongata - S , Castanopsis hystrix Lithocarpus elegans f | = | Lauraceae sp- 1 I • ' • Alnus nepalens is " o g" ? -O Lyonia ovalifolia 1 -• _ -i o y SchintS a uallichii ' « Castanopsis tribuloides Exbucklandia populnea „ 3 Lithocarpus fenestratus a' ^ ra • Persea robusta I —• Pinus roxburghii 2 5 —• Engelhardtia spicata Quercus glauca ' ll , Castanopsis indica Acer sterculiaceum Neocinnamomum caudataum

C mi n bl e 3be r o I o Phoebe cathla o ' Erythrïna sp. 3 c — o 3 BAMBOO CD reci d c re 3 Albizzia sp. c Betula alnoides c o re Terminalia myriocarpa

it u — (rt to' G' • Duabanga sonneratioides I -in e Ina ! 3 ee s c. Te trameles nudiflora S a -• Bombax ceiba Pterospermum acerifollum Bauhinia purpurea Di lbergia sisso Phoe be hainesiana 1 I I I I I I I I the number of species having upper or lower limit in respective altitudinal segements (200 m). According to this diagram, several vegetational boundaries, where the limits for the dominant species concentrate, can be observed at around 200, 1000, 2000, 3000, 3600, 4200, and 5000 m. Figure 6 illustrates floristic similarity of dominant species by using Jaccard's community coefficient between every 200 m altitudinal segments. At least six clusters of altitudinal segments were recognized from this dendrogram; 1) 100-800 m characterized by Tetrameles, Pterospermum, Phoebe and Duabanga as the principal dominants, 2) 800- 1800 m by Castanopsis, Schi m a, Lithocarpus, and Pinus, 3) 1800-2600 m by Quercus, Castanopsis, and Acer, 4) 2600-3600 m by Tsuga, Picea, and Pinus, 5) 3600-4200 m by Abies densa, 6) more than 4200 m by Rhododendron. The dendrogram also illustrates two larger groups of clusters separated at around 2600 m. The lower one below 2600 m is dominated mostly by evergreen broad-leaved trees of tropical to warm- temperate nature except two deciduous species, Acer campbellii and Quercus griffithii at the 1800-2600 m cluster. On the other hand, another group above 2600 m has conifers as the dominant up to the forest limit at 4200 m, and above this limit Rhododendron scrub dominates. Figures 7a, b, and c illustrate altitudinal ranges and the part where the said species become a dominant for the principal dominants, for mesic, xeric, and scree slope sites, separately. The distribution ranges of mesic trees fit to the zones defined by boundaries mentioned above. Only a few dominants occupy two zones, such as Castanopsis indica for both tropical (only very limited sites) and subtropical, Quercus semiserrata and Acer campbellii both warm- and cool-temperate zones. The distribution of Tsuga dumosa and Picea spinulosa also occupy both cool-temperate and subarctic (cold-temperate) zones. But in the case of these two species, the pattern of zonal distribution is different, i.e., at the transition zone between cool-temperate and subarctic zones. On the other hand, the distribution of xeric dominants is extrazonal, those species range into two or three zones of the mesic dominants (climax zonation) (Fig. 7b). However their upper or lower limits often coincide with the boundary for mesic dominants, e.g., the upper limit of Pinus roxburghii is at the upper limit of the subtropical zone, the upper limit of Quercus lanata and Q^ griffithii is at the upper

-14- 26 5000-•5200 25 4800-•5000 Rhododendron nivale 24 4600-•4800 Rhododendron setosum 23 4400-•4600 Rhododendron anthopogon 22 4200- 4400 21 4000- 4200 20 3800- 4000 Abies densa 19 3600-3800 17 3200- 3400 3600 Tsuga dumosa 18 3400- Picea spinulosa 16 3000- 3200 15 2800- 3000 Pinus wallichii 14 2600- 2800 13 2400-•2600 Quercus lamellosa 12 2200- 2400 Acer campbellii 11 2000-•2200 Quercus griffithii 10 1800- 2000 Castanopsis hystrix 9 16UU-T800 Castanopsis tribuloides en 8 1400- 1600 Schima wallichii I 7 1200- 1400 Lithocarpus elegans 6 1000- 1200 Pinus roxburghii 5 800- 1000 3 400- 600 Tetrameles nudiflora 4 600- 800 Pterospermum acerifolium 2 200- 400 Phobe hainesiana 1 100- 200 Duabanqa sonneratioides 100 0 P ALTITUDE DISIMILARITY PRINCIPAL DOMINANTS

Fig. 6. Dendrogram showing similarities between dominant species composition at every 200 m altitudinal segments. Principal dominants are common dominants in each cluster. -91-

ALTITUDE,

ALPINE DWARF SCRUB f i i ; : Juniperus squama ta | > i Rhododendron campanulatum ' ' r Juniperus recurva I i 1 Jumperus indica f- Abies densa J

|—1 Picea spinulosa

I J Cupressus corneyana F JH Tsuga dumosd < CD cr CD CD CD CD o 1 Acer Campbellii tati o CD o a *< Cl 3 2. us semiserr3ta 00 CD O CD -i i boun d ominan i O CL nge s o f 03 o f dis t I j | Percea ctarkeana o 3 —I rH Quer eus lame II osa ro [ | Litsea elongata tu e00 , n ibu t -< o 3

(se e te x :io n a s si c do m CD I 1 Castanopsis hystrix th e fo r an d 3 5 lithocarpus elegans

11 I Lauraceae sp. o CD

Cn ant s w t . Up p

o mino r Schi ma wallichii 3 H Castanopsis tribuloides CT er / O o CD [ | Exbucklandia populnea yr o CD 3 o CD •o j Lithocarpus fenestratus o CD 3 CD ~* CD CD ZJ J~^—I Engethardtia spicata c/> —I • CD "1 5! _J~~i Quercus g/auca

CD CO ine s ndi c r- pec i 3- Castanopsis indica CD Neocmnamomum caudatum f I Phoebe cathia I

I 1 Termin alia niyriocarpa

I Tetrame/es nudiflora I

Pt er o sper mum acerif ol turn

Phoebe hainesiana limit of the warm-temperate zone, and the lower limit of Quercus semecarpifolia and Pinus wallichii is at the lower limit of cool-temperate zone. Because of this coincidence of altitudinal limit for both mesic and xeric dominants, statistical analysis of species distribution of various habitat requirements may give a similar results. The xeric dominants (Fig. 7b), two pines and three Quercus species are all characteristic to dry to semi-dry regions in South to East Asia. The two pines are both West Himalayan elements flourishing in the dry west. Quercus griffithii is very similar to Japanese Q_ aliéna (Kitamura et al., 1979), and two evergreen sclerophyllous species, Q^ semecarpifolia and Q. lanata are similar to Japanese Q. phyllyraeoides which also grows in xeric habitats such as dry cliffs along sea shore in the southern part of Japan. Therefore they are wide-ranging not only altitudinally but horizontally, in a mainly west to east direction in South Asia through the southern slope of the Himalaya. Altitudinal distribution of scree or ravine dominants are rather sporadic, because of their limited habitat availability. Their distribution ranges are, in general, wide as shown in Fig. 7c. However, the sites where they can dominate are limited to only unstable scree slopes near streams. According to the results mentioned above, forest zones can be divided into five zones and one scrub zone at the following altitude.

1000 m, tropical/subtropical boundary 2000 m, subtropical/warm-temperate boundary 2500 m, warm-temperate/cool-temperate boundary 3000 m, cool-temperate/subarctMcold-temperate) boundary 3500 m, sub-boundary within a subarctic zone 4000 m, subarctic(cold-temperate)/arctic boundary

Although there has been much debate about the naming of vegetation zones (cf. Numata, 1981), here the zones are tentatively named with the northern temperate terminology to make comparisons with temperate vegetation easier. The proper naming of zones should be searched for through analytical study of vegetation zonation in the whole of East Asia. Some of these altitudes may correspond to the boundaries of the zonal vegetation in the northern Hemisphere.

-17- 5000 r

XERIC DOMINANTS

4000

-1- «0

O T

3000

O O

2000 T

1000

Fig. 7b. Vertical ranges of xeric dominants.

-18- 5000 r

SCREE, RAVINE DOMINANTS

4000

3000 c 5

2000

3 I Q

1000

Fig. 7c. Vertical ranges of scree or ravine dominants.

-19- CHARACTERISTICS OF VEGETATIONAL BOUNDARY

The detailed description of each vegetational boundary is as follows.

1) Tropical/subtropical boundary at 1000 m

This boundary between tropical and subtropical zones is in common with that of the other Himalayan regions as has been reported by many researchers (cf. Schweinfurth, 1957; Ohsawa et al., 1986). In the other Himalayan regions, this altitude coincides with the upper limit of a wide- ranging dominant of tropical elements, Shorea robusta. However in Bhutan this species can be found in only very limited sites in the Sarbhang district between Phuntsoling and Manas (Grierson & Long, 1983). Some other tropical trees of more humid type, such as Phoebe spp., Pterospermum acerifolium, Tetrameles nudiflora, and Duabanga sonneratioides, reach upper limit at around this altitude. This upper limit coincides with the lower limits for some important subtropical/warm- temperate trees, such as Schima wallichii, Lithocarpus elegans, Acer oblongum, Quercus griffithii, and Pinus roxburghii (Photo 1). A dominant tree, Duabanga sonneratioides, which grows on riverside terraces or scree slopes (Photo 2), reaches its upper limit at this boundary. However the other habitat specialists on river sides, Terminalia myriocarpa and bamboos, invade into the subtropical zone above along water courses.

2) Subtropical/warm-temperate boundary at 2000 m

The evergreen broad-leaved forests dominated by Castanopsis tribuloides, Schima wallichii, Q. glauca, and Lithocarpus elegans are developed widely below 2000 m (Photo 3). Above this altitude, the forests are still dominated by evergreen broad-leaved trees of mostly lauro-fagaceous species, such as Quercus semiserrata, Castanopsis hystrix, Litsea elongata, Quercus lamellosa, and Persea clarkeana. The forests dominated by Pinus roxburghii, are more or less restricted to the dry

-20- â .^ff^«^#Ai5ïSl

Photo 1. A forest at the boundary between tropical and subtropical zones. Dominants are Sloanea, Terminalia, Lithocarpus, Phoebe, Albizzia, Betula, etc. Alt. 1040 m, near Nagor, Oct. 23, 1985.

-21- Photo 2-1. Gallery trees of Duabanga along a small river near Dogar, alt. 650 m. Trees are entangled by a climber, Mikania. The lower slopes are covered by mixed bamboo forests.

Photo 2-2. Inside of the bamboo forest.

-22- Photo 3. Evergreen broad-leaved forests dominanted by Lithocarpus, Schima, Castanopsis, and Engelhardtia. A settlement of a family started on gentle slope. Near Jaina La, alt. 1900 m. Oct. 21, 1985.

-23- valleys of the subtropical zone. On the other hand Quercus griffithii range from the subtropical to the warm-temperate zone. These two species' habitats are often segregated along moisture gradients; Pinus roxburghii in the dry and Q^ griffithii in the less-dry sites. The semi-natural forests dominated by Quercus griffithii are extra zonal in their distribution and are under human influences. However, natural stands of this species are found to be restricted to ridges within the warm-temperate zone (Photo 4).

3) Cool-temperate/warm-temperate boundary at 2500 m

This is the boundary altitude where the tropical mountain elements of subtropical and warm-temperate zones mentioned above give way to temperate elements. Most of the evergreen broad-leaved forests dominated by Castanopsis hystrix, Quercus lamellosa, Q. semiserrata, Lithocarpus elegans, and some lauraceous species of Persea and Litsea reach their upper limit. However some evergreen fagaceous forests such as Quercus semiserrata reach up to the upper part of the cool-temperate zone. This is a characteristic feature of the Himalayan cool-temperate zone. The principal dominants in the cool-temperate forests of Bhutan are conifers such as Tsuga dumosa and Picea spinulosa, mixed with deciduous trees such as Acer campbellii, Magnolia campbellii, and Sorbus cuspidata (Photo 5). Moreover they are often mixed with evergreen broad-leaved trees such as Quercus semecarpifolia (Photo 6). The forests dominated by Pinus wallichii developed mainly in dry valleys and their distribution ranged from 2400 to 3500 m (Photo 7). Therefore the species is also extrazonal in its distribution.

4) Cool-temperate/subarctic (cold-temperate) boundary at 3000 m

This boundary is not very clear in the Bhutan Himalaya, because most of the cool-temperate trees invade into lower parts of the above subarctic zone. However the lower limit of Abies densa is clear and this characterize the boundary. The sub-boundary within the subarctic zone at 3500 m is characteristic to the Bhutan Himalaya. This is the upper limit of Tsuga dumosa and some other minor conifer trees such as

-24- Photo 4. A natural stand of Quercus griffithii, Rhododendron arboreum on a ridge near Jaina La (Plot 1921). Alt. 1892 m, Oct. 21, 1985.

-25- Photo 5. Abies-Tsuga forest with many deciduous trees, such as Acer spp. and Sorbus spp. Above Nikkachu, alt. 3000 m, Sep. 20, 1985.

Photo 6. Tsuga-Quercus semecarpifolia forest at Dochu La Alt. 3070 m, Sept. 17, 1985.

-26- Photo 7. Pinus wallichii-Picea spinulosa forest mixed with Tsuga dumosa, Quercus semecarpiforia. Alt. 2800 m, above Bumthang, Oct. 12, 1985.

Photo 8. Mixed forest at lower part of Abies zone. Abies densa, Picea apinulosa, Juniperus recurva, Acer caudatum, Betula utilis, Sorbus microphylla, etc. Dongshigang, alt. 3400 m, Oct. 6, 1985. -27- Larix griffithiana, Cupressus corneyana, and Picea spinulosa. These species often make mixed forests in these altitudinal ranges (Photo 8). The occurrence of mixed forests in the Bhutan Himalaya contrast with those in East Nepal, where almost pure Abies forests have developed between 3000 and 3800 m. The mixed nature of Abies forests in Bhutan is reflected by the zonation of soils, where Brown forest soils are distributed up to 3300 m, and Podzols have developed above this altitude (Okazaki, 1987). An abundant supply of mixed litter may favour the development of Brown forest soils even under the Abies dominant forests.

5) Subarctic (cold-temperatej/arctic boundary at 4000 m

This altitude coincides with the forest limit in this region. This forest limit is 200-250 m higher than that in East Nepal (cf. Ohsawa et al., 1986). Abies densa forests reach their upper limit at around 4000 m (Photo 9), and then Juniperus forests including J^ indica, J^ recurva, and J_^ squamata replace Abies forests, and climb up to around 4200 m mainly on ridges and rocky cliffs (Photo 10). Sometimes Juniperus forms a krummholz zone and shifted to dwarf shrub. The forest limit coincides with the lower limit of much shrubby and dwarf-shrubby Rhododendron scrub (Photo 11). The shrubby Rhododendrons are the extension of the understory trees of Abies forests into the zone above the forest limit. The similar phenomenon of replacement of dominance by understory shrub after the elimination of upper story of the forests is observed in tropical mountain vegetation (Ohsawa et al., 1985). Dwarf shrubby Rhododendrons such as R^ anthopogon, R. setosum, R. lepidotum, and R^_ nivale are restricted to the zone above the forest limit and their behaviour is different from shrubby Rhododendron. According to our observation, the highest records of woody plants (except cussion plants), were Rhododendron nivale at 4932 m.

STRUCTURE OF THE ZONAL FORESTS

As stated above, forest vegetation can be divided into more or less clear zones according to the boundary where the upper or lower limit of the principal dominant species concentrate. The zones in the Bhutan

-28- Photo 9. Forest limit of Abies densa at 3969 m. Abies forests are replaced by Rhododendron scrub. Oct. 5, 1985.

Photo 10. Juniperus recurva above forest limit of Abies. Alt. 3960 m, Oct. 5, 1985.

-29- Photo 11-1. Alpine scrub of Spiraea, Rhododendron, Juniperus, Berberis, etc. At 4150 m, Oct. 10, 1985.

Photo 11-2. Above timberline at Gophu La. Alt. 5370 m. Oct. 3 1985.

-30- Himalaya are similar to those in East Nepal. However there are some characteristic features of zonal forests compared with the . other Himalayan region.

1. Tropical monsoon forests (0-1000 m) Tetrameles-Pterospermum-Phoebe forest zone

This is a zone of various forest types belonging to the tropical zone. For example, Stainton (1972) divided the equivalent forest zone in Nepal into at least five forest types, such as tropical deciduous riverine forest, tropical evergreen forest, subtropical evergreen forest, Terminalia forest, and Dalbergia sisso-Acacia catechu forest. Floristic and structural features of the vegetation below 1000 m are similar to the tropical monsoon forests of Walter (1973) (Photo 12). There are several species having typical buttresses, such as Tetrameles nudiflora, Bombax malabaricum (Photos 13, 14), and many species having cauliflory habit including Ficus spp. Such forests are mainly developed on humid flood plains or terraces along big rivers or in humid deep valleys of side streams. These lowland tropical forests reach to the upper limit rather suddenly at around 1000 m. This altitude may correspond to the height of relatively open ridges, where the humid tropical forests developed in deep ravines give way to relatively dry subtropical forests on slopes or ridges. Some tropical elements penetrate into still higher altitudes along the deep ravine accompanied by bamboo forests. The dense bamboo forests along streams are another characteristic feature of tropical and subtropical vegetation in lowland Bhutan. The tropical forests developed on relatively high flood plain at about 200 m are composed of various canopy trees of Moraceae, Lauraceae, Fagaceae, Myrtaceae, Combretaceae, Euphorbiaceae, etc. with typical emergent trees of Tetrameles nudiflora. But those on the low flood plain at around 100 m are rather simple with supreme dominants adapted to flesh sandy habitats such as Bauhinia, Lagerstroemia, and Dalbergia with emergent trees of Bombax malabaricum. These differences may be due to the time since the formation of the flood plain, or since stabi- lization after catastropic floodings. Jain and Hajra (1975) described briefly the vegetation of the Manas Wildlife Sanctuary from the Assam side. They classified the vegetation into three types; 1) Tropical semi-

-31- Photo 12-1. Sparse vegetation at Manas. Alt. 100 m. Oct. 30, 1985.

*-ïi\

Photo 12-2. A distant view of Manas from the north. Alt. 250 m, Oct. 29, 1985.

-32- Photo 13, 14. Canopy and buttress of Tetrameles nudi flora. Alt. 150 m, Manas, Oct. 31, 1985.

-33- evergreen forests in the northern part near the Bhutan-India international boundary, 2) Tropical moist and dry deciduous forests, the commonest in the sanctuary, and 3) Alluvial grasslands, spotted widely. The forests on the Bhutan side are more of an evergreen nature especially on higher flood plains.

2. Subtropical forests (1000-2000 m) Schima-Lithocarpus-Castanopsis forest zone

The subtropical forests reach to around 2000 m, where such typical subtropical dominants as Lithocarpus, Castanopsis, and Schima reach to the upper limit. This is a forest zone equivalent to Stainton's Schima- Castanopsis forest, subtropical semi-evergreen hill forest (Stainton, 1972), and both the subtropical and warm-temperate zones of our previous report (Ohsawa et al., 1986). Stainton's subtropical semi-evergreen hill forest type is found mainly on disturbed sites by natural agents, such as scree slopes, cliff ridges, etc. in Bhutan, and various ecological groups coexist- ing in such habitat. Dry valleys of this zone are dominated by Pinüs roxburghii forests with various degree of canopy closure according to the humidity conditions of their habitats (Photo 15). In the Nepal Himalaya, natural forests can hardly be found in this zone, and it is difficult to know the exact situation of vegetation zonation in natural conditions. Therefore we sometimes divided this altitudinal range into two zones, the lower Schima wallichii zone and the upper Castanopsis tribuloides zone. But this may be due to lack of proper information on natural vegetation. According to our observations in Bhutan, these regions can be regarded as a single zone. There are characteristic strong dominants such as Castanopsis tribuloides, Schima wallichii, and Lithocarpus elegans throughout this range as shown in Fig. 7a (Photo 16). In the Nepal Himalaya the segregation of the dominant range between Schima and Castanopsis may be caused by human disturbances. Because Castanopsis tribuloides is a wide-ranging species very durable against human disturbances such as burning and cutting. There- fore the species can become a substitutionai dominant in heavily disturbed sites after the elimination of Schima wallichii and some other components due to disturbance.

-34- Photo 15. Pinus roxburghii forest in various density along Punakha Chu.

-35- Photo 16. Mixed subtropical forest dominated by Castanopsis tribuloides, Lithocarpus elegans, Schima wallichii, Quercus glauca, etc. Alt. 1500 m, Jaina La, Oct. 21, 1985.

-36- It is appropriate to call this a subtropical zone, because, Schima wallichii, a most typical dominant of this forest zone, is a common species of the subtropical region of east to south-east Asia. In equatorial mountains this species also forms a tropical mountain forest zone above lowland to lower montane dipterocarp's forests. Several characteristic elements of the Schima forests in equatrial mountains, such as Altingia excelsa in lower parts and Exbucklandia populnea in higher parts (Ohsawa et al., 1985), can also be found in similar altitudinal ranges of the Bhutan Himalaya (Photos 17,18). This may support strongly the equivalent nature of the equatorial mountain forests and the subtropical zone of the Bhutan Himalaya. Moreover the two characteristic species common to both equatorial and Himalayan mountains mentioned above, Altingia excelsa and Exbuck- landia (Symingtonia) populnea, are both interesting angiosperms belonging to Hammamelidaceae which link the primitive Magnoliales and the Amen- tiferae (Takhtajan, 1969). Ecologically those species are restricted to certain altitudinal ranges, but are a valuable indicator species in elucidat- ing eco-geographical connections between different regions. In this connection, floristic and structural comparisons between tropical mountain forests and the Bhutanese forests are interesting to understand regional diversification of vegetation in East Asia. The dominant type of such forests is, in Bhutan, the Engelhardtia-Castanopsis-Exbucklandia-Quercus- unknown(I508) type as in Plot 1901 at 1800 m near Lingmithang. The equivalent forest in Mount Kerinci, an equatorial mountain, is the Exbuck- landia (Bucklandia)-Schima-Ficus type found at around 1900 m on Mount Kerinci, Sumatra (Ohsawa et al., 1985). Table 2 compares the floristic composition of these two equivalent forests. This clearly shows the similarity and dissimilarity of the two equivalent forest types in the two regions. Exbucklandia and Schima are the two common dominants in these two regions. Another common species is Engelhardtia spicata. There are several other common elements at generic level, such as Daphne, Lithocarpus, Machilus (or Persea), and Symplocos. On the other hand, there are some dissimilarities between the two regions. The equatorial mountain has many groups derived from the lower altitudes of the same region (synpatric origin), but the Bhutanese mountain has many temperate elements such as Acer, Betula, Daphniphyllum, Juglans, and Prunus which can be regarded as the southern extension of the temperate

-37- Photo 17. Remnant tree of Exbucklandia populnea, 50 m high. Alt. 1980 m. Near Thaley. Nov. 9, 1985.

Photo 18. A mixed forest of Lithocarpus elegans, Exbucklandia populnea, Castanopsis hystrix, Acer oblongum, Daphniphyllum himalense, Acer campbellii etc. Alt. 1980 m. Nov. 9, 1985.

-38- Table 2. Floristic comparison of Exbucklandia forests in Bhutan and in Mount Kerinci, Sumatra.

BHUTAN SUMATRA

Plot 1901 1881 2871 AVERAGE ALTITUDE, m 1800 1810 1900 1900

Species RBA RBA RBA RBA

Acer Campbellii 4.6 1.5 Acer niveura 2.3 .8 Actinodaphne sp. .01 Ardisia javanica .1 Betula alnoides 3.6 1.2 B238 .3 B271 .2 Calamus sp. .01 Camellia lanceolata .3 Castanopsis hystrix 18.5 26.7 17.1 20.8 Castanopsis tribuloides 3.6 1.2 Champai shin (H88) 1.9 .6 Cyrtandra calyptribracteata .2 Daphne composita .2 Daphne sp. .01 Daphniphyllum himalense 3 1.0 Discocalyx effusa .1 Elaeocarpus obtusa 1 Endiandra sp. .01 Engelhardtia spicata 34.4 11.5 .01 Eugenia sp.-2 .01 Eurya sp. 1.3 .4 Exbucklandia populnea 13.7 40 10.6 21.4 32.7 Ficus sp. .5 Ficus sp. .1 Ficus variegata 22.2 Flacourtia inermis .4 Hypobathrum frutescens .01 Ilex sp. .1 Juglans regia var. kamaonia 4.6 1.5 Kayu Utan Alam 2.7 Kozom shin (1489) 1.8 .6 Kumpade shin (1508) 7.4 2.5 Lasianthus cf. barbiger .01 Ligustrum glomeratum 1.4 Lindera pulcherrima .1 4.3 1.5 Lithocarpus elegans .1 20.7 6.9 Lithocarpus sp. .3 Litsea sp.-2 .2 Macropanax dispermis .8 Mastixia trichotoma var. benculuana .01 Melioçma nitida .2 Myrsine îemiserrata .5 .2 Nenga pumila 2 Neolitsea foliosa .9 .3 Persea clarkeana 4 1.3 Psychotoria sp. .7 Purunus cerasoides 1.2 .4 Ouercus griffithii 12.9 4.3 Ouercus semiserrata .01 11.1 3.7 Rhododendron arboreum Schima wallichi i 4.8 11.6 27.9 14.8 28.4 Skinraia arborescens .2 .1 Symplocos .4 .1 Symplocos (1493) .3 .1 Symplocos (1494) .1 Symplocos laeteviridis .6 Trêves ia sumatrana .01 Turpinia montana .4 Unknown 1.4 .5 Unknown (1490) .3 .1 Unknown (1500) (11

-39- floras though it is another story whether they are derived from north to south or vice versa. Moreover very high dominance of Castanopsis and Quercus both evergreen and deciduous is another characteristic feature to the Bhutanese subtropical forests.

3. Warm temperate forests (2000-2500 m) Castanopsis-Quercus-Acer forest zone

The warm-temperate zone of the Bhutan Himalaya is rather narrow between 2000 and 2500 m. According to our previous report in East Nepal (Ohsawa et al., 1986), the name warm-temperate zone was assigned to the forests between 1500 and 2000 m, where the forests are dominated by Castanopsis tribuloides and there is little occurrence of Schima wallichii as mentioned above. And the forests above the zone, which are distributed between 2000 and 2500 m, were called "temperate" zone, where lauro-fagaceous trees dominate (Ohsawa et al., 1986). However, as already mentioned above, the forest between 1000 and 2000 m can be regarded as a single zone of subtropical nature, and accord- ingly the zone above the subtropical zone, should better be named a warm-temperate zone. The forests above 2000 m are composed of many species of lauro- fagaceous trees such as Castanopsis, Quercus, Persea, Litsea, and others (Photo 19). This is equivalent to the Quercus lamellosa forest of Stain- ton (1972). The floristic characteristics of these forests are quite similar to the warm-temperate forests in temperate region like Japan. In fact, the warm-temperate zone is a kind of transition zone, where the minor subtropical elements fade out with the increase of altitudes as shown in Fig. 5. The floristic composition of these forests also depauperate gradually along latitudinal gradients in East Asia as is observed in the equivalent forests in Japan.

4. Cool-temperate forests (2500-3000 m) Tsuga-Picea forest zone

The cool-temperate forests in the Bhutan Himalaya are characterized by the dominance of conifers such as Tsuga dumosa and Picea spinulosa and less development of deciduous forests compared with those

-40- Photo 19. Mixed evergreen forest dominated by Castanopsis, Quercus, Litsea etc. Emergent Calamus shoots can be seen. Alt. 2000 m, Oct 16, 1985.

-41- of East Nepal. This corresponds to upper temperate mixed broad-leaved forest, Tsuga dumosa forest, and Quercus semecarpifolia forest of Stainton

(1972). Tsuga dumosa forests often contain Pinus wallichiiT Picea spinulosa, Quercus semecarpifolia, Quercus semiserrata, and Acer campbellii as the accompanied species, and they often form respective single dominant forests or mixed forests in various proportion according to the different habitat conditions. According to our observation, their habitat preferences are xeric to mesic in the following order: Pinus wallichii (xeric)-Picea spinulosa-Quercus semecarpifolia-Tsuga dumosa-Quercus semiserrata-Acer campbellii (mesic). Tetracentron sinense, another characteristic primitive angiosperm of the cool-temperate humid forests in the Himalaya to S.W. China is also found at the lowest part of this zone around 2500 m (Photo 20). The occurrence of this species in the Bhutanese cool-temperate forests indicates their strong connection to both East Nepal and S.W. China. It may penetrate into East Himalaya from S.W. China through "Himalayan corridor", and reach to the Iswa valley, one of the tributaries of the Arun river, East Nepal (Ohsawa et al., 1983). Its west limit may be brought about by prolonged dry periods towards the west in the Nepal Himalaya, because the species is one of the vesselless angiosperms which grows only on humid sites.

5. Subarctic (cold-temperate, subalpine) forests (3000-4000m) Abies forest zone

This is a part of wide-ranging Abies forest zone common to all the Himalayan range, though the species change to Abies densa in Bhutan. Taxonomical treatment of high altitude fir, Abies spectabilis and Abies densa is still confusing as discussed by Stainton (1972). Here all the fir trees are treated as Abies densa according to Grierson & Long (1983). As has been discussed above, the subarctic fir forest of Bhutan often has a mixed canopy of several co-dominants. In the lower half of this zone (below ca. 3500 m), Abies mixed with other conifers, such as Tsuga dumosa, Larix griffithii, Cupressus corneyana, Picea spinulosa, Juniperus recurva, and Pinus wallichii (Photo 21). Moreover, there are many deciduous understory trees such as Hydrangea heteromalla, Acer pectinatum, Sorbus foliolosa, Prunus rufa, and Betula ermanii, as well as

-42- Photo 20. Mixed forest of evergreen and deciduous trees at 2550 m, below Dochu La. Tetracentron sinense (with a photo of hanging fruits), Acer campbellii, Quercus lamellosa, Persea clarkeana, Quercus semeserrata, Litsea elongata, etc. Oct. 16, 1985.

-43- I Photo 21. Larix griffithii ft along the river ft. in Abies forest 1 zone.

Photo 22. Abies densa forest at around 3550 m. Oct. 10, 1985.

Photo 23. Contrast of vegetation between south and north-facing slope at alpine zone. Near Tampey tso, alt. 4200 m, Sep. 24, 1985.

-44- evergreen rhododendrons such as R^ arboreum, R. campyrocarpum. On the other hand, Abies forests in the upper half (above 3500 m) are relatively simple and only sometimes mixed with Juniperus recurva and Sorbus spp. (Photo 22). The Abies forests reach the forest limit at around 4000 m. At the forest limit, especially along the ridges, Juniperus spp. often replaces Abies as mentioned above. Juniperus recurva appear from the lowest altitude at about 3400 m, where the species grow at the margin of the Abies forest or along road-sides. At the forest limit, three junipers, J^ recurva, _L_ indica, and ^L_ squamata appear at the forest margin. Juniperus indica grows even on rocky ridges or on sandy soils, and jj_ recurva grows on silty soils. On the other hand _L_ squamata usually grows above the forest limit. The juniper forms scrub together with other deciduous shrubs such as Spiraea, Berberis, Potentilla, Lonicera, etc. on- south facing slopes (Photo 23). And this is in clear contrast to the almost pure Rhododendron scrub present on north-facing slopes. This south/north contrast in scrub communities above the forest limit is also common in East Nepal (Ohsawa, et al., 1983).

DISTRIBUTION OF DRY VALLEYS AND THEIR VEGETATION

One of the most characteristic features of the Bhutanese vegetation is the occurrence of xeric type vegetation which thrives in dry valleys. Along our trekking route, xeric vegetation was observed in the valleys of Wang Chu, Punaka Chu, Mangde Chu, Chamkha Chu, and Kuru Chu. Figure 8 indicates topography and approximate boundary of dry valleys in Bhutan reproduced with some modifications from the map prepared by the Forest Department of the Royal Government of Bhutan and UNICEF. We could conduct only a preliminary observation into the vegetation of these dry valleys. According to climate diagrams of dry valleys (see Fig. 2), there is a prolonged dry season ranging from four to six months. The amount of precipitation is less than 700 mm. de Martonne's aridity index, AI=P/(T+10), for Wangdiphodrang is the lowest at 19.6, and this value is equivalent to that of prairies and not that of forests. The values for the other places are as follows:

-45- I

4 km DRY VALLEYS

Fig. 8. Topography and approximate boundaries of dry valleys (based on the map prepared for Royal Government of Bhutan, Fifth plan, 1981-1987, Planning Commission, and Forest Department of Royal Government of Bhutan and UNICEF). Two lines, 9-9 and 10-10, indicates the locations of topographical and vegetational profiles in Fig. 9 and Fig. 10, respectively.^ Locality Annual Annual mean AI Precipitation temperature (mm) (degree C)

Wangdiphodrang 622 21.8 19.6 Mongar 698 19.0 24.1 Thimphu 691 14.2 28.6 Paro 674 13.4 28.8 Bhumtang 730 11.1 34.6 Sharbang 4263 25.5 119.9

According to Tuhkanen (1980), T + 10 in AI have a good correlation with the value for evaporation, therefore the value of AI would seem to be good a correlation with P/E indices. According to de Martonne, AI<5 is for deserts, 5Sankosh river). The pattern is from Thimphu on the left side of the figure, a relatively dry area with a vegetation of scattered trees of Pinus wallichii, Quercus griffithii, Quercus lanata, and dwarf Quercus semecarpifolia, through a humid high pass of Dochu La (3120 m) with Tsuga dumosa, Acer campbellii, and tall Q^ semecarpifolia forests, to the humid forests on the east side of the pass. Then with the decrease of altitudes the forest shifts to the submesic type of Quercus griffithii and Pinus roxburghii (mainly south-facing slope) at ca. 1900 m. At the bottom of Punakha Chu (1200 m), a xeric type vegetation dominated by xeric shrubby species such as Terminthia paniculata, Phyllanthus emblica, Jatropha curcas, Woodfordia fruticosa, and Jasminum officinale flourishes (Photo 24). There is a dense bush of Opuntia on the river sides of Punakha Chu and on the slope of Wangdiphodrang zon. On the opposite side of Punakha Chu, i.e.,

-47- ALTITUOE -r 4000 WEST

Dochu La Abies densa Tsuga dumosa Belula utihs MESIC -- 3000 Picea Tsuga dumosa

Quercus semecarpilolia Tsuga dumosa

s inen s e MESIC Quercus sem iserra ta Quercus semiserrata Pinus wallichii Castanopsis hystn'x Quercus lamellosa Quercus griffithii Ouercus lamellosa "2000 •*- 1900 m Wong Chu Quercus griffithii (N) Engel ha rdtia spica ta (N) Schima wallichii (N) I Pinus roxburghi, (S) SUBMESIC Pinus roxburghii (S ) 00 Quercus griff it hi (N) Phylianthus emb/ica Terminthia paniculata Pinus roxburghii _XERIC " 1200 m Woodfordia fruticoss Sa pi um insigne Punakha Chu Jatropha curcas Terminthia paniculata PhyllanthuS emblica

Jasminum officinale Berberis asiatica 3 km

Fig. 9. A topographical and vegetational profile at Wong Chu and Punakha Chu divided by Dochu La. Humidity conditions, mesic, submesic, and xeric at the sites on the slope, are evaluated by vegetation. The location of profile is indicated in Fig. 8. ALTITUDE WEST 3500 T

Tsuga dumosa 3000 -- Acer Campbellii

EAST Quercus semiserrata

Quercus lamellosa 2500 -- Litsea elongata Exbucklandia populnea Castanopsis hystrix MESIC

2000 -- Castanopsis tribuloides Schima wallichii Schima wallichii

Quercus lanata Quercus griffithii SUBMESIC 1500 - Quercus griffithii Pinus roxburghii Pinus roxburghii

XERIC 1000 -- Duabanga sonneratioides

Duabanga sonneratioides Pinus roxburghii Bauhinia purpurea Pinus roxburghii Woodfordia furticosa 570 m Terminthia paniculate Eupatriu m o dora t um Kuru Chu 5 km Rhus javanica Chrysopogon aciculatus Phy/lanthus emblica Artemisia

Fig. 10. A topographical and vegetational profile at Kuru Chu. Explanations are same as Fig. 9. Photo 24. A xeric type vegetation at the bottom of Punakha Chu viwed from Chimi Rakan. Alt. 1200 m, Nov. 15, 1985.

-50- west-facing slope, xeric scrub shifts to submesic sparse forests dominated by Pinus roxburghii at around 1500 m. On this slope, a narrow zone of submesic forests and above 1700-1800 m mesic forests dominated by Schima wallichii and Castanopsis tribuloides start again (Photo 26). Therefore there are high and low dry valleys on both sides of Dochu La. The dry valley in Kuru Chu is developed in lower altitudes at around 500 m as shown in Fig. 10. The valley is rather narrow and xeric type vegetation is developed mainly on south-facing sub-slopes along the river. Both slopes facing the river are very steep and the change of vegetation is drastic from very humid cool-temperate forests dominated by Tsuga dumosa at around 3000 m near Sangor, through cool- to warm- temperate evergreen broad-leaved forests from 3000 to 2000 m, and to humid subtropical forests with banana and palms from 2000 to 1700 m. Below 1700 m, the submesic forests dominated by Quercus griffithii start to appear, and below 1500 m, Pinus roxburghii join them and shift to xeric vegetation. At the valley bottom, characteristic xeric shrubs, such as Terminthia paniculata, Woodfordia fruticosa, Phyllanths emblica, become the dominant species. In this valley, the vegetation pattern on both slopes are similar, and parallel configuration can be observed. Undoubtedly the formation of dry valley vegetation is due to low precipitation in those sites as discussed above. However, extension of its area may be due partly to human degradation of forests, because we could see many footpaths used by cattle on the slopes of dry valleys. In some places there are some tall, standing trees of Pinus spp., which indi- cate the possibility that tall trees may grow in some sites in dry valleys.

DISCUSSION

1. Vegetation zonation in the Bhutan Himalaya

Sargent (1985) stated that the boundary between vegetation zones coincides with every 1000 m in altitude, i.e. 1000, 2000, 3000 m. The present results conform to her results in most of the boundaries, however there are several other important boundaries, a boundary between the warm-temperate and cool-temperate zones at 2500 m and a sub-boundary within the subarctic zone at 3500 m (Fig. 11). Below the forest limit

-51- 7000

6000

5000

Rhododendron dwarf scrub

/ Rhododendron scrub •^Juniperus> - Berber is - Potent ill a \ - 4000

/ SUBARCTIC (COLD TEMPERATE) ZONE \ LJJ LU r— Z / Abies <: o / \ cc rvi LU 1 3000 I Quercus semecarpifolia \ / COOL-TEMPERATE ZONE O- -2L / Tsuga - Picea Pi nus wall ich ii \ r— WARM-TEMPERATE ZONE \ Quercus - Castanopsis -Acer 2000 LU

SUBTROPICAL ZONE Quercus lanata ZOI M i Schima- Lithocarpus - Castanopsis Quercus grif f it hit

1000 Pi nus roxbu rgh ii °~

TROPICAL ZONE PICA L o Tetrameles - Pterospermum - Phoebe cc r—

MESIC XERIC

Fig. 11. A scheme of vegetation zonation in the Bhutan Himalaya (see text).

-52- we could identify five forest zones, tropical, subtropical, warm-temperate, cool-temperate, and subarctic (cold-temperate), and one scrub zone of arctic nature, and these six can be grouped into two groups of higher category as shown in Fig. 6. The same zonal structure was observed in East Nepal as shown in Fig. 12 which is reproduced from Ohsawa et al. (1983). In this case the boundary is at somewhere between 2000 and 2600 m (there was no sampling plot between them). And in East Nepal, the differentiation of deciduous broad-leaved forests in the lower part (cool-temperate zone) of the upper group is the most characteristic. Cluster analysis for 45 forest plots sampled during our last three expeditions in East Nepal (including the results mentioned above in 1981) in 1971, 1977, 1981, also showed similar clusters (Ohsawa, 1983). In East Nepal, Numata (1966) had divided pioneer vegetation at 2000 m into two upper and lower zones. Ohsawa (1977) had also examined vertical distribution of pioneer and grassland species, pioneer shrub species, serai tree species, and climax tree species in East Nepal, and noticed that the most of the herbaceous species in open habitat had a main boundary of distribution at around 2000-2500 m. Ohsawa (1977) stated that this boundary between warm-temperate and cool-temperate zones is a broad transition zone in the Himalayan vegetation. Tsuchida (1987)'s A zone, which distribute below 2500 m is also coincide with this boundary of vegetation. The common nature of this boundary of a large scale structure of vegetation in the East Himalaya is a reflection of the large floristic kingdoms of the northern hemisphere, the Holarctic and the Palaeotropical floristic regions (Good, 1974; Takhtajan, 1986). Therefore these two groups of clusters which identified in the East Himalaya might be called a pan-zone, which may have at least some common floristic similarities as shown in the dendrograms. This pan-zone can be named tropical pan- zone for tropical, subtropical and warm-temperate zones, and temperate pan-zone, for cool-temperate, subarctic (cold-temperate), and arctic zones. Further analysis may need to clarify the relationships between the two pan-zones, and between respective vegetation zones.

2. Relation between vegetation zones and temperature climate

The basic pattern of vegetation distribution along altitudinal

-53- PLOT ALT. DOMINANT COMPONENT SPECIES m 1 12 3470 Abies spectabilis

11 2960 A. spectabilis-Gambleaî-Betula utilis

13 2900 A. spectabilis

10 2810 Sorbus cuspidata-Lindera (J953)

6 2670 Magnolia campbellii-Acer campbellii-Vibrunum erubescens- Unknown(J899)-Scheffiera(J894) 9 2570 Tetracentron sinense-M. campbellii-A. campbellii-Litsea (J943) 14 2580 Tsuga dumosa

7 2030 Quercus lineata-Daphniphyllum himalense-Machilus (J910).- Symplocos(J532J-A. campbellii-Quercus lamellosa • 8 1950 Q. lamellosa-Unknown (J875)-Castanopsis tribuloides- C. hystrix-Q. lineata

5 1900 C. tribuloidës-Eurya-Unknown (J314)

4 900 Schima wallichii-C.- tribuloides

3 300 Shorea robusta

1 320 Lagerstroemia parviflora-Adina cordifolia-Sapium insigne

2 230 L. parviflora-Unknown(J50)-S. insigne-A. cordifolia- Unknown(D13) I 1.0 0.5 DISSIMILARITY

Fig. 12. A dendrogram showing similarities between 14 forest plots in the Arun valley, East Nepal. gradients is controlled by the temperature climate though humidity which also control vegetation distribution in dry valleys. Figure 13 indicates the gradients of annual mean temperature along altitudes in the humid east part of the Himalaya including Bhutan, Sikkim, and East Nepal. Annual mean temperature for most of the locations is close to a line of -0.6 C/100 m in altitude. The towns in dry valleys, such as Mongar along Kuru Chu and Wangdiphodran along Punakha Chu, showed a little higher temperature. Several indices for temperature climate are illustrated in Fig. 14. The monthly mean temperature at every 500 m altitudes was estimated by using the temperature lapse rate estimated by using Eguchi (1987)'s method. On the left side of the figure, Kira's (1948) warmth index is plotted against altitude. The warmth index is calculated as the sum of monthly mean temperature above 5 C. The warmth-indices at boundaries of vegetation zones in northern temperate regions are as follows; 1) 15 degree-month for the boundary between subarctic (cold-temperate) coniferous forests and alpine scrub/grasslands (=the forest limit), 2) 45 for the boundary between subarctic forests and cool-temperate forests, and 3) 85 for the boundary between cool-temperate and warm-temperate forests. For Bhutanese vegetation the value of the warmth-index at each boundary within temperate pan-zone corresponds well to the value mentioned above. Therefore the zonation of Japanese mountains can be regarded as a parallel extension of the upper zones of the Himalaya as has been clarified by Ohsawa (1977). However, the zonation pattern and its climatic conditions in the zones below warm-temperate zone i.e. in tropical pan-zone, differs between Bhutan and Japan. For example warmth index at a boundary between warm-temperate and subtropical zones is 180 degree-month in the southern part of Japan. But in the Himalaya the altitude of 180 degree- month is at about 800 m in altitude, and this altitude is within the tropical zone as mentioned already. This discrepancy is not due to the differences in seasonal pattern of temperature. Figure 15 compares seasonal pattern of temperature between Chainpur, East Nepal and Tanegashima, a small island south of Japan. Both curves are quite similar. Therefore the different vegetation at the similar temperature condition for the Himalaya and Japan may not be due to temperature conditions. This discrepancy between the Himalayan vegetation and the

-55- 1000 r-

\ Walungchung Gola 3000 -

Bumthang

Thimph

O Darjeeling 2000 -

Mongar

Wangdiphodrang

1000 -

Sarbhang

Calcutta 10 20

ANNUAL MEAN TEMPERATURE. C

Fig. 13- Relationship between altitude and annual mean temperature in the East Himalaya. Closed circles are for Bhutan and open circles are for Nepal and Sikkim. A line indicates the lapse rate of 0.6 C/100 m.

-56- I I I I I 6000 -i 6000

I 5000 5000 I 4000 4000 I SUBARCTIC (COLD-TEMPERATE)

I 3000- 3000

I WARM-TEMPERATE 2000- 2000

I SUBTROPICAL I 1000- '1000 I 15 45 85 100 180 200 -100 -50 -10 0 I WARMTH INDEX COLDNESS INDEX (•) I I Fig. 14. Several indices for temperature climate in Bhutan (see text). I I I I -57- I 30

25 TANEGASHiMA \ 30.4 4 NL \ 200 m a. s.l.

20 \ Wl= 183

8 9 10 11 12

MONTH

Fig. 15. A comparison of annual courses of monthly mean temperature in the two sites having the similar warmth index value, Tanegashima, South Japan and Chainpur, East Nepal.

-58- Japanese one is another problem to be solved. Besides the warmth index, the upper limit for evergreen broad- leaved forests in Japan may be controlled by the low temperature. It is known that both -1 C for the mean monthly temperature of the coldest month and -10 degree-month of Kira's coldness index are well fitted to the northern or highest limit for the warm-temperate evergreen broad- leaved forests of Japan (Ohsawa et al., 1985). In Bhutan, these values are estimated to be found at an altitude of around 3000 m. This is the boundary between cool-temperate and subarctic zone rather than the upper limit for the evergreen broad-leaved forests of the warm-temperate zone in most parts of the Bhutan Himalaya. However as has been described above, some of the evergreen broad-leaved forests (Q^ semiserrata forest and Q^_ semecarpifolia forest) reach up to around 3000 m. The forests around this altitude in the Himalaya are a mixture of various forest types such as deciduous broad-leaved, evergreen broad-leaved, and coniferous forests. According to the mixed nature of vegetation in this zone, the relationships between temperature conditions and forest distribution might be very complex. The temperature conditions at around 3000 m can be summarized as follows: 1) minimum temperature is allowable for evergreen broad-leaved trees to grow, 2) accumulated temperature is not enough for evergreen broad-leaved trees to grow vigorously. Trade- off between evergreen broad-leaved trees and deciduous broad-leaved trees may be realized under such temperature conditions.

CONSERVATION IMPLICATIONS

Forest conservation in Bhutan requires urgent and proper evaluation of forest resources and human needs as is true for other countries all over the world. Cowan (1929) stated that in the Kalimpong area at that time, the development of the tea industry and the growing population inevitably diminishes such trees as Duabanga sonneratioides and Terminalia myriocarpa for timber resources. Castanopsis tribuloides is now prevalent everywhere in that area, but the areas nearest Kalimpong do not have even a single tree. This is the instance for places very close to Bhutan

-59- Photo 25. Huge stump of Castanopsis tribuloides with pollarded for trunk fire wood. Alt. 1790 m, Thaley.

Photo 26. Allocation of land for rotational use; forest-shifting cultivation -pasture-coppice wood-forest. Note smooth canopy surface in coppice woodland with rough canopy of natural forests surrounding it. Alt. 1790 m, Thaley. SÎSASK:

-60- in the west, but not those farther away. We also observed a drastic decrease in greenery surrounding small towns due to the increase of houses in East Nepal during seven years. The traditional technology of forest management, which we often encountered in the fields, is often quite rational from the viewpoint of the sciences. In many places, forest are managed by a system of coppice with standard (pines as standards and various fagaceous trees as coppice), and coppicing is a method of pollarding to prevent cattle brows- ing of young sprouts (Photos 25, 26). To conserve these technologies adapted to local ecosystems is also important.

CONCLUSION

According to the analysis of Bhutanese vegetation zones, it became clear that there is a main boundary between tropical and temperate vegetation on the southern slope of the Himalaya. And it is reflected by the two floristic regions which meet on the southern slopes of the Himalaya. The meeting altitudes are rather wide, with each element in- vading deeply into each other. It also became clear that the warm- temperate zone of evergreen lauro-fagaceous trees has a close relation with the tropical mountain vegetation as exemplified by the occurrence of common characteristic species in both forests. However the equivalent forests in Bhutan have been affected much from the northern forest elements. Temperature conditions for temperate pan-zone are comparable with Japanese one. However, those for tropical pan-zone are totally different from the temperate mountains like Japan. Southern islands of Japan have a temperature conditions comparable to the tropical zone of the Himalaya, but their vegetation is a subtropical in nature. The dry valley in Bhutan has not been fully analysed in this paper, but it shows a nature of being a connecting link between West Himalayan xeric vegetation and dry valleys in S.W. China.

REFERENCES

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-62- Plant Life of South-west Asia. Botanical Society of Edinburgh, 53-72. Meusel, H. & Schubert, R., (1971). Beitrage zur Pflanzengeographie des Westhimalajas, 1, 2, 3. Flora, 160:137-194, 373-432, 573-606. Nakao, S. (1959). Hikyo Bhutan. Mainichi Shimbun, Tokyo. (In Japanese). Nakao, S. & Nishioka, K. (1984). Flowers of Bhutan. Asahi Shimbun. Tokyo. Numata, M. (1966). Vegetation and conservation in Eastern Nepal. J. Coll. Arts & Sei., Chiba Univ. 4:559-569. Numata, M. (1981). The altitudinal vegetation and climate zone of the humid Himalayas. Pp. 1963-1970 in Liu Dong-sheng (ed.) Geological and ecological studies of Qinghai-Xizang plateau II. Science Press, Gordon & Breach, Beijing. 2138 pp. Ohashi, H. (1975). Flora of Eastern Himalaya. Third report. The University of Tokyo. Ohsawa, M.(1977). Altitudinal zonation of vegetation in eastern Nepal Himalaya. Pedologist, 21:76-94. (In Japanese with English summary). Ohsawa, M. (1981). A basic unit in forest community dynamics -a case study in the subalpine forest of Japan. In Halle, F. et al. (eds.), Forest Regeneration in Southeast Asia. BIOTROP Speial Publication No. 13, pp. 43-62. BIOTROP, Bogor. Ohsawa, M. (1983). Distribution, structure and regeneration of forest communities in eastern Nepal. Pp. 89-120 in M. Numata(ed.) Structure and dynamics of vegetation in eastern Nepal. Chiba University, Chiba. 184 pp. Ohsawa, M. (1987). Altitudinal zonation and succession of forests in the eastern Himalaya. Braun-Blanquetia (In press). Ohsawa, M., Tanaka, N., Shakya, P.R., and Numata, M. (1983).Forest types and distribution in the Arum Valley, East Nepal. In M. Numata (ed.) Ecological studies in the Arun valley, East epal and Mountaineering of Mt. Baruntse, 1981. Chiba University. Pp. 79-111. Ohsawa, M., Nainggolan, P.H.J., Tanaka, N., & Anwar, C. (1985). Altitudinal zonation of forest vegetation on Mount Kerinci, Sumatra:with comparisons to zonation in the temperate region of east Asia. Journ. Tropical Ecology, 1:193-216. Ohsawa, M., Shakya, P.R. & Numata M. (1986). Distribution and succession of West Himalayan forest types in the eastern part of the Nepal Himalaya. Mountain Research and Development, 6:143-157.

-63- Okazaki, M. (1987). Soils of the Bhutan Himalaya. (In this issue). Royal Government of Bhutan. Fifth plan, 1981-1987. Planning Commission. Sargent, C. (1985). The forest of Bhutan. Ambio, 14:75-80. Sargent, C, Sargent, O and Parsell, R. (1985). The forests of Bhutan: a vital resource for the Himalayas? Journal of Tropical Ecology, 1:265-286. Schweinfurth, U. (1957). Die horizontale und vertikale Verbreitung der Vegetation im Himalaya. Bonner Geogr. Abh., H. 20. Stainton, J.D.A. (1972). Forests of Nepal. 181 pp. John Murray. London. Takhtajan, A. (1969). Flowering Plants. Origin and dispersal. Oliver & Boyd. Edinburgh. Takhtajan, A. (1986). Floristic Region of the World. University of California Press. Berkeley. Troll, C. (1967). Die Klimatische und Vegetationsgeographische Gliederung des Himalaya-Systems. Khumbu Himal, Ergebnisse Liefg. 5. Tsuchida, K. (1987). Grassland vegetation and succession in Central Bhutan. (In this issue). Tuhkanen, S. (1980). Climatic parameters and indices in plant geography. Acta Phytogeographica Suecica 67. Walter, H. (1973). Vegetation of the Earth and Ecological Systems of the Geo-biosphere. Springer Verlag. NY. Walter, H., Harnickell, & Mueller-Dombois, D. (1975). Climate diagram Maps of the Individual Continents and the Ecological Climatic Regions of the Earth. Springer-Verlag. Berlin. Wu, C.Y. (1986). Wild Flowers of Yunnan 1,11,111. Japan Broadcast Publishing Co., Ltd. & Yunnan People's Publishing House. Tokyo & Kunming.

-64- Appendix 1. Dominance type of forests sampled along survey route. Arranged in an order of increasing altitudes. Plot number corresponds to Fig. 4. Altitude was adjusted according to the regression equation of Fig. 3. PU NO FOREST TYPE ADJUST AL ALT EXP TOPOGR MISC m m 34 2391 Tetrameles nudiflora-Dalbergia-Prerospermum acerifolium 102 20 Sandy river side 1741-Oa1bergia 102 20 35 2392 Tetraroeles nudiflora 152 70 33 2361 ßauhinia-Lagerstroemia-Dalbergia 162 80 Sandy river side 36 2401 Phoebe hainesiana 162 80 30 2321 Bakkarin shin (I696)-Phoebe hainesiana 182 100 38 2432 Bombax-Oalbergia-Sapiura insigne 182 100 Sandy river side 41 2482 Terminal ia myriocarpa 212 130 Sandy river side 42 2483 Bamboo 222 140 River side 32 2352 Tetrameles nudiflora-Duabanga-Terminalia myriocarpa 252 170 37 2431 Castanopsis indica-Castanopsis tribuloides-Tetrameles nudiflora 252 170 S45W 39 2441 Bamboo 252 170 W 2351 Duabanga-Terminalia 252 170 29 2301 Duabanga sonneratioides-Bauhinia 262 180 River side 40 2481 Tetrameles nudiflora-O. sonneratioides-Terminalia myriocarpa 312 230 31 '2351 Pterospermum acerifolium 342 260 28 2292 Duabanga sonneratioides-Bauhinia-ßombax 352 270 43 2541 Bamboo 442 360 48 2641 Phyllanthus emblica-Terrainthia paniculata 552 470 S 44 2551 Bamboo 562 480 5 1771 Ouabanga sonneratioides 642 560 Riverside 19 2171 Duabanga sonneratioides 652 570 River side 20 2181 Bamboo 682 600 River side 27 2291 Duabanga sonneratioides 682 600 6 1772 Quercus griffithii 722 640 N 7 1773 Pinus roxburghii 722 640 S 8 1774 Terminthia paniculata 722 640 49 2651 T. nudiflora-ßombax-Pterospermuin acerifolium-Callicarpa arborea 722 640 47 2631 Pinus roxburghii 732 650 S Rocky ridge 1 1521 P. roxburghii 762 680 S 2 1522 P. roxburghii 762 680 N 9 1781 P. roxburghii 812 730 E 10 1782 P. roxburghii 812 730 S 25 2281 Duabanga-Terminalia 832 750 Cove 26 2282 Bamboo 832 750 River side 50 2661 Quercus glauca-flallotus phillipinensis 852 770 21 2182 Lithocarpus elegans-C. indica 862 780 N 12 1792 Betula alnoides-Acer oblongum-Terminalia myriocarpa 882 800 River side 53 2771 P. roxburghii 912 830 S 22 2191 L. elegans 952 870 24 2271 Bamboo 972 890 River side 51 2662 P. roxburghii 982 900 S Rocky ridge 58 2981 P. roxburghii 982 900 S 23 2192 C. indica-Schima 1002 920 E 13 1801 Schima-(Ficus) 1012 930 S50E 4 1681 P. roxburghii 1022 940 S 54 2781 P. roxfurghii 1022 940S.E.W 55 2782 Q. griffithii-CaLLicarpa-Schima 1022 940 Small valley 17 2072 Sloanea sterculiaceus-Betula alnoides-Phoebe cathia 1032 950 45 2561 C. indica 1032 950 S 56 2941 Q. glauca-C. tribuloides-Schima 1032 950 N

-65- 57. 2942 C. tribuloides-Q. griffithii-Schima 1072 990 S H 1811 Betula alnoides-Q. griffithii 1082 1000 N80E 35 15 1812 Q. glauca 1082 1000 N80E 16 2071 Terminalia 1082 1000 River side 46 2621 L. elegans-Schima-C. indica 1082 1000 52 2761 û. griffithii 1082 1000 N 153 2951 P. roxburghii-Q. griffithii 1102 1020 S 154 2952 P. roxburghii 1102 1020 S Ridge 127 2751 P. roxburghii 1112 1030 S 130 2783 P. roxburghii 1112 1030 131 2784 P. roxburghii-Q. griffithii 1112 1030 2785 Rhus javanica 1112 1030 152 2931 B. alnoides 1122 1040 Forest margin 121 2692 Erythrina 1132 1050 125 2731 Ü. griffithii-P. roxburghii 1132 1050 N45U 126 2732 P. roxburghii 1132 1050 S45E 128 2752 Q. griffithii-Engelhardtia 1132 1050 U 120 2691 Q. griffithii-Schima-Albizzia 1152 1070 S20W 123 2711 P. roxburghii-B. alnoides 1152 1070 124 2712 P. roxburghii-Q. glauca-C. tribuloides-Albizzia 1152 1070 77 1821 Acer sterculiaceum 1162 1080 Valley 117 2622 Bamboo 1172 1090 118 2671 Albizzia-L. elegans-Neocinnamomum caudatum-Callicarpa-C. tribuloides 1172 1090 122 2701 P. roxburghii 1172 1090 S70W 100 2061 Schima-Engelhardtia-Q. griffith 1192 1110 101 2081 L. elegans-Q. glauca 1192 1110 Ridge 109 2211 L'. fenestratus-Schima-C. indica 1192 1110 N45W 102 2082 Q. griffithii-Engelhardtia-Q. glauca-Schima 1202 1120 S 111 2241 C. tribuloides 1202 1120 N70W 112 2571 C. tribuloides-L. elegans 1212 1130 119 2672 Bassya-Turpinia-Litsea sp.-Erythrina 1222 1140 2222 Lithocarpus fenestratus-P. cathia 1222 1140 N45W 155 2953 P. roxburghii 1232 1150 156 •2954 Q. glauca-C. tribuloides-Schima 1232 1150 161 3011 Schima 1232 1150 N 3 1531 P. roxburghii 1242 1160 110 2221 L. fenestratus-Engelhardtia-P. cathia 1242 1160 132 2791 P. roxburghii 1252 1170 Ridge 134 2793 L. elegans-N. caudatum-Engelhardtia 1282 1200 Small valley 151 2921 Q. griffithii-C. tribuloides-Schima 1282 1200 N30W 78 1822 Schima-L. elegans-Engelhardtia 1292 1210 N 133 2792 C. tribuloides 1292 1210 U 99 2052 Q. glauca 1302 1220 79 1823 Schima-Engelhardtia (Betula) 1322 1240 116 2601 Q. griffithii 1322 1240 E 1681 Ostodes paniculata 1332 1250 157 2991 P. roxburghii 1332 1250 159- 3002 Q. lanata-Q. griffithii-Schima-Albizzia 1372 1290 135 2801 P. roxburghii-Q. griffithii 1382 1300 S 73 1691 Q. griffithii 1392 1310 158 3001 Alnus nepalensis 1392 1310 Small valley 80 1831 Acer sterculiaceum 1412 1330 Small valley 72 1661 P. roxburghii 1422 1340 150 2911 Q. griffithii-Schima 1422 1340

-66- 141 2841 Schima-Engelhardtia-L. elegans 1432 1350 115 2591 Û. griffithii-Schima 1442 1360 81 1832 A. sterculiaceum 1452 1360 Small valley 162 3012 P. roxburghii 1452 1370 S 114 2592 Q. griffithii-Schima-Lyonia 1462 1380 113 2581 C. tribuloides 1472 1390 63 1511 P. roxburghii-Q. griffithii 1482 1400 64 1512 Û. griffithii 1482 1400 Small valley 82 1833 Schima-Engelhardtia 1482 1400 N 136 2802 Q. griffithii 1482 1400 N70W 137 2803 Q. glauca 1482 1400 98 2051 L. elegans-C. indica 1512 1430 W 170 3162 P. roxburghii 1512 1430 S 65 1532 P. roxburghii-û. griffithii 1522 1440 142 2842 Û. griffithii 1532 1450 E 171 3221 P. roxburghii 1532 1450 S 172 3222 Q. griffithii-Q. lanuginosa 1532 1450 N 83 1841 Schima-Engelhardtia 1562 1480 N 143 2851 Q. griffithii-Q. glauca-Schima-Rh. arboreum 1562 1480 E 160 3003 Alnus nepalensis 1562 1480 Small valley 66 f532 Û. griffithii 1582 1500 74 1692 C. tribuloides-Q. griffithii 1582 1500 173 3223 A. nepalensis 1582 1500 174 3224 P. roxburghii 1602 1520 S 59 321 Schima wallichii 1612 1530 N 92 1961 C. tribuloides 1632 1550 N45W 138 2811 C. tribuloides-C. indica-L. elegans-Q. griffithii 1632 1550 S 169 3161 Schima-Engelhardtia 1632 1550 139 2812 C. tribuloides-L. fenestratus-Q. glauca 1642 1560 N 144 2852 Q. griffithii 1672 1590 S45E 145 2853 P. roxburghii 1672 1590 S45E 67 1591 Q. lanuginosa 1682 1600 s.w 76 1742 Q. griffithii 1682 1600 103 2111 C. tribuloides 1682 1600 Ridge 140 2831 C. tribuloides-Lyonia-Q. griffithii 1682 1600 175 3231 Q. griffithii-Q. Lanata-Ü. glauca-Schima-Oalbergia 1682 1600 93 1971 Rh. arboreum-Q. griffithii-Q. lanata 1702 1620 Ridge 84 1842 Schima-Engelhardtia 1712 1630 70 1631 Q. griffithii 1762 1680E.N30W 69 1621 Q. lanata-Rh. arboreum 1772 1690 S70E Cliff 71 1632 Schima-C. tribuloides 1792 1710 N Small valley 91 1931 Q. lanata 1792 1710 S 45 97 2041 C. tribuloides-Lyonia 1792 1710 62 1502 S. wallichii 1802 1720 85 1843 Schima-C. hystrix 1822 1740 104 2121 Rhus javanica-flaesa chisia-fielastoina-Rubus 1832 1750 68 1592 Q. griffithii-Lyonia-Rh. arboreunt-Schima 1842 1760 E Ridge 146 2861 Elaeocarpus-C. tribuloides 1852 1770 S70E Small valley 147 2862 Q. griffithii 1852 1770 S70E 60 322 P. roxburghii 1862 1780 S 86 1851 Q. lanata-Lyonia-Rh. arboreum 1862 1780 Ridge 75 1741 Schima-C.tribuloides 1882 1800 S70W 89 1901 Engelhardtia-C. hystrix-Symingtonia-Q. griffithii 1882 1800 S30E 35 108 2152 Carpinus viminea 1882 1800 S45W

-67- 164 3091 Q. lanata 1882 1800 165 3092 Û. lanata-P. roxburghii 1882 1800 88 1881 Exbuckland ia-C.hystrix-Sch i ma-Q.sem i serrâta 1892 1810 N50W 30 90 1921 Û. griffithii-Rh. arboreum 1892 1810 Ridge 87 1830 C. tribuloides 1912 1830 2132 Persea robusta-Neolitsea foliosa 1932 1850 148 2871 Schima-L. fenestratus-C. hystrix-Symingtonia 1982 1900 Gentle ridge 105 2141 C. hystrix 1992 1910 61 1501 C. tribuloides 2002 1920 107 2151 Q. lamellosa-Talauma like-Acer campbellii 2002 1920 S 176 3232Q. griffithii 2002 1920 94 1981 C. tribuloides-Schima-Symingtonia 2022 1940 U 106 2142 Q. lamellosa 2032 1950 163 3081 Û. lanata-Lyonia 2032 1950 SE.S 96 2021 Talaumalike-C. hystrix 2062 1980 E 25 187 333 Û. griffithii-C. tribuloides-A. Campbellii-Schima-Q. lanata 2062 1980 N 149 2881 Schima-C. hystrix-C. tribuloides 2072 1990 W 166 3101 Q. lanata-Lyonia 2082 2000 E 177 3241 Q. lanata 2082 2000 223 1732 C. hystrix 2162 2080 224 1991 A. nepalensis 2182 2100 Small valley 225 1992 Û. lainellosa-C. hystrix-A. campbellii 2182 2100 228 2002 L. elegans-C. hystrix-Q. lamellosa-Exbucklandia 2182 2100 167 3102 Q. griffithii 2192 2110 242 3242 A. nepalensis 2192 2110 95 2022 Juglance-A. campbellii-Prunus 2212 2130 Small valley 188 332 Q. lanata 2212 2130 Rocky ridge 222 1731 Q. lamellosa-A. campbellii-L. elegans 2222 2140 Small valley 219 1493 Litsea elongata-Q. semiserrata-Q. lamellosa-L. elegans 2232 2150 243 3243 C. hystrix 2242 2160 221 1711 Q. lamellosa-Talauma like-L. elegans 2262 2180 S70E 50 226 1993 Q. lamellosa-A. campbellii-Q. semiserrata 2262 2180 168 3103 Û. griffithii 2282 2200 220 •1701 Q. lamellosa-A. campbellii-Q. semiserrata-Persea clarkeana 2282 2200 244 3244 Q. griffithii 2322 2240 227 2001 Q. lamellosa-P. clarkeana 2332 2250 186 291 Castanopsis 2352 2270 245 3252 C. hystrix . 2352 2270 A. 230 3111 Q. griffithii 2362 2280 231 3112 P. vallichii 2362 2280 229 2011 Persea clarkeana-Q.lamellosa 2372 2290 Ridge 232 3121 P. vallichii-Tsuga-Q. griffithii 2382 2300 233 3122 P. vallichii 2382 2300 218 1492 L elongata-Q. lamellosa-Q. semiserrata 2452 2370 234 3131 P. vallichii-Q. semecarpifolia 2462 2380 S 235 3132 P. vallichii 2462 2380 N 178 181 Quercus lanata 2482 2400 S 179 182 P. vallichii 2482 2400 N 180 191 Q. griffithii-P. vallichii-Q. lanuginosa 2482 2400 S30E 246 3253 Q. lamellosa-Q. semiserrata 2532 2450 247 3251 Q. semiserrata-P. clarkeana-A. campbellii 2552 2470 N 208 1431 P. vallichii 2592 2510 209 1432 P. vallichii-Picea 2592 2510 Small river 217 1491 Quercus 2662 2580

-68- 181 201 P. vallichii-Poputus ciliata 2682 2600 N445E 25 207 1371 Picea-Tsuga-Populus-Q. semecarpifolia-A. campbellii-Pinus waUichii 2692 2610 190 391 Û. semecarpifolia 2722 2640 S 205 1363 Q. semecarpifolia 2732 2650 Riverside 206 1364 Q. semecarpifolia-P. wallchii 2732 2650 River side 189 361 Salix-Ilex macropoda-Cornus 2762 2680 Small valley 191 392 Tsuga dumosa 2762 2680 210 1441 Picea spinulosa-Tsuga 2772 2690 204 1362 Û. semecarpifolia 2792 2710 185 272 T. dumosa 2812 2730 248 3261 Tsuga 2812 2730 Taxus 182 211 P. wallichii-Q. semecarpifolia 2822 2740 203 1361 Q. semecarpifolia-Tsuga-A. campbellii 2822 2740 192 393 T. dumosa-A. campbellii 2862 2780 W 202 1352 Tsuga-Pinus-Q. semecarpifolia 2862 2780 Small river 211 1443 P. wallichii 2862 2780 212 1442 P. spinulosa-Tsuga-Populus 2862 2780 Small valley 236 3141 Q. semecarpifolia 2862 2780 240 3153 Q. semecarpifolia 2872 2790 S 241 3154 Q. semiserrata-Tsuga-Magnolia campbelli i-Taxus 2872 2790 N 183 212 P. spinulosa-P. vallichii 2892 2810 S25E 40 193 401 T. dumosa 2892 2810 201 1351 P. spinulosa-Tsuga 2902 2820 N 237 3142 Q. semecarpifolia-Rh. aroboreum 2962 2880 S Rocky cliff 249 3271 Tsuga 2962 2880 Taxusi Ma 194 402 Abies-Tsuga 2982 2900 199 1321 Tsuga-Abies 3002 2920 198 1312 Abies-Tsuga 3022 2940 238 3143 Tsuga 3022 2940 S 239 3151 Q. semecarpifolia 3042 2960 200 1322 Tsuga-Abies 3052 2970 184 251 Q. semecarpifolia 3072 2990 S 32 197 1311 Tsuga-Abies-Cupressus 3082 3000 250 231 Tsuga-A. campbellii 3102 3020 N30U 13 195 403 Abies-Betula 3112 3030 U 312 1341 Q. semecarpifolia 3122 3040 S20E 32 311 1342 P. spinurosa-Tsuga-A. campbellii 3142 3060 S70E 252 341 Abies-Tsuga-Juniperus recurva 3152 3070 Small valley 319 1461 Tsuga 3172 3090 213 1446 P. wallichii-P. spinurosa 3182 3100 S 310 1331 P. spinurosa-P. wallichii 3182 3100 U 313 1444 Tsuga-P. spinurosa-P. wallichii 3182 3100 314 1445 Tsuga 3182 3100 N 315 1446 P. wallichii-P. spinurosa 3182 3100 S 196 404 Abies-Betula 3202 3120 E 254 402 Abies-Betula 3202 3120 E 309 1332 P. spinurosa 3202 3120 N 320 3152 Betula 3212 3130 NU 215 1462 P..spinurosa-P. waLLichi i-Larix-Abies 3242 3160 308 1301 Abies-Tsuga-P. spinulosa 3242 3160 S 306 1261 Abies-Tsuga 3252 3170 River terrace 316 1447 Tsuga 3262 3180 305 1251 Betula utilis-Abies 3272 3190 S 15 303 1241 Tsuga 3282 3200 River side

-69- 304 1242 Abies-Tsuga 3282 3200 N 307 1271 Abies-Tsuga 3282 3200 S40W 12 214 1452 P. wallichii-P. spinurosa-Abies 3322 3240 S 255 411 Abies 3322 3240 E 317 1451 Tsuga 3322 3240 N 278 1011 Abies 3332 3250 Level River terrace 280 1041 8. utilis-Abies 3332 3250 U 34 251 331 Abies spectabilis 3352 3270 279 1031 Abies 3352 3270 281 1051 Abies 3352 3270 302 1231 Abies 3352 3270 S25W 275 971 Abies 3362 3280 276 972 Larix 3362 3280 River side 277 991 Abies-Acer pectinatuni-Hydrangea heteromalla 3362 3280 S85W 32 282 1061 Betula 3382 3300 U 283 1062 Abies-Cupressus-J. recurva 3402 3320 u 28 274 961 J. recurva-Abies 3432 3350 Level River terrace 216 1463 Abies 3442 3360 301 1222 Abies 3442 3360 300 1221 Abies 3452 3370 298 1211 Abies-B. util is 3472 3390 N 299 1212 J. recurva 3472 3390 River terrace 318 1453 P. spinurosa-P. vallichii 3482 3400 296 1191 Abies 3492 3410 297 1192 J. recurva 3492 3410 Forest edge 273 951 Abies-Juniperus 3502 3420 S50E Cupressus 284 1071 J. recurva-Cupressus 3522 3440 295 1163 Abies 3532 3450 285 1072 Abies 3562 3480 S45W 272 941 Abies-J. recurva 3672 3590 S45E 294 1162 Abies 3702 3620 256 471 Abies 3722 3640 286 1081 Abies 3732 3650 287 1091 Abies 3742 3660 257 481 Abies 3782 3700 258 482 Abies-Juniperus 3862 3780 271 913 Abies 3882 3800 288 1092 Abies 3922 3840 292 1152 Abies 3932 3850 N50E 293 1161 Juniperus indica 3932 3850 289 1101 J. indica 3942 3860 Rocky ridge 264 562 Abies 3952 3870 E.N 265 563 Abies-Sorbus foliolosa-Rhododendron 3952 3870 E 32 266 581 Abies 3952 3870 River side 269 911 Abies 3962 3880 Ridge 270 912 J. recurva 3962 3880 259 491 Juniperus squamata 3972 3890 263 561 Abies 3992 3910 E Rocky ridge 267 591 Rhododendron scrub 4002 3920 290 1111 J. recurva 4012 3930 262 552 Abies 4022 3940 N 260 492 Rh. scrub 4032 3950 268 901 Sorbus microphylla-J. recurva 4032 3950 291 1151 Abies (forest limit) 4032 3950 E

-70- 261 551 J. indica 4082 4000 359 1141 Spiraea canescens-Rh. lepidotum-J. squamata-Berb 4132 4050 S 327 543 Rh. scrub 4202 4120 S 325 541 S. canescens-Ribes or ientale-Saüx 4212 4130 S50E 34 326 542 Salix 4212 4130 Small river 357 1131 Rh.campanulatum 4222 4140 N 358 1132 J. squamata-Berberis 4222 4140 S 351 841 Rh. lepidotum-C. microphylla 4232 4150 S 352 842 Rh. campanulatum-Sorbus-Salix 4232 4150 N 321 493 Rh. anthopogon 4252 4170 328 601 J. squamata 4302 4220 350 824 R. setosum-Rh. nivale-R, anthopogon 4302 4220 355 1121 Rh. anthopogon-Rh. setosum 4302 4220 349 823 Rh. setosum-Rh anthopogon 4322 4240 River side 329 621 Rh. setosum-Rh. lepidotum 4332 4250 323 522 J. squamata 4362 4280 S 324 523 Rh. scrub 4362 4280 N 353 891 J. recurva-Berberis 4372 4290 S 354 892 Rh. campanulatum 4372 4290 N 356 1122 Rh. campanulatum 4372 4290 N50W 330' 622 Rh. anthopogon-Rh. setosum-Rh. lepidotum 4382 4300 347 821 Rh. nivale 4382 4300 S30W 348 822 Rh. campanulatum 4382 4300 N30E 346 811 Rh. nivale-Rh setosum 4402 4320 W 34 322 521 Rh. anthopogon 4412 4330 345 801 Potentilia frut icosa-fiyricaria rosea-Rh. setosum 4462 4380 331 631 Rh. anthopogon-Rh. setosum 4582 4500 344 782 Rh. setosum-L. obovata-P. fruticosa-J. squamata 4622 4540 332 632 Rh. lepidotum 4632 4550 340 742 Rh. anthopogon-Rh. setosum 4632 4550 N 343 781 P. fruticosa-Astragallus-Lonicera 4702 4620 W 38 339 741 Rh. nivale 4782 4700 360 651 Rh. setosum 4802 4720 341 751 Rh. nivale-P. fruticosa-Rh. anthopogon 4832 4750 337 731 Astragallus-Berberis concinna-P. fruticosa 4842 4760 SE 333 652 Rh. nivale 4852 4770 336 711 Rh. anthopogon 4882 4800 N 342 761 Rh. nivale 4882 4800 335 691 J. squamata-Berberis-PotentiILa 4932 4850 S 338 732 Astragallus-PotentiUa biflora 4932 4850 E 334 653 Rh. nivale 5142 5060

-71- -72- M.Ohsawa(ed.), Life Zone Ecology of the Bhutan Himalaya.1987. Chiba University.

GRASSLAND VEGETATION AND SUCCESSION IN CENTRAL BHUTAN

K. TSUCHIDA

Laboratory of Nature Conservation, Faculty of Liberal Arts, Shinshu University, Matsumoto 390, Japan

ABSTRACT

The grassland vegetation in central Bhutan (including a part of western Bhutan) was surveyed in autumn 1985. As the result of survey, some grassland types were recognized according to the altitude and the humidity, and their successional relationships were also elucidated. There were four altitudinal grazing grassland zones (A, B, C and D) ranging from 150 m to about 5,000 m in altitude or from tropical to alpine in the climatic zone. In A zone (below 2,500 m), Chrysopogon (dry) /Cynodon (mesic)/Paspalum (humid) types occur in wide altitude range. In B zone (2,500 m-3,500 m), Agrostis (dry)/Arundinella (mesic)/Carex (humid) types develop and Festuca (dry)/Agrostis (mesic)/Carex (humid) types develop in C zone (3,500 m-4,000 m). In D zone (4, 000 m-5,000 m), Festuca (dry)/Kobresia (mesic & humid)/Kobresia-Juncus (humid) types develop. Besides these grassland types, many communities occur in the pasture lands and abandoned fields according to some human and biotic influences such as heavy grazing, rude grazing, burning, etc. Especially the unpalatable plant communities which are dominated by Eupatorium, Artemisia, Anaphalis, Rumex, Pterinium, Cassia, Berberis, Elaeagnus, Rubus, etc. widely extent and the productivity of grazing grassland is going down. In order to increase the grassland productivity for the cattle rearing which is one of the most important industries of Bhutan and in

-73- order to preserve the valuable forests from destruction due to useless expansion of pasture land, the adequate grassland management has to be carried out based on the ecological study.

INTRODUCTION

The Kingdom of Bhutan lying the eastern Himalaya is just recently opened and the outline of land and people is becoming clear. We get a chance to visit to Bhutan and to survey the nature in autumn 1985. The author took charge of grassland vegetation on this survey. There are few reports on the vegetational study in Bhutan, still more on the grassland. The grassland vegetation and succession were surveyed along the caravan route of our party. This route was ranging from 150 m to 5,300 m in altitude of central and western Bhutan. Bhutan is an agricultural and cattle breeding country as same as other Himalayan countries. There are large cultivated land and grazing grassland (pasture land) in Bhutan, but the forest also widely develops all over the country except high mountain areas above 4,000m in altitude. The grasslands in Bhutan are mostly established by human influences such as felling, grazing, mowing and burning. They distribute ranging from 150 m to 5,200 m in altitude, mainly from 2,000 m to alpine area. Most of grassland in Bhutan are used for grazing of cattle such as cow, sheep, goat and yak. The land use of Bhutan is divided into cultivated land below about 2,500 m, grazing grassland above 2,500 m, forest below 4,000 m, nival region above 5,200 m and others. We hear that the native forest remains more than 60 % of land because of low density of population and low development. The cattle breeding is very important for life of Bhutan people and they are usually engaged in both of agriculture and cattle breeding. However the agriculture is stronger than the cattle breeding below 2,000 m in altitude and the latter is stronger above 2,500 m. Thus the area of grassland establishes larger in high altitudes than in low altitudes. Most of grassland (pasture lands) are over used and are not in good condition. The author surveyed the grassland vegetation types, structure, succession and condition in each plots.

-74- Method of utilization and management, and history of grazing, etc. were also investigated. The actual condition of grassland vegetation and cattle rearing in Bhutan became ^ clear in some degree from above results.

OUTLINE OF STUDY AREA

Bhutan is very mountainous land where is situated in the south slope of eastern Himalaya and is ranging from 150 m to 7,500 m in altitude. The land is blessed with abundant precipitation by the influence of the monsoon and is covered with many forests. The tropical forests are spreading in the low altitudinal region, and the intermediate altitudes is covered with the temperate evergreen forests. The conifer forests are develops in higher part of Bhutan and the alpine zone lies above about 4,000 m. The snow line is approximately 5,000 m-5,300 m. The temperate forest zone also falls on the main cultivation zone (Nakao & Nishioka, 1984). The grasslands are locally developed in lower land and widely in higher land. The difference of those distributional pattern is owing to the cultivation controlled by temperature. The cultivation of such as rice, maize, vegetable and so on is below 2,400 m, while one of buckwheat and potato is below ca. 3,000 m high, namely the cultivation is carried out mainly in lower land of the country. With the increase in altitude, the cattle breeding becomes important instead of agriculture and the pasture lands widely establish. In the forest zone the development of grassland accompany with felling down the trees or burning out the forests. While the alpine zone is natural pasture land. The pasture land is generally shifted the alpine zone in summer season and the temperate zone in other seasons. The investigation of grassland vegetation, etc. was carried out following the caravan of our party in September to November, 1985. The areas studied were mainly central Bhutan and some western parts such as Thimphu, Paro and the route of Thimphu to Phuntsoling (Fig. 1). The vertical route section of caravan and survey is shown in Fig. 2. The areas of survey were ranging from 150 m to 5,000 m in altitude.

-75- China

-jjtum /^Gangkher Punsum J"N^PalBhutan f* Masakang 6oph-la ^/^s.dm A>^ fJ 7200m ^-fNamushila ^ ' ^ Chomolhari \ \ bSOOm 7320m / i -•«.^ J % 2370m Punakha { **i 7 Thimphu Q Peie^iaJ Tongsa S^Bumthang V , ( »_ JJ>ochu-la \^> si Nikkachü1-» \ o V Tashigang S~^ "° fiongar Shemgang 1LÄnni j „y -ij ri ri 11 m

>^C. Phuntsoling - ^-—^^ 0 30 bGklT^^^__ — flânas 140m

Fig. 1. Map showing the survey route of Bhutan in 1985-

Gophu-la

SQGO -

MQQG

3DGD -

2GQQ

1DDQ

Phuntsoling

S/lt, S/2? 0/2 0/10 N/l N/lb DATE

Fig. 2. Vertical route section of survey.

-76- METHODS

The investigation was carried out in the grasslands which appeared with the course of caravan. The sample plots were placed at each grassland and vegetation, environments, biotic factors, grassland condition, methods of use and so on were investigated. On the vegetation survey, several quadrats according to the types of grassland communities were set out in each plot and the plant cover and height of each species were measured in each quadrat. On the dominant value, Numata's summed dominance ratio (SDR %: Numata, 1964) based on the plant cover and height was calculated.

RESULTS

1. The grassland vegetation in each altitudinal zone

Firstly, the grazing grassland vegetation is compiled in nine altitudinal sections as follows: below 1,000 m, 1,000 m-1,500 m, 1,500 m- 2,000 m, 2,500 m-3,000 m, 3,000 m-3,500 m, 3,500 m-4,000 m, 4,000 m- 4,500 m and above 4,500 m. In each sections the kinds and types of grassland communities are explained.

(1) The grassland vegetation below 1,000 m in altitude The region below 1,000 m is very hot and belongs to tropical forest zone. There are not so many grasslands because of very steep slope toward Assam district of India and narrow valleys. The nine communities were investigated. The species composition of grazing grassland on Phuntsoling, south border of Bhutan is shown in Table 1. Plot no. 35-1 (P35-1) is light grazing or abandoned forbland, P35-2 is moderate grazing, P35-3 is humid community and P35-4 is heavy grazing community. The dominant species of grazing grassland are Chrysopogon aciculatus, Desmodium heterocarpon, Imperata cylindorica, Paspalum orbiculae (humid), some Cyperaceae spp. (humid), Digitaria sp. (heavy grazing) and Eleusine indica (humid). In the light or rude grazing area, some unpalatable plants for cattle such as Eupatorium adenophorum, Ageratum conyzoides, Sida sp. etc. dominate (Photos. 1&2). P30 and P32

-77- Table 1. Species composition of communities below 1,000 a in alt. by summud dominance ratio (SDR Z). G: grassland F: forbland S: shrubland (h): humid (d): dry

Plot No. 35-1 35-2 35-3 35-4 Locality Phuntsollng Ibid. Ibid. Ibid. Altitude (in) 350 350 350 350 G round cover (Z) 90 85 90 70 Community type F G G(h) G No. of Species 1 1 12 14 16 Eupatorium adenophorum 100 Ageratum conygoides 23 17 25 Sida sp. 38 42 38 50 Microstaglum sp. 21 Mimoza sp. 13 17 16 17 Galinsoga parviflora 25 Cynodon dactylon 19 Commelina difusa 6 Graminea sp. 6 Cassia occidentalis 13 17 Digitaria sp. 6 75 Chrysopogon aciculatus 92 50 Labia ta sp. 22 26 Fimbris tylis sp.1 24 41 17 Desraodlum heterocarpon 100 28 Imperata cylindrica 58 Paspalura orbiculae 19 75 1 1 Kyllinga sp. 6 28 Phyllanthus virgatus 17 Justlcia adhatoda 35 Eragrostis tenella 25 47 Eragrostis unidoides 25 17 Eleusine indica 25 45 Lipocarpha sp. 25 Drymaria iandra 25 Potentilla kleiniana 9 Fimbristylis sp.2 17 Carex sp. 27 Borreria alata 17 Crotalaria sp. 9 Rungia parviflora 9 Synedrella nodiflora 9

Table 2. Species composition of communities below 1,000 ro in alt.

Plot Ho. 30 32 Locality Kurichu Lingme thang Altitude (m) 560 720 Ground cover (%) 100 70 Community type G(h) F No. of Species 13 17 Paspalum scrobiculatum 63 Cassia occidentalis 38 5 Euphorbia hirta 51 Eragrostis tenella 28 Fimbristylis sp. 14 Ageratum conizoides 25 Desraodium heterocarpon 14 Amaranthus sessilis 5 Digi taria sp. 28 13 Sida sp. 7 Dyctyloctenium aegyptium 13 Eleusine indica 14 Cymbopogon gidarba 49 Selaginella sp. 52 Phyllanthus virgathus 7 Bidens sp. 15 Heteropogon sp. 20 Acasia phennata 16 Libia tae sp. 2 Horaceae sp. 8 Eupatorium odratura 58 Barleria cristata 10 Tridex procurobens 8 Inula cappa 12 Linum sp. 10 Arundinella nepalensis 12 Triumfetta rhorafoides 12

-78- Photo. 1. Waste grazing land dominated by unpalatable plants in Phuntsoling (350 m in alt.).

Photo. 2. Various fodder plants in tropical region (Phuntsoling)

-79- are in the lower and dry region of central Bhutan (Table 2). P30 is very small and humid community, and P32 is a forb community in dry habitat. The dominant species is Paspalum scrobiculatum. The forb community which the impact of grazing is weak consists of Eupatorium odoratum, Cymbopogon gidarba, Heteropogon sp., etc. and Selaginella sp. which is a xerophyte dominates in the lower layer of community. In this zone, Gramineae spp. such as Chrysopogon, Digitaria and Paspalum are dominant species in grazing grasslands. As the grazing becomes weak, Eupatorium, Ageratum, tall Gramineae spp., etc. increase.

(2) The grassland vegetation in 1,000 m-1,500 m in altitude The regions surveyed were Chimilakang (P43) and Kurthung (P41 and P42) which are in very dry and warm valley of central Bhutan. The slope of the valley is mostly covered with secondary forests of pine (Pinus roxburgii). A series of P43 shown in Table 3 establishes on the river bench. P43-1 is very dry community, which is dominated by Chrysopogon aciculatus, Heteropogon contortus and Eragrostis tenella. P43-3 is humid community and the dominant species are Cynodon dactylon and Bidens sp. P43-2 is shrub community which consists of many unpalatable plants such as Artemisia indica, Cactacea sp., Berberis sp. Cassia tora and so on. The species composition of grassland in Kur- thang near Chimilakang is shown in Table 4. This region is not so dry as Chimilakang. P42-1 is mesic community and Chrysopogon aciculatus, Cynodon dactylon and Eragrostis tenella dominate. P42-2 which occurs in slightly dry place is dominated by Chrysopogon aciculatus and Heteropogon contortus. P43-3 is a little wet community and Cynodon dactylon and Digitaria setigera dominate. P41 is dry community near P42 and under little light grazing which Chrysopogon aciculatus and Ischaemum rugosum dominate accompanying forbs such as Artemisia indica, Lespedeza cuneata, Spilanthes iabadicensis, etc. The regions surveyed in this altitudinal zone are all in dry place and the dominant species are mostly xeromorphic plants (Photos 3 & 4).

(3) The grassland vegetation in 1,500 m-2,000 m in altitude In this zone, the grasslands of Mongar in the border of eastern Bhutan and of Shemgang in southern central Bhutan were investigated. These regions are humid and become mostly cultivation land, and the

-80- Table 3. Species composition of communities in 1,000 m - 1,500 m in alt.

Plot No. 43-1 43-2 43-3 Locality Chimilakang Ibid. Ibid. Altitude (m) 1 ,200 1 ,200 1 ,200 Ground cover (%) 70 80 100 Community type G(d) S G(h) No. of Species 19 19 5

Chrysopogon aciculatus 100 Eragrostis tenella 46 Leguminosae sp. 9 Heteropogon contortus 62 Cynodon dactylon 12 100 Ischaemum rugosum 38 Oxalis corniculata 9 Ageratum conyzoides 15 38 38 Euphorbia hirta 9 19 Artemisia indica 5 77 13 Panicum sp. 15 Zornia gibbosa 8 Lespedeza cuneata 15 Sida sp. 8 Eragrostis unioloides 15 28 Cyperus sp. 15 Paspalum sp. 15 Phyllanthus virgatus 8 Eleusine indica 8 Gnaphalium sp. 22 Emilia sonchifolia 8 Spilanthes iabadicensis 28 Bidens sp. 13 51 Cactacea sp. 75 Berberis sp. 36 Dactyloctenium aegypticum 11 Cassia tora 29 Jasminum sp. 23 Xanthium strumarium 19 Setaria sp. 13 Siegesbeckia orientalis 19 Phamnus sp. 19 Chloris sp. U Arthraxon sp. 7

Table 4. Species composition of communities in 1,000 m - 1,500 m in alt.

Plot No. 42-1 42-2 42-3 41 Locality Kurthung Ibid. Ibid. Ibid. Altitude (m) 1 ,300 1 ,300 1 ,300 1 ,300 Ground cover (%) 80 75 70 100 Community type G G G G No. of Species 12 9 6 12 Chrysopogon aciculatus 50 100 70 Eragrostis tenella 46 19 Euphorbia hirta 27 12 9 Eragrostis unioloides 28 11 Eleusine indica 1 2 Artemisia indica 25 45 30 Sida sp. 13 U Zornia gibbosa 13 12 Dactyloctenium aegypticum 25 25 Cassia tora 26 29 Eragrostis sp. 50 Cynodon dactylon 63 88 1 6 Heteropogon contortus 58 Saccharum spontaneum 47 Digitaris setigera 4 55 Bidens sp. _ 27 Amaranthus sessilis 15 7 Embrustylis sp. 1 1 Ischaemum rugosum 71 Phyllumthus virgatus 7 Lespedeza cuneata 37 Spilanthes iabadicensis 30 Se taria sp. 7

-81- Photo. 3. Grassland in arid region (Chirailakang: 1,200 m in alt.)

Photo. 4.. Heteropogon contortus which is a dominant species of the above community.

-82- grasslands are not so many and wide. A series of P31 is four communities in Mongar(Table 5). P31-1 is dry grazing grassland community which is dominated by Chrysopogon aciculatus. P31-2 is humid one and Digitaria sp. with some subdominant species such as Chrysopogon, Sporobolus fertilis, S^ diander etc. dominates. P31-3 is heavy grazing community and Chrysopogon aciculatus dominates and Sporobolus fertilis, Eragrostis tenella, etc. are also dominate. P32-4 is forb community which is dominated by some unpalatable plants such as Artemisia indica, Rubus ellipticus, etc. A series of P38 was selected in Shemgang which is also humid place (Table 6). P38-1 is mesic grassland community and Cynodon dactylon and Eragrostis nigra dominate, but the forbs such as Artemisia indica and Anaphalis margaritacea are abundant, too. P38-2 is bare ground which is usually trampling, and the dominant species are as same as P38-1, but Plantago erosa occurs high value. P38-3 and P38-4 are both similar communities which are abandoned or under light grazing. P38-3 is dominated by Anaphalis and Artemisia, and P38-4 is dominated by Artemisia, Rubus ellipticus, Aconogonum mole, etc. The most of the dominant species in these plots are unpalatable plants. In the grazing grasslands of this zone, Chrysopogon aciculatus (dry community), Paspalum sp. (humid community) and Cynodon dactylon (mesic community) dominate, and Artemisia indica, Anaphalis margaritacea, Rubus ellipticus and so on dominate in the waste or rude communities.

(4) The grassland vegetation in 2,000 m-2,500 m in altitude In this zone, the grasslands of Thimphu which is situated in western Bhutan and Tongsa which is lying in central Bhutan were investigated. A series of P33 and P34 were surveyed in Thimphu which is under warm- temperate and mesic climate (Table 7). P33-1 is mesic grassland community and consists of the small number of species and the some mixed dominant species of Digitaria stricta, Cynodon dactylon, Chrysopogon aciculatus and Eragrostis nigra. P33-2 is bare ground with low vegetation cover (30 %) and is dominated only by Digitaria stricta. P33-3 is a little light grazing community than P33-1, and Chrysopogon aciculatus dominates accompanying with Eragrostis nigra, Carex nubigena, Galinsoga parviflora, Erigeron canadensis, etc. P34 is slightly humid community, and Chrysopogon aciculatus and Carex nubigena are dominant with some Cyperaceae spp. such as Fimbristylis sp., Cyperus sp. and Picreus sp. A

-83- Table 5. Species composition of coiiunities in 1,500 m - 2,000 m in alt.

Plot No. 31-1 31-2 31-3 31-4 Locality Hongar Ibid. Ibid. Ibid. Altitude (m) 1 ,680 1 ,680 1 ,680 1 ,680 Ground cover (Z) 100 100 85 85 Community type C(d) G(h) G F No. of Species 11 18 12 19

Chrysopogon aciculatus 100 58 100 16 Plantago erosa 21 7 3 Cynodon dactylon 21 18 22 15 Desoodium multiflorm 27 10 Paspalum sp. 13 83 10 .3 Digitaria sp. 5 17 Agrostis inaequigluois 22 Equisetum sp. 7 Oxalis corniculata 5 7 1 Centella asiatica 5 7 Fimbristylis sp. 5 17 10 Potentilla klelniana 10 Poa annua 10 Sporobolus fertilis 33 £2 S. diander 33 Eragrostis nigra 17 Setaria pallidefusca 17 Arthraxon sp. 17 22 7 Echinochloa sp. 17 Bothriochloa intermedia 17 Eragrostis tenella 31 Euphorbia hirta 10 Verbena offlcinalis 32 1 1 Leguiminosae sp. 7 Mariscus sp. 14 Kyllinga sp. 14 Artemisia indica 88 Ageratum conyzoides 19 Geranium nepalensis 1 Spilanthes iabadicensis 22 Rumex nepalensis 3 Rubus ellipticus 53 Viola sp. 8 Cos mos sp. 18 Rubia wallichiana 10 Lepidium virginicum 1 Agrimonia pilosa var. nepalensis 15

Table 6. Species composition of communities in 1,500 m - 2,000 m in alt. B: bare ground Plot No. 38-1 38-2 38-3 38-4 Locality Shemgang Ibid. Ibid. Ibid. Altitude (m) 1 ,820 1 ,820 1 ,820 1 ,820 Ground cover ( X )• * 100 20 85 100 Community type G B S S No. of Species U 6 17 12 Cynodon dactylon 75 60 Eragrostis nigra 56 55 38 Artemisia indica 48 60 71 96 Anaphalis marganitacea 52 77 28 Rumex nepalensis U Centella asiatica 15 29 Geranium nepalensis 9 5 Oxialis corniculata 5 3 Plantago erosa 10 35 17 Cosmos sp. 38 Lamium amplexicaule 38 Setaria sp. 20 1 1 Pers icaria sp. 5 Sporobolus fertilis 40 Fimbristylis sp. 25 13 Galinsoga parviflora 22 Dipsacus inerimis var.mitis 19 Laguminosae sp. 8 Potentilla kleiniana 5 Ageratum conyzoides 7 Arthraxon sp. 21 13 12 Prunella vulgaris 9 Fagopyrum sp. U Myriactis nepalensis 15 Rubus ellipticus 73 Pterinium aquilinura 63 var. uightianum Rubia wallichiana 23 Aconogonuro mole 67 Achyranthes sp. 9 Spilanthes iabadicensis 8 Ranunculus laetus 20

-84- Table 7. Species composition of communities in 2,000 m - 2,500 m in alt. Plot No. 33-1 33-2 33-3 34 Locality Thimphu Ibid. Ibid. Ibid. Altitude (m) 2,370 2,370 2,370 2,370 G round cover (Z) 95 30 90 85 Community type G B G 0(h) No. of Species 6 2 13 20 Digitaria stricta 67 100 12 3 Cynodon dactylon 42 22 5 13 Chrysopogon aciculatus 51 100 65 Eragrostis nigra 51 32 16 Carex nubigena 18 16 60 Poa annua 10 Cassia mimosoides 17 Vigna umbellata 9 Sporobolus fertilis 16 Potentilla sp. 5 Flmbristylis sp. 7 Galinsoga parviflora 18 Erigeron canadensis U Plantago erosa 5 Cyperus sp. 28 Smithia ciliata 28 Hypericum sp. 6 Artemisia indlca 6 Picreus sp. 10 Ixeris sp. 6 Arundinella hookerl 5 Echinochloa cf. colonum 3 Leguminosae sp. 3 Bethriochloa intermedia 3 Labiatae sp. 2

Table 8. Species composition of communities in 2,000 m - 2 , 500 m in alt. Plot No. 36-1 36-2 36-3 37-1 37-2 Locality Thimphu Ibid. Ibid. Ibid. Ibid. Altitude (m) 2,370 2,370 2,370 2,370 2,370 Ground cover (%) 100 85 80 30 100 Community type G(h) G(d) S%F B SZF No. of Species 13 13 13 5 25 Paspalum scrobiculatum 59 Chrysopogon aciculatus 36 75 24 Artemisia indica 41 74 1 1 56 Rumex nepalensls 43 Fimbristylis sp. 1 1 1 1 Cassia mimosoides 7 13 Prunella vulgaris 7 Pycreus sp. 4 Kyllinga sp. 3 Eragrostis nigra 39 47 19 54 Miscanthus nudipes 51 13 46 Cosmos sp.1 12 41 24 Se ter ia sp. 6 12 Legminosae sp. U Stellaria vestita 10 6 Sporobolus fertilis 20 Conyza s trie ta 3 Taraxacum sp. 3 Helictotrichon pariviflorum 51 13 17 Cosmos sp.2 18 30 Rosa sericea 18 75 Elaeagnus parvifolia 55 30 Verbascum sp. 16 29 Smithia ciliata 14 Dichrocephalia integrifolia 12 Cynodon dactylon 67 7 Plantago erosa 1 2 Carex nubigena 35 5 Salvia campanula ta 81 Boenninghausenia alliflora 23 Pteriniura aquilium 18 var. wigh tianura Gnaphalium sp. 1 1 Potentilla sp. 9 Halenia elliptica 7 Arundinella hookeri 16 Brachypodium sp. 15 Tripogon trifidus 12

-85- series of P36 and P37 are also grasslands of Thimphu (Table 8). P36-1 is humid community dominated by Paspalum scrobiculatum with some Cyperaceae spp. P36-2 is dry community and Chrysopogon aciculatus dominates with Eragrostis nigra and Helictotrichon parviflorum. P36-3 is shrub and forb community near P36-2. Chrysopogon aciculatus appears under the community, while the tall plants such as Miscanthus nudipes, Helictotrichon parviflorum, Artemisia indica, etc. and some shrubs such as Rosa sericea, Elaeagnus parvifolia occupy the upper layer of community. P37-1 is bare ground owing to heavy trampling, and Cynodon dactylon and Eragrostis nigra dominate. P37-2 is more dense shrub and forb community than P36-3, and is covered with Salvia campanulata, Artemisia indica, Rosa sericea, Elaeagnus parvifolia etc. In Table 9, P39-1 is mesic grassland community and some grasses such as Sporobolus fertilis, Chrysopogon aciculatus, Arundinella hookeri and Eragrostis nigra dominate. P39-2 is humid community dominated by Setaria sp., Contella asiatica, Picreus sp., Spilanthes iabadicensis and so on. P40 is higher place than P39. P40-1 is dry community dominated by Arundinella hookeri and consists of a few species. P40-2 is moderate grazing community and Eularia sp. dominates with some grasses such as Arundinella hookeri, Eragrostis nigra and Helictotrichon parviflorum, and some herbs such as Artemisia indica, Anaphalis margaritacea and Potentilla fulgens. In this zone, there are many dominant grasses such as Digitaria, Cynodon, Chrysopogon, Eragrostis, Paspalum, Sporobolus, Eularia, Arun- dinella according to the conditions of grazing and humidity. The dominant species of shrub and forb communities are Artemisia, Rosa, Elaeagnus, Helictotrichon, Anaphalis, Cosmos, etc.

(5) The grassland vegetation in 2,500 m -3,000 m in altitude In this zone three regions, namely, Nikkachu, Sengor and Bumthang in central Bhutan were surveyed. A series of PI were investigated in Nikkachu which is widely covered with grazing grassland using for winter season (Table 10, Photo. 5). Pl-1 is mesic grassland community and Arun- dinella hookeri dominates with Eragrostis nigra and Fimbristylis sp.(Photo. 6). Pl-2 is dwarf bamboo community under light grazing dominated by Arundinaria falconeri accompanying Arundinella hookeri, Potentilla fulgens, Agromonia pilosa var. nepalensis, etc. Pl-3 is bracken community and some unpalatable plants for cattle such as Pterinium aquilinum var. wigh-

-86- Table 9- Species composition of communities in 2,000 m -. 2,500 m in alt.

Plot No. 39-1 39-2 40-1 40-2 Locality Tongsa Ibid. Ibid. Ibid. Altitude (m) 2 ,200 2,200 2,400 2,400 Ground cover (Z) 100 100 70 100 Community type G C(h) G(d) G No. of Species 13 17 14 15

Spolobolus fertilis 94 10 Eragrostis nigra 54 9 25 Chrysopogon aciculatus 81 20 Arundinella hookori 67 76 30 Flmbristylis ap. 27 Hiacanthus nudipes 52 Anaphalis margaritacea 32 33 23 33 Imperata cylindrica 32 Trifollum repens 8 Potentilla fulgens 14 5 23 Smithia ciliata 1 1 10 Contella asiatica 5 58 Stellaria vestita 7 18 Setaria sp. 71 Cynodon dactylon 25 Juncus s p. 33 Prunella vulgaris 18 13 Picreus sp. 50 Agrimonia pilosa var.nepal« n sis 20 Cirsium sp. 10 13 Gnaphalium sp. 35 Myriactia nepalensia 25 Spilanthes iabadicensis 52 Artemisia lndica 27 1 5 38 Eularla sp. 35 100 Plantago erosa 4 Salix sp. 54 Pterinium aqullinum 24 4 var.wightianum Desmodium- multifloruci 1 1 9 Helictotrichon parvifloruo 39 34 Cotoneaster microphyllus 20 Vibrunuo coriaceum 44 Quercus sp. 38 Pimpinella sp. 13 Primula capitata 8 Euphrasia schlagintweitii 17 Microstegium sp. 9

Table 10. Species composition of communities in 2,500 m - 3,000 m in alt. Pc: Pterinium community Be.: Bamboo community Cc: Cotoneaster community

Plot Ho. 1-1 1-2 1-3 1-4 1-5 Locality Nikkachu Ibid. Ibid. Ibid. Ibid Altitude (m) 2,580 2,580 2,580 2,580 2,580 Ground cover (Z) 80 80 100 100 100 Community type G Be. Pc. Cc. Be. No. of Species 1 1 17 13 15 12

Pteriniun aquilinun var. 39 88 50 13 vightianum Halenia elliptica 17 .43 30 34 11 Arundinella hookeri 100 45 21 Potentilla fulgens 27 33 35 34 Hypericum elodeoides I 1 12 Fimbristylis sp. 25 7 Anaphalis margaritacea 18 22 27 35 Eragrotstis nigra 26 35 Prunella vulgaris 8 9 Geranium nepalensis 6 Persicaria nepalense I1 9 7 Arundinaria falconer! 69 52 86 Senesio chrysanthemoides 5 Agrimonia pilosa var. nepaïensis 50 19 18 Hyriactis nepalensis 26 Hemiphragma heterophyllum 19 Delphynium stapeliosmus 17 Potentilla fragarioides 4 Clinopodium umbrosum 13 Elaeagnus parvifolia 41 55 53 Erigeron bellioides 39 34 Artemisia indica 10 12 Ar thraxon s p. 12 Agropyron "sp. 38 Cotoneaster microphyllus 87 Rabdosia repens 17 Lon icera sp. 36 Picea spinulosa 45 Rubus sp. 52 46 Agrostis nervosa 35 Helictotrichon parviflorum 41 1 5 Berberis hookeri 23 Pinus oxcols.i 1 2 Brachpodium sp. 9

-87- Photo. 5. Middle altitudinal region which the pasture land widely develops (Nikkachu: 2,580 m in alt.).

Photo. 6. Representative grassland community in Nikkachu which is dominated by Arundinella hookeri. tianum, Anaphalis margaritacea, Elaeagnus parvifolia etc. Pl-4 is Cotoneaster communities and is also dominated by some unpalatable plants such as Cotoneaster microphyllus, Pterinium, Elaeagnus, Rubus sp. Lonicera sp. and so on. Pl-5 is tall Arundinaria community which is abandoned, and Arundinaria falconeri dominates with Elaeagnus parvifolia, Rubus sp., Berberis hookeri, etc. A series of P29 is the grassland communities of Sengor which is the highest place in this altitudinal zone (Table 11). P29-1 is dry community which has some dominant species such as Potentilla fulgens, Fimbristylis sp. and Eragrostis nigra. P29-2 is light grazing or rude community dominated by some unpalatable plants such as Senecio chrysanthemoides, Primula capitata, Prunella vulgaris, etc. P26-3 is humid grazing community and Carex albata, Eriocaulon sp., Luzula sp. and moss dominate. P29-4 is bare ground under heavy grazing and Potentilla fulgens, Poa annua, Persicaria nepalensis, Plantago erosa, Elsholtzia strobilifera, Digitaria violascens appear. P27-1 and P27-2 are grazing communities of Bumthang which develops in the wide valley (Table 12). P27-1 is dry community and Eragrostis nigra dominates with Setaria sp. and some herbs such as Chenopodium album, Artemisia indica, Erigeron canadensis, etc. P27-2 is abandoned forb community which is covered by many f orbs such as Artemisia indica, Boehmeria sp., Cosmos sp. Cirsium sp., etc. and some shrubs. In this zone, Arundinella hookeri and Eragrostis nigra are dominant species in the dry and mesic grazing grasslands. The unpalatable plants such as Artemisia, Anaphalis, Senecio, Pterinium, Cotoneaster, Rubus, Berberis, Elaeagnus and tall grasses such as Helictotrichon increase under light grazing or rude grazing, and the bamboo community (Arundinaria community) establishes soon.

(6) The grassland vegetation in 3,000m -3,500 m in altitude In this zone, the grasslands of five regions were investigated. The PE series is in the forest of Dochu-la where is a pass hear Thimphu (Table 13, Photo.7). PE-1 is bare community by heavy grazing and trampling. The dominant species are Carex nubigena and Plantago erosa. PE-2 is forb community consisting of many unpalatable plants such as Rumex nepalensis, Artemisia indica, Senecio chrysanthemoides, etc. PE-3 is shrub community which some shrubs such as Juniperus sp., Rubus ellipticus, Berberis umbellata and a kind of bamboo, Arundinaria falconeri

-89- Table 11. Species composition of communities in 2,500 m - 3,000 m in alt.

Plot No. 29-1 29-2 29-3 29-4 Locality Sengor Ibid. Ibid. Ibid. Altitude (m) 3,000 3,000 3,000 3,000 Ground cover (Z) 90 100 70 15 Community type G(d) G G(h) B No. of Species 15 15 11 9

Anaphalis margaritacea 19 5 44 Potentilla fulgens 57 75 Arundinella hookeri 47 Firabristylis sp.1 67 26 Eragrostis nigra 61 35 Heraiphragma heterophyllum 10 27 Cyanotis voga 5 7 Halenia elliptica 28 Persicaria nepalensis 7 9 52 Poa annua 5 55 Carex albata 16 67 Prunella vulgaris 14 57 24 Agrostis nervosa 9 28 42 Cotoneaster microphyllus U Aster sp. 28 Iris sp. 19 Helictotrichon parviflorum 47 Senecio chrysanthemoides 67 Primula capitata 61 45 Rumex nepalensis 10 Carex nubigena 5 Hypericum sp. 16 43 Solanum sp. 14 Myriactis nepalensis 14 Fimbristylis sp.2 28 Eriocaulon sp. 58 Elymus sikkimensis 53 moss 63 Luyzula sp. 58 Coelachne simpliciuscula 42 Plantago erosa 67 Elsholtzia strobilifera 60 Digitaria violascens 55

Table 12. Species composition of communities in 2,500 m - 3,000 m in alt.

Plot No. 27-1 27-2 Locality Bumthang Ibid. Altitude (m) 2,580 2,580 Ground cover (Z) 90 100 Community type G(d) F No. of Species 18 23

Eragrostis nigra 86 15 Setaria sp. 46 Cynodon dactylon 8 Rumex nepalensis 24 17 Gnaphalium hypoleucum 12 Geranium nepalense 10 Galinsoga parviflora 22 Siegesbeckia orientalis 15 Agromonia pilosa var. 10 24 nepalensis Hyricactis nepalensis 18 Artemisia indica 30 96 Cosmos sp. 29 26 Erigeron canadensis 36 Carex nubigena 22 4 Potentilla flugens 15 Trisetum sp. 16 Compositae sp. 51 Chenopodium album 50 Boehmeria sp. 66 Cirsium sp. 20 Elaeagnus parviflolia 65 Anaphalis margaritacea 19 Rubus sp. 24 Helictotrichon parviflorum 24 Agrostis nervosa 8 Stellaria vestita 8 Persicaria runcinata 1 1 Digitaria setigera 13 Echinochloa crusgalli 8 Elyraus thomsnii 12 Agrophyron sp. 20 Pycreus sp. 4 Bulbostylis sp. 8 Poa sp. 6 Tripogon trifidus 13 -90- Table 13- Species composition of communities in 3,000 a - 3,500 n in alt. Plot No. E-1 E-2 E-3 Locality Dochu-la Ibid. Ibid. Altitude (m) 3,120 3,120 3,120 Ground cover (Z) 50 100 100 Community type B F S No. of Species 4 13 11 Carex nubigena 100 19 Poa annua 44 Plantago erosa 75 8 Potentilla fulgens 36 23 Rumex nepalensis 98 Senecio chrysanthemoides 59 Iris sp. 48 Artemisia indica 75 Persicaria runcinata 17 Galium asperifolium 14 Paro chetus communis 14 Geranium procurrens 14 Umbelliferae sp. 25 Hypericum elodeoides 10 Pterinium aquilinum 56 var. wightianum Clinopodium umbrosum 33 Juniperus sp. 71 Rubus ellipticus 98 Allium «allichii 29 Sambucus adnata 57 Berberis umbellata 50 Arundinaria falconeri 83 Stellaria vestita 20 Aconitum sp. 47 Halenia ellipitica 34

Table 14. Species composition of communities in 3,000 m - 3,500 m in alt.

Plot No. 24-1 24-2 24-3 25 26 Locality Gorseum Ibid. Ibid. Ibid. Ibid Altitude (m) 3,120 3,120 3,120 3,100 3,010 Ground cover (Z) 100 100 100 80 80 . Community type G(d) G F Bc. G(d) No. of Species 20 19 16 17 14

Elholtzia strobilifera 48 32 24 Umbelliferae sp. 47 22 7 Potentilla fulgens 76 48 13 15 63 Anaphalis margaritacea 43 34 63 Senecio chrysanthemoides 32 46 63 23 Agrostis nervosa 48 36 • 6 13 Euphrasia sp. 31 12 Cyanotus sp. 10 Fimbristylis sp. 27 23 Festuca undata var. aristat 5 51 36 17 16 9 Hemiphrangma heterophyllum 1 1 4 5 Carex nubigena 24 7 7 8 4 Hyriactis nepalensis 20 22 8 21 Leibnitzia nepalensis 20 8 Agrostis sp. 21 Cirsiura sp. 7 . 18 7 Arundinella hookeri 11 16 44 Elymus slkkimensis 20 Brachypodium sp. 20 Helictotrichon parviflorum 30 Berberis umbellata 42 Pterinium aquilinium 85 var. wightianum Arundinaria falconeri 40 100 Cupressus torulosa 42 Saussurea sp. 7 Anthoxanthum sikkimense 12 Bromus staintonii 80 Aconogonum mole 68 Rumex nepalensis 28 Rosa macrophylla 53 28 Persicaria runcinata 18 9 Prunella vulgalis 16 12 1 1 Halenia elliptica 6 22 Artemisia indica 16 33 51 Miscanthus nudipes 17 Rhododendron lepidotum 25 Cotoneaster microphyllus 17 Rosa sericea 21 Eragrostis nigra 44 Poa s p . 17 -91- Photo. 7. Pasture land in cool-temperate forest (Dochu-la: 3,120 m in alt.).

Photo. 8. Bamboo grassland under light grazing in Dochu-la.

-92- dominate (Photo 8). A series of P24, P25, and P26 are grassland communities in Gorseum, the north of Bumthang (Table 14). P24-1 is dry community which is dominated by forbs such as Potentilla fulgens, El- sholtzia strobilifera and Umbelliferae sp., and some grasses such as Fes- tuca undata var. aristato and Agrostis nervosa. P24-2 is waste community dominated by Bromus staintonii and some unpalatable plants such as Pterinium aquilinum var. wightianum, Senecio chrysanthemoides, Poten- tilla fulgens, etc. P24-3 is forb community which is not disturbed by grazing, and Aconogonum mole, Senecio chrysanthemoides and Rosa macrophylla dominate. P25 is abandoned bamboo community which was ever grazed, and is dominated by Arundinaria falconeri accompanied with some shrubs and tall forbs. P26 is dry community and the herbs such as Poten- tilla fulgens and Anaphalis margaritacea dominate with Arundinella hookeri and Eragrostis nigra. P13 is humid community in the Abies forest of Donshigang and Luzula sp. dominates in the lower layer of the community, and some shrubs, Salix sp. and Berberis umbellata in the upper layer of community dominate (Table 15). P14 is dry grazing community in Duersachu near Donshigang and Deyeuxia scabrescens dominates with several unpalatable plants such as Salix sp., Anaphalis margaritacea, Halenia ellipticus, Selinum candollei, Rosa macrophylla, etc. P16 is near P15 and dry community which is difficult to estimate the dominant species. Rhododendron lepidotum, Anaphalis margaritacea, Selinum candollei, Deyeuxia scabrescens, Festuca spp., etc. show relatively high dominance value. Table 16 shows the species compositions of the grassland communities in Kurbang. P22-1 is mesic grassland and floristic richness. Agrostis pilosula dominates and many unpalatable plants such as Prunella vulgaris, Primula capitata, Rumex nepalensis, Juniperus recurva, Berberis umbellata, fern and so on occur. P22-2 is dwarf bamboo community under light grazing which Arundinaria falconeri dominates and some forbs accompany. P22-3 is humid grazing community and Carex sp., Juncus sp., Agrostis inaequiglumis, etc. dominate with fern. P23 is humid community near P22 and Arundinaria falconeri is dominant with some forbs and Çarex nubigena. In this zone, the number of dominant grasses is few, and many forbs, ferns and shrubs occur with high frequency and high dominant value. A type of bamboo, Arundinaria falconeri is very characteristic species.

-93- I

I Table 15. Species composition of communities in 3,000 o - 3,500 m In alt. Plot No. 13 14 16 Locality Donshigang Duersachu Ibid. Altitude (n>) 3,480 3,400 3,400 Ground cove r (Z) 95 70 90 . I Commun!ty type G(h) C(d) G(d) No. of Species 21 17 20

Salix sp. 53 45 Berber!s uobeliata 52 12 I Prunella vulgar!s 20 Senesio chrysantheooides 19 7 Luzula so. 56 Elsholtsia atrobilifera 6 Persicaria runcinata 5 Agrostls sp. U 19 I Poa sp. 12 AconituQ sp. 8 Carsx nubigena 9 7 Potent!lia fragarloidea 2 7 Geranium donlanuo 3 4 I Gallluo aaper!folium 3 Rubus pedunculosus 5 Runax nepalensis 5 Ciraium sp. 11 Epilobium wallichlanua 6 32 Acer pectinatum 7 I 3 Anaphalia margaritacea 34 60 Cotoneaster olcrophyllua 12 7 Halenia elllptica 30 18 Potentilla fulgens 15 43 16 7 I Carsx sp. 29 Agrostis pilosula 26 Selinun candollei 42 53 77 42 Pollgonatum curvistylum 24 12 ' I fern 19 29 Berberis uobellata 28 Ephedra gerardiana 14 var. sikkimensis Potentilla cuneata 38 I Parnassia ap. 9 Rhododendron lepldotum 73 Featuca ovlna 36 Festuca sp. 26 Leontopodium sp. 34 I Artemisia lndica 23

Table 16. Species composition of communities in 3,000 o - 3,500 m in alt.

Plot No. 22-1 22-2 22-3 23 I Locality Kurbang Ibid. Ibid. Ibid. Altitude (o) 3,500 3,450 3,500 3,300 Ground cover (Z) 95 90 60 90 Community type G Be. G(d) G(h) No. of Species 22 9 7 14 I Prunella vurgaris 38 7 41 Primulla capitata 35 Elahortzia atrobilifera 14 Rumex nepalensis 34 Seneclo chrysanthamoidea 18 44 I Juniperus recurva 50 Berberis umbellata 42 Peralcaria runcinata 17 14 Agroatis pilosula 68 fern 36 26 76 Ranunculus sp. 5 I Epilobium uallichlanum 26 Festica ovina 15 Carex nubigena 27 41 38 Potentilla fulgens 18 7 Potentilla fragarioides 17 20 I Plantago erosa 14 7 Poa ap. 18 Agrostis oyriantha 17 43 Deyeuxia scabresaens 18 Glyceria sp. 34 Strobilanthes sp. 20 I Senesio tetrenthus 44 (Jmbellif erae sp. 45 moss 7 Arundinaria falconer! 100 100 Geranium domianum 22 14 Cacalia pentaloba 33 I Streptopus simplex 14 Carex sp. 100 Juncus ap. 68 Kobresia duthiei 53 Agrostis inaequiglunii3 63 I Anaphalis margaritacea 6 Galliuo aope rif oliutn 26 Agrostis nervosa 51 Stellaria slkklmensis 7 Aconogonum mole 51 I -94- I (7) The grassland vegetation in 3,500 m -4,000 m in altitude In this zone, the grasslands of three regions were surveyed. A series of P2 is in Morathang, upper Nikkachu of central Bhutan (Table 17, Photo.9 ). P2-1 is forb community consisting of Senecio chrysanthemoides, Persicaria nepalensis, Rumex nepalensis, Cirsium falconeri, etc. which are mostly unpalatable plants (Photo. 10). P2-2 is special community on sandy soil in river bed and Myricaria rosea is dominant, and the subdominant species are Anaphalis margaritacea, Festuca sp., Epilobium wallichianum, etc. P2-3 is humid grazing community which Juncus sp., Poa sp. and Carex sp. dominate. P2-4 is mesic and heavy grazing community dominated by Plantago erosa, Aconogonum mole, Carex nubigena accompanied with Agrostis pilosula and Agrostis inaequiglumis. P4, P21 and P2-5 are shown in table 18. P4 is humid community in Tampeytso and Agrostis inaequiglumis dominates with subdominant species such as Glyceria tonglensis, Carex nubigena, etc. P21 is mesic grassland in Kurbang and Kobresia cf. royleana, Kobresia duthiei, and Carex nubigena dominate. P2-5 is shrub community of preceding Morathang, and Juniperus recurva dominate with Berberis umbellata. In this zone, the number and dominance of Gramineae spp. reduce and Cyperaceae such as Carex and Kobresia spp., Compositae spp., Rosaceae spp. and shrubs increase in the grazing grasslands than below this zone.

(8) The grassland vegetation in 4,000 m -4,500 m in altitude Four plots were investigated in this zone which belongs to the alpine zone above timber line. Thus grasslands are so-called alpine meadows. In Table 19, the plots of Umatatso and Tsongtsothang where are situated in the north of central Bhutan, namely, central Bhutan Himalaya are shown (Photo. 11). P3-1 is mesic grazing community dominated by Potentilla microphylla and Poa sp. accompanied with some grasses such as Poa sp, Agrostis inaequiglumis and Festuca sp., and some sedges such as Juncus sp. and Kobresia cf. royleana (Photo. 12). P3-2 is shrub community on the steep slope near P3-1 and small Ericaceae spp. such as Rhododendron setosum, R. campanulatum var. wallichii and Cassiope fastigiata dominate (Photo. 13). P5-1 is humid community dominated by Agrostis inaequiglumis and Kobresia spp. accompanied with moss. P5-2 is light grazing community and Potentilla

-95- I

I Table 17. Species composition of communities In 3,500 m - 4,000 m in alt. Plot No. 2-1 2-2 2-3 2-4 Locality Mora thang Ibid. Ibid. Ibid. Altitude (m) 3,580 3,580 3,580 3,580 I Ground cover (X) 100 100 60 95 Conounity type F G G(h) G Ho. of Species 17 17 7 14

72 18 Parsicaria nepalensia 79 18 I Clrsium falconeri 58 Rumex nepalensls 67 Corydalla longylas 28 Geranium donianluo 21 17 Stellia restlta 14 13 Aconogonum mole , 25 52 I Parochetus comaunis 17 14 Persicaria sp. 13 Uoberlferao sp. 41 9 Epiloblum uallichianum 25 33 4 Cerastlum glooeratum 7 I Poa sp. 20 51 Carex nubigena 19 42 45 Clinopodluo unbroaum 9 Agrostis nervosa 21 38 Potentllla amblgua 6 Poa annua 6 9 I Anaphalls triplinervia 52 73 Festuca sp. 53 Carex sp. 13 Euphrasla schlagen tuet til 13 I Trlsetum spicatuo 32 Delphinium nepalense 4 Prunella vulgalis 13 33 18 Orchidaceae sp. 25 Lonianum sp. 3 Lomatogonium carinthiacum 7 I Parnassia sp. 13 Saxifraga sphaeradena 15 Potentilla fragarioldes 7 Prlnula sp. 45 17 Juncus ap. 75 Plantago erosa 58 I 9 Agrostis pllosula 38 Glyceria tonglensis 26 I Agrostis lnaequiglumis 34 Table 18. Species composition of communities in 3,500 m - 4,000 n in alt.

Plot No. 4 21 2-5 Locality TaoDeytso Kurbang Mora thang Altitude (m) 3,750 3,850 3,580 I Ground cover (Z) 100 100 100 Community type G(h) G S Ho. of Species 15 10 25

Aconitum sp. 35 I Carex nubigena 50 83 32 Potentilla oicrophylla 13 38 Carex sp. 20 Poa sp. 18 52 Persicaria runcinata 22 Plantago erosa 11 I Prunella vulgaris 13 4 Senecio chrysanthemoides 28 28. Deyeuxia pulchella 22 Agrostis pllosula 23 35 28 Agrostis inaequiglumis 100 42 Kobresia duthiei 27 67 I Glyceria tonglensis 52 Potentllla fragarioides 17 2 Kobresia cf. royleana 100 Gnaphalium sp. 42 Persicaria nepalensis 38 4 I Gentianaceae sp. 13 Juniperus recurva 100 Barberia umbellata 60 fern 1 13 Saxifraga moorcroftiana 7 Taraxacum sp. 6 I Anaphalis margaritace 19 Geranium lambertil 23 Legminosae sp. 14 Geranium donianum 2 Saussurea sp. 26 Tern 2 21 I Bromus stalntonii 28 Salvia sp. 27 Trisetum sp. 7 Nepeta lamiopsis 21 Erigeron bellioldes 7 I Potentilla ambigus 2 Cotoneaster microphyllus 4

I -96- I Photo. ?/• Open grassland in the river bed of Morathang (3,580 m in alt.).

Photo. 10. Unpalatable plant community composed of Artemisia, Senecio, Cirsium, Aconogonum, etc. in Morathang.

-97- Table 19. Species composition of communities in 4,000 m - 4,500 on in alt

Plot No. 3-1 3-2 5-1 5-2 Locality Uma ta tso Ibid. Tsongtsothang Ibid. Altitude (m) 4,300 4,300 4,340 4,340 Ground cover (Z) 75 90 70 100 Community type G S C(h) G No. of Species 17 14 10 8 Potentilla microphyylla 60 16 20 71 Taraxacum sp. 35 Pedicularis siphonantha 21 Agroatis inaequiglimis 30 • 18 64 46 Gentiana algida 21 18 7 Poa sp 53 50 Poa annua 21 Potentilla cuneata 7 4 Persicaria runcinata 4 18 23 Cortia depressa 6 J uncu s sp. 25 54 Chrysosplenium sp. 20 Ranunculus sp. 2 Fes tuca sp. 30 35 22 Kobresia cf. royleana 31 36 45 Bistorta vivipana 20 Deyeuxia pulchella 21 Rhododendron setosum 83 Cassiope fastigiata 48 Rhododendron campanulatum 70 var. walllchii moss 67 50 4 Carex sp. 1 1 15 Lomatogonium sp. 13 Centiana aglaia 7 Aster sp. 6 Gaultheria trlchephytla 7 Primula prlmulina 1 1 Kobresia duthiei 67 Umbelliferae sp. 18

Table 20. Species composition of communities in 4,000 m - 4,500 m in alt.

Plot No. 1 1 17 18 Locality Tanchenmo below Ibid. Juree-la Altitude (o) 4,300 4,200 4,200 Ground cover (X) 60 60 80 Community type C(d) G(h) G No. of Species 13 17 22

Taraxacum sp. • • * 16 19 '2 5 Erigeron sp. 22 Fes tuca ovina 80 23 Leontopodium sp. 22 Cassiope fastigiata 33 Anaphlis triplinervis 51 Potentilla mycrophylla 35 58 24 Rhododendron campanula turn 58 var. wallichii Berberis umbellata 63 43 Agrostis sp. 33 Angelica sp. 26 Juniperus recurva 53 53 Gentiana algida 16 Poa s p. 80 Rumex nepalensis 45 Senecio chrysanthemoides 44 Sanguisorba sp. 33 31 Potentilla fragarioides 19 7 Umbelliferae sp. 21 1 1 Aconitum sp. 53 Persicaria runcinata 28 21 Potentilla cuneata 23 Geranium domiatum 17 1 1 Carex sp. 19 Agrostis inaequiglurais 23 17 Gramineae sp. 33 Gentiana sp. 19 1 1 Saussurea sp. 13 17 Cotoneaster microphylla 63 Kobresia cf. royleana 80 Primula sp. 21 moss 8 Trisetum spicatum 22 Juncus sp. 21 Ranunculus sp. 10 Meconops is sp. 27 Fes tuca sp. 27 -98- Photo. 11. Lower alpine meadow in Umatatso (^,300 m in ait.)

Photo. 12. Alpine meadow which Potentilla, Agrostis, Gentiana, etc. dominate (Umatatso).

-99- Photo. 13• Dwarf shrub community dominated by Rhododendron, Cassiope and Juniperus in alpine meadow (Uraatatso)

Photo. 14.. Alpine collapse land in which Festuca community occurs (Tanchenmo: 4.,300 m) .

-100- microphylla dominates with subdominants of Agrostis inaequiglumis and Poa sp. In Table 20, three plots of Tanchenmo and Juree-la. Pll is dry community on the collapse land in Tanchenmo and Festuca ovina dominates accompanied with some alpine plants such as Leontopodium sp., Anaphalis triplinervis, Gentiana algida, etc. and some shrubs as same as P3-1 (Photo. 14). P17 is light grazing or waste community below Juree- la and Poa sp. is dominant, but many forbs (mostly unpalatable plants) such as Rumex nepalensis, Senecio chrysanthemoides, Sanguisorba sp., Aconitum sp., etc. are also dominant, too. P18 is mesic and general grazing community which Festuca spp., Kobresia spp., Potentilla spp. and shrubs (Cotoneaster microphylla and Juniperus recurva), etc. mix. In this zone, these alpine meadows consist of some dominant species, Kobresia spp. and some herbs with small or dwarf Ericaceae spp. and the dominance of Gramineae spp. is low.

(9) The grassland vegetation above 4,500 m in altitude Many variety communities and alpine plants occur in this zone (Photos 15 & 16). Seven plots was investigated in this zone. In Table 21, the plots of Gechewoma, Juree-la, Yak camp and Saga-la are shown. PI0-1 and PI0-2 are in Gechewoma below Gophu-la, and the former is shrubland consisting of Potentilla saudersiana, Rhododendron anthopogon, Berberis sp. and so on accompanying Poa. sp., Swertia sp., Rhodiola sp., etc. as other prominent herbs and grasses. The latter is grazing community dominated by grasses and sedges such as Poa sp, Festuca ovina, Agrostis sp., Kobresia duthiei, K. cf. royleana and Carex sp. P19 in Juree-la which is a pass above Duersachu is dominated by Kobresia cf. royleana and K^ duthiei dominate with moss. P12-1 was investigated in Yak camp which is wide grazing and dry meadow, and Festuca ovina as grass and Delphinium caeruleum, Gentiana sp., Rhodiola sp., etc. as herb dominate. PI2-2 is mesic community in Saga-la which wide meadow develops and is covered with some dominant species such as Kobresia duthiei, K. cf. royleana, Gentiana cf. depressa and many alpine plants. The plots in Table 22 are of more than 4,800 m in altitude. P6 is moderate grazing community in Yango and Kobresia duthiei, Leontopodium sp., Festuca sp., Juncus sp. and moss are prominent, while P7 is rude grazing community occurring in the river bed in Yango and Kobresia cf. royleana, Arenaria sp. and Rhododendron anthopogon. P8-1 and 8-2 are

-101- Photo. 15. Cushion plant community which occurs in the gravel land (near Dangjoy: 4,600 m in alt.).

Photo. 16. An alpine plant, Saussurea gossypiphora in cushion plant community (near Yango: 5,000 m in alt.).

-102- Table 21. Species coraposi tion of conimunities above 4,500 ra in alt Plot No. 10-1 10-2 19 12-1 12-2 Locality Gechewoma Ibid. Juree-la Yak camp Saga-la Altitude (ra) 4,600 4,600 4,700 4,660 4,800 G round cover (Z) 95 100 60 50 80 Community type S G G G(d) G No. of Species 17 14 6 9 16 Rhodiola sp. 65 58 67 10 Potentilla saundersiana 100 Rhododendron anthopogon 75 52 Poa sp. 67 46 Berberis sp. 75 Primula" ap. 8 43 6 Suertia sp. 47 Geranium donianum 47 Bistoria macrophylla 18 21 10 Potentilla mlcrophylla 36 1 1 46 10 Kobresia duthlei 18 32 67 54 Kobresia cf. royleana 11 23 100 42 moss 26 53 54 14 34 Carex sp. 29 46 Festuca ovina 24 39 92 10 Anaphalis triplinervis 11 25 38 12 Umbelliferae sp. 12 14 Gentiana cf. depressa 30 52 Agrostis sp. 39 Leontopodium sp. 54 Rheum nobile 54 Gentiana sp. 71 Cortella hookeri 36 Saussurea hookeri 26 Arenaria polytrichoides 100 10 Delphinium caeruleum 6 Aster sp. 7 Artemisia sp. 9 Deyeuxia nivicola 10 Brachypodium sp. 9

Table 22. Species composition of communities above 4,500 m in alt.

Plot No. 6 7 8-1 8-2 9 Locality Yango Ibid. Jichudagmo Ibid. Dangjoy Altitude (m) 4,840 4,900 4,920 4,920 4,800 Ground cover (%) 80 80 70 60 100 Community type G G G G G No. of Species 12 12 14 12 24

Gentiana cf. depressa 28 22 10 Leontopodium sp. 55 36 Kobresia duthiei 55 13 67 55 40 Potentilla cuneata 18 30 Festica sp. 53 41 29 J une us sp. 58 55 10 55 Agrostis inaequiglumis 53 80 moss 60 16 30 28 Potentilla microphylla 13 16 30 12 45 Bistorta macrophylla 13 16 30 12 45 Anaphalis triplinervis 28 16 Trisetum spicatum 52 Care x s p. 30 30 Kobresia cf. royleana 75 18 1 1 Arenaria sp. 57 lichen 12 Rhododendron anthopogon 30 26 Suertia sp. 9 5 Gentiana sp. 8 1 1 Rhodiola crenulata 8 Androsace sp. 16 Rhododendron nivale 45 51 65 Deyeuxia pulchella 35 18 Ephedra gerardiana 41 Ranunculus brotherusi 17 30 Potentilla fructiosa 18 Poa sp. 50 Agrostis sp. 40 Gentiana algida 25 Aconi turn sp. 35 Potentilla saundersiana 50 Berb«ri s sp. 30 Taraxacum s p. 35 Primula sp. 19 35 Cassiops fastigiata 40 Festuca ovina 53 Lomatogonium sp. 23 Silene gonosperma subsp. himnlayensis 23 Lonicera myrtillus 25 Deyeuxia sp. 30 -103- over grazing communities in Jichudagmo in which is the moraine of glacier. P8-1 is dominated by Kobresia duthiei, Rhododendron nivale, etc, and P8-2 is little humid community and is dominated by Agrostis inaequiglumis, Juncus sp. and Rhododendron nivale, P9 is general alpine meadow under moderate grazing in Dangjoy near Tsoreim and Agrostis inaequiglumis and other Gramineae spp. dominate accompanying many herbs and Rhododendron nivale. This zone is the altitudinal limit of grazing community or alpine meadow, and Kobresia spp., Festuca spp. and Juncus spp. dominate with some cushion plants and dwarf Rhododendron spp. (Photos. 17 & 18).

2. The grazing grassland types and their vertical distribution in central Bhutan 1

As abovementioned, the grassland vegetations change according to the altitude, humidity and grazing pressure and so on. The vegetations of grazing grassland were rearranged along the altitude ranging from 150 m to 5,000 m, namely, from tropical zone to alpine zone, and according to humidity, namely, dry, music and humid as shown in Table 23. The grazing grassland vegetation was generally divided into four vertical zones as follows: Chrysopogon (dry)/Cynodon (mesic) /Paspalum (humid) zone (A zone) below 2,500 m, Agrostis (dry) /Arundinella (mesic) /Carex (humid) zone (B zone) in 2,500 m-3,500 m, Festuca (dry) /Agrostis (mesic) /Carex (humid) zone (C zone ) in 3,500 m-4,000 m and Festuca (dry) /Kobresia (mesic and humid) zone (D zone) in 4,000 m-5,000 m. Climatically A zone belongs to tropical, subtropical and warm-temperate zones, B zone is in cool-temperate and subalpine zones, C zone is in upper subalpine zone and D zone coincides with alpine zone.

(1) The grazing grassland types in A zone In dry habitat, Chrysopogon aciculatus type is generally developed, and Heteropogon contortus, Eragrostis tenella and Ischaemum rugosum dominate according to various conditions such as grazing pressure and physical environment. Cynodon dactylon type often occurs in mesic land and accompanies with some dominant grass species such as Digitaria setigera, D. stricta and Chrysopogon aciculatus. In humid place, Paspalum scrobiculatum type widely establishes and Fimbristylis spp.,

-104- Photo. 17. Higher alpine meadow which Kobresia spp. dominate (Tsoreim: 5,200 m in ait.).

Photo. 18. Kobresia duthiei community with Leontopodiura sp., etc. in Rinchenze-la (5,240 m).

-105- Table 23. The dominont species of grazing grasslands along the altitudes in central and western Bhutan.

Altitude(m) dry mesic humid

1 50 Chrysopogon Cynodon Paspalum aciculatus dactylon •scrobiculatum

Heteropogon Digitaria Fimbristylis spp. contortus setigera

Eragrostis Digitaria Picreus spp. tenella stricta

Ishaemum Digitaria spp. Eleusine rugosum indica Chrysopogon aciculatus

Agrostis Arundinella Carex nervosa hookeri nubigena

Eragrostis Eragrostis Juncus sp. nigra nigra

Festuca sp. Agrostis Fimbristylis spp. pilosula

Eriocaulon sp.

Luzula sp.

Kobresia dutiei

mosses

Festuca Agrostis Carex ovina inaequiglumis nubigena

Festuca spp. Carex Juncus sp. nubigena

Anaphalis Agrostis Kobresia duthiei triplinervis pilosula

Anaphalis Poa sp. triplinervis 4,000 - Juncus sp.

Kobresia duthiei

Kobresia cf. royleana

Poa sp.

Potentilla microphylla

Deyeuxia pulchella

-106- Picreus spp. and Eleusine indica dominate under certain circumstances. Since A zone occupies very wide range in altitude, the dominance of dominant species gradually changes according to the altitude.

(2) The grazing grassland types in B zone Agrostis nervosa type generally occupies in dry place, but Eragros- tis nigra type occasionally occurs, too. Festuca sp. type is rare in this zone. In mesic habitat, Arundinella hookeri type is main, and Eragrostis nigra and Àgrostis pilosula types often develop. Carex nubigena type occurs in humid place, but this type includes some dominant species such as Juncus sp., Fimbristylis spp., Eriocaulon sp., Luzula sp., Kobresia duthiei and moss. These dominants often alternate under various conditions. All the grasslands in B zone consist of monopolistic dominant species.

(3) The grazing grassland types in C zone As it becomes high altitude, the dry habitat occurs only in special place such as collapse land or ridge. Festuca type grassland mixed some herb dominants establishes in thus place. In mesic place, Agrostis inaequiglumis type with some dominants such as Carex nubigena, Agrostis pilosula and Poa sp. develops. Carex nubigena type which is the same type as one in B zone was recognized in humid region, but Juncus sp. and Kobresia duthiei are more prominent than one in B zone. The influence of Gramineae spp. also decreases in the grasslands of this zone, and some Cyperaceae spp., herbs and shrubs become prominent.

(4) The grazing grassland types in D zone In dry place, Festuca type as same as in C zone develops as it is, but accompanies with many alpine plants. Most of alpine meadows are Kobresia type with some dominant species such as Poa sp., Potentilla microphylla and Deyeuxia pulchella, and with Juncus sp. in special humid habitat. Besides these type, the cushion plant community often develops in this zone.

3. The grassland succession in central Bhutan

The grassland is usually established by various human and biotic ac-

-107- tivities such as cutting, grazing, mowing, burning, etc. The grazing grassland is maintained by grazing of cattle, but the grassland vegetation changes according to the grazing pressure and cattle's behavior. If the grazing pressure decreases, the succession of grassland progresses to forbland or shrubland. As the grazing become heavy, it retrogresses and finally becomes bare ground. While, if the grassland is not adequately managed, the unpalatable plants for cattle such as poisonous, harmful and thorny plants increase, and it becomes waste or rude community (forbland-shrubland dominated by unpalatable plants). Those successions are also different in the altitude. The dominant species of seres of grassland succession according to the altitude are shown in Table 24.

(1) Succession of grassland below 1,500 m in altitude As abovementioned, the grazing grasslands below 2,500 m are Chrysopogon/Cynodon/Paspalum types. If they are strongly disturbed by heavy grazing or trampling, they retrogress toward Digitaria spp.- Cynodon dactylon community. If the grazing became light or was stopped, they progress toward forbland dominated by Eupatorium adenophorum, Artemisia indica and Ageratum conyzoides, and after that the shrubland dominated by Berberis sp., Acacia pennata, etc. with some dominant forbs such as Eupatorium adenophorum and Cassia occidentalis develops.

(2) Succession of grassland in 1,500 m - 2,500 m Digitaria-Cynodon community under heavy grazing also occurs in this zone as same as below 1,500 m. As the grazing pressure becomes weak, the forblands dominated by Artemisia indica, Anaphalis margaritacea, Helictotrichon parviflorum and Arthraxon spp. develop. Accord- ing to the progress of succession, the shrublands dominated by Rubus spp., Rosa spp., Lyonia villosa, Elaeagnus parvifolia and Salix spp. develop.

(3) Succession of grassland in 2,500 m- 4,000 m As mentioned in Table 23, Agrostis/Arundinella/Carex types in 2,500 m-3,500 m (B zone) and Festuca/Agrostis/Carex types in 3,500 m-4,000 m (C zone) develop in the grazing grasslands. If these types were more heavily grazed, it becomes the community dominated by Carex nubigena,

-108- Table 24. The dominant species of seres in grassland succession according to grazing pressure along the altitudes in central and western Bhutan.

Altitude(m) heavy light (forbland) shrubland 1 c n — 1 50 Digitaria spp. Eupatoriura Eupatorium adenophorura adenophorura

Cynodon Artemis ia Cassia dactylon indica occidentalis

Ageratura Berberis sp. conyzoides

Acacia pennata 1,500 - Artemisia Rubus spp. , indica

Anaphalis Rosa s pp. margari tacea

Helictotrichon Lyonia parviflorum villosa

Arthraxon spp. Elaeagnus parvifolia

Salix spp. 2,500 — Carex Artemisia Arundinaria nubigena indica falconeri

Plantago Rumex Berberis erosa nepalensis umbellata

Potentilla spp. Anaphalis Elaeagnus raargaritacea parvifolia

Pterinium aquilinum Rosa spp. var. wightianum

Senesio Cotoneaster chrysanthemoides microphyllus

Arundinaria Rhododendron falconeri lepidotum / nnn 4 i UU U Potentilla Potentilla Rhododendron microphylla sauders iana carapanulatum var. wallichii Potentilla spp. : Berberis spp. Rhododendron Juncus spp. Aconitum spp. se tosura

Leontopodium sp. Cirsium sp. Rhododendron anthopogon Anaphalis Bis tor ta triplinervis vivipana Rhododendron nivale Primula spp. Juniperus recurva

Juniperus squamata

Cas s iope fas tigiata

-109- Plantago erosa and Potentiüa spp. through this zone. If the grazing grassland was abandoned or the unpalatable plants increased, it progresses toward the forbland which Artemisia indica, Rumex nepalensis, Anaphalis margaritacea, Pterinium aquilinum var, wightianum, Senecio chrysanthemoides and Arundinaria falconeri are prominent or the shrubland which Arundinaria falconeri, Berberis umbellata, Elaeagnus parvifolia, Rosa spp., Cotoneaster microphyllus and Rhododendron lepidotum are prominent.

(4) Succession of grassland above 4,000 m The grazing grassland in this zone is Festuca/Kobresia type. As this type is over grazed, it retrogresses toward the community dominated by Potentilla microphylla, P. spp., Juncus spp., Leontopodium sp. and Anaphalis triplinervis which are mostly small unpalatable plants. The forbland which Aconitum spp., Cirsium sp., Bistorta vivipana, Primula spp., Potentilla saudersiana (shrub), Berberis spp. (shrub) and so on dominate develops under the light grazing or inadequate grassland management. If the succession progressed, the shrubland dominated by Rhododendron spp., Juniperus recurva, J. squamata, Cassiope fastigiata and Sorbus spp. establishes.

DISCUSSION

1. Grassland vegetation in central Bhutan

Except the high altitudinal region of Himalaya mountains, Bhutan is mostly covered with dense forests, since it has abundant precipitation and the human impacts are low because of few population number ( about 1.2 million). While, there are few exceptional dry valleys along the mid- streams of the main rivers like Wang-chu, Mo-chu, and so on. In these dry valleys, the thin or open forests and the scattered shrub land spread out. Owing to human activities, the cultivation land and grazing grassland develop among the forest land and the ratio of both changes according to the altitude. In the alpine zone, natural grassland (meadow) is often used for grazing. The vegetational zone in western and central Bhutan was preliminarily proposed by Ohsawa (1987) as follows: 1) tropical zone ( 150 m-1,000 m) covered with moist mixed forests dominated by

-110- Pterospermum, Tetrameles, Terminalia, Cinnamomum, Sloanea, etc. 2) subtropical zone ( 1,000 m-2,000 m) covered with shiny evergreen forests dominated by Shima, Castanopsis and Lithocarpus. 3) . warm-temperate zone (2,000 m-2,500 m) covered with forests dominated by Quercus, Cas- tanopsis, Acer, Persea and Litsea. 4) cool-temperate zone (2,500 m-3,000 m) covered with mixed forest types dominated by Quercus, Acer and Tsuga. 5) cold-temperate zone (2,500 m-3,000 m) covered with mixed coniferous forest of Abies densa, Juniperus recurva, J^ indica and j. squamata. 6) subarctic zone (4,000 m-4,500 m), shrubby Rhododendron zone. 7) arctic zone (above 4,500 m), dwarf Rhododendron zone with alpine plants. In comparison with these zones, the grazing grassland is divided into four altitudinal zones as Table 23. Namely, 1) A zone (300 m-2,500 m), Chrysopogon/Cynodon/Paspalum types zone. 2) B zone (2,500 m/3,500 m), Agrostis/Arundinella/Carex types zone. 3) C zone (3,500 m-4,000 m), Festuca/Agrostis/Carex types zone. 4) D zone (4,000 m-5,000 m), Festuca/Kobresia/J uncus types zone. These grassland zones do not coincide with the preceding vegetational zones and spread over them as follows: A zone occurs in tropical to warm-temperate zone, B zone develops between cool-temperate and cold-temperate zone, C zone occurs in upper cold-temperate zone and D zone develops in subarctic and arctic zone. Thus the dominant species of grasslands can more widely extend over the vegetational or forest zones. There are few reports about the grassland vegetation in the Himalayan region. Numata (1965,1966) suggested that two main zones of grazing grassland, namely, Cynodon/Imperata/Paspalum types in low altitudes (below 2,000 m), and Agrostis/Festuca types in high altitudes (above 2,000 m) in the area of Mt. Numbur, eastern Nepal. Tsuchida (1983) compiled about the grassland vegetational zone along the Arun valley, more eastern region than Numbur as follows: A zone (below 1,100 m) is Cynodon/Chrysopogon types, B zone (1,100 m-2,600 m) is Paspalum /Picreus types, C zone (2,600 m-3,800 m) is Carex type and D zone (above 3,800 m) is Carex/Festuca/(Kobresia) types. Comparison with these reports in eastern Nepal, there are some different appearances from the grassland vegetation in central Bhutan such as floristic composition, types and zonation. Namely,s 1) Chrysopogon aciculatus type accompanying the dry grasses (xerophytes) such as Heteropogon contortus, Eragrostis tenella

-111- and Ischaemum rugosum occurs in the wide range from 300 m to 2,500 m in altitude. 2) the dominance of Digitaria spp. in mesic grassland in the same region. 3) the occurrence of Paspalum type (hygrophyte type) in humid grassland ranging from low altitudes to high altitudes. 4) Agrostis type and Arundinella type occur ranging from 2,500 m to 3,500 m. 5) Kobresia type widely develops in the alpine zone. The author thinks that there are not so large floristic differences in the component species of grasslands between eastern Nepal and central Bhutan. However eastern Bhutan is under drier climate than eastern Nepal and is rich in environmental diversities. Judging from the grassland vegetation in eastern Nepal, the more the altitude rises up, the more wet is in climate up to the timber line. As the altitude becomes high in eastern Nepal, Paspalum type zone (1,100 m-2,600 m) and Carex type zone ( 2,600 m-3,800 m) widely develop. While, in central Bhutan even if the altitude increases, such tendency doesn't occur and various communities occur. Therefore the environments of Bhutan may be more diverse. In alpine zone (D zone) Kobresia type widely develops, but Fes- tuca type is very few. Judging from this, alpine zone in central Bhutan may be rather humid. In the temperate alpine zone in Himalaya, the grassland composed of Agropyron.Agrostis, Calamagrostis, Poa, Eragrostis, Festuca and so on was reported (Dabadghao quoted by Why te, 1974). The author also reported such an alpine grassland type in the preceding report in eastern Nepal and confirmed in Langtang area in central Nepal (unpublished). It is called that Kobresia type grassland distributes all over the alpine zone of the Eurasian Continental and the North American Continental, and Kobresia spp. are characteristic species of the alpine vegetation in all of the world ( Ohba, 1983). The most representative Kobresia species is Kobresia bellardii which distributes in the alpine regions of the Northern hemisphere including Japan. In Colorad mountains of North America, IC_ bellardii community occurs in little snowy and weak windy alpine region (Bell & Bliss, 1979). However this species does not appear in Nepal Himalaya (Hara, et al., 1978). There is not in author's collections of Bhutan, too. In Chingtsuang Highland of Tibet Plateau, Kobresia bellardii occurs only one as common Kobresia species with boreal region (Koizumi, 1986). Thus most of Kobresia spp. in Himalaya (also central Asia) are endemic and do not necessarily dis-

-112- tribute only in the alpine zone or high altitudinal regions, but in low altitudes such as Kobresia capillifolia (1,200 m-2,000 m in Nepal). Kobresia spp. in central Bhutan surveyed appear from about 3,500 m in altitude which belongs to subarctic coniferous forest zone. Thus Kobresia spp. are not necessarily characteristic species (indicator) of alpine vegetation. In any case, the floristic study and identification of Bhutan plants are not yet making progress and are expected in future.

2. The grassland succession

The successional relationships of the grassland vegetation in central Bhutan are different in each altitudinal grassland zone. In A zone (below 2,500 m in altitude), there are two types which are below 1,500 m and above 1,500 m. The natural succession below 1,500 m progresses as follows: bare ground-pioneer community (Ageratum conyzoides, Digitaria spp., Galinsoga parviflora, Cassia spp., etc.) -Mixed grassland ( Eupatorium spp. Artemisia indica, Cymbopogon gidarba, Saccharum spontaneum, Ar- temisia indica, etc.)-shrubland (Acacia phennata, Jasminium sp., etc.)-forest (tropical forest). The natural succession above 1,500 m is as follows: pioneer community (same)-mixed community (Artemisia indica, Anaphalis margaritacea, Helictotrichon parviflorum, etc.)-shrubland (Rubus spp., Rosa spp., Lyonia villosa, etc.)-forest (tropical, subtropical and warm-temperate forests). According to the human activities in thus successional courses, various retrogressive successions occur as follows: Chrysopogon /Cynodon/Paspalum grassland types under continual grazing, Digitaria- Cynodon community type under heavy grazing or trampling, and Eupatorium-Artemisia-Ajeratum-Imperata type and the preceding shrubland (below 1,500m) and Artemisia-Anaphalis-Helictotrichon-Arthraxon type and the preceding shrub type (above 1,500 m) under light or rude grazing. In B zone (2,500 m -3,500 m), the natural succession progresses as follows: pioneer community (Setaria sp., Elsholtzia strobilifera, Hemiph- rangma heterophyllum, Myriactis nepalensis, etc.)-mixed community (Artemisia indica, Anaphalis margaritacea, Senecio chrysanthemoides, Arun- dinaria falconeri, etc.)-shrubland (Arundinaria falconeri, Berberis umbellata, Elaeagnus parvifolia, etc.)-forest (cool-temperate and cold-temperate forests). If these seres are disturbed by human influences, they change to various vegetations as follows: Festuca/Agrostis/Carex types under

-113- continual grazing, Carex-Plantago-Potentilla type under heavy grazing and trampling, Artemisia-Rumex-Anaphalis-Pterinium-Senecio-Arundinaria forb type under light or rude grazing and Arundinaria-Berberis-Elaeagnus- Cotoneaster shrub type in abandoned land. In C zone (above 4,000 m), the succession is very complexity because there are various natural and biotic influenced communities. Generally dwarf Rhododendron and Juniperus shrub communities are climax in the lower alpine zone, and the cushion plant community is also climax in the upper alpine zone. The alpine meadow is established by grazing and mowing. The original vegetations of alpine meadow are not still well known. One of them is the preceding shrub community which was cut and burnt. The other natural vegetations except shrub community and cushion plant community hardly appeared along our caravan route because the most part of alpine region was disturbed by biotic impacts. If the grazing was stopped, the alpine meadows which are Festuca/Kobresia/Juncus types progress to shrub community or forb community as Table 24. In any case, the studies on the alpine vegetation are more needed.

CONCLUSION AND CONSERVATION OF PASTURE LANDS

The vegetation of grazing grassland in central Bhutan (including a part of eastern Bhutan) changes according to the altitude and four grassland type zones were recognized as follows: A zone (Chrysopogon/Cynodon/Paspalum types below 2,500 m in altitude), B zone ( Agrost is/Arundinella/Carex types in 2,500 m-3,500 m), C zone (Festuca/Agrostis/Carex types in 3,500 m-4,000 m) and D zone (Festuca/Kobresia/Juncus types above 4,000 m). A zone widely develops in altitude and C zone occurs in narrow range. The pasture land in Bhutan mostly develops in the region above 1,500 m in altitude, especially above 2,400 m which is the altitudinal limit of rice crop in Bhutan. The most of the alpine zone is used for grazing as so-called alpine meadow. In relation to the succession, many and wide inadequate communities for grazing develop in almost all pasture lands owing to over grazing, rude grazing and noninterference. For example, the waste forblands dominated by unpalatable forbs such as Eupatorium, Artemisia, Anaphalis, Pterinium, etc. develop under rude grazing and the waste

-114- shrublands dominated by unpalatable shrubs such as Berberis, Rosa, Elaeagnus, Cotoneaster, Rhododendron, Juniperus, etc. develop under abandoned land. Except a part of alpine meadow, the establishment of pasture land is caused by felling and burning of natural forest in Bhutan. The expansion of forest destruction is parallel to that of pasture and agricultural lands throughout the Himalayas (Schweinfurth, 1983). The natural forest is very important for the natural resources and the conservation of mountain, soil and water for Bhutan and other Himalayan countries. The destruction of forest and the establishment of pasture land have to minimize. There are some ideas to contribute them. One is to increase the grassland productivity by adequate utilization based on the period of use, number of cattle, kind of cattle in each grassland zone (Numata, 1980). The temporary rest or shifting grazing are also useful. The removal of unpalatable plant communities by cutting and burning is very important (Tsuchida, 1983). Once more, the introduction of foreign pasture plants have to be consider. However the basic studies to carry out these methods are still insufficient. It is hoped that more floristic, ecological and experimental studies promote for nature conservation and the increase of grassland productivity of Bhutan. The author is happy if this report will be any useful to them.

ACKNOWLEDGMENT

I wish to thanks the member of the ecological survey of the Himalayan Expedition of Chiba University 1985, Dr. M. Numata, Dr. M. Ohsawa, Dr. M. Okazaki and Mr. T. Eguchi, for their kind help. I also wish to thank Dr. H. Ohba and his University Museum of the University of Tokyo, Dr. T. Yamazaki and his Koishikawa Botanical Garden and Dr. K. B. Rajibhandari, Dept. of Medicinal Plants, H.M.G. of Nepal, for their kind identification of the specimens collected. Finally, we owe sincere thanks to the staffs of Bhutan Tourism Corporation.

-115- REFERENCES

Bell, K.L. & L.C. Bliss (1979). Autoecology of Kobresia bellardii: Why winter snow accumulation limits local distribution. Ecol. Monogr., 49: 377-402. Hara. H. et al. (1978-1982). An enumeration of the flowering plants of Nepal. Vol. 1-3. London. Koizumi, T. (1986). Vegetation of the region of source of the Whang River, Tibet. Kagaku, 56 (9), 554-565. Nakao, S. & K. Nishioka (1984). Flowers of Bhutan. Ashahi Shinbun Pub., Tokyo. Numata, M. (1964). Methods of measuring grassland vegetation. Methods of ecological field survey, II. Bull. Chosi Mra. Lab., Chiba Univ., 6, 115-139. Numata, M. (1966). Vegetation and conservation in eastern Nepal. J. Coll. Arts Sei., Chiba Univ. 4, 559-569. Numata. M. (1979). Distribution of grasses and grasslands in Asia. Ecology of grasslands and bamboolands in the world (M. Numata ed.), 92-102, Dr. W.Junk Pub., Hague. Numata, M. (1980). Semi-natural pastures and their management in the Himalayas. Tropical ecology & development, 339-409. Ohba, T. (1983). Vegetation and plants of Pinus pumila community and short-type grassland. Illustration of vegetation in Japan vol.1 Forest Vegetation (by N. Nakanishi et al.), Ohsaka. Ohsawa, M. (1987). Vegetation zones of the Bhutan Himalaya. (In this issue.) Schweinfurth, U. (1983). Man's impact on vegetation and landscape in the Himalayas. Man's impact on vegetation(eds. by W. Holzner et al.). 297-309, Dr. W. J. Pub., Hague. Tsuchida, K. (1983). Grassland vegetation and succession in eastern Nepal. Structure and dynamics of vegetation in eastern Nepal (edt. M. Numata), 47-87, Chiba Univ. Whyte, R.O. (1974). Tropical grazing lands, Dr. W. J. Pub., Hague.

-116- M.Ohsawa(ed.), Life Zone Ecology of the Bhutan Himalaya.1987. I Chiba University. OBSERVATIONS OF FARMLANDS AND PASTURES IN CENTRAL BHUTAN

M. NUMATA

Shukutoku University, Daiganji, Chiba, Japan

INTRODUCTION

We conducted preliminary observations in Bhutan, particularly of its forests, grasslands and farmlands in 1984. My interest was to document gradual changes in vegetation from natural to secondary forests, from forests to grasslands, particularly pastures, and from natural and semi- natural vegetation to farmlands or plantations. In 1985, we conducted further observations of similar objects with a climatologist and a soil scientist as part of a research group. Many VIPs assisted us. Dasho C. Dorji (Secretary, Ministry of Trade, Industry and Power, former Director of the Department of Forestry), Dasho Dorjee Tenzin (Director, Depart- ment of Forestry, former Director of the Department of Animal Husbandry), Dasho Tseten Dorji (Director, Department of Animal Husbandry) and Dasho K. Nishioka (Bonday Farm) gave me useful information on the bio-industry of Bhutan. On general affairs, Lyonpo Sangye Penjor (Minister for Social Services), Dasho Lam Penjor (Deputy Minister, Planning Commission), Dasho K. Letho (Deputy Minister, Ministry of Communication and Tourism) and Mr. Jigmi Tshultim (General Manager, Bhutan Tourism Corporation) also helped us very much. "An Unexplored Land-Bhutan" is the title of a book written by S. Nakao (1959). It is well known that before that, Tokan Tada entered into Lhasa via Bhutan to study Buddhism. Recently, television films and some books, such as "Flowers of Bhutan" (1984) written by S. Nakao and K. Nishioka have provided us rich information. Also, "Bhutan, A Kingdom of the Eastern Himalayas" (1984) by F. P. Imaeda and Y. Imaeda (in French, English and Japanese) is a very good manual for foreign researchers. After Nakao, the Tokyo University team (Leader; H. Hara) and the Kyoto University team (Leader; M. Matsuo) conducted nature ex-

-117- peditions both in 1967.

OUR OBSERVATIONS

According to recent statistics of land use in Bhutan, the forest land is 67.39 % of the whole land area. This is almost the same as the rate of forest land in Japan. The area of pasture land is 3 %, that of agricultural land including settlement, orchard and shifting cultivation (Photo 1) is 8 %, and the rest is ice and snow, and barren, exposed and rocky areas. The grazing animals are said to be yak, brownswiss, jerjy, etc., however in my observation in central Bhutan in 1985, cows, Indian cows and horses seemed to be the most popular (Photo 2). When we visited central Bhutan in September of that year, sheep and goats were still in higher places, and some pigs were grazed in small areas. A farmer in the Rukubji District near Nikkachu told me that he contracted to exchange his sheep and goats with those of a friend in a higher place for the management depending on the season. That is, sheep and goats are in the highlands in the summer and in lower places in the winter. He said that his and his friend's sheep and goats will come back to Rukubji together at the end of September. The forest grazing of sheep and goats is prohibited because it causes great damage to forest regeneration. There are many pastures in the Rokubji District, and the forested area is small. The soil profile there includes charcoal indicating that forests that existed in the early days were burnt to make pastures. The soil profile also has the dung of cattle in the layer of several cen- timeters beneath the surface. This may suggest repeated land slides. There are terraces on the slope and a network of cattle paths, a very characteristic topography. The network of cattle paths tends to be seen on most terraces suggesting that the terraces were formed by repeated small-scale land slides. In the central and southern part of Bhutan, forage plants such as Italian ryegrass, fescues and clovers are sometimes used. For fodder in the winter, fodder trees are the recommended plant. In Nepal, the leaves with twigs of various kinds of tree are used as fodder, not only in the winter (Panday, 1982). However in Bhutan, the utilization of tree leaves as fodder is prohibited from the standpoint of forest conservation.

-118- Photo 1. Shifting cultivation in central Bhutan.

Photo 2. Gazing in the paddy field after harvesting rice and the network of cattle paths behind.

-119- Straws of rice, barley and wheat are used as winter fodder. To my surprise, in a barley field there was a large quantity of weeds, mostly Persicaria nepalensis which may be noxious weeds (Photo 3). When I asked a farmer on the most prevailing weed Persicaria nepalensis, he told me that it is not a weed, but an important fodder in the winter. It actually decreases the yield of barley, but it is more important as a fodder. After the ripening of barley, the heads are harvested and then the straws and Persicaria nepalensis are cut together to make hay which is used in the winter. However, Persicaria nepalensis is actually a noxious weed for potato, buckwheat and winter wheat. The height of barley was 65cm and that of Persicaria was 25cm when I measured them on Sep- tember 19th. There are some rotations of barley-winter wheat, and barley-potato-radish-turnip. Radish and turnip are widely cultivated as the fodder of pigs, etc. I saw a characteristic .rotation of forest- pasture-farmland in eastern Nepal (Numata, 1966a), however, I could not see such a rotation in land use in Central Bhutan, because 99 % of the forest is state forest and the authorities lay heavy emphasis on forest conservation (C. Dorji, 1985). Main crops are rice, barley, wheat and maize, and shifting cultivation is prohibited by the Government policy. Dasho C. Dorji said "We must get this evil practice out of the people's hand, help them in their livelihood, and reduce manpower demands. Shifting cultivation will be very difficult to eradicate in a short time, because it has been practised since time immemorial, and affects the poorer section of the community. In order to try and curb it, the Government has launched a regular resettlement programme, and they think that over the next five or ten years, they will be able to solve this problem" (C. Dorji, 1985). The relict of charcoal in the soil profile mentioned above might be related to shifting cultivation. I frequently observed the cultivation of small fields on river banks and steep slopes. In such cases in eastern Nepal, farmers select those places judging the productivity by the height of native grasses. I wonder whether farmers in Bhutan have such a criterium. There is very little flat land, and the farmland sites selected are not always suitable. When I wanted to examine the weeds in a farmland, it was difficult to enter, because farmlands were usually rigidly fenced off (Photo 4). Usually fences are made of bamboo to avoid the entrance of domes-

-120- 'mmm

Photo 3. Barley field with weeds such as Persicaria nepalensis.

Photo 4. A farmer's house and his farmland on the left. There is a fence between them.

-121- tic and wild animals. Recently, the Department of Animal Husbandry recommends that farmers make double fences, bamboo and electric. The former is only to make it difficult for large animals to gain entry. For the domestic animals, the Government is considering the promotion of en- silage in Central Bhutan. One more characteristic feature of pastures is the use of bamboo. In front of the Guest House of Dochula (3050m in alt.), there is a good Tsuga-Acer forest stand. Around the stupa along the road, there was an overgrazed pasture dominated by Carex nubigena and Sagina japonica with Iris cf. clarkei and Rumex nepalensis and without bamboo (Photo 5). However, there were many bamboos (Arundinaria falconeri) under the forest on the opposite side of the overgrazed pasture. The bamboos were shorter to taller from the margin near the road to the inner part of the forest. The shape of bamboo shoots also changed from the dwarf form with the dense gathering of leaves on the nodes to normal growth (Photo 6). The heights of aerial shoots were 13.3cm in the edge, then 36.7cm, 43.8cm, and 85.2cm in the middle, and 2-3m in the interior. The density of aboveground separately measurable shoots did not have such a clear trend, because it was affected by other constituent species. Arundinaria type pastures and meadows are found in southwestern Japan, particularly in Kyushu (Numata, 1974). However, their ecological susceptibility and tolerance to the grazing is different. Arundinaria (Pleioblastus) chino var. viridis in Japan is very tolerable to grazing, and its form is almost similar to Zoysia japonica under strong grazing pressure. However, Arundinaria chino in central Japan is ecologically different from Arundinaria chino var. viridis and deteriorates under strong grazing pressure, and the bamboo bushes become annual grassland (Numata, 1966b). In eastern Nepal, I saw bamboo similar to the undergrowth of Tsuga dumosa and Abies wallichii forests. The growth form of the bamboo at the edge of the forests was very similar to the Bhutanese one described before. In central Bhutan, I found the almost all pastures have dwarf bamboo with shortened culms as perennial grasses with many other grasses and herbs (Photo 7). However, I could not find similar type of pasture with dwarf bamboos in eastern Nepal.

-122- Photo 5. An overgrazed pasture dominated by Carex nubigena and Sagina japonica.

Photo 6. The growth form of Arundinaria falconeri under the pressure of grazing as the undergrowth of the Tsuga-Acer forest.

-123- Photo 7. A properly grazed pasture including Arundinaria falconeri (a dwarf bamboo) in Central Bhutan, 3000 m in alt.

-124- I I REFERENCES I Dorji, C. (1985). An interview. Forestry in Himalayan Bhutan. I Unasylva 37 (149). Numata, M. (1966a). Vegetation and conservation in Eastern Nepal. I J. Coll. Arts & Sei., Chiba Univ. 4 (4): 559-569. Numata, M. (1966b). Northern Arundinaria type grasslands in Japan, I particularly related to autecology of A^ china. Rep. Fuji Bamboo Garden No. 11, 59-65. • Numata, M. (1974). The Flora and Vegetation of Japan, 125-148. Kodansha & Elsevier. • Panday, K. K. (1982). Fodder Trees and Tree Fodder in Nepal. Swiss Develop. Coop. Bern.

-125- OBTAINED DATA ON FARMLAND WEED COMMUNITIES AND GRASSLANDS

I surveyed some farmland weed communities and grasslands between Thimpu and Nikkachu. Regarding grasslands for cattle raising, there are many important issues discussed in The Journal of Animal Husbandry since 1976. Ecologial characteristics of weed and grassland vegetation will be discussed in detail in the next opportunity. Here, I'll only describe the vegetation data on the floristic composition with SDR (summed dominance ratio). On the identification of collected species, I am very much obliged to Dr. K. Tsuchida for his kindness.

No.O A roadside fragment of vegetation, Thimpu, 24.00m in alt., ground cover(v)=100 %, Sept. 16

Species SDR Cynodon dactylon 67 Cosmos bipinnatus 55 Galinsoga parviflora A3 Chrysopogon aciculatus 40 Potentilla griffithii 40 Lepidium virginicum 20 Oxalis corniculatus 10 Mazus delavayi 9

-126- No. 1 A roadside fragment of vegetation, outskirt of Thimpu, 2400m in alt., v=100 %, Sept. 16

Species SDR Artemisia dubia 63 Cynodon dactylon 62 Crotalaria sp. 54- Callicarpa rubella 54- Themeda sp. 51 Desmodium multiflorum 51 Gnaphalium hypoleucum 4-2 Senecio chrysanthemoides 4-2 Galinsoga parviflora 29 Digitaria ciliaris 21 Verbascum thapsus 19 Acacia pennata 17 Gulldenstaedtia himalaica 17 Lespedeza gerardiana 9 Cassia mimosoides subsp. mimosoides 9 Carex nubigena 9 Viola tuberifera 9

No. 2-1 A weed community at a cabbage field, suburbs of Thimpu, 2600m in alt., v=70%, SDR of cabbage=75, sept. 16. Quercus semecarpifolia forest and bracken grassland were closely found.

Species SDR Rumex nepalensis 57 Amaranthus viridis 54- Conyza stricta 4-8 Galinsoga parviflora 4-0 Echinochloa crus-galli 34- Digitaria cruciata 32 Persicaria nepalensis 29 Picreus sp. 26 Chenopodium album 26 Cyperus sp. 19 Oxalis corniculata 7

-127- No. 2-2 A weed community at a maize field, height and cover of maize are 300 cm and 90 %, v of weed community=5 %, at a field after burning of forests, potato, maize and pumpkin were cultivated.

Species SDR Amaranthus lividus 67 Chenopodium album 51 Digitaria cruciata 37 Galinsoga parviflora 18 Geranium nepalensis 10 Persicaria nepalensis 10

No. 3 A fragment of vegetation along the road from Thimpu to Dochula, 2800m in alt., v=100 %, Picea spinulosa forest, fields of potato and radish were closely found.

Species SDR Pteridium aquilinum var. wightianum 82 Gnaphalium hypoleucum 67 Onychium japonicum 52 Umbellifereae sp. 4-2 Picea spinulosa 38 Pinus wallichiana . :--T 32 Agropyron sp. 20 Populus ciliata 20 Adenophora triphylla 20 Agrimonia pilosa var. nepalensis 13 Gulldenstaedtia himalaica 7

No. 4 A pasture in front of Dochula Cafeteria, 3050m in alt., v=100 %, Sept. 16.

Species SDR

Sagina japonica 52 Senecio chrysanthemoides 51 Iris clarkei 42 Rumex nepalensis 34 Arundinaria falconeri 22 Plantago erosa 19 Poa annua 14 Potentilla griffithii 14 Galium asperifolium 13 Carex nubigena 6

-128- No. 5 A pasture for horses under the canopy of Acer-Tsuga forest, 3050m in alt., v=100 %, at Dochula

Species SDR Arundinaria falconeri 90 Duchsenea indica 51 Senecio chrysanthemoides ' 4-3 Iris clarkei 38 Daphne bholua 23 Aconitum laciniatum 21 Myriactis nepalensis 18 Geranium procurrens 17 Pterium aquilinum var. wightianum 16 Athyrum strigollosum 1 5 Potentilla chrysanthemoides 14 Hypnum daajeelingense 14 Prunella vulgäre 13 Aspidiaceae sp. 11 Galium asperifolium 6

No. 6 An overgrazed pasture along the road, calcareous sandstone soil, Dochula, 17 Sept.

Species SDR

Pteridium aquilinum var. wightianum 59 Senecio chrysanthemoides 59 Potentilla griffithii 53 Carex nibigena 46 Iris clarkei 40 Plantago erosa 37 Sagina japonica 36 Duchesnea indica 32 Prunella vulgaris 29 Rumex nepalensis 16 Anaphalis busua 13 Agrostis pilosula . 7 Climopodium umbrogum 4-

-129- No. 7 A pasture near the guest house at Nikkachu, 2530m in alt., Sept. 18. Species SDR

Senecio chrysanthemoides 78 Arthraxon sikkimensis 55 Paspalum commersoni 55 Pteridium aquilinum var. wightianum 33 Arundinaria falconeri 31 Elymus sikkimensis 28 Rosa sericea 28 Potentilla griffithii 28 Digitaria ciliaris 25 Persicaria nepalensis 2-4 Poa annua 23 Geranium nepalensis 16 Commelina paludora 16 Anaphalis triplinervis 16 Amaranthus viridis 1 5 Artemisia indica 1 5 Eleochalis congesta 14- Bulbostylis densa 12 Plantago erosa 12 Setaria glauca 8 Poa sikkimensis 7

No. 8-1 A weed community at a radish field, scattered seeding of radish, v (radish)=75 %, Nikkachu, Sept. 18.

Species SDR

Galinsoga parviflora 100 Amaranthus lividus 83 Vicia angustifolia 74 Poa annua 60 Stellaria media 57

-130- No. 8-2 A weed community at a barley field used for fodder of yak, scattered weeding, v=20 % (barley), 80 % (weeds), Nikkachu.

Species SDR Galinsoga parviflora 78 Amaranthus viridis 72 Persicaria nepalensis 60 Digitaria ciliaris 54- Pteridium aquilinum var wightianum 51 Siegesbeckia orientalis 34- Geranium procurrens 27 Setaria glauca 26

NO. 8-3 A weed community in a radish field, scattered seeding, strong weeding.

Species SDR Raphanus sativus 100 Persicaria nepalensis 34- Stellaria media 22 Poa annua 21

No. 8-4. A weed community in a barley field, barley is cut at the end of September, winter wheat is cultivated from Oc- tober to June.

Species SDR Hordeum vulgäre 94 Persicaria nepalensis 67 Siegesbeckia orientalis 23 Digitaria ciliaris 17 Rumex nepalensis 17 Galium asperifolium 16 Poa annua 1 4

-131- No. 8-5 A weed community in a barley field near the guest house of Nikkachu.

Species SDR Hordeum vulgäre 100 Persicaria nepalensis . 56 Galium asperifolium * 31 Raphanus sativus 31 Brassica rapa 28 Galinsoga parviflora 28

No. 9 Pasture under grazing of horses and cattle near the guest house of Nikkachu, Picea spinulosa saplings 2 m high.

Species SDR Arundinaria falconeri 65 Arundinella hookeri 60 Eleagnus parviflora 53 Eragrostis nigra 4.8 Dryopteris paleacea 4-3 Echinochloa crus-galli 33 Artemisia indica 33 Potentilla griffithii 32 Pteridium aquilinum var. wightianum 28 Haloragis micrantha . 23 Onychium japonicum 18 Primula listeri 18 Hallenia elliptica 18 Anaphalis margaritacea 13 Eleocharis congesta 10 Drymaria diandra 8 Selaginella tamariscina 6

i'A

-132- M.Ohsawa(ed.), Life Zone Ecology of the Bhutan Himalaya.1987. Chiba University.

VEGETATION, PLANT INDUSTRY AND NATURE CONSERVATION IN BHUTAN

M. NUMATA

Shukutoku University, Daiganji, Chiba, Japan

INTRODUCTION

We have studied the biota and ecology of the humid Himalayas, particularly in Eastern Nepal since 1963. Some of our results were compiled in a book "Biota and Ecology of Eastern Nepal" (1983, Chiba University). Since then, we have been studying the plants and vegetation, climate and soils with the same objective as that of the Nepal studies. Nepal and Bhutan are floristically common to parts of China and Japan which are in the Sino-Japanese Region. In Nepal, population has increased, agricultural development has progressed, and the area of natural vegetation has become smaller and smaller. On the other hand, in Bhutan, the original natural environment is well preserved to the extent that it actually remains an unexplored part of the world. Bhutan is the only independent country in the Tibetan Circle. There, one can find a kind of theocracy that is a unity of religion (Lamaism) and political administration. The population is about 1.3 million in an area a little larger than Kyushu, Japan. The population of the Capital Thimphu is about 12,000. Nakao's book "An Unexplored Land-Bhutan" states that the population of Bhutan in 1959 was 650,000. Therefore, even in sparsely populated Bhutan, the population doubled in 30 years. In Nepal, we selected Eastern Nepal for our study, because the biota and ecology of the humid Himalayas are similar to those in Japan. The same can be said of Bhutan. In addition to nature, the people are very similar to the Japanese physically and mentally. Thus, we felt that the country is like a place dear to our hearts. I was in Tibet in 1980 after the Tibet Plateau Symposium in Beijing (Numata, 1980), therefore my

-133- Photo 1. Dzong of Wangdiphodrang.

— 134 — experience in Bhutan gives me additional, dorsiventral knowledge of the Eastern Himalayas.

FIFTH PLAN AND PLANT INDUSTRY

The Royal Government of Bhutan Fifth Plan (1981-1987) Main Docu- ment of the Planning Commission describes the present state and target of the plant industry. No comprehensive land use survey has so far been conducted in that country. However, the aerial surveys show the area of natural forest to be 74.0 %, that of cultivated or inhabited land to be 8.5 %, that under snow cover to be 0.7 %, lakes and water spreading over 0.5% and the area under cloud cover to be 0.4%. The above document described it as follows; the inner valleys consist of oak and often deciduous trees giving way to conifers with increasing altitude. Broad- leaved tropical and subtropical hardwoods dominate up to an altitude of 1,000 m. Beyond these, up to 3000 m, temperate forests of pine and oak are found. The latter is concentrated mainly on the southern slopes which receive most of the monsoon rains. Beyond 3000 m and up to about 4000 m which is the tree line, valuable reserves of pine, spruce and fir are found. Sargent (1985) says that the distribution of vegetation coincides broadly with the 2000, 3000 and 4000 m contours where the approximate tree line occurs. According to the above document, the exploitation of forests at present is low mainly due to lack of accessibility. Of the net allowable cut, only about 20 % is currently being harvested, a large portion of which meet household fuel needs. The per capita availability of agricultural land is about two hectares. However, in most parts, agricultural productivity is low. At present, the "tsheri" land under shifting cultivation is about 30 % of the total agricultural land, but the target of "tscheri" land area at the end of The Fifth Plan will be zero. The area cultivated for crops are 24 % for paddies, 11 % for wheat and barley, 50 % for maize, 15 % for buckwheat and millet. The total area cultivated for foodgrains is 112,6000 ha. In The Fifth Plan, the Government wants the area for foodgrain production to be 41 % for paddies, 11 % for wheat and barley, 42 % for maize, and 6 % for buckwheat and millets. Besides these, pulses, mustard, potato, chillies and

-135- Photo 2. Gompa at Dochula.

Photo 3. Terraced fields and pastures (upper slopes).

-136- vegetables, orange, apple and cardamom will be produced. The increase of production of milk, egg and broiler, improvement of grasslands and fodder tree plantation are the main targets for animal husbandry. In the forestry sector, afforestation, wildlife management, social forestry, logging roads and paths, mechanical harvesting and ropeways, and wood industry are the main targets. The above document says that exist- ing wildlife sanctuaries will be further developed by improving the in- frastructure for regulation and management through the construction of buildings, elephant track, etc. Hunting and fishing will also be regulated appropriately. In Central Bhutan I observed that the grazing animals are mostly cows, Indian cows and horses on large pastures and in forests. The forest grazing of sheep and goats is prohibited, because it causes great damage to the forest. In central-south Bhutan, ryegrass, fescue and clovers are sometimes used. The planting of fodder trees is recommended particularly for the winter. Straw from rice, wheat and barley, and some weeds such as Persicaria nepalensis are used as hay. Dwarf bamboo leaves are mown for sheep and goats. Leaves of radish and turnip are widely used as fodder. The main crops are rice, barley, wheat and maize. Shifting cultivation is basically prohibited. About 20-30 % of crops are damaged by noxious insects and weeds, thus recently farmers have become interested in pesticides and herbicides. Besides national forests, plantations by social forestry contribute to greening and timber production. For the private land registered for planting, nursery stock of pines, cedar, cypress, elm, leguminous tree such as Robinia, walnut, etc. are supplied without fee, and farmers can learn how to grow those trees. Social forestry like this is more successful than community forestry. In social forestry, participants must plant more than ten trees, however they can harvest timber without being taxed when the trees grown.

NATURE CONSERVATION

On the table of the Director of the Forestry Department, there was a notice "the tree you plant today will support life tomorrow." It indi-

-137- Photo 4. Land slide along the road.

Photo 5. Many cars were stopped by the landslide.

-138- moxkeb GirMin be felléi hills a

f cl/ing of trees vPitboutniarkiïiFS is illegal

Photo 6. A notice at a Range Forest Office (Wangdi) showing that marked ree is only to be felled, felling of trees without markings is illegal, and girdling kills a tree.

Photo 7. An example of Agricultural Extension centre/subcentre.

-139- cated Bhutanese enthusiasm for greening which impressed me very much. Some 9020 sq. km of National Parks, Wildlife Sanctuaries and Reserved Forests have been designated in a total of seven places and six more places are in preparation (Fig. 1 ). Among these, the first one was designated in 1965. The training of wardens is being done in Canada and other countries. In protected areas, cattle raising and timber felling are strictly prohibited. Legal or illegal transportation of timber is checked at checkpoints on the road. Bhutan is a Lamaism country in which, as a rule, there is no hunting. However, we can enjoy the observation of plants and wildlife even in protected areas if one has permission. Sometimes poachers and elephants act violently outside the protected area, so, armed wardens patrol the area. The vicinity of the northern protected area is uninhabited, therefore there is no warden. Recently, the problem of felling national forests to construct a factory occurred. In such a case, officials fight against the problem and try to stop the development through debate in the parliament. Foreign tourists now number 2000 per year, but are increasing, I sincerely hope that the unexplored nature of Bhutan will be preserved against the impact of development and tourism. The Bhutan Forest Act was enacted in 1969, and National Parks, Wildlife Sanctuaries and Protected Forests are regulated under The Act. For the most part, forests belongto National Forests. In the protected area, not only hunting but also trapping and poisoning wildlife is prohibited. However, when some species increase abnormally and may influence other species, catching and killing a definite number of them by special permission of His Majesty King is allowed. Fishing in rivers is permitted at a charge by the local Forestry Office, however poisoning, using explosives and the netting of fish are strictly prohibited. My young assistant during trekking said that his mother is an en- thusiastic Lamaist and she thinks killing living things a great immorality. He made fishing tools by hand, but his mother found and broke them. According to him, plants have life but not souls, and animals have souls as well as life. This is the reason why they cannot kill animals. However, I felt some contradictions, because they eat meat and chicken. The Department of Forestry, Ministry of Agriculture and Forests of the Royal Government of Bhutan is responsible for the preservation of the protected area. The felling of trees and shrubs for agriculture and hous-

-140- MAP SHOWING WILD LIFE SANCTUARIES IN BHUTAN Ref. No. Name of Sanctuaries Area in sq. ha ® Laya Wild Life Sanctuary 147.682.frl ha ©Gasa Wild Life Sanctuary- 271.792.21 CD Jigme Dorjee wild life Sanctua y 370.971.62 © Doga National Park 2.17251 (D Pachu Reserved Forest 14.197.71 © Mochu Reserved Forest 27.851.55 ®Goley Game Reserve 19.701.21 ® Manas Wild Life Sanctuary 44.a35.98 (1) Khaling Reserved Forest 43,573.075

NG N0BD E L E LA TAKSANG r °\. ^-.r. D E CH ? THIMPHU? SA^A:'K0R0KA •• >TONGSA , •• •,GOSEINOÇHENBÉ?S|'.CHANGRA ^•D0CH0LAWNG9^0P

KALIKHOLA

Fig. 1. Map showing wild life sanctuaries in Bhutan.

-141- ing is prohibited, however mining is possible by special permission. Cattle raising is permitted, if necessary, too, by the Department of Forestry. If people go against The Act, they are sentenced to six months imprisonment or a penalty of 1000 nutrum (one nutrum is about 25 yen). If a place is designated as a protected area, people are requested to move to a house outside the area and are given the compensation. The Department of Forestry sometimes makes plantations within a protected area.

REFERENCES

Department of Forestry, Royal Government of Bhutan (1974). Creation of Wild Life Sanctuaries/Parks/Forest Reserves. Grieson, A. J. C. and D. G. Long (1983). Flora of Bhutan, Including a Record of Plants from Sikkim. Vol. 1, Part 1. Royal Botanic Garden, Edinburgh. Nakao, S. (1959). An Unexplored Land-Bhutan. Mainichi Shinbun Co. (in Japanese). Numata, M. (1980). The altitudinal vegetation and climate zones of the humid Himalayas. Geological and Ecological Studies of Quinghai-Xizang Plateau, Vol. 2: 1963-1969. Numata M. ed. (1983). Biota and Ecology of Eastern Nepal. Chiba Univ. Numata, M. (1985). An Unexplored Bhutan, and after that. Ecologial research on life zones. Nature Conservation, No. 283, 14-15 (in Japanese). Planning Commission (1981). Fifth Plan 1981-1987. Main Document. Royal Government of Bhutan. Sargent, Caroline (1985). The forests of Bhutan. Ambio, 14 (2): 75-80.

-142- PART II

SOILS AND TOPOGRAPHY M.Ohsawa(ed.), Life Zone Ecology of the Bhutan Himalaya.1987. Chiba University.

SOILS OF THE BHUTAN HIMALAYA

M. OKAZAKI

Faculty of Agriculture Tokyo University of Agriculture and Technology Fuchu, Tokyo, 183 Japan

INTRODUCTION

The kingdom of Bhutan lies in the eastern Himalayas between the coordinates N 26 45 00 to 28 30 50 and E 88 45 to 92 00 and covers an area of 47000 sq. km which is 1.1 times of the Kyushu island of Japan. It is bound by Tibet in the north, Bengal and Assam in the south, Arunachal Pradesh in the east and Sikkim to the west. The altitude of Bhutan rises abruptly from 140 m in the Sub-Himalaya in the south to more than 7000 m in the Great Himalaya in the north. The Bhutan Himalaya can be divided climatically and geographically into three sections, the Sub-Himalaya (Outer Himalaya) in the south, the Inner Himalaya in the middle and the Great Himalaya in the north ( Geological survey of India, 1977). Three major climatic zones can be recognized, the hot and humid tropical to sub-tropical climate in the Sub-Himalaya, the temperate climate in the Inner Himalaya and the cold climate in the Great Himalaya. The Sub-Himalaya (Foothills) ranges from the Brah- maputran Duar Plains to 600 m in the south to over 1500m. The Inner Himalaya rises from 1500 m to about 5000 m, radiating southward from the Great Himalaya. The Great Himalaya is over 5000 m chains of snow-clad peaks. The reliable maps of Bhutan with the scale of 1:50000 was not available. Karan (1967) prepared the map with the scale of 1:253440, but it was unavailable for our study. The World Bank (1982) published a map with the scale of 1:250000 based on LANDSAT 2 images. The information on soils in Bhutan is seriously limited. Due to the steep gradient, dense vegetation, and severe accessibility, the soil survey in the

-145- Bhutan Himalaya was inadequately carried out until now. However, Karan (1967) showed zonal soils which consisted of Alpine meadow soils, Podzols, Brown soils and Red and yellow soils, according to the elevation, although he did not show the detailed physical and chemical data. Recently FAO took the soil and soil engineering survey as a basic study for developing agriculture aspects in the four areas of Thashigang and Mongar districts (FAO, 1983). This report indicated the distribution of soils in the districts and land capability and preliminary geotechnical maps. In the soil classification, a legend of the system adopted in Soil Map of the World Vol. I (FAO-UNESCO, 1974) was used as a base. Therefore, Bhutan soils distributed in their districts could be compared with world soils. The main object of the present study is to elucidate the distribution and properties of soils in Bhutan. At present stage, this report is only a preliminary one, because chemical and physical analysis has not been completed yet.

STUDY AREA AND SAMPLING SITES

The soil survey research was carried out in September to November of 1985. The study area is ranging from 150 m to 5300 m in altitude of the Bhutan Himalaya, as shown in Fig. 1. The lack of topographical maps made a pedological survey difficult. The pedological observation points were described with an altitude meter and a clinometer to locate the pedological observations. The plotting of these survey points was made in 1:250000 map published by the World Bank(1982).

METHODS OF FIELD SOIL SURVEY

A soil survey was conducted according to the FAO Guidelines for soil profile description (1977) in order to make comparison with other world soils.

-146- 8 9V 8 9'30' 90*0' 9O"3O' 91'0' 91*3 0' 92'0' BHUTAN CHINA / ^^

+28*0'

""->. «NIKKACHU \ +2T30' '^ "A.T0NGSA >O\. _ + t 27*30- WANGDI ) -PHODRANG

.•'•JSHEMGANG

,/. (CV + 27*0'- •PEMAGATSEL

-JONKHAR 91*30'

Fig. 1. Topographical map of Bhutan METHODS OF SOIL ANALYSIS

Soil samples were collected from 69 sites of various altitudes, as shown in Table 1 and Fig. 1. These samples were sent in a moist state to our laboratory in Tokyo, Japan for their analysis. Water content by weight was measured by an oven dry method. Soil pH was measured in water with the soil/solution ratio of 1/2.5 by a Hitachi-Horiba pH meter M-7. Electric conductivity of soil water with the soil/solution ratio of 1/5 was determined by a Toa EC meter. Or- ganic carbon and total nitrogen were determined by a dry combustion using a Yanagimoto CN Corder MT-500. Available phosphate was extracted by Truogs method (Truog, 1930) and determined by the molyb- dophosphoric blue color method (Murphy and Riley, 1962). Phosphate absorption coefficient was determined by Japanese method (Committee of Standard Analysis and Measurement of Soil, 1986). Cation exchange capacity (CEC) was determined by the modified analytical method of the saturation with 1 M ammonium acetate (pH 7). The first step of the replacement of adsorbed ammonium ion was with 1 M sodium chloride, then washing with methanol, and the second step of the replacement of adsorbed sodium ion with 1 M ammonium acetate. The replaced sodium ion was determined by atomic absorption spectrometry (AAS)(ISRIC, 1986). Exchangeable cations, Ca, Mg, K and Na, were extracted by the percola- tion tube method using 1 M ammonium acetate and determined by AAS (ISRIC, 1986). Base saturation was calculated by the equation of exchangeable Ca+Mg+K+Na/CEC x 100 (%). Clay mineralogy of the clay fractions separated from soil samples after the treatment with hydroperoxide and the dispersion of NaOH was investigated by the X-ray diffraction (XRD) method.

RESULTS AND DISCUSSION

1. Vertical distribution of soils in Bhutan

Vertical distribution pattern of soils of Bhutan showed a pattern of vertical distribution along altituding gradients (Fig. 2). Five major zonal soil groups, Alpine meadow soils, Podzols, Brown forest soils, Yellow

-148- Table 1. Numbers of soil profiles surveyed

Soils Elevation (m) Profiles surveyed Profiles sampled

Alpine meadow soils more than 4200 16 15 Podzols 4200 - 3300 14 12

Brown forest soils 3300 - 2400 14 9 CD Yellow brown forest 2400 - 1300 20 20

soils

Yellow soils less than 1300 16 13

Total 80 69 6000 _

5000

4000

o 3000 •H -P Brown forest soils > 2000 Yellow brown forest soils

1000

Yellow soils O L Dry Wet

Fig. 2 Vertical distribution of soils in Bhutan

Himalaya.

-150- brown forest soils, and Yellow soils, were identified by the field survey and the physical and chemical analysis. The typical five zonal soil profiles are shown in Fig. 3. A distinct difference in soil morphology could be observed amongthem. The Alpine meadow soils, which have been developed in the shallow soil overlying hard rock on the steep slope, occur at higher altitudes of more than 4200 m under the alpine meadow. They have shallow weakly structured A horizons and relatively sandy brown colored B horizons. Below a zone of Alpine meadow soils, a zone of Podzols was distributed, ranging from 3300 to 4200 m. The Podzols are developed under Abies- Rhodorendoron forest. A well-developed Podzols remarkably showed organic Al horizons, eluvial A2 horizons and iron and/or humus illuvial Blh, Blir or Blhir horizons. Brown forest soils were distributed in the elevation ranging from 2400 to 3300 m under the Acer-Tsuga forest. They consist of relatively thin dark porous A horizons and brown colored B horizons. Yellow brown forest soils have been developed under the evergreen broad-leaved (shiny leaved) forests. These were found at the altitudes of 1300 to 2400 m, which have brighter yellow colored B horizon than those of Brown forest soils. A zone of Yellow soils was distributed in the lowest altitudes of less than 1300 m. They showed thin A horizons and yellow colored B horizons under the tropical mixed forests. The descriptions for typical soil profiles are as follows:

1) Alpine meadow soils Profile 19 Location: Dangjay Topography and elevation: Lower side slope, sloping 15 to the west, 4650 m Parent material: Granitic gneisses Vegetation: Alpine meadow Profile description: A (0-11 cm): Brownish black (7.5YR3/2), sandy clay loam, weak fine granular structure, moist, slightly sticky and slightly plastic, friable many fine roots, abrupt wavy boundary.

-151- Alpine Podzols Brown Yellow Yellow meadow forest brown soils soils soils forest soils Dangj ay Jurée Dochu-La Taley Umshalbi Depth Site 19 Site 34 Site 2 Site 73 Site 55 (cm) 4650 m 4280 m 3120 m 17 40 m 670 m

0 r 7.5YR3/2 7.5YR3/2 7.5YR2/2 4 7.5YR3/3 7.5YR3/3 Brownish 9 Brownish Brownish Dark Dark 11 black black black brown brown SCL 15 CL CL SiL SiCL 7.5YR4/3 5Y3/1 7.5YR3/3 7..5YR5/6 Brown 24 Gray 22 Dark brown Bright SiL SiCL CL brown 25 en 7.5YR3/3 SiL CO Dark brown 7.5YR4/3 SiCL Brown 10YR6/6 42 10YR4/4 LiC Bright 50 - Brown 45 yellowish SiCL 55 brown SiCL

5YR4/4 Dull reddish brown SiCL 8 5 loo L 93

Fig. 3. Typical soil profiles of Bhutan Photo 1 . Dang jay

-153- B (11-25 cm): Brown (7.5Yr4/3), silt loam, weak fine subangular blocky structure, moist, non-sticky and non- plastic, firm, few fine roots. Remarks: This soil shows a shallow weakly structured A horizon and silty brown colored B horizon on steep lower side slope and is well-drained.

2) Podzols Profile 34 Location: Juree Topography and elevation: Concave topography, sloping 10, S80W, 4280 m Parent material: Gneisses Vegetation: Abies-Rhododendoron forest Profile description: Al (0-9 cm): Brownish black (7.5YR3/2), clay loam, weak fine granular structure, moist, slightly sticky and slightly plastic, friable, many medium roots, clear and wavy boundary. A2 (9-15 cm): Gray (5Y3/1), silty clay loam, massive to weak angular blocy structure, moist, sticky and slightly plastic, firm, few fine roots, clear and wavy boundary. Blhir (15-24 cm): Dark brown (7.5YR2/3), silty clay loam, weak angular blocky structure, moist, slightly sticky and plastic, friable, few fine roots, abrupt and wavy boundary. B2 (24-44 cm): Brown (10YR4/4), silty clay loam, weak angular blocky structure, moist, slightly sticky and plastic, friable, very few fine roots. Remarks: This soil shows a well developed Podzol having a humus and iron illuvial Blhir horizon underlying an Al and an iron eluvial A2 horizon. The Al horizon accumulated organic matter. The loss of iron in an A2 horizon is one of the feature of Podzol. This B horizon is enough to identify the soil as a Podzol by the definition of the spodic B horizon in the FAO system

-154- Photo 2 . Jurée

Photo 3. Dochu-La

-155- (FAO-UNESCO, 1974) which shows a subhorizon more than 2.5 cm thick that is continuously cemented by a combination of organic matter with iron or aluminum or with both below a depth of 12.5 cm.

3) Brown forest soils Profile 2 Location: Dochu-La Topography and elevation: Side slope, sloping 22, N78W, 3120 m Parent material: Vegetation: Acer-Tsuga Profile description: All (0-6 cm): Brownish black (7.5YR2/2), clay loam, moderate fine granular structure, moist, sticky and plastic, friable, many medium roots, gradual and smooth boundary. A12 (6-22 cm): Dark brown 87.5YR3/3), clay loam, moderate medium granular structure, moist, slightly sticky and slightly plastic, friable, common fine roots, gradual and wavy boundary. Bl (22-55 cm): Brown (7.5YR4/3), light clay, weak medium angular blocky structure, moist, sticky and plastic, firm, few fine roots, clear and wavy boundary. B2 (55-93 cm): Dull reddish brown (5YR4/4), silty clay, moderate medium angular blocky structure, moist, slightly sticky and slightly plastic, firm, very few fine roots. Remarks: This soil consists of a brownish and dark black A horizon and brownish B horizon. The B horizon is identified as a Cambic B horizon in the FAO system (FAO, 1974).

4) Yellow brown forest soils Profile 73 Location: Taley Topography and elevation: Side slope, sloping 17, to the south, 1740 m Parent material: Granite

-156- Photo 4 . Talev

Photo 5 . Umshelb

— 157 — 1

I Vegetation: Broad ever green leaves forest Profile description: I A (0-4 cm): Dark brown (7.5YR3/3), silt loam, weak medium granular structure, moist, nonsticky and slightly I plastic, friable, many fine roots, clear and wavy boundary. I B (4-45 cm): Bright brown (7.5YR5/6), silt loam, weak medium subangular blocky structure, moist, nonsticky and I slightly plastic, friable, few fine roots. Remarks: This soil has a brighter yellow brown colored B I horizon than that of Brown forest soil. According to the definition of Nagatsuka (1986) the color of B horizon of I Yellow brown forest soil represents 7.5YR to 2.5 YR for the hue, more than 4 for the value and more than 4 for I chroma. This B horizon is identified as the B horizon of Yellow brown forest soil. I 5) Yellow soils I Profile 55 i Location: Umshalbi I Topography and elevation: Lower terrace, sloping 15, to the i west, 670 m ; Vegetation: Tropical mixed forest ! I Profile description: j A (0-5 cm): Dark brown (7.5YR3/3), silty loam, weak medium I granular structure, moist, slightly sticky and slightly plastic, friable, few fine roots, clear and wavy < I boundary. j B (5-85 cm): Bright yellow brown (10YR6/6), silty clay loam, I moderate medium subangular blocky structure, moist, slightly sticky and slightly plastic, firm, very few fine I roots- Remarks: This soil consists of a dark brown A horizon and a I bright yellowish brown colored B horizon. The characteristic B horizon is in the extent of 7.5YR to I 2.5 YR for the hue, more than 4 for the value and more than 4 for the chroma as the definition of Red and Yellow

I -158- I soils.

2. Chemical and physical properties of typical soils in Bhutan

The water content by weight (%) is shown for the samples of typical soil types from Bhutan in the function of soil depth (Fig. 4). There is much difference in the water content among the soil types, ranging from 24.6 to 105 %. The water content of Brown forest soils were larger than that of other soil types. The pH values of all samples were strong to weakly acidic below 6, ranging from 4.33 to 5.91 (Fig. 5). They did not show large changes between upper and lower horizons. The soil pH seems to be correlated with the amount of exchangeable cations derived from parent material. However, the low pH of the surface horizon of Brown forest soil at Dochu-La was due to organic substances supplied from the Acer-Tsuga forest. Sargent et al.(1985) have shown that pH reactions were fairly neutral, with a mean reading of 5.6 + 0.47 at 10 cm depth of Brown forest soils. However, the present study on typical Brown forest soil did not coincide with the result of Sargent et al.(1985). Soil reaction of Japanese Yellow brown forest soils derived from basic rock is 4.7 to 6.8 (Nagatsuka, 1975). Bhutanese Yellow brown forest soils showed the intermediate pH values with 5.40 to 5.91. The electric conductivity in water with the soil/solution ratio of 1/5 of samples is shown in Fig. 6. The EC values of samples ranged from 26.1 to 252 uS/cm, of which higher valuesare for the samples from Brown forest soils and Yellow brownforest soils. Organic carbon content of the samples ranged from 0.392 to 15.2 %, as shown in Fig. 7. Organic carbon content in the surface soil increased in the following order; Yellow soil < Alpinemeadow soil < Podzol < Yellow brown soil < Brown forest soil. More than 10% of organic carbon content was observed in the A horizon of the samples from Yel- low brown soil and Brown forest soil. The Blhir horizon of Podzol which is a diagnostic horizon for identifying the soil as a Podzol indicated a high organiccarbon content caused by the humus supply from the upper A horizons. Sargent et al.(1985) reported that organic content was more than 35 % on average within the top 30 cm. However, their results are more than twice of the present study ( organic content or humus content

-159- Water content

^ oO »0 0 100 £ 15 I 50 r Q. 0 Q 30 50L 100L

O) o Dangjay Juree Dochu-La Tatey Umshalbi

Fig. 4. Water content of typical soils in Bhutan Himalaya, Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil pH(H2O) O 10 O 5 10 O 5 10 O 5 JO 0 5 10 o -• o —' O —• O

£ 15 15 50 25 50 I CL O Q30 30 100 50 100 Dangjay Juree Dochu-La Taley Umshalbi

Fig. 5. Soil pH of typical soils in Bhutan Himalaya Dangjay: Alpine meadow soil Juree: Podzol Döchu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil EC |jS/cm 0 200 0 200 0 200 0 200 0 200 0 —• 0 0

£ 15 15 o 30 30 100L CO I Dangjay Juree Dochu-La Tatey Umshalbi

Fig.6. Electric conductivity of typical soils in Bhutan Himalaya, Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil Organic Carbon

0 12.5 25 Q 12.5 25^ 0 125 25 0 125 25 0 12.5 25 0' n n n n

15 15 50 25 a ƒ 50 a 30 30 100 50 100'

CO I Dangjay Juree Dochu-La Ta ley Umshalbi

Fig.7. Organic carbon content of typical soils in Bhutan Himalaya

Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil = organic carbon content x 1.723). This discrepancy might be derived from the large differences in the amount and composition of organic matter supplied from the various types of plant communities. Endo (1975) reported that the organic carbon content of soils in Nepal were 1 to 6 % for forests 0.5 to 4 % for grassland and 0.5 to 4.5 % for cultivated soils in a range from several hundreds to 5000 m. Total nitrogen content of the samples is shown in Fig. 8. The values of them , ranging from 0.029 to 0.91 %, had the same tendency with the results of the organic carbon content. The highest value was also obtained in the Blhir horizon of Podzol. Endo's results in Eastern Nepal were 0.15 to 0.65, 0.05 to 0.6 and 0.05 to 0.6 % in forests, grasslands and cultivated lands, respectively. These results indicated the same total nitrogen content level as the present result. The values of C/N ratio ranged from 13.4 to 27.3. There is little fluctuation of the values of C/N ratios within the profiles. The highest value was also in the Blhir horizon of Podzol, which is due to the con- tribution of humus with high C/N ratio. Figure 9 shows the amount of available phosphate of the typical soil samples in the function of soil depth. The amount ranged from 0.0169 to 1.07 mgP/100g. Available phosphate in the surface soil are larger than that in the subsurface soil. Phosphate is one of the most important nutrient for plant growth, especially for the initial stage of plant growth. Forest soils and yellow soils generally show the low content of phosphate. Phosphate absorption coefficient of the samples is shown in Fig.

10, which ranged from 120 to 2280 mgP2O5/100 g. There was a great variation among soil types and horizons. The high value of phosphate absorption coefficient suggests the high content of active iron and/or aluminum compounds and organic matter. The Blhir horizon of Podzol represented the highest value of phosphate absorption coefficient. On the other hand Yellow soils showed the lowest values among the typical Bhutan soils. CEC of the samples of the typical soil types is shown in Fig 11. The values of CEC ranged from 5.41 to 47.9 me/100 g. CEC of the surface horizons of all typical soils was apparently higher than that in the subsurface horizons without Blhir horizon of Podzols. This finding suggests that CEC depends upon the amount and composition of clay

-164- Total Nitrogen

O 0.5 1 O 0.5 10 0.5 1 0 0.5 Q5 ] ~ o 0 0 0 -1 o° o 15 50 25 50 £ 15 •/ 0 30 30 100 50 100' Dangjay Juree Dochu-La Taley Umshalbi

Fig. 8. Total nitrogen content of typical soils in Bhutan Himalaya Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil Available P mg P/100g dried soil

0 0.5 1 0 0.5 1 0 0.5 1 ß 0.5 1 Q0 0.5 1 0 - 0 x^_:> 15 15 r o. G> Û L L 1 30 30 100 50 100 166 - Dangjay Juree Dochu-La Taley Umshalbi

Fig. 9. Available phosphate content of typical soils in Bhutan Himalaya, Dangjay: Alpine meadow soil Jurée: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil P Absorption Coefficient

mgP2O5/100g dried soil 0 1000 0 2000 .0 2000 .0 2000 0 1000 0 , Qr* • 0

15 7 50 I

30 30L 100 en -o Dangjay Jurée Dochu-La Taley Umshalbi

Fig. 10. Phosphate absorption coefficient of typical soils in Bhutan Himalaya Dangjay: Alpine meadow soil Jurée: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil Cation Exchange Capacity me/100g dried soil O 25 50 O 25 50 0 25 50 0 25 50 0 25 50 0 • ' 0 —• 0 •" 0 o £ 15 25 50 I CL O Q 30 50 100 en co I Dangjay Jurée Dochu-La Taley Umshalbi

Fig. 11. Cation exchange capacity of typical soils in Bhutan Himalaya Dangjay: Alpine meadow soil Jurée: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil minerals and organic matter. CEC of the samples of soils on the old river terraces and mountain slopes from Nepal ranged from 4.0 to 20.2 me/100 g (Kaddah,1967). The CEC of the Bhutanese soil samples was higher than the Nepalese soil samples. The decrease in CEC of the Nepalese soils probably depends on the serious topsoil degradation by human beings, which especially bring about loss of organic matter. Fig. 12 shows exchangeable calcium content of the samples. The content of exchangeable calcium ranged from 0.142 to 14.2 me/100 g. It is appeared to be low exchangeable calcium content except Yellow brown forest soil. The exchangeable calcium in the surface horizons of Alpine meadow soils, Yellow brown soils and Yellow soils were larger amount than that in the subsurface horizons. The higher values of exchangeable calcium in Yellow brown forest soil was presumably caused by parent materials. Himalayan soils in eastern Nepal showed the low exchangeable calcium content (8.5 me/100 g for forest, 6 for grassland and 4.5 for cultivated soil), as reported by Endo (1975). Bhutan soils also indicated the low exchangeable calcium content. There can be recognized no correlation between pH (H2O) and exchangeable calcium in this study. This result was similar to that obtained in eastern Nepal by Endo (1975). Exchangeable magnesium content of the samples is shown in Fig. 13, which ranged from 0.0616 to 5.48 me/100 g. The amount of exchangeable magnesium in the surface horizons was higher than that of the subsurface ones. This trend was similar to that of exchangeable calcium. Comparing with the content of exchangeable magnesium of eastern Nepal soils, in whichi the content was in the ranges from 0.6 to 2.5 me/100 g for forest soils, from 0.1 to 1.2 for grassland soils, and from 0.04 to 0.7 for cultivated land, the present result indicates wider variation. Figure 14 shows exchangeable potassium content of the samples. The amount of exchangeable potassium in the samples, which ranged from 0.0539 to 6.11 me/ 100 g, decreased with increasing soil depth. The highest value could be observed in All horizon of Brown forest soil. Ex- changeable potassium content in soils of eastern Nepal were 0.46 to 0.64 me/100 g for forest soils, 0.21 to 1.4 for grassland soils and 0.26 to 1.8 for cultivated soils (Endo, 1975). Bhutan soils contain larger amount of exchangeable potassium than Nepali soils. According to Gansser (1983), the gneisses, Paro metasediment and leucogranites are widely distributed in

-169- Exchangeable Ca me/100g dried soil 10 0 5 10 0 10 15 0 5 10 -• Of • • 0Hf

50 25 50

100L 50L 100 Dangjay Juree Dochu-La Taley Umshalbi

Fig. 12. Exchangeable calcium content of typical soils in Bhutan Himalaya. Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil Exchangeable Mg me/100g dried soil 2.5 5 0 25 5 0 25 2.5 5 O 25 5 - 0

15 50

30 100 -a Dangjay Juree Dochu-La Taley Umshalbi

Fig. 13. Exchangeable magnesium content of typical soils in Bhutan Himalaya, Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil Exchangeable K me/100g dried soil 25 5 0 2.5 5 0 2.5 5 0 2.5 5 0 2.5 5 - 0 -• Oi—- ' '* 0 • ' 0

15 50 25 50

30 100 100 to I Dangjay Juree Dochu-La Taley Umshalbi

Fig. 14. Exchangeable potassium content of typical soils in Bhutan Himalaya, Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil the Bhutan Himalaya. They contain the muscovite and biotite to some extent, resulting in the supply of potassium to the Bhutan soils- Exchangeable sodium content of the samples is shown in Fig. 15, which ranged from 0.0124 to 0.413 me/100 g. The amount of exchangeable sodium in the surface horizons was higher than that in the subsurface horizons without Podzol profile. Exchangeable sodium content of the samples with low altitude in Nepal were on average 0.087 for forest soil, 0.13 for grassland soil and 0.17 for arable land soil. As for base saturation, there is a distinct difference between the Bhutan soils (Fig. 16). Base saturation of the samples ranged from 2.1 to 53.2 %. The highest values can be observed in Yellow brown soils, while the lowest values in Yellow soils. Although Yellow brown forest soils in Japan revealed high base saturation (more than 46 %) derived from basic parent materials, the base saturation for the subsurface horizon of Yellow brown forest soil in Bhutan Himalaya was less than 46

3. Clay mineralogy of typical soils in Bhutan

Fig. 17 to 21 show XRD patterns of clay fractions of Bhutan soils which were treated with DCB (dithionite-citrate-bicarbonate) solution. The clay fractions of Alpine meadow soil were characterized by the X-ray diffraction peaks at about 14,10, 5, 4 and 3.4 A. The peak at 14 A indicates 2:1 type clay minerals. The 14 A peak did not shift to a new peak with longer lattice space upon glycerol solvation, which indicated the presence of vermiculite or intermediate minerals. The high and sharp peak at 10 A shows 10 A minerals as predominant species. It shows that the presence of mica type minerals, which might be due to the micaceous parent materials, was confirmed by the persistance of 10 A peak after glycerol solvation. The 7 A peak indicates kaolin minerals. The high and sharp peak at about 3.4 A were from quartz. The X-ray diffraction from clay fractions of Podzol also reveals the peaks at about 14, 10, 7, 5, 4 and 3.4 A, indicating 2:1 type, mica type, kaolin minerals and quartz. It shows that no essential difference is found between the samples from the profile. Distinguishable difference in the clay mineral composition, however, can be observed between the samples. The diffraction at 14 A, which indicates vermiculite and inter-

-173- Exchangeable Na me/100g dried soil

0 0.5 1 0 0.5 1 .0 05 1 0 0.5 1 n0 0.5 1 O 0 •• ou?—•—• o "• 0

-£ 1 RI 15 50 25 50 I

L 30 30 100L 50' 100 -g Dangjay Juree Dochu-La Taley Umshalbi

Fig. 15. Exchangeable sodium content of typical soils in Bhutan Himalaya Dangjay: Alpine meadow soil Juree: Podzol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshalbi: Yellow soil

.v _ . Base Saturation

0 25 50 0 25 50 0 25 50 0 25 50 .0 25 50 ~ 0 • ' 0 0

£ 15 50 25 50 Q. û30 30 100 50L 100' en I Dangjay Jurée Dochu-La Taley Umshaibi

Pig. 16. Base saturation of typical soils in Bhutan Himalaya. Dangjay: Alpine meadow soil Juree: PocUol Dochu-La: Brown forest soil Taley: Yellow brown forest soil Umshaibi: Yellow soil 3.4A

3.4A

ÏOA 10A 14A 14A Mg-20 Mg-2 O

Mg-Gly Mg-Gly

K-20 K-20 K-350 K-35O K-550 K-550 A Uw, horizon B horizon

15 25 35 5 15 25 35 2 e for Cu K« Radiation

Fig. 17. XRD patterns of clay fractions from Alpine meadow soil. Mg-2 0: Mg-saturated clay for untreated sample, Mg-Gly: Mg-saturated clay for glycerol-treated sample, K-20: K-saturated clay for untreated sample, K-350: K-saturated clay for 350 C-treated sample, K-550: K-saturated clay for 550 C-treated sample.

-176- 14A 3.4A 14A 3.4A

Mg-2 0 Mg-20

Mg-Gly

Mg-Gly K-20 K-20 K-350 K-350 K-550 K-550 A2 horizon

15 25 35 15 25 35

14A 4A

14A 4A 3.4A

3.4A Mg-2 0

Mg-20

Mg-Gly Mg-Gly

K-20 Hl K-20 K-350 K-350 K-550 K-550

BI horizon B2 horizon

5 15 25 35 5 15 25 35 2 G for Cu K« Radiation Fig. 18. XRD patterns of clay fractions from Podzol. For samples see Fig. 17. -177- 3. 4 A, 3.4A

14A 14A 10A Mg-20 V 11OA,7A Mg-20 I

Mg-Gly Mg-Gly

f.. K-20

K-350

K-550

All horizon A12 horizon

15 25 35

3.4A

14A Mg-2 0 Mg-20 14A 7A

Mg-Gly

K-350 K-2 0 K-350

K-550 K-550 BI horizon ^ B2 horizon

15 25 35 5 15 25 35 2 e for Cu K« Radiation Fig. 19. XRD patterns of clay fractions from Brown forest soil. For samples see Fig. 17.

-178- 14A

14A

3.4A

Mg-2 O

Mg-Gly

K-20

K-350

K-550

horizon

15 25 35 15 25 35

2 e for Cu Ko< Radiation Fig. 20. XRD patterns of clay fractions from Yellow brown forest soil. For samples see Fig. 17.

-179- 3.4A

Mg-20

B horizon

5 15 25 35 2 e for Cu K« Radiation

Fig. 21 XRD patterns of clay fractions from Yellow soil For samples see Fig- 17.

-180- mediate minerals, in B2 horizon had stronger intensity than that in the surface horizon. It may be attributed from the parent materials. This fact is the same as the peaks at 10 and 7 A. The clear and high peaks at 3.4 A, which showed the presence of quartz, were found in the clay fraction from surface horizons. The clay fractions of Brown forest soil remarkablly showed the peaks at about 14, 7, 4 and 3.4 A. All clay samples revealed the presence of the 14 and 7 A layer silicates along with a small amount of 10 A clay minerals. The diffraction intensity at 3.4 A became clearer toward the surface horizon. The X-ray diffraction from the clay samples of Yellow brown forest soil shows the sharp peaks at 14, 10, 7, 4 and 3.4 A. The predominant layer silicates are vermiculite, mica type minerals and kaolinite groups in the samples of Yellow brown forest soil. Although the presence of mixed-layer minerals is characteristic for the clay mineral composition of Yellow brown forest soil in Japan (Nagatsuka, 1975), Yel- low brown forest soil in Bhutan did not reveal the clear presence of the mixed-layer minerals. The clay fractions of Yellow soil revealed the sharp peaks at about 14, 10, 7, 5 and 3.4 A. The high intensity of X-ray diffraction at 10 and 5 A shows the presence of mica type layer silicate minerals and the strong peaks at 3.4 A reveals the presence of quartz.

SUMMARY

The five major soil groups, Alpine meadow soils, Podzols, Brown forest soils, Yellow brown forest soils and Yellow soils, were vertically distributed in the Bhutan Himalaya according to altitude.

1) Alpine meadow soils Alpine meadow soils occur at higher elevation of more than 4200m under the alpine meadows. They have shallow weakly structured organic A horizons and relatively sandy brown colored B horizons. They shows weakly acidic soil reaction, medium humus content, and low phosphate retention, CEC and exchangeable cations content. The predominant clay minerals of Dangjay profile is the mica type clay minerals.

-181- 2) Podzols A zone of Podzols occurs below Alpine meadow soils zone ranging from 3300 to 4200 m under the Abies-Rhododendron forest. The humus and iron accumulated Blhir horizon can be observed in the well-developed Podzols. Their characteristics are acidic soil reaction caused by low exchangeable cations content, and high humus content and phosphate retention. The vermiculite is a predominant clay mineral in the subsurface samples of Juree profile.

3) Brown forest soils Brown forest soils are distributed from 2400 to 3300 m under the Acer-Tsuga forests. The soils consist of relatively thin porous A horizons and brown colored B horizons. The brown forest soils at Dochu-La profile show strongly acidic soil reaction, high humus content, considerably high phosphate retention and low base saturation. The vermiculite and kaolin minerals are found in the samples of Dochu-La profile.

4) Yellow brown forest soils Yellow brown forest soils develop at the elevation of 1300 to 2400 m under the temperate evergreen broad-leaved forests, which is characteristic to East Asia. They are distinguished by brighter yellow colored B horizons than those of Brown forest soils. The features of chemical properties of Yellow brown forest soils are slightly acidic soil reaction, medium humus content, high CEC and exchangeable cations content. The predominant clay minerals of the samples from Taley profile are vermiculite, mica type clay minerals and kaolin minerals.

5) Yellow soils A zone of Yellow soils appear in the lowest altitude of less than 1300 m. These soils show thin A horizons and yellow colored B horizons. They show weakly acidic soil reaction, and low humus content, phosphate retention, CEC, exchangeable cations content, and base saturation. The predominant clay minerals are mica type.

-182- ACKNOWLEDGEMENT

The author is indebted to the students of the Laboratory of Soil and Aquatic Environment, Faculty of Agriculture, Tokyo University of Agriculture and Technology for their analytical assistance and to Mr. Yukio SATO, Department of Horticulture, Chiba University, for the management of the X-ray diffractometer.

REFERENCES

Committee of Standard Analysis and Measurement of Soil. (1986). Standard analysis and measurement of soil. 354 pp. Hakuyusha, Tokyo. Endo, M. (1975). Soil in Eastern Nepal, in Mountaineering of Mt. MakuluII and Scientific Studies in Eastern Nepal, 1971. ed. Numata M., Himalayan Committee of Chiba Univ., Chiba. pp. 174-214. FAO-UNESCO. (1974). Soil Map of the World. UNESCO, Paris, p. 59. Food and Agriculture Organization of the United Nations. (1977). Guidelines for Soil Profile Description. FAO, Rome. p. 66. FAO. 1983. Soil and Land Capability Survey, Bhutan, Tashigang and Mongor District, Project RAS 79/123. Gansser, A. (1983). Geology of the Bhutan Himalaya. Birkhauser Verlag, Basel, Boston, Stuttgart, p. 181. Geological Survey of India. (1977). Geology and Mineral Resources of Bhutan. Calcutta, pp. 1-12. ISRIC. (1986). Procedures for Soil Analysis, Technical Paper 9. ISRIC, Wageningen, p. 106. Kaddah, M.T. (1967). Land For and Use and Characteristics of Some Soils in Nepal. Soil Sei. (104): 350-357. Karan, P. P. (1967). Bhutan, A Physical and Cultural Geography. Univ. of Kentucky Press, Lexington. P. 103. Murphy, J. and Riley, J. P. (1962). A Modified Single Solution Method for the Determination of Phosphate in Natural Waters. Anal. Chim. Acta (27): Nagatsuka, S. (1975). Genesis and Classification of Yellow-Brown

-183- Forest Soils and Red Soils in Southwest Japan. Bull National Inst. Agr. Sei., Series B (26): 133-257. Sargent, C, Sargent, O. and Parsell, R. (1985). The Forest of Bhutan: A Vital Resource for the Himalayas? J. Tropical Ecology (1): 265-286. Truog, E. (1930). The Determination of the Readily Available Phosphorus of Soils. J. Am. Soc. Agron. (22):874-882. World Bank. (1982). Bhutan, Landcover, Soil and Water Reflections from Landsat Imagery, 1:250000.

-184- of the Bhutan Himalaya.1987. Chiba University.

TOPOGRAPHIC FEATURES IN THE CENTRAL PART OF THE BHUTAN HIMALAYAS

T. EGUCHI

Department of Geography, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan

ABSTRACT

The Bhutan Himalaya is tentatively divided into four geomorphic zones from south to north as follows; 1. The southern foothills 2. The southern High Himalaya 3. The lower Midland(of the High Himalaya) 4. The northern High Himalaya The topographic features in the lower Midland is that the altitude of ridge is relatively low in comparison with that of the southern and northern High Himalaya, the slope of river bed is small and the relatively wide valley river plains are developed along the bottoms of valleys. The transition point from the U-shaped valley to the V- shaped valley is around 3,500m in the central part of Bhutan and the present glacier tongue is located around 5,000m. The basinlike low relief landforms are developed around 5,000m.

INTRODUCTION

Bhutan is located in the eastern part of the Himalayas and the area is around 46,500 sq. Km. In Bhutan, the distance between the northern and southern borders is around 150Km and the maximum and minimum altitude is above 7000m along the northern border with the

-185- Tibetan Plateau and around 150m along the southern border with Assam, respectively. Bhutan is a mountainous country and plains are distributed only in the valley bottoms of middle parts and along the mountain foot near the southern border. Although Gansser(1983) clarified many important features of geology and topography of Bhutan, many important problems are rest as he pointed out. In particular, the topographic features are not sufficiently clarified. In this paper, the author intends to show some geomorphic features mainly in the central part of the Bhutan Himalaya on the basis of the survey in 1985(Fig. 1, Fig. 2).

GENERAL TOPOGRAPHIC FEATURES

Gansser(1983) proposed five main geological zones for the whole Himalayan chain extending west-east direction and recognized only four zones the Bhutan; i.e. a Sub-Himalaya, the Lower Himalaya, the High Himalaya, the Tibetan Himalaya or Tethys Himalaya(Fig. 3). He shows that the sediments representing the Tetys or Tibetan Himalaya occur only as basinlike embayments in northwest and central Bhutan and as a thin margin just along the Tibetan border in north-central and northeast Bhutan and the larger part of Bhutan consists of crystalline sheets representing the crystalline of the High Himalaya. According to the geological map of Gansser, the Bhutan Lower Himalaya extends west-east direction to the south of the wide Bhutan High Himalaya and is narrow in comparison with that of the other parts of the Himalayas. To the south of the Bhutan Lower Himalaya, the Bhutan Sub-Himalaya is distributed intermittently and is also narrow. One of the geological features of Bhutan is the north-south arrangement of the wide High Himalaya, the narrow Lower Himalaya and the intermittent and narrow Sub-Himalaya. This geological arrangement is eminent in the western and central part of Bhutan. The topographic features of the Himalayas is the most well-known in Nepal. Iwata et al.(1984) show that the topographic zones of the Great Himalayan Range, the Midlands, the Mahabharat Range, and the Siwalik mountain, extending west-east direction, are distributed from north to south, to the south of main range of the Himalayas and the north-

-186- 8 9V 8 9'30' BHUTAN CHINA / ^n

BANGLA J i DESH'i.i +28'0'

0 10 20 30 40 SO 1 i i i i i oo +27-30' t- 27'3O'- WANGD1 ) -PHODRANG

+ 27'0'- "PEMAGATSEL

PHUNTSOLING

+SAMDRUP -JONKHAR 89*0' 9 1*30'

Figure 1. Survey route map of Bhutan. 90*00' 90*15' 2 8*00-

JICHUDAGMO B

GECHEWOMAf-

,_; NIKKACHU^ , 2 7*3 0- oo 00

90*15'

Figure 2. Survey routs

in the central part 2000

of Bhutan.

27*00

90*30' 90*4 5' 91*00' Structural Map of the Bhutan Himalaya

1980

oo CD

Main Ihru.l» MFT.M»ln Iron I »I Ihrusl UBT.Maln boundary thrust MCT.ftUin ctniril (hru*l

Figure 3. Structural map of the Bhutan Himalaya(Gansser, 1983). south arrangement of the topographic zones is typical in central Nepal. They also show that two prominent geological boundaries, the Main Central Thrust and the Main Boundary Fault exactly coincide with two steep slopes on the summit level map: one is the southern flank of the Great Himalayan Range and the other is the boundary between the Mahabharat Range and the Siwalik mountains. Topographic features show a good correspondence with the distribution of geology in central Nepal. The north-south arrangement of topography is also recognized in Bhutan, however, the topographic features are not so good correspond with the geology. The geological zones of the Sub-Himalaya and the Lower Himalaya are narrow and distributed only along the southern foothills and the southern lower slopes near Assam. The topographic features corresponding these narrow geological zones are recognized but obscure. The zone of the High Himalaya is covering a large part of Bhutan. This geological zone is topographically divided into three sub- zones,such as the northern zone, the middle zone and the southern zone, by the relatively low altitudinal zone extending west-east in the middle part of Bhutan(Fig. 4). The southern zone is the mountain region and the Black Mountains is located in the central part of this zone. The northern zone is correspondent to, so called, the Great Himalayan Range of the central Nepal and its maximum altitude is above 7000m or more. The middle zone is distributed between two mountain ranges which extend west-east, being interrupted by rivers. The large cities such as, Thimphu, Punakha, Tongsa, and Bumthang show a chain through this zone. The rivers running north to south show low gradient when they cross this zone and the valley plains are developed through this zone. Considering these topographic features, at least four geomorphic zones are tentatively proposed from south to north as follows; 1. The southern foothills 2. The southern High Himalaya 3. The lower Midland(of the High Himalaya) 4. The northern High Himalaya. The arrangement of the four geomorphic zones are clearly recognized in the western and central parts of Bhutan west of the Kuru Chhu(River), though it is difficult to place exactly the boundaries between zones. Along the Kuru Chhu, the Lower Himalaya extends north judging from the geological map of Gansser and, east of the Kuru Chhu, the

-190- (m) -6000

Eastern ridge -5000

Western ridge

Pho Chhu -2000

-1000 Punakha Wangdhu Phodrang 1-0 —i— —r~ —r~ 1 "I 0 130 120 110 100 90 80 70 60 50 30 20 10 (Km) Distance

Figure 4. Longitudinal profile of the Sankosh River and its western and eastern ranges. zones of the Sub-Himalaya and the Lower Himalaya is distributed wider than in the area west of the Kuru Chhu. Since the survey area in 1985 is restricted to the west of the Kuru Chhu. It is a problem for future research whether the proposed four geomorphic zones are applicable to the east of the Kuru Chhu.

LOCAL FEATURES OF THE GEOMORPHIC ZONES

1. The southern foothills

Along the southern border of Bhutan, the Sub-Himalaya is distributed intermittently, and the Lower Himalaya directly contacts with the Assam Plain in the area lack of the Sub-Himalaya. In the Sub- Himalaya around Manas(Photo 1), the altitudes of mountain peaks are around 500m and the mountain slope of the Sub-Himalaya facing Assam is not so steep. To the contrary, around Phuntsoling, the Lower Himalaya directly contacts with the Assam Plain. The mountain slope facing Assam is steep and the relative altitude between the peak and the foot of mountain slope is around 2,000m.

2. The southern High Himalaya

This region is the mountain region and the main mountain range of this region is, so called, the Black Mountains. The maximum peaks of the Black mountains between the Sankosh river and the Mangde Chhu are above 5000m or more and the altitude of peaks decrease toward the eastern part. In this region, rivers mainly flow from north to south and make deep canyons(Photo 2). The bottom of valley is narrow and the lower part of the slope is steep. The middle and upper part of slope, between 1000m and 2000m, mainly around 1500m(Photo 3), is relatively gentle and villages are many located in this altitudinal zone. It is difficult to show the northern and southern boundary of this region.

-192- 3. The lower Midland in the High Himalaya

This region is distributed in the middle part of Bhutan extending from west to east and large cities such as Ha, Paro, Thimphu, Punakha, Wangdhu Phodrang, Tongsa, Bumthang are located in this region. The characteristics of topographic features of this region are as follows; 1. The altitude of ridges is relatively low in comparison with that of the southern and northern High Himalayas. 2. The slope of river bed is small and the relatively wide river plains are developed along the bottoms of valleys. These features are eminent around Bumthang in the central part of Bhutan. The Local difference of topographic features is also recognized. One of the local differences is that the altitude of river plains in this region is different between rivers. The altitudes of Paro (Paro Chhu), Thimphu (Wang Chhu) and Bumthang (Chamka Chhu) are 2000-2500m. To the contrary, the altitude of Wangdhu Phodrang(Sankosh River) is 1200- 1400m and that near Mongar(Kuru Chhu) is below 1000m. The depth of valley, the relative altitude between the mountain ridge and the valley bottom, is relatively small around Paro, Thimphu and Bumthang. In particular, around Bumthang, the area of river plains is larger than in the other parts of the lower Midland and the slope of mountains is relatively gentle. These low relief areas are distributed between 2500m and 3500m. Along the eastern range of the Chamka Chhu (northeast, east and southeast of Bumthang), the slopes on ridges, extending northwest- southeast, are relatively gentle(Photo 4). The flat river plains and gentle mountain slopes are also developed around Nikkachu west of Tongsa and the geomorphic contrast between the east side and the west side of Pele La(Pass) is eminent. This local difference is expected to depend on the difference of basin area.

4. The northern High Himalaya

The main survey area of the first-half of the survey in 1985 is in the central part of the northern High Himalaya. In this region, the glacial landforms and the low relief area around 5000m are developed. Con- cerning the glacial landforms, Gansser (1983) shows the glacial map using

-193- the Landsat images and field observation. In this section, the author in- tend to show the following remarks on the basis of our observation along the survey route.

4-1. Nikka Chhu The Nikka Chhu is one of tributaries of the Mangde Chhu and joins the Mangde Chhu south of Tongsa. The U-shaped valley appears around Morathang(3500m), the talus slopes are developed on the both sides of the river and the bottom of valley is filled with the talus(Photo 5). At the uppermost of the river, the cliff with relative height of 300m or more is formed and cirques are formed above the cliff. The cirques are divided into at least three steps by their altitude of cirque bottom, i.e. 4000m, 4200m and 4300m(Photo 6, Photo 7, Photo 8). The middle one is the widest and the wide glacial lake(Umata Tso) is formed. The pass, located at the drainage divide between the Nikka Chhu and the Tampey Chhu, is Tampey La(pass) and its altitude is 4500m. Around this pass, bare land is developed and the structural landform is observed.

4-2. Tampey Chhu The short tributaries of the Tampey Chhu is formed the drainage to the north of the Tampey La. The valley walls are asymmetric and the structural landform is developed in this drainage. The rock basin, the whole or part of which the lake, Tampey Tso(Lake), occupy, is formed around 4300m. The small terminal moraine is observed at the upper side of this lake and the steep slope is developed at the downside of of this lake. This tributaries runs rapidly on this steep slope and joins the main stream of the Tampey Chhu. The Tampey Chhu is also one of the tributaries of the Mangde Chhu and the drainage area is greater than that of the Nikka Chhu. The confluence of the two rivers is located around 3500m and is covered with forests. The transition point from the U-shaped valley to the V-shaped valley is located at a little higher than the confluence point. The relative altitude of valley wall is low in comparison with the width of the valley in the U-shaped valley region(Photo 9). The relative altitude of valley wall is lower and the coverage of vegetation is smaller as the altitude is higher.

-194- The wide plain is developed in the upper part of the river, above 5000m(Photo 10). The plain shows the basin-like landform and at least four large glacial lakes are distributed(Photo 11). The southernmost lake is wide and shallow. The other three lakes are located at the end of the glacier. At the uppermost of the river, the steep rock slope is developed south of the Rinchenze La(5240m).

4-3. The Inner northern area The northernmost area of the survey route, the Inner northern area, is located south of the main range area bordering with China and the large Lunana valley extends west-east between the two areas(Photo 12). The low-relief landforms are developed between the Pho Chhu and the Mangde Chhu in the Inner northern area. The present glacier is distributed along the range, extending north-south direction, between the tributary of the Pho Chhu and the Mangde Chhu, and the present glacier tongues reach around 5000m. The hills extend westward between Jichudagmo and Tsochena from the range where the present glacier is distributed, and the relative altitude between the tops of hills and the bottoms of valleys are around 200m. The glacier lakes are distributed in the valleys. The basinlike low relief landforms are developed to the north of Mt. Namshila and to the west of Mt. Gangkar Puensum(Photo 13,Photo 14).

4-4. Mangde Chhu The Mangde Chhu originates around Mt. Gangkar Puensum and the uppermost part of the Mangde Chhu valley is filled with the moraines(Photo 15). This valley is the widest U-shaped valley along our survey route(Photo 17). The transition point from the U-shaped valley to the V-shaped valley is located around 3,500m near Yak Camp(Photo 18). The hot springs are distributed at Duersachu.

4-5. Bumthang Chhu The pass between the Mangde Chhu and the tributary of the Bum- thang Chhu is Jurée La and the glacier lakes are distributed in the both sides of Jurée La. The transition point from the U-shaped valley to the V-shaped valley is located around 3,500m to the north of Kurbang.The relatively low relief landforms and the wide valleys are developed to the

-195- north of Bumthang.

REFERENCES

Gansser, A. (1983). Geology of the Bhutan Himalaya. Birkhauser Verlag. Basel, pp 181. Iwata, S., Sharma, S. and Yamanaka, H. (1984). A preliminary report on geomorphology of central Nepal and Himalayan uplift. Jour. Nepal Geol. Soc, 4: 141-149.

-196- Photo 1. The southern foothills around Manas

Photo 2. The southern High Himalaya around Dummonp; Tsachu The Mangde Chhu makes the deep canyon.

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Photo 3- I The southern High Himalaya around I Nagor. I I I I

I Photo i\. The lower Midland I around Bumthang. I I I I I Photo 5. The upper part of I the Nikka Chhu.

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I Photo 6. The lower cirque of I the Nikka Chhu. I I I I

I Photo 7- The middle cirque of the Nikka Chhu. I (Umata Tso) I I I I

I Photo 8. The upper cirque of the Nikka Chhu. I (Tampey La).

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I Photo 9- U-shaped valley I of the Tampey Chhu I I I I

Photo 10. I The baslnlike low relief landform in the uppermost part I of the Tampey Chhu I I I I

Photo 11. I Glacial lakes in the uppermost part of the Tampey Chhu. I (upward of Photo 10)

I -200- I Photo 12. The Inner northern area, the large Lunana valley and the main range bordering China from fore side to back side The low relief area and the gentle slopes are developed in the Inner northern area. CO o

Photo 13. The basinlike landform to the north of Mt. Namshila Photo U. The basinlike landforra O CO to the west of Mt. Gangkar Puensum.

Photo 15. The uppermost of the Mangde Chhu(around 5,000m Photo 16. The glacial landform around Jichudagmo (around 5,000m).

Photo 17. U-shaped valley of the Mangde Chhu (around 4,500m)

Photo 18. The transition point from the U-shaped valley to the V-shaped valley near Yak Camp along the Mangde Chhu.

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^ EAST Photo 19- Panoramic view of the Bhutan Himalaya from Dochu La.