NAT. NAT. HIST. BULL. SIAM Soc. 51(2): 185-196 ， 2003
STRUCTURE AND ECOLOGICAL FUNCTION IN A TROPICAL MONTANE SPHAGNUM BOG OF THE ELEPHANT MOUNTAINS ，BOKOR NATIONAL PARK ，CAMBODIA
Philip Philip W. Rundel 1，David J. Middleton 2，Mark T. Patterson 3，and Meng Monyrak 4
ABSTRA Cf
百le s釦 dstone plateau of the southem tip of the Elephant Mountains in Bokor National Park ，southeastem Cambodia ，receives mo 問 than 5， 000 mm of annual rainfal l. τ'h ese condi- tions tions produce sha l1 0w acid soils and a we l1 -developed sphagnum bog called the Popkvil bog. The of matrix plant cover in the bog is dominated by four graminoid species: Eremochloa eriopoda eriopoda (Poaceae) ， Eriocaulon cf. henryanum (Eriocaulaceae) ， Leptocarpus disjunctus (R ωtionao 倒的，釦 d Centrolepis cambodiana (Cen 回 lepidaceae). Sphagnum is abundant ， growing
in in rings around graminoid c1 umps and low shrub islands of Hedyotis ros 脚 rin 静lia (R ubiaceae) ， Ploiarium Ploiarium alternifolium (Bonnetiaceae) ， Calophyllum calaba (Clusiaceae) ， Syzygium zeylanicum (M 戸伽ceae) ， and Hygrophila angustifolia (Acanthaceae). Maximum photosyn 血etic ra 伽 ranged from from 4.4 ・8.1 μ.m ol m. 2 S-1 in four herbaceous perennials and from 5ふ 14.7μmol m. 2 S-1 泊 the the five shrub species measured ，while 恥 one <: 4 ~pecies 抑制t，Fimbri. 均的 dic. 加 toma 2 (Cyperaceae) ， had a higher value of 18.6 J.l mol m- S・1. Carbon isotope ratios (o) r如 ged from -26.110 -26.110 -28.80/00 泊 nine C 3 species measured ，indicating 問 latively high water use efficiencies for for such a wet environmen t. In creasing ecotourism in Bokor National Park will require special attention attention in managing the 合agile habitat of 白e Popokvil bog.
問 τ'R ODUC 百ON
百le sandstone massif of the Elephant Mountains rises abruptly 合om a narrow coastal plain plain along the Gulf of 百lail 佃 d in southem Cambodia to an elevation of 1079 m. 百le combination of the steep south-facing slopes of the r佃 ge and close proximity of the sea produces unusually wet conditions on 出esouthwestem slopes and upper plateau of this range where more 出an 5000 mm of rain falls annually. 百世 s heavy rainfall ac 也19on 白e quartz quartz sandstone of the plateau bedrock of the Elephant Range has produced skeletal and highly leached acid soils. As a result of these conditions ， the plateau supports unusual communities of dwarf forest and sclerophyllous shrubland despite the high rainfall (Dy PHON ， 1970). Within this matrix of dwarf forest and shrubland 釘 .e small 釘 .eas of permanent bog habitat where soils remain saturated 血roughout 出e ye 紅 because of indurated soil
1Department 1Department of Org 組 ismic Biology ，Ec ology and Evolution ，University of Califomia ， Los Angeles CA 90095 USA
185 185 186 186 PHILIP w. RUNDEL ，DAVID J. MIDDLETON ，MARK T. PATTERSON ，AND MENG MONYRAK
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Figure Figure 1. Location of Bokor National Park in southeastem Cambodia. layers. layers. Bogs of this type are relatively rare in mainland Southeast Asia and remain poorly studied. studied. In this paper we report on the community structure of the Popokvil bog located in in Bokor National Park near the southem margin of the Elephant Mountains (Fig. 1). We further further characterize ecophysiological traits of ten of the important bog species to provide comp 紅 ative data on photosynthetic capacity and water use efficiency for both herbaceous perennials perennials and low shrub species.
MATERIALS AND METHODS
Site Site Description
Field Field studies were carried out over the period March 6- 13 ，2001 ，on the area plateau of of the Elephant Mountains in Bokor National Park ，Kampot Province ，Cambodia (Fig. 1). Bokor National Park was established in 1997 and covers an area of 140 ，000 ha of largely undisturbed undisturbed habita t. Wh ile small areas of rocky soils and vemal pools occur throughout the sclerophyll sclerophyll shrublands on the plateau area ，we focused our attention on a unique sphagnum bog near the former village site of Popokvi l. Sphagnum and many of the other bog species TROPICAL MONT ANE SPHAGNUM BOG 187
described described here 紅 e present in scattered patches on other rocky basins with poor drainage on the upper portions of the Bokor plateau ， but only at the Popokvil site is there a well- developed developed bog community. Th e Popokvil sphagnum bog is located approximately 4 km NNE of the old Hotel Bokor on the road to the former site of Popokvil (Fig. 2). Although an open area of grassy cover cover extends about 0.5 km in a north-south and east-west direction around the bog itself ， most of this area is well enough drained to support tall grasses and low shrub cover. Th e sphagnum bog itself extends over a smaller area of approximately 200 x 80 m to the east of of the road. Th e bog soils 訂 e saturated or have standing water over much of the year ， drying drying out at their surface only in February and March. We classified plant species into growth form categories of perennial graminoids ， herbaceous herbaceous perennials (non-graminoid ，including petaloid monocots) ， subshrubs (perennials with with a woody base) ，and low shrubs. Both of these latter groups would be considered to be be chamaephytes as they do not reach 0.5 m in heigh t. Plant collections made during our fieldwork fieldwork were identified by DJM and other appropriate taxonomic experts for special groups. groups. Voucher collections are filed as accessions to the Amold Arboretum Herbarium (A) (A) in the Harvard University Herbaria. Rainfall Rainfall is extremely high on the Bokor Plateau ， averaging more than 5000 mm annually. annually. Records for Bokor (950 m elevation) at the southem end of the plateau show a mean annual rainfall of 5309 mm (TIXIER ，1979 ， Fig. 3) ， while the Val d'Emeraude at a slightly slightly lower elevation on the southeast margin of the plateau receives a mean of 5384 mm (Dy PHON ，1970). 官 le distribution of this rain ，however ，is strongly seasonal ， peaking
Elephant Elephant Mountains Mountains Plateau Plateau
o 1 2 3 4 kilometers kilometers
Figure Figure 2. Map of fi 巴Id study site of Popokvil bog at the southem portion of Bokor National Park. 188 188 PHILIP W. RUNDEL ，DAVID J. MIDDLETON ，M 級 K T. PA 廿 ERSON ，AND MENG MONYRAK
(00)
円 FOnU5 Ln/ 巴コ官』 C602
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70 1200 1200
1000 1000
，..、 E 800 、旬-E 。E 600 600 4ω 喝・-4a a 。。‘ー a.. a.. 400
200 200 。 J F M A M J J A S 0 N D Month
Figure Figure 3. Seasonal course of mean daily 飽mperaωre ，me 釦 daily relative humidity (RH) ， and rainfall at Bokor ， Bokor National Park ， Elephant Mountains ，Carnbodia. Data from Dy Phon (1972) and Tixier (1979). TROPICAL MONT ANE SPHAGNUM BOG 189
July July and August and dr 'O pping t 'O 50 mm 'O r less in January and February at b'O血 stati 'O ns. 百le Val d'Emeraude experiences rain v位制ally every day 合om May thr 'O ugh Oct 'O ber ， but 'O n 'O nly 12 days 'O n average in March ， the m 'O nth 'O f 'O ur sampling (DY PHON ， 1970). M 'O mings during 'O ur field studies were typically partially sunny with scattered cl 'O uds m 'O ving 'O verhead ， while heavier 'O vercast and brief peri 'O ds 'O f intense rain were present alm 'O st every aftem 'O'O n. Mean m 'O nthly temperatures are relatively c'O nstant 白r'O ugh 'O utthe ye 紅 at B 'O k'O r (Fig. 3) ， varying 'O nly from al 'O w 'O f 19.2 0 C in July and August t 'O a high 'O f2 1. 5・C in April (DY PHON ， 1970). Th e sandst 'O ne substrate 'O f the plateau 'O f 由e Elephant M 'O untains weathers int 'O組 acidic acidic C 'O訂 se white sand. S 'O il profiles 'O f the sphagnum b'O g as described by Dy Ph 'O n (1970) (1970) c 'O nsist 'O f upper sandy A h'O riz 'O ns n 'O m 'O re 出an 90 cm in thickness with declining rganic 'O rganic matter and increasing saturati 'O n with depth. Th e B h'O riz 'O n is a 出in indurated layer 'O f white sand ， with yell 'O wish sandst 'O ne p紅 ent material bel 'O w this leve l. We measured the pH 'O f the s 'O il s'O luti 'O n al 'O ng the margin 'O f the b'O g and in b'O gs 'O ils as 4.6 during 'O ur sωdy.
Experimental Experimental Methods
Th ec 'O mmunity structure 'O f the Sphagnum b'O g was s創npled using line transects. Semi-quantitative Semi-quantitative c'O ver estimates were made by sampling a series 0.05 ・m 2 pl 'O ts (20 x 25 cm) 釦可ed every 2m al 'O ng 100 m 'O f line 甘加sects running acr 'O ss the central b'O g 訂 'ea. Fr 'O m these data ， the relative f記quency 'O f 'O ccu 町'ence within the 50 pl 'O ts was calculated. F 'O r each 'O f the pl 'O t pl 'O ts sampled ， every species present was categ 'O rized int 'O 'O ne 'O f six levels levels 'O fc 'O verage: + = present with <1% c'O ver ，1= 1-5% c'O ver ，2 =ι10% c'O ver ，3= 11-25% c'O ver ，4= 2ι50% c'O ver ， and 5= >50% c 'O ver. A mean c'O verage indicat 'O r value f'O r all pl 'O ts was calculated f'O r each species by summing the numerical categ 'O ry values and dividing dividing by 50 ， the number 'O f pl 'O ts sampled. Als 'O calculated was a mean c'O verage indicat 'O r value value f'O r th 'O se pl 'O ts where that particular species was presen t. Th us ， an in 企equent but l 'O cally abundant species w 'O uld have al 'O w value f'O r all pl 'O ts but a relatively high value f'O r pl 'O ts where it was presen t. Neither 'O f these tw 'O indicat 'O r values is truly quantitative as 血 ey represent a semi-quantitative indicati 'O n 'O f the relative am 'O unt 'O fc 'O ver f'O r each specles. specles. Ec 'O physi 'O l 'O gical measurements we 問 carried 'O ut t 'O characterize the ph 'O t'O synthetic rates ， water use efficiencies as measured by carb 'O n is 'O t'O pe rati 'O s， and metab 'O lic systems f'O r five c'O mm 'O n herbac 泡'O us perennials and five c'O mm 'O nl 'O w subshrub and shrub species in in the P'O p 'O kvil b 'O g. Gas exchange measurements were made under naturallight c'O nditi 'O ns in in the m 'O ming using a LICOR ・6200 gas exchange system (LICOR ，Li nc 'O ln ，Nebraska). Individual Individual measurements were made 'O n leaf tissue fr 'O m each 'O f three individuals 'O f each study study species. Samples Samples 'O f ph 'O t'O syn 出etic tissues we 陀 c'O llected 合om each 'O f three individual pl 佃 ts 'O f all study species at the field site and air-dried. Natural o13 C rati 'O s were measured 'O n these these samples at the Duke University Phyt 'O tr 'O n (Durh 創 n，N 'O rth Car 'O lina) 'O na SIRA Series Series II is 'O t'O pe rati 'O mass spectr 'O meter (VG Is 'O tech ，Middlewich ， U.K.) 'O perated in aut 'O matic trapping m 'O de after c'O mbusti 'O n 'O f samples in an elemental analyzer (NAI500 ，
C 紅 1'0 Erba Instrumentazi 'O n，Milan ，Italy). 百le reference CO 2，calibrated against standard Pee Dee belemnite (PDB) ，was 'O btained fr 'O m Oztech (Dallas ， Texas). 190 190 PHILIP W. RUNDEL ，DAVID 1. MIDDLETON ，MARK T. PATTERSON ，AND MENG MONYRAK
RESUL TS AND DISCUSSION
Community Structure and Diversity
百lere are relatively sharp fores t/ grassland boundaries around the margin of the open 紅 ea that supports the Popokvil bog. A west-east gradient across this habitat begins with dense dense bracken and low shrub cover on disturbed areas with less saturated soils along the Popokvil Popokvil road. Dominant speci 回 indicative of disturbance included Pteridium aquilinum (L.) (L.) Kuhn (Dennstaediaceae) ，Melastoma malabathricum L. ssp. normale (D.Don) K. Meyer (Melastomataceae) ，Rhodomyrtus tomentosa Wight (Myrtaceae) ，Dicranopteris linearis (Burm.) (Burm.) Underwood (Gleicheniaceae) ， and Elephantopus scaber L. (Asteraceae). 四 is community graded into the waterlogged central bog habitat where sphagnum and typical bog graminoids 紅 e presen t. At the other m 訂 gin of the bog there was a rapid transition to a low forest community 5-15 m in height dominated by Dacrydium elatum (Roxb.) Wallich ex Hook. (Podocarpaceae) ， with Podocarpus pilgeri Foxw. (Podocarpaceae) ， Vaccinium viscifolium viscifolium King & Gamble (Ericaceae) ， and Lithoca 中山leiophyllus A. Camus (Fagaceae) as as com 町lon assocmtes. A diverse community of graminoids dominated the general s住uc 仰re of the bog ， forming a low matrix 20 ー30 cm in heigh t. Scattered through this matrix with a very low total cover were small islands of shrub establishment where soils had built up to allow better drainage. Four graminoid species ， each representing a different family ， provided the major p制 of the the matrix cover. Th ese were Eremochloa eriopoda C.E. Hubb (Poaceae) ， Eriocaulon cf. henryanum Ruh l. (Eriocaulaceae) ， Leptocarpus disjunctus Mast. (Restionaceae) ，and Centrolepis Centrolepis cambodiana Hance (Centrolepidaceae). Th ese were the only four vascular plant plant species that occurred with a coverage of 25% or more in 加 y single 0.05 m 2 plo t. Eremochloa and Eriocaulon were almost ubiquitous in their distribution in the bog. 百le highest highest coverage occurred with Eremochloa eriopoda which had a mean cover value of 2.6 (Table (Table 1) ，indicating that the average plot had close to 10% cover. 百1I s species was present in in 92% of the plots sampled. Second in importance was Eriocaulon cf. henryanum with a mean cover value of 1.5 (2.3 in plots where it was present) and a relative frequency of 86%. Leptocarpus disjunctus and Centrolepis cambodiana were each present in 50% of the plots plots sampled ，and had mean cover values of 1. 2 and 1.1， respectively. Both had mean cover cover values above 2 in plots where they were presen t. Two other monocot species had relatively high 台equency values in the sample plots but but low cover values (Table 1). Xyris complanata R. B r. (Xyridaceae) was present in 44% of of the sampled plots and had a mean cover value of 0.7. An unidentified species of Panicum had a relative frequency of 38% 叩 da mean cover value of 0.6. Next in importance among species forming elements of the matrix of graminoid cover in the bog was the sedge Fimbristylis Fimbristylis dichotoma (L.) Vahl subsp. dichotoma with a relative frequency of 16% and a mean cover value of 0.3. This low mean cover value masks the local abundance of this species species which occurred with up to 25% cover in some plots where it was presen t. Sphagnum was found in 86% of the plots sampled ，usually as rings around graminoid clumps or small shrub islands ，and had a mean cover value of 2.0. Tixier (1979) identified these these as S. beccarii Hpe. and S. cuspidatum Her. Microbial crusts of cyanobacteria cementing
areas areas of open soil were present in 24% of the plots s創 npled and had a mean cover value of of 1.3 (Table 1). TROPICAL TROPICAL MONTANE SPHAGNUM BOG 191
An additional eight vascular plant species were encountered in low frequencies in less than than 10% of the sample plots (Table 1). Eight species were observed in the area of the sample sample plots but not sampled ，giving a total of 23 species present. Th e flora included four species species of small camivorous plants. 百lese were Drosera burmannii Vah l. (Droseraceae) ， Nepenthes Nepenthes kampotiana Lecomte (Nepenthaceae) ， and Utricularia bifida L. and U. caerulea (Lentibulariaceae). L. (Lentibulariaceae). Nepenthes kampotiana ，a tiny plant with pitchers only a few cm in length ， has been considered to be a local endemic at Bokor. However ，there is a distinct gradation gradation in morphological form between this taxon and the larger N. thorelii ， which is common at the forest edge 紅 ound the bog ，suggesting that 出e two forms may not w 紅 rant specles specles separatlon. Other Other small herb species present in the bog included the tiny Gentiana ting-nung-hoae Halda Halda (Gentianaceae) ， Xyris capensis Thunb. (Xyridaceae) ，Burmannia disticha L. (Burmanniaceae) ， Salomonia longiciliata Kurz. (Polygalaceae) ， and Lycopodium cernuum L. L. (Lycopodiaceae). Other species reported 仕om this bog (Dy Phnon 1970) 血at were not collected collected in our study included Drosera peltata Smith (Droseraceae) ，Carex indica L. (Cyperaceae) ， and an unidentified terrestrial species of Dendrobium (Orchidaceae). Small Small shrub islands scattered across the bog were dominated by single or multiple species species reaching to no more than 30- 50 cm in height and low mounds 0.5-2 m across.
Table Table 1. Relative frequency and coverage values for dominant plant species in 由ePopokvil bog of Bokor National Park. See text for discussion of the mean cover values and and how they were calculated. A value of 1 = a cover of 1-5% ，2 = a cover of ι10% ， and 3 = a cover of 11-25%. Mean Relative Relative Mean cover Species Species Family Growth form frequency cover value (%) (%) value where present present Eremoch/oa Eremoch/oa eriopoda Poaceae perenni aI graminoid 92 2.6 2.8 Eriocau/on Eriocau/on cf. henryanum Eriocaulaceae perenni aI gr. 制 inoid 86 1. 5 2 .3 Leptocarpus Leptocarpus disjunc t. ω Restionaceae perenni aI graminoid 50 1. 2 2 .4 Centrolepis Centrolepis cambodiana Centrolepidaceae perenni aI gr. 削 inoid 50 1.1 2.2 Xyris Xyris complanata Xyridaceae herbaceous perenni aI 44 0.7 1. 5 Panicum Panicum sp. Poaceae perenni aI graminoid 38 0.6 1. 5 Fimbris. 砂 lis dichotoma Cyperaceae perenni aI graminoid 16 0.3 2.0 Hedyotis Hedyotis rosmar 的φlia Rubiaceae subshrub 10 0.1 1. 4 Nepenthes Nepenthes kampotiana Nepenthaceae herbaceous pe 犯 nnial 10 0.1 1. 0 tricularia U tricularia bifida Le ntibulariaceae herbaceous perennial 10 0.1 1. 0 Drosera Drosera burmannij Droseraceae herbaceous perenni aI 10 0.1 1. 0 Ploiarium Ploiarium alternifolium Bonnetiaceae shrub 8 0.1 1. 2 Gentiana Gentiana ting-nung-hoae Gentianaceae herbaceous perenni aI 6 0.1 1. 0 Syzygium Syzygium zey/anicum Myrtaceae s肘ub 2 + 1. 0 Lycopodium Lycopodium cernuum Lycopodiaceae herbaceous pe 児 nnial 2 + 1. 0 Sphagnum Sphagnum spp. Sphagnaceae moss 86 2.2 2.0 Microbi aI crust cyanobacteria 70 1. 9 1. 3 192 192 PHn. IP W. RUNDEL ，DA Vl D J. MIDDLETON ，MARK T. PATI 冨RSON ，AND MENG MONYRAK
τ'h ese isl 佃 ds were small mounds rising a few centimeters above the general soil level of the the bog. Rin gs of Sphagnum were commonly present around the edges of these shrub islands islands at 血.e edge of the canopies. Low subshrubs and shrubs forming these islands were Hedyotis Hedyotis rosmarinifolia (Pitard) Craib (Rubiaceae) ， Ploiarium alternifolium (V 剥) Melchior (Bonnetiaceae) ， Calophyllum calaba L. (Clusiaceae) ，Syzygium zeylanicum (L.) DC. (Myrtaceae) ，組d Hygrophila angustifolia R. Br. (Acantha 回 ae). Al though not present wi 由加 出e Popokvil bog itself ， other nearby wetlands have small populations of the tree Melaleuca cajuputi cajuputi Roxb. (Myrtaceae) ，a species more characteristic of brackish wetlands near 血e coast coast or along the Mekong delta 紅 ea. Vascular Vascular plant species richness 泊 the sample plots was moderately high despite their small small size of 0.05 m2• Only one of the 50 plots sampled had less th 組曲ree species present ， with with a modal number of 5 species and a high of 8 species presen t.
Physiological Physiological Ecology
Comparisons Comparisons of photosynthetic rates between herbaceous perennial and subs 胎ub/s 耐ub species species did not fmd clear differences. 百le highest me 阻 rate measured was 18.6μmol 2 m- S-I in Fimbristylis dichotoma ，a species 白at uses C ，，- metabolism as shown by carbon isotope isotope ratios (Table 2). Photosynthetic rates ranged from 4. 4- 8.1μmol m- 2 s-I in the other four four herbaceous perennials measured (Eriocaulon cf. henryanum ， Leptocarpus disjunctus ， Xyris Xyris complanata ，and Nepenthes kampotiana). Th ese values are gener al1 y lower th 血 those those of the five subshrub and shrub species ， but without a statistically si 伊出cant difference. Hygrophila Hygrophila angustifolia had a moderately high mean photosynthetic rate of 14.7 !l mol m- 2 S-I ， while the other four shrub and subshrub species (Syzygium zeylanicum ， Ploiarium alternifolium ， Calophyllum calaba ， and Hedyotis rosmarinifolia) varied from 5.8-10.2 !l mol m- 2 S-I. 百lese photosynthetic rates are those present under conditions when light is not limi 出19. It It is almost certainly 佐ue ，however ，that light is limiting over much of the year at this site. Li ght saturation occurs at about 400 !l mol m- 2 s-I in 出e Bokor shrub species that we have studied. studied. Even under the relatively dry conditions in March when we carried out or measurements ，light w 出合'equently below 出is level for much of the day ，p 紅 ticularly 血 the the afternoon. We would expect that light is limiting on most days of 白e year 針。 m April through through November when rains are heavy. 百le mean carbon isotope ratio (o 13 c) measured 泊 Fimbristylis dichotoma was -1 1. 5
0/00 (Table 2) ，clearly indicating the presence of C ，，- metabolism in this species. 百le five subshrub subshrub and shrub species showed a moderately small range of O 13 C values from -27.5 0/00 in Ploiarium alternifolium to -28.7 0/00 泊 bo 出 Syzygium zeylanicum and Hedio 砂s rosmarinifolia. rosmarinifolia. Nepenthes kampotiana had a simil 紅 value of -28.8 0/00. Th e 伽 'ee other herbaceous herbaceous perennials ，however ， all showed lower O values of -26.0 to -26.9 0/00 ， suggesting suggesting a higher water use efficiency 白an that present 加出e five subshrub and shrub species. species. Th ese are high values for a site with such high annual rainfall ， but consistent with hypotheses hypotheses about the physiological consequences of xeromorphy 加 response to low nu 位ient availab i1i ty in bog habitats (SMALL ， 1972). Li mited rooting dis 凶bution on raised mounds in in saturated bog soils may produce periods of physiological drought for sub-shrub and shrub shrub species during 血e brief periods of sunny weather. TROPICAL TROPICAL MONTANE SPHAGNUM BOG 193
Table Table 2. Photosynthetic maximum (mean and standard deviation) ，relative water use efficiency efficiency as measured by carbon isotope ratios (o J3 C; mean and standard deviation) ， and metabolic sy 胸 ms for five important herbaceous perennials and five five low subshrub and shrub species 泊 the Popokvil bog ，Bokor National Park.
Photo 母iynthetic maximum d13 C Metabolic (問。 Im -28"" I) Species Species Growth form (0/00) system mean mean sd mean sd
Eriocaulon Eriocaulon cf. henryanum perennial gr 細泊。 id 5.1 1. 0 -26 .1 1. 6 C3 Leptocarpus Leptocarpus disjunctus pe 陀nnial gr 釦IIn oid 8.1 2.6 -26.0 0.5 C3 Xyris ωmplana ω herbaceous perennial 4.4 2.7 -26.9 0.2 C3 Nepenthes Nepenthes kampotiana herbaceous perennial 5.7 1. 7 -28.8 0.8 C3 mbristylis Fi mbristylis dichotoma perennial gr 加n泊。 id 18.6 7.2 -1 1. 5 0.1 C4 Ploiarium Ploiarium alternifolium subshrub 6.7 2.9 -27 .5 0.8 C3 Hedyotis Hedyotis ros 問， r初ifolia subshrub 11. 4 1. 6 -28.7 0.4 C3 Syzygi 附， Z仰 nic 附 low shrub 5.8 1.3 -28.7 1.1 C3 Calophy l/ um calaba low shrub 9.6 0.1 -28.0 0.9 C3 Hygrophila Hygrophila angustifolia subshrub 14.7 1. 2 ー28.2 1. 0 C3
CONCLUSIONS
Peat Peat bog forests are widespread in Southeast Asia and have been described in some tai1 de tai1 (PAGE ，1997) ，in c1 uding Cambodia where they are widespread around Tonle Sap and in in the Mekong Delta area. 百le Popokvil sphagnum bog in 血e Eleph 叩 t Mountains is very different ，however ， in that large peat deposits have not formed. Only scattered descriptions of of bog habitats in Southeast Asia have been previously published. One such account is 白at of of sphagnum bogs ne 釘 Dalat 泊 Vietnam (BARRY EJ AL. ，1956). Perhaps the most relevant ecological ecological literature for understanding the Popokvil bog and its isolation comes from studies studies of 甘opical inselbergs in South America and A 合ica (POREMBSKI EJ AL. ， 1994; POREMBSKI & BAR Tl江 OTT ，2002). Th e carnivorous genus Nepenthes r叩 ges through Southeast Asia in open peat bog forests forests and acid swamps (PHILLIPS ， 1996; DE FOUCAULT ，2000) ，indicating an ecological linkage linkage with the Popokvil bog. However ， the genus has a relatively limited distribution in mainland mainland Southeast Asia where seasonal rainfall regimes are typical. Similarly ，Drosera species species are present in scattered mont 叩 e location across Southeast Asia where skeletal acid and and nutrient poor soils are present ，as 泊 pine forests at Phu Kr adung in Thailand. 百le flora of the Popokvil bog ，like those of Indomalesian bogs ， shows interesting affmities affmities with the Southern Hemisphere (Table 3). 官 le importance of such families as 出e Restionaceae Restionaceae and Centrolepidaceae among the bog herbs and the added presence of s c1 erophyll shrublands with Proteaceae and Myrtaceae and the conifer genus Dacrydium in 出 e surrounding dwarf forests all 紅 e reminiscent of a Gondwanaland element in the flora. The Elephant Mountains are home to a number of endemic vascular plant species (DY PHON ，1970) ， and at least two of these 紅 e present in 白e bog flora at Popokvi l.百 lese 釘 e Gentiana Gentiana ting-nung-hoae and Nepenthes kampotiana ，if it the latter is indeed distinct from N. N. thorelii. 194 194 PHILIP w. RUNDEL ，DAVID J. MIDDLETON ，MARK T. PA'π 'E RSON ，AND MENG MONYRAK
Table Table 3. Bi ogeographic dis 住ibutions of Popokvil bog species. Th ese dis 凶butions reflect 出e cuη'ent literature but these species may well occur in other places that are poorly poorly collected.
Burmannia Burmannia disticha.-Widely distributed in the Asian and Australasian tropics and inhabits a wide range of ecological conditions including permanently waterlogged soil to fiss 町 'es in rock up to 3500 m altitude. Centrolepis Centrolepis cambodiana. 一一 Known 企om Cambodia ， Laos and northem and eastem Th ailand. It It is described as on1 y tolerating seasonally waterlogged soil rather than permanently waterlogged waterlogged soil (see Larsen ，Fl ora of 百lailand 2: 161; 1972) Drosera Drosera burmannii.- K.n own from In dia to Japan and 白rough In dochina and Malaysia to nor 仕leastem Australia. Eremochloa Eremochloa eriopoda.- K.n own from Th ailand and In dochina. Eriocaulon Eriocaulon cf. henryanum.- This species is known from China and Vietnam but has not previously previously been recorded for Cambodia; fertile material should be collected to verify this this identification. Gentiana Gentiana ting-nung みoae- K.n own only from Bokor. F 抑制抑lis dichotoma-Pantropical edyotis H edyotis rosmarinifoli α-C ambodia and 百 ailand. Leptocarpus Leptocarpus disjunctus- An outlier in a genus otherwise found in Chile and Australasia. In In its Southeast Asian and Malesian distribution it is considered typically as a plant of of sandy areas near the sea or inland saline sandy soi l. It is known from Hainan ， Vietnam ，La os ，Cambodia ，Th ailand and tl1 e Malay Peninsula. Ploiarium Ploiarium alternifolium ー百出species is p制 of a westem Malesian dis 住ibution 血at extends into into Peninsular 百lailand and then makes tl1 e jump over to Cambodia. It is otl1 erwise known in Malaysia ，Bomeo and Sumatra. It is clearly very rainfall dependent and will will not tolerate prolonged dry periods. Salomonia Salomonia longiciliata ー， Burma ，Cambodia ，Vietnam ，Bomeo and tl1 e Philippines; in bogs ， grassy grassy areas 組 d fores t. Syzygium Syzygium zeylanicum-From In dia and Sri Lanka tlrrough Malaysia; in peat swamp ，mixed deciduous deciduous and evergreen forests. Utricularia Utricularia bifida-From In dia to Japan and tlrrough In dωhina and Malaysia to northeastem Australia. Australia. Utricularia Utricularia caerulea-From In dia to Japan and 血rough In dochina and Malaysia to no 叫1・ eastem eastem Australia. Xyris Xyris capensis-Pantropical in Sou tl1 Am erica ，Sou tl1 A 剖 .ca ，In dia ，China ，In dochina and Malaysia Malaysia in wet open places. Xyris Xyris complanata-A widespread species found from In dia and China to Australia in wet open places. TROPICAL MONTANE SPHAGNUM BOG 195
As Bokor National Park becomes increasingly visible for ecotourism and visitor usage increases ， there w i1l be increasing press 町田on preserving the naωral fi 伺仰向s and biodiversity of the p 釘 k (ANONYMOUS ，2002). 官le 企agile habitat of the Popokvil bog w i1l require special special attention in managing this area.
ACKNOWLEDGMENTS
We acknowledge the cooperation of the Cambodian Department of Nature Conservation and Pr ote 氾tion of the Ministry of Environment and the staff of Bokor National Park in allowing us to carry out 仙 pr' 吋ec t. We 山 o 出叫Hong Lork ，Sok So 伽，Judith King ， Kansri Boonpragob ，and Rasoul Sharifi in helping carry out the field studies described here. here.
REFERENCES
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