See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/320087385 The flora of the Bokor Plateau, southeastern Cambodia: a homage to Pauline Dy Phon Article · January 2017 CITATIONS READS 4 817 2 authors: Philip W. Rundel David John Middleton University of California, Los Angeles Singapore Botanic Gardens 392 PUBLICATIONS 16,844 CITATIONS 198 PUBLICATIONS 1,471 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Plant taxonomy View project Factors Influencing Invasion of Giant Reed (Arundo donax) in Riparian Ecosystems of Mediterranean-type Climate Regions View project All content following this page was uploaded by Philip W. Rundel on 28 September 2017. The user has requested enhancement of the downloaded file. Flora of Bokor Plateau 17 The fl ora of the Bokor Plateau, southeastern Cambodia: a homage to Pauline Dy Phon Philip W. RUNDEL1,* & David J. MIDDLETON2 1 Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA. 2 Singapore Botanic Gardens, National Parks Board, 1 Cluny Road, Singapore 259569, Singapore. * Corresponding author. Email [email protected] Paper submitted 7 April 2017, revised manuscript accepted 6 June 2017. ɊɮɍɅʂɋɑɳȶɆſ ȳƕȶɽǍɆɆɮȲɳƵɑɩɁɳǷNJȴǕɳȴƏ ƒɋɿɵɅƙɆɳɃɑȲɊɭƕƺ ƺɃɪȹƙɊȲɌɆɑɽƙɆɳɉɃɌȲɭ ſƺɁɩȲƙɊɅɩȶɑɒȴɊɅɿɌȲɭ ſƺɁɩɑɸƴɅɽʉɵɅɵƙɈƙȲɩɅ ɅɩȶɵƙɈɍɮɁɌɒʂɑ ƙɈɊDŽɸȶNjɅɌȲɭ ſƺɁɩɑɊƓɌɴɆɆʆ ɈƙȶɪȲɆɴɅƏɊɳɍˊƳɌƷɌɌɆɑɽ ɴȼɍNjɅǕɋɭƳɍƺȶ ɮ PaulineȱDyȱPhon ljȲɽȲǁƎ ɍɑɁɎɁƞȲɅƚȶɊȲɳɒˊɋ ɳɋˊȶLJɅɳɄˊƛɆȷɭƃɆƓɅƒNJɈɳɍˊɌȲɭ ſƺɁɩNjɅɑɌɵɑdžɸɳǷɁɸɆɅɽȳȶƕ ɽǍɆɳɅɹʆ Ɇȥƅ ɪȲɸɀɁɽƙǂɌȲɭ ſ ƺɁɩɌɆɑɽɳɋˊȶNjɅʓʕʙƙɆɳɉɃ ɴȼɍʒʒƙɆɳɉɃƺƙɆɳɉɃɴȼɍNjɅɴɁȲɭƒȶɁɸɆɅɽɆɮȲɳƵɆɻɭɳǁƍ ɹʆ Abstract The Bokor Plateau in southeastern Cambodia is home to rare and signifi cant plant communities of stunted forest and heathland, as well as a rich fl ora. Expanding on the pioneering work of Pauline Dy Phon more than half a century ago, we update the current knowledge of the vascular plant fl ora of the plateau. Our checklist includes 359 species, with 22 of these endemic to Bokor. Keywords Bokor Plateau, Cambodia, stunted forest, heathland, Preah Monivong National Park, endemic species. Introduction and water-logged depressions at higher elevations on the gently sloping Bokor Plateau exhibit dwarf forests with Bokor National Park (offi cially known as Preah Monivong relatively low sclerophyllous evergreen trees (Dy Phon, National Park) in southeastern Cambodia represents 1970; Rundel et al., 2016). A complex interaction of high a biodiversity hotspot with a rich plant diversity and a winds, saturated soils, impeded root respiration, physi- high level of endemism. Within this park the sandstone ological drought, high soil leaching with low nutrient massif of the Elephant Mountains rises very steeply from availability, limited rooting volume of shallow soils, a narrow coastal plain along the Gulf of Thailand to an reduced solar insolation, and high humidity combine to elevation of 1,080 m (Fig. 1). The combination of the steep produce these low forests (Grubb, 1971; 1977; Weaver et south-facing slopes of the range and close proximity of al., 1973). the ocean produces unusually wet conditions on the southwestern slopes and upper plateau. Tall species-rich Much of what we know about the plant ecology and wet forests are present on the lower and middle eleva- fl ora of Bokor National Park broadly, and the Bokor tion slopes at Bokor. However, as with tropical montane Plateau more specifi cally, comes from the remarkable forests in many other areas of the world, the shallow soils work conducted by Pauline Dy Phon which was carried CITATION: Rundel, P.W. & Middleton, D.J. (2017) The fl ora of the Bokor Plateau, southeastern Cambodia: a homage to Pauline Dy Phon. Cambodian Journal of Natural History, 2017, 17–37. Cambodian Journal of Natural History 2017 (1) 17–37 © Centre for Biodiversity Conservation, Phnom Penh 18 P. Rundel & D. Middleton out in the context of her PhD studies at the University Our study has focused on the gently sloping and of Toulouse in the late 1950s. This detailed study (Dy weathered Bokor Plateau itself. Here a distinct commu- Phon, 1970) has long formed the basis for understanding nity of stunted forest (Fig. 2) appears, termed forêt the rich plant diversity of global signifi cance in Bokor sempervirente basse de montagne by Dy Phon (1970). This National Park. Her work has been the stimulus for our transition between forest types can be seen near Popokvil studies and for others as well, and we are pleased to Waterfall at about 920 m with mosaics of taller wet forest dedicate this article to Pauline Dy Phon (see box). and lower stunted forest (Fig. 3). The dwarfi ng of what are commonly tall trees at lower elevations results from a complex interaction of soil depth, elevation, wind The Bokor Plateau exposure, and distance from the coast. This community, which we have called stunted forest, commonly has a Despite its seasonal patt ern, rainfall on the Bokor Plateau matrix that reaches no more than 4 m, while the canopy reaches very high levels. Records at 950 m elevation at the dominant Dacrydium elatum (Roxb.) Wall. ex Hook. with southern end of the plateau had a mean annual rainfall of Dacrycarpus imbricatus (Blume) de Laub., Tristaniopsis 5,309 mm (Tixier, 1979), while the Val d’Emeraude on the merguensis (Griff .) Peter G.Wilson & J.T.Waterh., and southeast margin of the plateau was reported to receive Vaccinium viscifolium King & Gamble can reach greater a mean of 5,384 mm (Dy Phon, 1970). The distribution heights. The gradient of height for D. elatum across the of this rain peaks sharply in July and August, dropping plateau illustrates the eff ect of environment on stature. to a mean of 50 mm or less in January and February at Trees near Popkvil Waterfall are 14–16 m in height, but both stations. The Val d’Emeraude experiences rain mean height drops to 8–10 m moving across the plateau, virtually every day from May through October, but and fi nally only 4–6 m to the south near the developed on only 12 days on average in March (Dy Phon, 1970). area (Rundel et al., 2016). Despite changes in commuity During the dry season mornings are semi-sunny with structure, tree diversity and density remain relatively scatt ered clouds moving overhead, while heavier over- unchanged across this gradient (Zhang et al., 2016). cast and brief periods of intense showers can occur in the afternoon. Mean monthly temperatures are relatively Lianas are common in taller forest stands, including constant throughout the year, varying only from a low the notable presence of spiny ratt ans. In addition, there is of 19.2°C in July and August to a high of 21.5°C in April a moderate diversity of epiphytic and lithophyllic orchids (Dy Phon, 1970). and ferns present. However as soil and wind conditions produce a lower forest canopy, the lianas largely disap- The sandstone substrate of the plateau of the pear and Pandanus cupribasalis H.St.John and Pinanga Elephant Mountains weathers into an acidic coarse white sylvestris (Lour.) Hodel appear in the semi-open under- sand with a pH of 4.6. Soil profi les of the sphagnum bog storey. as described by Dy Phon (1970) consist of upper sandy A horizons 90 cm in thickness with declining organic As soils become shallower and winds increase matt er and increasing saturation with depth. Even in moving from Popokvil south across the plateau toward forested areas of the plateau there is often a B horizon the coastal escarpment, the stunted forest is replaced by at 90–105 cm consisting of an indurated layer of white an irregular cover of sclerophyllous shrubland with a sand, with yellowish sandstone parent material below typical height of 1–2 m. Dy Phon (1970) termed this la lande de myrtacées et vacciniacées, which we have trans- this level. As a result there are mosaics present of season- lated as sclerophyllous heathland. As Dy Phon’s name ally water-logged soils. suggests, this community is dominated by species of The wet forests encountered at middle elevations Myrtaceae and Ericaceae. The former include Rhodamnia below the plateau on Bokor were termed forest submon- dumetorum (DC.) Merr. & L.M.Perry, Rhodomyrtus tomen- tagnardee a fagacées et cibotium by Dy Phon (1970). These tosa (Aiton) Hassk., and Syzygium antisepticum (Blume) replace the lower wet evergreen forests at elevations of Merr. & L.M.Perry together with Vaccinium bracteatum 500–800 or higher. In many ways these are comparable Thunb., V. viscifolium King & Gamble, and Rhododen- to the hill evergreen forests described in Thailand with dron moulmainense Hook. Epiphytes are rare. Open rocky a dominant role of Fagaceae and Podocarpaceae in the areas that are waterlogged for major portions of the year canopy and the relative absence of Dipterocarpaceae have a scatt ered cover of herbaceous perennial such as (Rundel et al., 1999). This community changes at about Hedyotis rosmarinifolia (Pit.) Craib and Polygonum chin- 920 m with the transition from montane wet forest to the ense in a matrix of the graminoids Carex indica L., Fimbry- Bokor Plateau with its associated edaphic and climatic stylis eragrostis (Nees) Hance, and Dapsilanthus disjunctus conditions. (Mast.) B.G.Briggs & L.A.S.Johnson. © Centre for Biodiversity Conservation, Phnom Penh Cambodian Journal of Natural History 2017 (1) 17–37 Flora of Bokor Plateau 19 Localized bog communities (Fig. 4) on the plateau datum Ehr. ex Hoff m. Low shrubs forming these islands are dominated by a diverse community of low-growing include Hedyotis rosmarinifolia (Rubiaceae), Ploiarium herbaceous perennials 20–30 cm in height. Scatt ered alternifolium (Vahl) Melch. (Bonnetiaceae), Calophyllum through this matrix are small islands of shrub establish- calaba L. var. cuneatum (Symington ex M.R.Henderson & ment where soils have built up to allow bett er drainage. Wyatt -Smith) P.F.Stevens (Calophyllaceae), Ilex wallichii Four graminoid species provide the major part of the Hook.f.