Cambodian Journal of Natural History Butterfl ies, Snails & Fruit Flies Aquatic Insects in Urban Ponds Leaf Traits on the Bokor Plateau Rewilding in Western Siem Pang December 2019 Vol. 2019 No. 2 Cambodian Journal of Natural History Editors Email: [email protected], [email protected] • Dr Neil M. Furey, Chief Editor, Fauna & Flora International, Cambodia. • Dr Jenny C. Daltry, Senior Conservation Biologist, Fauna & Flora International, UK. • Dr Nicholas J. Souter, Greater Mekong Freshwater Manager, Conservation International, Australia. • Dr Ith Saveng, Project Manager, University Capacity Building Project, Fauna & Flora International, Cambodia. International Editorial Board • Dr Alison Behie, Australia National University, • Ms Meas Seanghun, Royal University of Phnom Penh, Australia. Cambodia. • Dr Stephen J. Browne, Fauna & Flora International, • Dr Ou Chouly, Virginia Polytechnic Institute and State UK. University, USA. • Dr Chet Chealy, Royal University of Phnom Penh, • Dr Nophea Sasaki, Asian Institute of Technology, Cambodia. Thailand. • Mr Chhin Sophea, Ministry of Environment, Cambodia. • Dr Sok Serey, Royal University of Phnom Penh, • Dr Martin Fisher, Editor of Oryx – The International Cambodia. Journal of Conservation, UK. • Dr Thomas N.E. Gray, Wildlife Alliance, Cambodia. • Dr Bryan L. Stuart, North Carolina Museum of Natural Sciences, USA. • Mr Khou Eang Hourt, National Authority for Preah Vihear, Cambodia. • Dr Sor Ratha, Chea Sim University of Kamchaymear, • Dr Keo Omaliss, Forestry Administration, Cambodia. Cambodia. The Cambodian Journal of Natural History (ISSN 2226–969X) is an open access journal published by the Centre for Biodi- versity Conservation, Royal University of Phnom Penh. The Centre for Biodiversity Conservation is a non-profi t making unit dedicated to training Cambodian biologists and to the study and conservation of Cambodian biodiversity. Cover image: Banteng Bos javanicus, Thporng District, Kampong Speu Province, 21 April 2019 (© J.C. Eames). The prospects for rewilding in northeastern Cambodia through this and other globally threatened species is reviewed in the present issue by Gray et al. (pages 98–112). Leaf traits on the Bokor Plateau 77 Leaf traits in the dwarf montane heathland of the Bokor Plateau, Cambodia Philip W. RUNDEL1,*, M. Rasoul SHARIFI1, Judith KING-RUNDEL2 & David J. MIDDLETON3 1 Department of Ecology and Evolutionary Biology, University of California, Los Angeles, California 90095, USA. 2 Department of Earth Sciences, California State University Dominguez Hills, Carson, California 90747, USA. 3 Singapore Botanic Gardens, National Parks Board, 1 Cluny Road, Singapore 259569, Singapore. * Corresponding author. Email [email protected] Paper submitted 1 August 2019, revised manuscript accepted 7 November 2019. ɊɮɍɅʂɋɑɳȶſɆ NJɈƙȴɆȼɀƎ ɆɽɳƽɋɈɈȲƺȻɫȲƼɆɽ ɌɊƺɊɯ ɯɋɅɫȶɌɆɆɃɫȲɳɉƚȣȶȲƙɊɩɁȳƕɑɽ ɅɩȶȳƘɍɽƴƚ ɸȶ ɇƞƺɊɸ ɯɋȲǂƎ ƙɆɳɉɃȼɪɂƗɉȲɽȱ (sandstoneȱ soils) ɴȼɍNjɅȲƙɊɩɁǕɑɭɪɁDŽɆɳǷɳɍˊɁɸɆɅɽȳƕȶɽǍɆɆɮȲɳƵɵɅȹɯɌɉɸƒȼɸɌ ɪ ǏɆɳȶˊɁɣƘNjɅɍȲž ſȳɀƋ ȲɸɀɁɽɊɯɋ ɴȼɍɳɄˊƛNjɅɅɮɎƙɆɳɉɃɵƙɈƙȲɩɅɵɅɁɸɆɅɽɉɸƙɁƒ ɈȪ ɩȲʆ ǏNjɅȲɊƕɑɽɳȼˊɊɳȺˊȳɭɑƵƒ ƴƚ ɸȶ ȴɬɈɪʒʐ-ʓʐɴɊɻƙɁ ɑƙNjɆɽɵƙɈɌȶɃɫȲɳɉƚȣȶɳǷ ǂɊɃɪȹƙNjɍɉɸ ƒ ɅɩȶɆdžƐ ɆɽɊȲƺƙɆɳɉɃɵƙɈɳȺˊɴȼɍNjɅȲɊƕɑɽDŽɆʉ ɅɩȶȷɭȶɳƙƳɋȴɬNjɅɈɈɯȲɌȲɭ ſƺɁɩƙȲɩɅɑɫȲɌƚ ȶɫ ȱȲɊɑƕ ɽɈɪ ʓ-ʔ ɴɊɻƙɁ (sclerophyllȱ heathland) NjɅɎɁƎNjɅɳǷǎɋɓɸƺɊɯɋɈɈɯȲɳȼˊɊɳȺˊDŽɆʉȱ (shrubȱ canopyȱ matrix)ʆ ɍȲſɀɺɌɆǒȝɑɯ ɵɅɃƎ ɸɒɸɅɩȶɃɊƂɅɽɑɫȲƚ ɍȲſɀɺɌɑɪɑƗ ɸɳnjȴɵɅɊɄƘɊɔɁɩɆɌNjɵɅɔƙǂɑƙɊȪɆ ɌɊɯ (assimilationȱ rate)ȱ 13 ƺɊɯɋɅɫȶƙɆɑɩɃƑNJɈɵɅƳɌɳƙɆˊƙLJɑɽɃɫȲ (Έ C) ȱȱȴɬNjɅNJɈȳɭɑƵƒ ɌǏȶɈɈɯȲɌȲɭ ſƺɁɩƙȲɩɅ ɅɩȶɈɈɯȲɳȼˊɊɳȺˊDŽɆʉ (DŽɸȶ woodyȱshrubs ɅɩȶlowȬstatureȱcolonizingȱshrubs) ɅɮɎɍȲſɀɺɴɁɊɯɋȴɬNJɈNjɅɃɸɒɸɑɫȲɄƚ ɸƺɆɽǎɆɽʆ ɴȳƞɌɳƳȶɳȸˊɋƚ ɁɆɳǵɅɫȶɍȲȳɀſ Ƌ ɈɅɬƚLJɅɆƷƟ ȻɣƘɳȵˊȻǃ ȹƙNjɆɴȸɁɵɅǃɊɈɍɈɅơ ɬƚ ɳȲˊɁNjɅɳǷȷɳdžƚ ɹɈɪʔʐʐ ȱ(saturatingȱirradiance)ȱ - Ȭ2 Ȭ1 ʕʐʐΐmolȱ m ȱ s ȴɬɁɩȷƺȶʑ/ʔɵɅɈɅɬƙɈɹǕɃƚ ɩɁƘ(fullȱ sun)ʆ ɳDŽɹɆɪƺɳɈɍɌɳɑȢɍǓȲɽȼɮȷƺɍȲȳɀſ Ƌ ƙɆɳɑˊɌɑƙNjɆɽɳɄˊƛ ɌɑɪɑƗ ɸɳnjȴ ƙɆɳɉɃɌȲɭ ſƺɁɩɴȼɍLJɅɑɩȲǜɳdžɹɴɁȶɆƷƟ ȻɍȲſɀɺɆɩɃɑɮNjƎ ɻ ɁƺȻɫȲƼɆɽ ɅɩȶɆdžƐ ɆȲƙɊɩɁɔƙǂȯɑȪɆɈɅɬƚɌɆɑɽǏ ɌɒɮɁȼɍɽɁɵɊƺɔɎƚ ȹɩ ƅNjɅʆ Abstract The frequent cloud cover and associated high levels of rainfall and strong winds combined with shallow acidic sand- stone soils on the Bokor Plateau of the Elephant Mountains produce classic limiting conditions that lead to the forma- tion of a dwarf tropical montane forest. Tree stature grades quickly from rainforest canopies 20–30 m in height on sheltered slopes, to lower stunted forest, and fi nally to a low sclerophyll heathland with scatt ered dwarfed treelets 3–4 m in height in a low shrub canopy matrix. Leaf morphological traits of size and specifi c leaf weight, photosynthetic traits of mean maximum assimilation rate and integrated water use effi ciency (δ13C) diff ered between dwarfed treelets and both woody shrubs and low-stature colonizing shrubs in only the single trait of having consistently larger leaves. Light response curves showed that saturating irradiance occurred at 400–500 μmol m-2 s-1, less than one quarter of full sun. Despite seemingly favourable conditions for photosynthesis in the afternoon, study species frequently exhibited stomatal closure and low to even negative rates of net assimilation. Keywords Bokor National Park, dwarf forest, heathland, leaf traits, tropical mountain cloud forest. CITATION: Rundel, P.W., Sharifi , M.R., King-Rundel, J. & Middleton, D.J. (2019) Leaf traits in the dwarf montane heathland of the Bokor Plateau, Cambodia. Cambodian Journal of Natural History, 2019, 77–84. Cambodian Journal of Natural History 2019 (2) 77–84 © Centre for Biodiversity Conservation, Phnom Penh 78 P. Rundel et al. Introduction Our objective in this study was to investigate compar- ative patt erns of leaf morphological and ecophysiological Tropical montane cloud forests, characterized by the traits in a group of 19 woody species growing near the persistent presence of mist or low clouds that result in coastal escarpment of the Bokor Plateau where high deposition of water on the vegetation, are widespread rainfall and shallow heavily weathered soils produce throughout tropical regions of the world (Hamilton et al., dwarfi ng conditions for forest trees. Our study species 1995; Aldrich et al., 1997). These forests are typically low included monopodial treelets dwarfed from their normal in stature with slow growth and are commonly described canopy height, shrubby taxa of intermediate height, and as dwarf forests. Their low stature and associated slow low-growing shrubs that colonize open sites (Table 1). rates of growth have been att ributed to a complex inter- We looked for traits that might be associated with the action of diverse potential limiting factors. These include dwarfed tree species and help explain their slow growth. cloud cover that reduces solar radiation levels for photo- An additional objective was to use measurements of net synthesis, relatively low ambient air temperatures, photosynthetic assimilation to establish the maximum strong winds, high rainfall that leaches soils and slows rates present and potential role of heavy cloud cover and rates of mineralization and decomposition, and limited reduced irradiance in limiting photosynthesis. nutrient availability (Bruijnzeel & Proctor, 1995; Tanner et al., 1998; Bruijnzeel & Veneklaas, 1998; Bruijnzeel et al., 2011). Field Site and Methods Examples of tropical montane cloud forests can Study site and species be seen in southern Cambodia in the Cardamom and Elephant Mountains where proximity to the Gulf of Field studies were carried out from 3–13 March 2001 on Thailand brings unusually high levels of rainfall (Daltry the Bokor Plateau of the Elephant Mountains in Bokor & Momberg, 2000; Rundel et al., 2016). These mountain National Park, Kampot Province, Cambodia. Bokor ranges are largely Mesozoic sandstone, with localized National Park was established in 1997 and covers an area areas of limestone and volcanic rock. Acid lithosols of 140,000 ha (Rundel et al., 2003; Tagane et al., 2017). Our develop over the sandstone parent material that char- measurements took place about 0.8–1.0 km north of the acterizes much of the Elephant Mountains. These thin old hotel in sclerophyllous heathland habitat. The sand- acidic soils are heavily leached by the high rainfall and stone substrate of this area of the plateau was heavily easily eroded in disturbed conditions. weathered with shallow rocky soil and fracture lines forming soil pockets of coarse acidic white sand. Soil pH The weathered Bokor Plateau exhibits a classic was 4.7. example of a tropical montane cloud forest with dwarf trees. As the plateau slopes gently over a linear distance of Rainfall is extremely high on the Bokor Plateau, aver- about 4 km from near Popokvil Waterfall (920 m) south- aging more than 5,000 mm annually. Records for Bokor wards towards the coastal escarpment at the old Bokor (950 m elevation) at the southern end of the plateau Hotel (1,062 m), rainforest canopies 20–30 m in height show a mean annual rainfall of 5,309 mm (Tixier, 1979), fi rst give way to a stunted forest 10–15 m in height, and while the Val d’Emeraude on the southeast margin of the fi nally to a low sclerophyllous heathland with scatt ered plateau receives a mean rainfall of 5,384 mm (Dy Phon, dwarfed treelets 3–4 m in height in a low shrub canopy 1970). The distribution of this rain, however, is strongly matrix of only 1–2 m. Dy Phon (1970) termed this la lande seasonal, peaking in July and August. These stations have de myrtacées et vacciniacées because of the dominance of been reported to receive an average of 170 and 223 days a these two families. year of rainfall, respectively (Anonymous, 1979). The dry season at