Phorophyte Diversity, Substrate Requirements and Fruit Set in Dendrobium Scabrilingue Lindl. (Asparagales: Orchidaceae): Basic
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The Natural History Journal of Chulalongkorn University 8(2): 135-142, October 2008 ©2008 by Chulalongkorn University Phorophyte Diversity, Substrate Requirements and Fruit Set in Dendrobium scabrilingue Lindl. (Asparagales: Orchidaceae): Basic Observations for Re-introduction Experiments SANTI WATTHANA1* AND HENRIK ÆRENLUND PEDERSEN2 1Queen Sirikit Botanic Garden, P.O. Box 7, Mae Rim, Chiang Mai 50180, Thailand. 2Botanical Garden & Museum, Natural History Museum of Denmark, University of Copenhagen, Gothersgade 130, DK-1123 Copenhagen K, Denmark. ABSTRACT.– In February-March 2007 a population of the epiphytic orchid, Dendrobium scabrilingue, from Salawin Wildlife Sanctuary (province of Mae Hong Son, northern Thailand), was studied with regard to substrate diversity, demography and fruit set. Among the 10 tree species that occurred in the 50 × 50 m study plot, all but Aporosa villosa served as phorophytes for D. scabrilingue. The orchid was found growing at (1-)2-4(-7) m above the ground, usually on bark densely covered with lichens (Aporosa villosa was the only tree species with bark consistently devoid of lichens). The orchid population was dominated by small individuals, thus demonstrating successful reproduction by seed. As indicated by a positive correlation between plant size and frequency of flowering, larger individuals appear to be of major importance for the sexual reproduction. A low relative fruit set in the population (18.5 %), and the shape of a Lorenz curve plotted from fruit set data, suggest a mainly allogamous breeding system operated by insects (probably bees, judging from the floral morphology). Based on our observations of this natural population, specific recommendations are given that may increase the success rates in re-introduction experiments with the rare D. scabrilingue. KEY WORDS: Orchids, Conservation, Flora of Thailand, Epiphytes, Ecology. showing small scattered or hyperdispersed INTRODUCTION populations (Ackerman, 1986; Kress, 1986). Although the global distribution patterns of The Orchidaceae are one of the largest orchids are fairly well known, the patterns angiosperm families with an estimated within forests are complex and poorly 20,000 epiphytic species from 500 genera understood. Moreover, although some (Dressler, 1981, 1993), often with species species are common, many are rare and exhibit large variations in life forms, habitat * Corresponding author: distributions and trophic patterns within Tel: (6653)-298-171 genera. This limits the reliable cross-species Fax: (6653)- 298 177 E-mail: [email protected] 136 NAT. HIST. J. CHULALONGKORN UNIV. 8(2), OCTOBER 2008 rough-lipped dendrobium (Fig. 1), is an epiphytic autotrophic orchid that occurs at 600–1400 m altitude–partly in hill evergreen forests and partly in the transition zone to dry deciduous dipterocarp forests. Flower- ing is seasonal and takes place from December until February (-March). The species is distributed in Myanmar, Thailand and Laos, and has its stronghold in the lower Salawin valley, on both sides of the border between Thailand and Myanmar (Wanandon, 1968; Seidenfaden, 1985). FIGURE 1. A flowering plant of D. scabrilingue growing on a tree trunk densely covered with lichens. Within this region the local Thais, Shans, (Photo by S. Watthana). Lawas and Karens all have vernacular names for this attractive species (Wanandon, generalizations of statistically well-supported 1968). information attained from common species Dendrobium scabrilingue is sympodial to the rare, where information on the roles with up to approximately 10 tufted, erect of dispersal, germination and disturbance shoots. Each shoot is up to 17(-30) cm tall regimes for controlling population dynamics and is dominated by a fleshy (up to 1.8 cm are desperately needed, for example for in thick) clavate stem, the internodes of which situ conservation and for re-introduction are tightly covered with initially black- programmes. pubescent (later glabrous) leaf sheaths. The ongoing general decrease in the Young leaves are produced distally, whilst number and size of orchid populations is old leaves are shed from below as the shoot mainly due to the loss and degradation of grows. Short, 1- to 2-flowered (rarely 3- their habitats (e.g. Koopowitz, 2001; flowered) racemes are produced from the Koopowitz et al. 2003). Collecting for distal part of leafy (occasionally leafless) cultivation and medicinal purposes is in shoots (Fig. 1). The strongly fragrant general a lesser threat, but it can be flowers each measure 1.5-3.5 cm across, significantly devastating and the main threat they are resupinate and remarkably for particularly sought after species (e.g. persistent, lasting for 1-2 months. The Schuiteman and de Vogel, 2000; Cribb et sepals and petals are white and relatively al. 2003). Particularly in such cases, broad, the lateral sepals forming a saccate transloca-tion of ex situ propagated indivi- mentum at base. The labellum is 3-lobed duals to the wild through re-introduction with erect, incurved side lobes and a projects can be a useful supplement to the porrect, slightly decurved mid-lobe. protection of habitats (Ramsay and Dixon, Whereas the side lobes are consistently 2003; Yam and Thame, 2005). white with numerous green nectar guides on Dendrobium scabrilingue Lindl. their dorsal surface, the color of the mid- (Asparagales: Orchidaceae), known as lobe changes from pale greenish yellow over Ueang Sae Luang, or in English as the pale yellow to golden yellow (rarely deep WATTHANA AND PEDERSEN — PHOROPHYTE DIVERSITY IN DENDROBIUM 137 orange) during anthesis. The stigma is late February 2007, the first author found a placed in a cavity on the front of the population of D. scabrilingue growing at c. column, the rostellum produces a fragile sac 900 m altitude. The forest, standing on a of adhesive, and the versatile anther contains slope of reddish sandy soil, was dominated 4 naked pollinia. The fruit is a unilocular by dipterocarps and oak species. At the time capsule dehiscing by longitudinal slits. when flowering ceased, observations were In the early 1900s, Mae Hong Son was made on the phorophyte (host plant) and a province tributary to Chiang Mai. At that microhabitat requirements of D. scabrilin- time flowering plants of D. scabrilingue gue as well as on its fruit set. We anticipate were one of the prescribed articles of tribute that utilization of such biological data from a that inhabitants of Muang Yuam in Mae natural population may help to increase the Hong Son had to pay annually to Chao success rates in re-introduction experiments Vijayanondh, the then ruling chief of Chiang with this presently rare species. Mai (Wanandon, 1968). Today, Muang Yuam has changed its name to Mae Sariang, MATERIALS AND METHODS but flowering shoots of D. scabrilingue are still being collected and used for hair A plot measuring 50 × 50 m was decoration and adornment at private homes, demarcated, and a 6 m tall ladder was used and for paying respect to the images and to access the canopy throughout this area shrines of Buddha. At a hotel in Mae (the trees being up to 7-8(-10) m tall). All Sariang District, a bouquet comprised of at tree species in the plot were recorded, and least 50 flowering stems of D. scabrilingue for each species it was noted if it served as a in a silver bowl could recently be admired, phorophyte for one or more individuals of filling the lobby with their strong, pleasantly D. scabrilingue. Additionally, the maximum sweet perfume. and minimum heights of orchids above An unfortunate effect of its local ground level were estimated as well as the popularity as a cut flower is the illegal canopy cover. collecting activities. Most herbarium collect- The length of the longest stem of every ions of this species are of older date individual was measured and used as a (Watthana and Pedersen, unpubl.), which general indicator of plant size. The number suggests a dramatic decline of D. scabrilin- of flowering stems and the numbers of fruits gue in the wild. To counteract this develop- and scars left after shedding of the flower(s) ment, Mae Jo University has initiated a on each stem were counted in each conservation project based on the in vitro individual. propagation of D. scabrilingue from seed. Using the program SPSS for Windows Some of the reared young plants are then 11.5, Spearman's correlation coefficient was used for re-inforcement of natural popula- used to test for correlations between plant tions, whereas the others are given to local size (as expressed by stem length) and (1) villagers for cultivation purposes (Kaewka- the number of individuals, (2) the number of mnoed, pers. comm.). flowers produced and (3) the frequency of During orchid studies at Salawin flowering. Wildlife Sanctuary, Mae Sariang District, in 138 NAT. HIST. J. CHULALONGKORN UNIV. 8(2), OCTOBER 2008 50 100 (Wall. ex. Lindl.) Baill., did not serve as a 40 80 phorophyte for the orchid. Dendrobium scabrilingue was observed to grow on vertical to horizontal trunks and branches at 30 60 1-7 m (mostly 2-4 m) above ground level, usually on bark that was densely covered 20 40 % Flowering with lichens (Fig. 1). The estimated visual Number of Individuals of Number canopy cover over the orchids varied from 10 20 10-40%. In general, the number of individuals 0 0 was found to decrease with increasing plant 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-1010-17 size (P < 0.01; Fig. 2). The smallest plant Stem length (cm) in which flowering was observed had a FIGURE 2. Population structure of D. scabrilingue maximum stem length of 1.5 cm. The share according to size classes (columns), and the share of of flowering individuals generally increased flowering individuals in each size class (dots). with increasing plant size (P < 0.01; Fig. Fruit set and relative fruit set were 2), with ca.