Richness and Distribution of Orchids (Orchidaceae) in the Forests of Mount Busa, Sarangani, Southern Mindanao, Philippines
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Philippine Journal of Science 150 (S1): 151-163, Special Issue on Biodiversity ISSN 0031 - 7683 Date Received: 21 Sep 2020 Richness and Distribution of Orchids (Orchidaceae) in the Forests of Mount Busa, Sarangani, Southern Mindanao, Philippines Aljohn Jay L. Saavedra1,2 and Kier Mitchel E. Pitogo2 1Philippine Taxonomic Initiative, Inc. El Nido, Palawan 5313 Philippines 2Department of Environment and Natural Resources Provincial Environment and Natural Resources Office South Cotabato Block 1, Martinez Subdivision, Koronadal City 9506 Philippines Orchids are one of the most diverse yet threatened plant families in the world and the Philippines. Despite the new species discoveries of orchids in the country in recent years, diversity and distribution studies are still severely lacking. Here, we provide a list of orchid species found among different forest types in Mount Busa and provide information on the species’ altitudinal and vertical distributions and ornamental use. We recorded 108 species of orchids from 51 genera, of which 53 species are endemic to the Philippines and 15 species are known only to occur on Mindanao island. Species composition differed among forest types, with the MASLEF (mixed advanced secondary lowland evergreen forest) hosting the highest number of orchid species recorded, followed by the UMF (upper montane forest), LMF (lower montane forest), and MESLEF (mixed early secondary lowland evergreen forest). Our results suggest a relatively rich and distinct orchid diversity among different forest types in Mount Busa that reinforces the high conservation value of the mountain range. Keywords: Mindanao biodiversity, Oberonia serrulata, orchid conservation, orchid distribution, orchid inventory, Philippine orchids INTRODUCTION orchids are the most threatened group of plants globally (Gale et al. 2018) and in the Philippines (Fernando et Orchids are one of the largest and most diverse groups al. 2008a). It is estimated that 56.5% of the 948 orchid among the Philippine flowering plants harboring over species assessed in the Global IUCN Red List in 2017 1200 species, varieties, and forms (Cootes 2011), with are threatened with extinction (Gale et al. 2018). In more new species and genera being discovered and the Philippines, 97 species are already threatened that recorded yearly (e.g. de Leon et al. 2017; Naive and represents ~ 8.1% of the orchid species recorded in the Martyr 2018; Meneses and Cootes 2019; Naive et al. country (DENR 2017). 2019; Tamayo et al. 2020; Tandang et al. 2020). This group of plants is mostly habitat specialists owing to Habitat destruction and unsustainable harvesting are the their specialized reproductive strategies and mycorrhizal major global threats to orchids (Fay 2018; Gale et al. 2018). specificity (Gravendeel et al. 2004). Unfortunately, Habitat fragmentation negatively impacts species richness of orchids (Hundera et al. 2013; Parra Sánchez et al. 2016), *Corresponding Authors: [email protected] 151 Philippine Journal of Science Saavedra and Pitogo: Orchids of Mt. Busa Vol. 150 No. S1, Special Issue on Biodiversity and their highly specialized habit makes orchids more ecology and addresses the gaps in our knowledge and vulnerable to global environmental changes (Fay 2018). distribution of Philippine orchids. Our results would be Orchids are also highly traded mainly for horticulture, helpful not only in elucidating the level of biodiversity in medicine, and food (Hinsley et al. 2017). Despite being southern Mindanao but also in inferring patterns of plant regulated under the Convention on International Trade in diversity and biogeography in the Philippines. Endangered Species, many of the species are still being collected and traded undocumented negatively affecting wild populations around the world (Fay 2015). MATERIALS AND METHODS The increasing pressure on wild orchid populations put orchids as a group of urgent conservation concern. Despite the new orchid species discoveries in recent years, Study Area diversity and distribution studies are still severely lacking We surveyed orchid species richness along the southern (Buenavista 2017; Betanio and Buenavista 2018). This gap slope of Mount Busa, Kiamba Municipality, Sarangani may pose conservation challenges for this highly threatened Province between July 2019 and August 2020. Mount plant family, as assemblage-level studies may serve as Busa, known as “Bulul Tembob” among the local Tboli, baselines for future monitoring programs in Philippine is located at N 06°06.537’ E 124°41.026’ and reaches montane ecosystems, particularly for the highly collected 2046 m in elevation, which makes it the highest point in and traded orchids. Distribution studies also help inform Sarangani. It houses one of the last remaining primary species conservation assessments (e.g. IUCN Red List forests in southern Mindanao. On 10 Mar 2020, the of Threatened Species and Philippine Red List), as these Provincial Government of Sarangani formally declared provide information on the species’ extent of occurrence the southern slope of Mount Busa a local conservation and geographic range. area by resolution 2020-10-042. One of the major mountains in southern Mindanao with Mount Busa was stratified into forest types based on the relatively intact lowland and montane forests is Mount classification of Fernando and colleagues (2008b). We Busa. It is a key biodiversity area (KBA) and one of the further classified the lowland evergreen forest into two: extremely high conservation priority sites in the Philippines the forest ranging in elevation from 400–600 m is the (Ong et al. 2002). Portions of Mount Busa may have formed MESLEF and the forest from 700–1100 m elevation is the part of the older landmass of the Zamboanga Peninsula– MASLEF. The lower elevation of Mount Busa (400–1000 Daguma Range block, which collided with the more recent m) was hardly hit during the logging concession in the central and eastern Mindanao blocks in the Middle Miocene, early 1990s, hence the dominance of secondary-growth thus forming the present-day Mindanao island (Sajona et trees at this elevation (see Brown 2015). al. 1997; Hall 2002; Yumul et al. 2004). The accreted The forest from 1200–1600 m elevation is the LMF and Mindanao island was intermittently connected directly to from 1700–2046 m elevation is the UMF (Figure 1). Five Borneo and the rest of the Sundaland through land bridges sampling points with more than 200-m distance in between due to repeated sea-level oscillations during the Pleistocene were randomly chosen in each forest type to maximize the glacial cycle (Brown et al. 2013). These events may have diversity of other habitat types surveyed, although we did shaped the present-day patterns of diversity in southern not limit our search to pre-defined plots. Habitats surveyed Mindanao, which necessitates more field-based biodiversity include agricultural plots of abaca, riparian areas, moist studies in Mount Busa. This is relevant for orchids, as the ravines, grasslands, shrublands, leaf litter, and forest trails. diversity of some orchid genera in the Philippines were shaped by this complex geological history (Guo et al. 2015; Tsai et al. 2015, 2020). In addition, biodiversity studies in Field Sampling southern Mindanao remain scanty, especially for orchids in Opportunistic sampling was done in each sampling site by the region that do not have empirical field data yet available four to five experienced individuals, which entailed careful in published literature. and extensive examinations of understory and midstory layers of the forest for ground and epiphytic orchids. This Here, we provide an inventory of orchid species found in was done with the caveat that orchid species beyond 4 m Mount Busa with information on altitudinal and vertical above the ground might have not been recorded due to distributions and their ornamental uses. Since orchid inaccessibility or observer bias. Encountered fallen trees distribution is influenced by elevation and species’ traits and branches, however, were thoroughly searched for (Jacquemyn et al. 2005; Zhang et al. 2015; Ding et al. 2016), canopy-dwelling orchids. we also examined the pattern of orchid species richness among different forest types in the area. This information The altitudinal range and vertical distribution were noted helps improve our understanding of orchid diversity and for each orchid species observed in the wild. The altitude 152 Philippine Journal of Science Saavedra and Pitogo: Orchids of Mt. Busa Vol. 150 No. S1, Special Issue on Biodiversity Figure 1. A contour map of the southern slope of Mount Busa, Sarangani Province showing the sampling sites in different forest types. MESLEF – mixed early secondary lowland evergreen forest, MASLEF – mixed advanced secondary lowland evergreen forest, LMF – lower montane forest, UMF – upper montane forest. was recorded using a Global Positioning System (Garmin et al. 2020), and the species’ conservation status was 64sc, USA), and the height at which the orchid was based on the DAO 2017-11 of the Philippine Department observed (vertical distribution) was visually estimated of Environment and Natural Resources (DENR 2017). using the height of AJS as reference. Only flowering The Philippine Department of Environment and Natural orchid species were included in the list. We also surveyed Resources (DENR) issued the fieldwork and collection houses in four villages, locally called as “sitios,” around permit for this study (Gratuitous Permit No. 2020-09). the vicinity