Diversity and distribution of orchids of Goa, Western Ghats, India

The Botanical Survey of India launched a pilot project during 2015–2017 on exploration of orchids of Goa State covering all the protected areas. A total of 68 orchid species belonging to 28 genera were documented of which 42 are epiphytic and 26 are terrestrial. Twenty-eight species are endemic, of which 23 species are strictly endemic to the Western Ghats, two are endemic to peninsular India, and three are endemic to the country. Distribution of orchids in Goa is concentrated mainly in the Western Ghats region, which accounts for 86% of the total orchid species richness of the state. The most favourable habitat was found to be semi-evergreen forests followed by moist-deciduous forests. Among all the protected areas, the Mhadei Wildlife Sanctuary was found to be rich in orchid diversity (39 species) followed by Bhagwan Mahavir Wildlife Sanctuary, and Cotigaon Wildlife Sanctuary. The MaxEnt data shows the highly suitable area for orchids in Goa is approximately 1,005km2, which is 27% of the total geographic area of the state.


INTRODUCTION
The Western Ghats region of Goa lies in the extreme east of the state and consists of a wide belt of rich forest with abundant biodiversity. This area is extensively protected by national parks and wildlife sanctuaries. It covers almost 600km 2 and has an average elevation of about 800m. Though, Goa State occupies just 2% area of the Western Ghats, it harbours c. 7% of the endemic flowering plant species of the Western Ghats (Joshi & Janarthanam 2004). Garcia de Orta described some interesting medicinal plants from this region way back in 1565 which marks the initiation of the botanical studies in the region, but, thereafter, for almost three centuries there was no contribution to the botany of Goa. Roxburgh (1820) occasionally referred to plants of this region as belonging to Konkan. Graham (1839) in his Catalogue of Bombay Plants often referred to Lush, who had earlier collected plants from Goa. Dalzell & Gibson (1861) and Nairne (1894) have also referred to plants from this region in their works. Most of these previous workers were often referred to by Hooker (1872Hooker ( -1897 in his majestic work on the Flora of British India in the context of plants occurring in Konkan and Goa in particular. Dalgado (1898) enumerated plants occurring in Goa and Sawantwadi based on earlier published reports but there was no orchid included in the enumeration. Subsequently, several botanists have made extensive plant collections in adjacent parts of Goa. Vartak (1966) reported 65 species of orchids belonging to 30 genera from Karnataka and Maharashtra including a few orchids from Goa, followed by Rao (1986) 21 species from Goa, Parab (2009) 26 species belonging to 20 genera from Goa and Mandar & Lakshminarasimhan (2013) presented the floristic account of Molem National Park which includes 34 species of orchids. Despite all these, the state of Goa is poorly explored in terms of orchid diversity. As such, the Botanical Survey of India launched a pilot project on exploration of orchids of Goa State covering all the protected areas (PAs), which resulted in several new distributional records of orchids for Goa (Jalal et al. 2015a,b;Jalal & Jayanthi 2016a,b;Jalal 2017). During the survey, taxonomic inventory of orchids was carried out in different PAs, and the status of orchids was documented. In the present work, an attempt has also been made to predict the suitability of potential orchid rich area based on MaxEnt (maximum entropy) niche approach (Phillips et al. 2006;Phillips & Dudik 2008).

Study area
The state of Goa is located on the Indian west coast nestled between Maharashtra and Karnataka. The total geographical area of the state is approximately 3,702km 2 . The state stretches out to a length of 105km from north to south and 60km wide from east to west and is divided into two districts, North Goa and South Goa ( Figure  1). North Goa district comprises of six talukas, namely, Pernem, Bardez, Tiswadi, Bicholim, Ponda, and Sattari while the South Goa district comprises of six talukas, namely, Dharbandora, Mormugao, Salcete, Quepem, Sanguem, and Canacona ( Figure 1). Physiographically, Goa is divided into three main regions, viz., i) the eastern Sahyadris-sub-region of the Western Ghats, and covering ~4 3% of the total state area, ii) the central uplands-the tract between the coast and the Ghats, consisting of rolling hills, slopes and valleys, which covers ~35% of the state area, and iii) the western coastal plains-the coastal belt which accounts for ~22% of the total area of the state. As per Champion & Seth (1968) classification of forest types of India, the forests of Goa fall in the following types: i) estuarine vegetation consisting of mangrove species along narrow muddy banks of rivers, ii) strand vegetation along the coastal belts, iii) plateau vegetation confined especially in low altitudes, and iv) semi-evergreen and evergreen forests. It has a tropical monsoon climate and the region is generally warm and humid throughout the year. The temperature ranges from 20°C to 34°C, and atmospheric humidity ranges from 60% to 90% throughout the year due to the proximity of the state to the Arabian Sea. The average annual rainfall received in the state is about 3200mm. Over 90% of annual rainfall occurs during monsoon months of June to September (Ibrampurkar 2012). Goa is the only state in India which has protected the complete Western Ghats section within the state. The state has one national park (Bhagwan Mahavir) and six wildlife sanctuaries, which contributes about 52% of the forested area.

Data collection
After obtaining the survey permission from Forest Department of Goa, botanical explorations were undertaken from August 2015 to 2017, in different districts of Goa covering all the protected areas. Orchid species in flowering and fruiting stages were collected and photographed. All macro-morphological characters, such as vegetative and floral structures, were likewise recorded in the field. Species in the non-flowering stage were collected and maintained as living collections for further studies. The geographical co-ordinate of each orchid was recorded using Garmin GPS etrex30. The herbarium specimens were processed following Jain & Rao (1977). Collected specimens were identified using Cooke (1967), Santapau & Kapadia (1966) and Abraham & Vatsala (1981). All the herbarium specimens collected, were deposited in the Herbarium of the Botanical Survey of India, Pune (BSI). A total 552 GPS records were collected during the field survey for species distribution model. This study was restricted only to species with five or more occurrence records, thus 49 species were taken for modeling purposes. Nineteen bioclimatic variables (Hijmans et al. 2005) derived from climatic data from the 1950-2000 period were used. All variables were reduced to a grid resolution of 30 arc-seconds or 0.008333 0 (approximately 1km 2 ) for the analysis. MaxEnt ver. 3.3 was used for species prediction modeling as it works with presence-only data (Phillips et al. 2006). The analysis was performed using the default parameters: maximum iterations to 500 and using convergence threshold in 1.0E-5. Duplicate presence records were removed by the program prior to model development. For the potential habitat mapcells reported by MaxEnt, cell values of 1 are considered the most suitable, whereas closer to zero regarded as less suitable. The probability values that were equal or greater than a threshold value of 0.5 indicates the potential suitable habitat of a species (Phillips et al. 2006). The MaxEnt produces continous outputs of potential habitat suitability ranging from 0 to 1, which were further reclassified into two classessuitable and unsuitable. The threshold was selected as per 'minimum training presence' threshold technique limits. The priority areas were calculated by summing up the thresholded binary maps of all 49 species and reclassifing the grid cells. The priority zones were further divided into low, medium and high zones for the sake of convenience.

RESULTS AND DISCUSSION
The present outcome is based on intensive field surveys as well as information collected from different herbaria and literature. A total of 68 species of orchids belonging to 28 genera were documented, of which 42 are epiphytic and 26 are terrestrial (Table 1) (Images 1-3). In the present survey presence of 58 species were confirmed and the remaining 10 species were included based on herbarium records and literature (Images 4-67). Habenaria, Dendrobium and Oberonia were the most species rich genera in the study area. Twentyeight species were endemic, of which 23 species are restricted to the Western Ghats, while two are endemic to peninsular India and three are Indian endemic. Three broad habitats were categorized for orchids, viz., semievergreen forests, moist-deciduous forests, and plateaus (Fig 2). The most favourable habitat was found to be semi-evergreen forests hosting 40 species followed by moist-deciduous forests (37 species). Very few terrestrial orchids were reported from plateaus (6 species), which are mainly found at higher elevations. These plateaus are threatened due to local grazing. In Goa, these plateaus are known as 'sada'.
Distribution of orchids in Goa is concentrated mainly in the Western Ghats region, which accounts for 86% of the total orchid diversity of the state (Fig. 3). The high undulating mountains are covered with semi-evergreen forests and provide suitable habitats for many endemic orchids. Half a dozen important rivers, e.g., Mandovi, Mhadei, and Zuari, flow between these mountains and maintain high humidity levels throughout the year which is an important factor for the growth and development of epiphytic orchids.
The entire Western Ghats of the state is covered under protected areas and there is no direct threat to these orchids; however, a few human settlements still exist inside the wildlife sanctuary as a result of which some pockets of these natural habitats are disturbed due to lopping of forests and from cattle grazing. The central upland is a transition zone between the Western Ghats and the coastal plains. The area, adjoining the Western Ghats, has semi-evergreen and moist-deciduous forests at the base of the hills which provide a very favorable habitat for epiphytic as well as terrestrial orchids. These forests are moderately dense and receive less   intense sunlight and have high humidity as well. It has an average height ranging 30-100 m and most of the landscape is covered with coconut palms, paddy fields, betelnut farms, commercial establishments, human settlements, and many active iron ore mines. A total of 18 species are distributed in this part of which eight are endemic. Threats to the orchids are high in this part as many forest patches are being cleared for developmental purposes and new mining activities. Large forest patches are private or community land for which mining clearance is not necessary. The rampant encroachment is destroying the pristine forest habitat. Species such as Acampe praemorsa, Bulbophyllum sterile, Cymbidium bicolor, Dendrobium ovatum, and Rhynchostylis retusa are encountered mostly in such disturbed habitats, along roadside and forests edges. The coastal plains have no orchid presence. This is a narrow stretch of low-lying area dominated by estuarine mangroves.
In the present survey all the protected areas of Goa were also surveyed to know the orchid diversity and to identify the best protected area for in situ conservation. The findings reveal that Mhadei Wildlife Sanctuary has orchid richness (Fig. 4). This sanctuary covers most of the northeastern portion of Goa and the average rainfall in this region is above 3,200mm.   Figure 5 represents summation of potential orchid distribution of 49 orchid species in Goa (constituting 72% of total orchids of Goa) which was predicted using MaxEnt algorithm. The output has been further categorized into areas with high (21-34 species), medium (8-21 species) and low (less than 8 species) richness or suitability zones. The high richness zone is dominated by moist-decidous forests interspersed with semi-evergreen forests and open plateaus, which are suitable for orchids. Many endemic species are restricted to the evergreen forest habitat pointing towards high habitat specificity and also towards the ecological importance of these habitats. Approximately, 1,005km 2 is found to be highly suitable for orchids, which is 27% of the total geographic area of Goa State. www.threatenedtaxa.org The Journal of Threatened Taxa (JoTT) is dedicated to building evidence for conservation globally by publishing peer-reviewed articles online every month at a reasonably rapid rate at www.threatenedtaxa.org. All articles published in JoTT are registered under Creative Commons Attribution 4.0 International License unless otherwise mentioned. JoTT allows allows unrestricted use, reproduction, and distribution of articles in any medium by providing adequate credit to the author(s) and the source of publication.