Conservation status of Dendrobium tenuicauleHook. f. (Orchidaceae),
a Middle Andaman Island endemic, India
Boyina Ravi Prasad Rao1, Kothareddy Prasad 2, Madiga Bheemalingappa 3,Mudavath Chennakesavulu Naik 4, K.N. Ganeshaiah5 & M. Sanjappa 6
1,2,3,4 Biodiversity
Conservation Division, Department of Botany, Sri KrishnadevarayaUniversity, Anantapur, Andhra Pradesh 515003, India
5 Department
of Forestry and Environemental Sciences And School of
Ecology and Conservation, University of Agricultural Sciences, GKVK, Bengaluru,
Karnataka 560065, India
6 Botanical Garden, University of Agricultural Sciences, GKVK,
Bengaluru, Karnataka 560065, India
Email: 1biodiversityravi@gmail.com (corresponding author), 2 prasad.orchids@gmail.com,3 bheemantp@gmail.com, 4 chenna.phd@gmail.com, 5 knganeshaiah@gmail.com,6 sanjappas@gmail.com
Date of publication (online): 26
December 2012
Date of publication (print): 26
December 2012
ISSN 0974-7907 (online) | 0974-7893
(print)
Editor: Pankaj Kumar
Manuscript details:
Ms # o3186
Received 28 April 2012
Final received 13 November 2012
Finally accepted 21 November 2012
Citation: Rao, B.R.P., K. Prasad, M. Bheemalingappa, M.C. Naik, K.N. Ganeshaiah & M. Sanjappa(2012). Conservation status of Dendrobium tenuicaule Hook. f. (Orchidaceae), a Middle Andaman Island endemic,
India. Journal of Threatened Taxa4(15): 3410–3414.
Copyright: © Boyina Ravi Prasad Rao, Kothareddy Prasad, Madiga Bheemalingappa, Mudavath Chennakesavulu Naik, K.N. Ganeshaiah & M. Sanjappa 2012. Creative Commons
Attribution 3.0 Unported License. JoTT allows unrestricted use of this article in any medium
for non-profit purposes, reproduction and distribution by providing adequate
credit to the authors and the source of publication.
Acknowledgements: Authors are thankful to Dr.Murugan, Scientist C, InchargeDirector, Botanical Survey of India, Port Blair.
Authors also thank the forest officials of Middle Andaman Division for their
kind help in field work. Authors acknowledge
Department of Biotechnology, Government of India, New Delhi for financial
assistance.
Abstract:The current distribution and threat assessment of Dendrobium tenuicaule Hook. f.
(Orchidaceae), an endemic orchid of Middle Andaman
Island is presented here. New data
available from field surveys indicated the species is Critically Endangered as
per the 2001 IUCN Red List Catagories and Criteria.
Keywords:Conservation status, Critically Endangered, Dendrobium tenuicaule,
distribution, Middle Andaman.
For
figure, image -- click here
Andaman and Nicobar Islands are located
about 1200km from the mainland, India, comprising 572 islands and islets. The Middle Andaman Island (12015’–130N & 92030’–930E)
(Fig. 1) is the largest among the 324 islands of the Andaman group. The Andaman group of
islands are part of Indo-Burma Biodiversity Hotspot, one of the 34 in
the world (Myers et al. 2000). The
climate is warm and humid with the temperature ranging between 220C
and 300C with average annual rainfall ranging from 3000–3500
mm and mean relative humidity between 82–85%. Currently, the Andaman and Nicobar
Islands are known to harbor 2650 species of plants (Pandey& Diwakar 2008), of which 308 are considered as
strict endemics.
Endemism is a significant
attribute of any taxon with reference to its restricted distribution and
endemic species especially of islands hold immense significance, as it can be
assumed that the smaller its geographical distribution and population size and
the more specific its habitat preferences, the rarer the species (IUCN/SSC
Orchid Specialist Group, 1996). An
in-depth assessment of their distribution pattern within a small geographical
range is of great conservation concern. The IUCN system (IUCN 2001) assesses the threat to a species based on
five core criteria: decline in populations over a period that is relevant for
the species (based on generation time); the distribution of the species
together with factors that may influence ongoing survival within its current
distribution; small population size and continuing decline; very small
populations or small distribution area; and quantitative assessment of
extinction risk. Assessments are
always done using the best available information, however, there is a dearth of
knowledge in the case of the distribution pattern for many endemic species,
especially those in remote islands. The recent studies by Rao et al. (2010,
2011) regarding conservation status on Cycas beddomei Dyer; and Hildegardia populifolia (Roxb.) Schott & Endl. has provided valuable information for population status
assessments. In the present study,
an attempt has been made to assess the population and conservation status of an
orchid species, Dendrobium tenuicaule Hook. f., endemic
to Middle Andaman Island, India.
The family Orchidaceae is one of the largest groups in the plant
kingdom comprising 22,075 species (APG III 2009). The family represent1331 taxa in India (Misra 2007) and 151 species from
Andaman and Nicobar Islands (Pandey & Diwakar 2008). The genus Dendrobium Sw., is one of the largest genera of Orchidaceaerepresented by ca. 900 species and mostly distributed in the Indo-Malesio-Austrasian region (Kumar
& Manilal 1994). In India, the genus is represented by
116 species (Misra 2007) and in Andaman and Nicobar
Islands, 19 species (Pandey & Diwakar2008), of which three are endemic to Andaman and Nicobar Islands: Dendrobium gunnariiP.S.N. Rao, D. shompeniiB.K. Sinha & P.S.N. Raoand D. tenuicaule Hook. f.
Methods
Study area and species: Dendrobium tenuicaule Hook. f. isendemic to Middle Andaman Island and categorised as
Endangered (Balakrishnan & Rao1983; Nayar & Sastry1990; Rao et al. 2003); Extinct or Endangered (IUCN
1996). The species is also a part
in CITES Appendix II (UNEP-WCMC 2003).
A perusal of literature and
herbarium consultation in CAL and PBL herbaria has revealed interesting
information about the species distribution. J.D. Hooker (1890) described the species
based on a drawing of King along with a few dried flowers and cited the
distribution of the species as Andaman Islands. Later, the illustration was published in
King’s Annals of the Calcutta Garden (King 1895). Since the first
herbarium collection of the species was by Bhargava(Voucher No. 6372 in PBL) from Rangat forests of
Middle Andaman in 1977, it was claimed as endemic to Middle Andaman Island by Nayar & Sastry(1990). There was no record of
further collections of this extremely rare orchid from Middle Andaman till November, 2011 in Kousalyanagarforest, Middle Andaman Division, when it was recollected by the current
authors. The voucher specimens are
deposited in SKU (Department of Botany, S.K.University).
Dendrobium tenuicaule Hook. f. isan epiphytic orchid, with many stems clustered together and grow 40cm long with
rooting at base of the branches. Pseudobulbs grow to 8cm long and 5cm thick. Leaves linear, 15x2 mm, acute, entire
with sheathing base. Flowers few, terminal,solitary on axils of nodes, labellum with white and
yellow stripes on lip, very delicate, sweet scented. Ovary pedicellate,
slender, 1.5cm long. Dorsal sepal
elliptic-ovate, 7-nerved; lateral sepals falcate, acute. Petals as long as sepals, lanceolate, acute, mentum twice
as long as the lateral sepals, trumpet-shaped. Lip wedge-shaped, sessile at the base of
the mentum, membranous; lobes thin, flimsy, rounded;
mid lobe strongly bent downward, orbicular; side lobes short, erect; disc
pubescent. Pollinia 4, in pairs, unequal, ellipsoid. Fruits oblong-ellipsoid, grayish-brown,
4–5 x 0.4–0.5cm (Image 1).
Sampling design and population census: After the first sighting of
the species on Mangifera indica in Kousalya Nagar
Forest, an intensive survey was made in Rangat Forest
Division for the next eight months taking into consideration the first
historical collection in Rangat forest. Random sampling method was adopted for
the study. In epiphyte ecology, the
sampling unit is often defined as one host tree (or part thereof), but unit
area and unit forest-volume have also been used (van Dunne 2002). Hence we adopted IUCN sampling
methodology (IUCN Standards and Petitions Subcommittee 2011) for determining the
area of occupancy. Accordingly, the
whole terrain of Middle Andamans was stratified into
4km2 grids for this purpose. Within each grid, all the trees for locating the individuals of D. tenuicaule were observed. The localities of
occurrence were recorded by Garmin Global Positioning System.
Following Garcia-Gonzalez et
al. (2011), we counted all the individuals of D. tenuicauleinhabited on phorophytes that were found from the
base of the trunk to the first primary branches; intersection between branches
at various heights; and branches. We also classified the plants of the species by seedlings, earliest
stage after the protocorm in which the young plant
first acquires differentiated structures (2mm to 2cm);juvenile, sexually immature but well developed plants (>2cm) and adults,
sexually mature plants that have flowered at least once. We counted all the individuals of each
life stage on each of the microsites of every phorophytewithin the study sites.
The species has been assessed
for its conservation status based on 3.1 version of IUCN red list (IUCN,
2001). The Extent of Occurrence
(EOO) and Area of Occupancy (AOO) are estimated.
Results and Discussion
Of the 100 grids laid in Rangat Forest Division, we located the D. tenuicaule only in three grids in KousalyanagarForest area of Bakunthala Range. We found only 56 clumps in the three
grids comprising 41 mature and 12 juvenile individuals and three
seedlings. All these individuals
were found on 41 phorophytes (host trees) which were either Mangifera indica or Areca catechu. No other tree species was found hosting
this orchid species. Of the 56
clumps, 47 were found on Mangifera indica, which represents 84% of the total
population and nine clumps on A. catechu. It was observed that the species was found at an altitudinal range of
5–40 m. The maximum number of clumps (29) were found between 10–20 m
covering about 52% of the total population. Further, this species was not found in
the interior forests and appears to prefer open areas and forest edges. It was also observed that only one of the
adult clumps was found in the fruiting stage.
Timber harvesting and
commercial plantations in Kousalyanagar forests are
threatening the species existence. Further, the historical collection site of the species by Bhargava (1977), 25km south-west of Rangatin the present Bakultala range is now converted into
a forest plantation and despite our repeated visits we could not locate the
species at this point.
Conservation status
D. tenuicaule has been assessed as Endangered (Balakrishnan& Rao 1983; Nayar &Sastry 1990; Rao et al.
2003). Based on the field
observations during the present study, the conservation status of the species
has been evaluated following the latest IUCN Red List Criteria (Version 3.1;
IUCN 2011). Of the five criteria
(A–E) pertaining to threat categories the species qualifies for criterion B1
(Extent of Occurrence - EOO) and B2 (Area of Occupancy - AOO) (Fig. 1);
criterion C and D.
Criterion B: Dendrobium tenuicaule is restricted to a single location and has a
highly restricted Extent of Occurrence (EOO; B1) and Area of Occupancy (AOO;
B2).
Criterion B1: The EOO of Dendrobium tenuicaule is estimated to be 2.8km2. Continuing decline of population is observed
and inferred (subcriterion b) in terms of area,
extent or quality of habitats (iii) and in the number of mature individuals
(v). Hence the species falls under
Critically Endangered category as its geographical range is less than 100km2and satisfies subcriterion b(iii
and v).
Criterion B2: The AOO is 1km2, and since this estimate is less than
10km2, the species qualifies for Critically Endangered category
under subcriterion b(iii and
v).
Criterion C: Restricted population size and continuing decline. The total estimated population of the
species comprises of 41 mature individuals. The species qualifies for Critically
Endangered category. Further, there
is a continuous decline observed, projected, inferred in numbers of individuals
(subcriterion 2) there are no subpopulations and as
the whole population contains not more than 50 mature individuals it further
qualifies for subcriterion a(i).
Criterion D: Very small or restricted populations. Since the species
population comprises only 41 mature individuals it falls under Critically
Endangered category.
Based on field observations
and overall assessment, Dendrobium tenuicaule is assessed as Critically Endangered [B1ab(iii,v)+2ab(iii,v); C2a(i); D].
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