Plant species
composition on two rock outcrops from the northern Western Ghats, Maharashtra,
India
Savita S. Rahangdale 1& Sanjaykumar R. Rahangdale 2
1 Hon. B.J. Arts, Commerce and
Science College, Ale, Junnar Taluk, Pune District, Maharashtra 412411, India
2 PDEA’s A. W. College of
Science, Arts and Commerce, Otur, Junnar Taluk, Pune District, Maharashtra
412409, India
1 gauriyana@hotmail.com, 2 rsanjay2@hotmail.com
(corresponding author)
Abstract: The Western Ghats are full of high altitude plateaus/rock outcrops amidst
mesic forests. Throughout the
world, rock outcrops are isolated habitats and known for their uniqueness with
respect to environmental variables and biodiversity and well known as centers
of species endemism. In India such
special habitats are geographically known but very less information is
available about their floristic wealth. Available studies are occasional and limited to ecology. Due to a lack of appropriate information
and errors in the study models of random sampling, important habitats may get
misinterpreted and pose a threat to conservation. A comprehensive botanical study of two
rock outcrops, Durgawadi Plateau (DP) and Naneghat Plateau (NP), on the
escarpment of the northern Western Ghats revealed a very high within-site (360
taxa on DP and 249 taxa on NP) and between-site plant diversity totaling to 443
taxa of specific and infraspecific ranks. The individual outcrop areas are very small (2.8793km2 and
0.7524km2 respectively for DP and NP) but harbor a huge diversity of
flowering plants. The commonly
shared taxa are relatively low (37% of the taxa recorded) indicating that the
two outcrops are floristically very distinct from each other. They are also distinct in terms of soil
composition, though on the same crest line of Sahyadri and quite close to each
other. The study emphasizes the
need for micro-level inventories of smaller areas by taking intensive surveys
for documentation of different aspects of the abiotic and biotic diversity as
well as other environmental and anthropogenic variables.
Keyword: Angiosperm diversity,
Durgawadi, floristic composition, microhabitats, Naneghat, plateaus, rock
outcrops.
Abbreviations: EIA - Environmental impact assessment; DP - Durgawadi Plateau;
NP - Naneghat Plateau; RO - Rock outcrop.
doi: http://dx.doi.org/10.11609/JoTT.o3616.5593-612
Editor: Aparna Watve, Pune, India. Date of publication: 26
April 2014 (online & print)
Manuscript details: Ms # o3616 | Received 07 May
2013 | Final received 09 April 2014 | Finally accepted 11 April 2014
Citation: Rahangdale, S.R. & S.R. Rahangdale (2014). Plant species
composition on two rock outcrops from the northern Western Ghats, Maharashtra,
India. Journal of Threatened Taxa 6(4): 5593–5612; http://dx.doi.org/10.11609/JoTT.o3616.5593-612
Copyright: © Rahangdale & Rahangdale 2014. Creative
Commons Attribution 4.0 International License. JoTT allows unrestricted
use of this article in any medium, reproduction and distribution by providing
adequate credit to the authors and the source of publication.
Funding: None.
Competing Interest: The authors declare no
competing interests.
Author Contributions: SSR dealt with the taxonomic part along with the endemic taxa,
while SRR has taken exhaustive field works and collection of the information
for present study.
Author Details: Savita S. Rahangdaleholds a PhD in angiosperm taxonomy, with special reference to impact of
anthropocentric developmental activities on floristic composition, from
Agharkar Research Institute, Pune and works as Assistant Professor in Botany.
She is a Fellow of the Indian Association for Angiosperm Taxonomy (IAAT). Sanjaykumar R. Rahangdale holds a PhD in
classical genetics from Agharkar Research Institute, Pune and works as
Assistant Professor in Botany.
Acknowledgements: The authors sincerely
acknowledge the constant support and help from Department of Forests,
Government of Maharashtra, during field works; Dr. Aparna Watve for suggestions
and technical support during the work on plateaus; Director and in-charge of
Botanical Survey of India, Western Regional Centre, Pune and Agharkar Research
Institute, Pune for permission to refer the herbaria for confirmation of
doubtful specimens; and Principals of B.J. College, Ale and A.W. College, Otur
for facilities.
For images, tables -- click here
INTRODUCTION
Rock
outcrops are well known throughout the world but less studied. Most of the studies are from African,
American and Australian outcrops (Porembski et al. 1994, 2000; Burke 2005 a,b; Jacobi et al. 2007) describing the habitat types and
associated vegetation composition. In India, relatively very few reports exist about vegetation on these
special habitats (Porembski & Watve 2005; Watve 2008, 2013; Lekhak &
Yadav 2012; Bhattarai et al. 2012). High altitude rock outcrops are found throughout the Western Ghats in
India. Rock outcrops are naturally
occurring landforms where open rock surface is visible over a large area that
has very little soil or only pockets of deep soil. The rock outcrops in the Western Ghats
are of two types based on the rock formation and soil type developed from it:
(i) Lateritic—lateritic rock cover is well preserved over the parent
basalt rock and soil rich in iron e.g., Kas Plateau and other low altitude
plateaus in the Konkan region and (ii) Basaltic—having black hard rock
and soil, e.g., plateaus with forts, such as Naneghat Plateau. Some plateaus in the northwestern corner
of Pune District are entirely basaltic but have some lateritic soil due to
weathering. Such rock outcrops have
a distinct geographical feature, of a little porous rock and yellowish-gravelly
soil. They have a diversity of micro-habitats and are rich in flora and fauna. Trees or shrubs are less in number, but
herbaceous angiosperms, algae, mosses, ferns and lichens are generally abundant
in these habitats. Many of the
endemic ephemerals, herbaceous angiosperms, pteridophytes and lichens are
restricted to these special habitats. Species composition patterns and outcrop communities are influenced by
multiple environmental factors like soil type, elevation, aspect of that rock
outcrop and micro-environments. Transect studies of plateaus in the
northern Western Ghats and Konkan region by Watve (2008, 2013) are confined to
the vegetation composition and pattern of only some microhabitats on plateaus.
Complete diversity on the plateaus in the northern Western Ghats is not yet
revealed satisfactorily.
Though
the rock outcrops are considered to be isolated from the surrounding landscape,they are always surrounded by some vegetation or ecological
niches. These surrounding
areas and biotypes on it are indispensable factors of any rock outcrop; because the biota from the surrounding area greatly
influences the plateau biota as well as the ecological conditions on it.
The
present study represents the total floristic diversity observed for the last 10
years on and around two important rock outcrop areas, the Durgawadi Plateau
(DP) and the Naneghat Plateau (NP) in the northern Western Ghats. A comprehensive study with respect to
total floristic diversity along with microhabitats is reported for the first
time from these unique areas showing basaltic rock outcrops. The comparative account of the
ecological and floristic aspects between them is discussed.
Study Area
Ghod Project Division, Junnar, Department
of Forests, falls under district Pune, Maharashtra State, India. The area comprises of late creataceous
to early tertiary high hill escarpment of Sahyadri (Ollier & Sheth 2008) on
the West to north-west side. The undulating spurs of the escarpment
spread on the east southward ending in plains and low altitude small basaltic
outcrops. The escarpment receives the headwater
during the monsoon months and the eastern plains are under the watershed. The forest types vary from moist
semi-evergreen montane types with some evergreen patches within them on the
hills and valleys to dry scrub forests on the east, through moist and dry
deciduous forests. The forests are
interspersed by many small rocky outcrops, of them 14 outcrops are identified
in the Ghod Project division boundary. The present study describes floristic diversity on two
significant outcrops among them (Images 1 & 2).
The
Junnar Forest Division (JFD) (18027’51.48”–19024’03.6”N
& 73031’18.84”–74°35’09.24”E) has a total geographic area
of 4360km2; of this about 12.5% area is under semi-evergreen to
thorny scrub type of vegetation (reserved and unclassified forests). The annual rainfall varies from 2800mm
on the west of the hilly sections to 240–600 mm on the eastern side
slopes and plains.
Durgawadi Plateau
The
Durgawadi Plateau (Image 3) is one of the largest and florally rich basalt
outcrops in Pune District; located 30km from Junnar Town at the south-west
corner in Junnar Taluka between 19011’37.99”N
& 73041’42.57”E to 19013’3.59”N & 73038’33.92”E
with an elevation that ranges from 1037–1156 m. This plateau spreads over an area of
2.8793km2 out of a total geographic area of 16.28km2 of
village Ambe-Hatvij and its ‘wadis’, Pimparwadi and Durgawadi. RO area is mainly basalt with a few
pockets of lateritic soil supporting small forest patches out of a total
reserve forest area of 2.11km2. Most of the areas of RO are private lands extensively cultivated for
rice and ‘nachni’ (finger millet). There are four sacred groves on the plateau with a good broad leaved
montane forest community of large trees comprising Mangifera indica,
Memecylon umbellatum, Xantolis tomentosa, Atalantia racemosa and Syzygiumspecies. The climate at Durgawadi
Plateau is cool and humid with an average minimum and maximum temperature of 110C
and 380C, respectively, and an average annual rainfall of
1500–2000 mm or even higher.
Botanical history of the
Durgawadi Plateau
The
Durgawadi Plateau is floristically very important because a number of new taxa
are described from this region or associated region viz., Ceropegia rollae (Hemadri
1968a); Chlorophytum bharuchae Ansari et al. (1970); Leucas
deodikarii Billore & Hemadri (1970); Ischaemum raizadae Hemadri & Billore (1970); Isachne borii Hemadri (1971a); Alysicarpus
vasavadae and Smithia agharkarii Hemadri (1971b); Bothriochola
jainii Deshpande & Hemadri (1971); Ceropegia mahabalei Hemadri
& Ansari (1971); Arthraxon junnerensis Jain & Hemadri
(1971). Hemadri (1968b) also
reported some new records for Maharashtra State from the study area, viz., Cucumis
setosus and Blyxa aubertii; similarly Rahangdale et al. (2009)
reported Garnotia courtallensis as a new record for Maharashtra. Recent plant descriptions from the study
area are Jansenella neglecta Yadav et al. (2010); Ceropegia mahabalei var. hemlatae Rahangdale & Rahangdale
(2012) and Mucuna sanjappae Aitawade & Yadav (2012). All new taxa
described from the location are endemic.
Naneghat Plateau
Naneghat
is a famous historical and archaeological place near Ghatghar Village (19016’45.63”N & 73041’19.96”E to 19017’53.29”N
& 73040’26.37”E) located 36km away from Junnar as an ancient
mountain pass, from the period of Satvahan kings (approximately 700 A.D.). This plateau spreads over an area of
0.7524km2 out of 10.97km2 total geographic area of
Ghatghar Village (Image 4). Most of
the area is under private ownership, while the mountain pass and surrounding
areas are under reserve forests (3.2518km2). The highest point is about 750m. The hill fort ‘Jeevdhan’ on this plain
area rises steeply to 900m. The
basalt is exposed as a broad expanse at a low altitude and bounded by sacred
groves, reserve forest patches, rice fields and vertical slopes. The outcrop and its
surroundings are affected by biotic pressures. There are two sacred groves on the
plateau comprising Terminalia chebula, Meyna laxiflora, Heterophragma
quadriloculare, Flacourtia sp., Xantolis tomentosa, Bambusa sp. and Sterculia sp. Floristically this area is rich in diversity, Hemadri (1970) and
Rahangdale (2009) explored this region for floristic diversity, while ephemeral plant communities on the outcrops were studied by
Watve (2008, 2013).
Micro
habitats on study areas
Plant
communities on these ROs are associated with different microhabitats. According to the microhabitats, the
biota is different on these ROs. Each microhabitat has characteristic features with respect to soil,
water and species composition. The
microhabitats are classified into rock surfaces, boulders, rock crevices,
ephemeral pools, soil-filled depressions and ephemeral flush vegetation (Watve
2008, 2013). In the present study,
11 microhabitats are observed on ROs and mentioned in the results. The sacred groves, tree cover on
plateaus and surrounding slope vegetation are also an integral part of a RO as
their influence on it is indispensable and therefore such vegetations are also
considered while taking floristic diversity into account.
METHODS
Data Collection
Extensive
and repeated field surveys were carried out from 1999 to 2012 at both the
locations to cover all the seasons of the year. A comprehensive list of plants has been
prepared for each location so as to get the range of distribution, ecological
variations and frequency of particular species in the area under study. Occurrence
of the taxa is recorded on the visual observations during field
work in the study area and the taxa are grouped in four categories of
occurrence. Common (C)—when the taxon occurs in all the habitats and
population size is large; Frequent (F)—the taxon occurs in most of the
habitats but with relatively smaller population than common; Occasional
(O)—taxon occurs in a few habitats and population is also small; Rare
(R)—the taxon is restricted to very specific habitats and population is of
a few individuals. During field surveys emphasis
was given to documenting the type of vegetation, habit, habitat, phenology and
associated species. Monsoon
ephemerals, tuberous, cormatous and rhizomatous plants with a short life span
were given special attention to get data on their life cycle and
phenology. Morphological characters
were recorded on the basis of fresh material in the field.
Laboratory Studies
Collected
plant specimens were processed for the herbarium following standard techniques
(Jain & Rao 1977). In most of
the cases the specimens were identified afresh. All the herbarium specimens were
carefully checked in the laboratory and their identity was confirmed with help
of the floras (Dalzell & Gibson 1861; Hooker 1872–1897; Cooke
1901–1908 (Rep.1958); Santapau 1957, 1960; Hemadri 1970; Matthew 1982;
Sharma et al. 1996; Singh & Karthikeyan 2000; Singh et al. 2001; Almeida
1996, 1998, 2001, 2003, 2009); relevant monographs (Blatter & McCann 1935;
Santapau & Kapadia 1966; Hemadri 1980; Ansari & Balakrishnan 1994);
fascicles (Ansari 1984) and published literature in scientific journals. Doubtful specimens were checked and
confirmed by comparing with earlier identified specimens at the following
herbaria: (i) Botanical Survey of India, Western Circle, (BSI), Pune, (ii)
Agharkar Herbarium (AHMA), Agharkar Research Institute, Pune.
Any
deviation from earlier descriptions or authentic herbarium specimens are
recorded and duly documented as a critical note. The voucher specimens are deposited in
the Herbarium of Balsaheb Jadhav College, Ale. The plant names have
been checked by using online database of IPNI (2013). The status of the taxa (Table 1) was
assigned at the level of BSI on the basis of Ahmedullah & Nayar (1987);
Nayar & Sastry (1987–89); Mishra & Singh (2001) and at IUCN level
on the basis of the information available on www.iucnredlist.org (accessed on
22 April 2014).
Results
and Discussion
The
observations about the rock outcrops and vegetation are subdivided into the
following heads.
Habitats
Durgawadi
and Naneghat are quite adjacent to each other with an aerial distance of 5km
between the two study areas, while the farthest distance is about 10.5km
because of the elongated nature of the DP towards the south-east. These ROs are relatively different in
the composition of the soil strata. DP is mainly basalt with a few areas of lateritic soil and has yellowish
to brown gravelly soil. DP is
topped by a hillock, composed entirely of large boulders and fractured rocks,
similar to ‘kopje’ or tor formations. Generally, the soil thickness ranges from 1cm to a few meters. The porosity of the strata is relatively
more on it, than that in NP. NP is purely basaltic with brown-black hard rock and very little soil on
it. The soil thickness usually
ranges from 0–1 m. The
dominant habitat on both the ROs is quite different. DP has more diversity in the
microhabitats than NP. The
diversity of microhabitats and larger area could be the reasons for
accommodating more angiosperm species. These ecological settings support the moist semi-evergreen forest type
on DP. On NP the forest type tend towards moist to dry deciduous types. A total of 11 types of
microhabitats are identified in the study area following the microhabitat
classification in the Western Ghats by Watve (2008) and Lekhak & Yadav(2012) with some modifications. Each microhabitat has characteristic features with respect to soil,
water and species composition and are described below.
1.Boulders [B]: They are large rocks found on the plateau either
aggregated or scattered. They are usually covered by algae, lichens and mosses. Some angiosperms found on them are, Aerides
crispa, Begonia crenata, Dendrobium herbaceum, D. barbatulum, Eria reticosaamidst mosses.
2. Cliffs or Crust Edges [CE]: The cliff is a specific habitat on the edges
of the plateau with steep, almost 900 drop from the plateau (Image
5). The cliffs support populations
of Pinda concanensis, Heracleum grande,
Ceropegia rollae, Chlorophytum glaucoides andPancratium triflorum. Besides these there are Utricularia striatula, Begonia
crenata, Sonerila scapigera and grasses like Arthraxon sp.,
Arundinella metzi, Themeda spp.
3. Exposed Rock Surfaces [ERS]: The
flat or uneven rock surfaces, exposed to direct sunlight. During the rainy season they are covered
by grasses and other ephemerals (Image 6). Common plants occupying this microhabitat are Eriocaulon cookie,
E. minutum, E. ritchieanum, E. stellulatum and Utricularia spp.
4. Rock Crevices [RC]: The rock
crevices are on the plateaus as well as on crests again providing a different
microhabitat. The small crevices
support populations of Murdania, Eriocaulon and some grass species. Larger crevices support a population of Curcuma
pseudomontana, Ceropegia rollae, C. media, Pimpinella adscendens, P. tomentosa, Senecio bombayensis,
S. dalzellii, ferns and grasses.
5. Seasonal Ponds [SP]: They are small
ponds that have deep bowl like depressions filled with water during and post
monsoon. They are occupied by
common aquatic species, such as Nymphoides indica, Persicaria glabra, Rotala
ritchiei and Marsilea minuta. Some grasses, sedges and Isachne species
are found on the margins. Typha
angustifolia was also recorded in one of the seasonal ponds on DP.
6. Small Ephemeral Pools [SEP]: The
very shallow depressions which get filled with water during rains. Generally, there is none or very less
deposition of soil. These are
occupied by Pogostemon stellatus, Rotala sp.and some algal members. They
support the growth of frog tadpoles, crabs and small fishes.
7. Soil-covered Areas [SCA]: The large
areas or slopes having about 10–20 cm thick soil covering the bedrock
forms this habitat. It is generally not inundated during the monsoons. It supports the ephemeral flush
vegetation giving a mass effect of individual or composition of species (Image 7). The SCAs are
occupied by large populations of Isoetes dixitei, Ophioglossum spp., Drosera indica, Habenaria grandifloriformis, H.
heyneana, Hypoxis aurea, Curculigo orchoides, Impatiens lawii, Iphigenia
stellata, Smithia spp., Linum, Senecio spp., Rhamphicarpa
longiflora, Utricularia albocaerulea, U. praeterita,
U. reticulata, U. purpurascens and grasses.
8. Soil-filled Depressions [SFD]:
These are small convex areas within or outside the SCA having about 20–30
cm thick humus rich soil. SFDs are generally inundated temporarily
after rains. The
species found in this microhabitat are Eriocaulon tuberiferum, Isachne
lisboae, Paspalum canarae var. canarae, Pycreus sanguinolentus, Rotala
densiflora and Smithia racemosa.
9. Soil-rich Areas [SRA]: These
habitats have soil to a depth of about 30–60cm. SRAs are found
scattered in interrupted plateau tree cover and fringes of sacred groves. SRAs are occupied by Curcuma
pseudomontana, Curculigo orchioides, Cyanotis tuberosa, Cajanus
lineatus, Pancratium sanctae-marae, P. triflorum, Crinum latifolium, Drimia
indica, Fimbristylis dichotoma, Hypoxis aurea, Smithia racemosa, S.
capitata, S. purpurea and S. setulosa. Some SRAs
are private lands and on it rice and finger millet are cultivated. In some places Maytenus senegalensis,
Gnidia glauca, Leea indica and other species form shrub
vegetation supporting Ceropegia media, Senecio dalzellii, S. hewrensis,Asparagus ramosissimus and other herbaceous species.
10. Plateau Tree Cover [PTC]: The soil
rich areas with soil depth of about 60–100 cm support the dwarf tree
cover on the plateaus. The vegetation is mainly composed of Memecylon umbellatum andAtalantia racemosa with infrequent
occurrence of Gnidia glauca and Actinodaphne angustifolia.
The average plant height is 3m. PTC is discontinuous and open canopy is
occupied by shrubs such as Maytenus senegalensis, Leea indicaand herbaceous vegetation. The
vegetation supports the population of diverse
herbaceous species mentioned in category 9 above. The trees support
luxuriant growth of orchids—Aerides maculosum, A. crispa,Dendrobium herbaceum, D. barbatulum and epiphytic ferns like Microsorium
membranaceum and Lepisorus nudus. On the ground the
community of Impatiens lawii, I. minor, I. oppositifolia, Pimpinella
adscendens, P. tomentosa and Pinda concanensis is
predominant.
11. Sacred groves [SG]: The DP has a
total of four sacred groves, three in the Ambe Village and one at Durgawadi. Soil depth is >100cm. These sacred groves have a typical
floristic composition (Image 8). The main sacred grove of Durgadevihas a semi-evergreen composition of Mangifera indica, Olea dioica,
Memecylon umbellatum, Syzygium cumini, Xantolis tomentosa, Atalantia racemosa, Actinodaphne angustifolia, Diospyros montana,
Terminalia bellirica and T. chebula having
infrequent elements such as Caryota urens and Allophylus cobbe. The understory of the
sacred grove is rich in Rubia cordifolia,
Sonerila scapigera, Habenaria foliosa and Cynoglossum amabile. Among the epiphytes orchids dominate with Hoya wightii and ferns like Lepisorus
nudus and Microsorium membranaceum.
At NP
there are two sacred grove, that have a community of Bambusa arundinacea,
Flacourtia indica, F. latifolia, Memecylon umbellatum,
Terminalia bellirica, T. chebula, T. elliptica, Maytenus senegalensis andHeterophragma quadriloculare. All the above microhabitats are recorded on DP, while on NP the boulders and seasonal ponds are
absent while soil rich areas are very less.
General vegetation on the
rock outcrops
General
vegetation shows a great variation especially during the monsoon months.
Different plant communities successively dominate in the monsoon season. During May–June, i.e., at the
onset of the monsoon bulbous and cormatous species Amorphophalus commutatus,
Drimia indica, Sauromatum venosum, Pancratium spp., and Crinum
latifolium flower first.
The
pre-monsoon vegetation is followed by the flush of ground orchids during
June–July including Habenaria grandifloriformis, H. rarifloraalong with Curculigo orchoides, Isoetes dixitei, Ophioglossum
graminium and O. nudicaule.
In
the month of July–August the entire RO becomes lush green with vegetative
growth of Senecio sp., Exacum sp., Smithia sp. and
grasses. During this period, Drosera
indica, Utricularia graminifolia, U. striatula andExacum lawii are found in the flowering state.
September–October
is the period of the greatest changes in the vegetation on the ROs. Smithiasp. along with Cythocline purpurea bloom first, which are then replaced
by Senecio sp. along with Pogostemon stellatus and Cythocline
lutea and then grasses follow the sequence of flowering. The abundance of Smithia purpureaand Cythocline lutea are unique features of the basaltic plateau, not
observed on lateritic plateaus.
Floristic composition
The
total area of both these ROs in the present study is very small but great floristic
diversity exists on them. The total species and infra specific phanerogamic taxa recorded are 443 on both
the plateaus belonging to 297 genera of 90 families (Table 1). The species and infraspecific taxa
consist of 161 monocots and 282 dicots. DP harbors 360 species and infraspecific taxa of 242 genera and 85
families, while NP has 249 species and infraspecific taxa of 203 genera and 74
families. A total of 1390 species
including cultivated ones have been reported in the Flora of Junnar Taluka (Rahangdale
2009). The area under study
represents almost 1/3rd the floristic diversity of Junnar by species
number, which indicates the species richness in this relatively small
geographic area.
A
total of 165 species and taxa of infraspecific rank, 148 genera and 68 families
are commonly shared by both the ROs. The common shared taxa constitute only 37.16% species and infraspecific
taxa, 49.83% genera and 75.56% families of the total taxa recorded (Table 2). This indicates that the ROs studied are
close to each other and share common taxa of higher ranks, i.e., families to
above 75%; but it is significant to note that the taxa below the genus level
are not commonly shared and difference with respect to them is about 63%. Therefore floristically, these two ROs
are very different and diverse from each other, indicating a high level of beta
diversity for these communities. Burke (2003) had suggested a high level of beta diversity for tropical
rock outcrops in general due to their isolation. In the present case these two locations
are not much isolated from surrounding low lying landscapes but topographically
and ecologically are diverse from each other. Classically, the more the distance is
between the sites, less the floristic affinity/similarity among them (Burke
2005b), which means there must be more similarities among adjacent sites. Plant communities are dynamic entities
and influenced by many seen and unseen factors such as environmental variables,
diversity of surrounding areas with respect to species, climate, topography,
connectivity and appropriate corridors for different communities between the
sites. Sites in the present study
are connected geographically but separated by a valley and one fortress between
them. The anthropogenic influence on NP is relatively more than on DP. This indicates that the area under study
is heterogeneous though adjacent to each other and must be considered as
floristically and ecologically separate entities.
The
present study brings a significant finding about the floristic composition
studies; that random sampling done during many of the studies or EIAs could be
misleading and may not provide complete floristic diversity as evident in this
case. Though these ROs are only
about 5–10.5 km apart by aerial distance and fall under the same
vegetation and climatic zones of the Western Ghats, the sharing of species is
only 37% and they differ significantly in 2/3 diversity of
the taxa. This is typical of
a hotspot like the Western Ghats, where geographical isolation can lead to
speciation and floristic diversification below genus level even at short
distances; this is supported by the findings of the present study. Hence, it can be concluded that
micro-level inventories of any area under study for any purpose must be taken
to reveal actual diversity and its significance.
Of
the total 443 taxa, 140 are Indian endemics belonging to 96 genera and 42
families; categorized under different threat categories (Ahmedullah & Nayar
1987; Nayar & Sastry 1987–89; Mishra & Singh 2001; Gaikwad &
Yadav 2004). The endemic taxa in
the study area comprises 31.53% of the total recorded species and infraspecific
taxa indicating existence of significant number of endemic taxa at these two
ROs. At DP the endemic taxa are,
133 (36.94%) belonging to 94 genera and 41 families out of 360 taxa recorded
from RO while, that from NP are 64 taxa (25.70% of 249) of 51 genera and 27
families. The rock outcrops and
isolated special habitats are places of origin and evolution of many narrow
endemic taxa throughout the world especially in Africa, America, Australia and
India (Watve 2008). It is also
evident from studies in the past that new taxa are being described continuously
from DP and its surrounding habitats by taxonomists (Rahangdale 2009).
The
10 most speciose families in the outcrops are Poaceae (88 spp.), Asteraceae (35
spp.), Fabaceae (28 spp.), Orchidaceae (18 spp.), Rubiaceae (14 spp.),
Cyperaceae and Lamiaceae (13 spp. each), Acanthaceae and Euphorbiaceae (11 spp.
each) and Asclepiadaceae (10 spp.). Comparison of the occurrence of most speciose families on both the ROs
shows that, the family Orchidaceae and Cyperaceae are poorly represented at NP
(5 spp. each). The members of
Orchidaceae inhabit diverse niches such as, epiphytic, understorey of forests
and open soil rich areas and sometimes saxicolousconditions, which are dominant at DP. The Cyperaceae are water loving plants and require
pools and water saturated soils. Such microhabitats are again predominant at DP and less at NP. These observations are in accordance
with the ecological and climatic conditions on both the ROs.
It
is evident from the list of species in Table 1 that, ROs have a higher number
of annual and ephemeral taxa comprising Poaceae, Asteraceae and Anthericaceae
members. These species generally
form ephemeral flush vegetation on the outcrop during pre and post monsoon
months: Smithia sp., Utricularia sp., Eriocaulon sp., Seneciosp., Habenaria sp. and grasses especially Arundinella metzii, A.
spicata, Arthraxon hispidus, A. jubatus, Dimeria hohenakeri, Eragrostis sp.
and Garnotia stricta. The
tree cover in the sacred grove is of normal height with big trees attaining a
height of about 20m in case of Mangifera indica, Diospyros montana and about 10–15 m for Memecylon
umbellatum. But the tree cover
on the plateau is of stunted growth with an average height of 3m for Memecylon
umbellatum, Gnidia glauca, Atalantia racemosa due
to shallow soil strata on it. The
average grass and herb height on the DP is 0.3m on the outcrop. The unique species of which only a
single specimen each was recorded is Salix tetrasperma and Careya
arborea at DP.
Conclusion
The study area comprised two rock outcrop areas on the high hill
escarpment of Western Ghats and an aerial distance between them ranging from
5–10.5 km. These ROs fall under
the same climatic zone and have a high level of floristic diversity within the
boundaries of these small ROs. In
such situations it is generally presumed that both the areas must have maximum
similarities with respect to ecology and floristic compositions. The present study washes out such
presumptions of similarity between the two areas, showing 63% differences
between floristic compositions of these two ROs. They also differ in having diverse
microhabitats on the plateaus. It
is also noteworthy that, the microhabitats on these ROs have specific
representatives of the flora. The
dissimilarity in the floristic composition is attributed to environmental
variables; especially altitude, topography,
connectivity and appropriate corridors for different communities between the
sites. On this basis DP and NP
should be considered as separate entities while considering further studies.
The
studied sites are geographically adjacent to each other, but at the same time
are different in floristic composition and microhabitat types. Therefore, the study emphasizes the need
of micro level inventories of smaller areas by taking intensive surveys for
documentation of different aspects of the abiotic and biotic diversity as well
as other environmental and anthropogenic variables. Care should be taken not to neglect a
small area/outcrop while designing random sampling models as the method
followed in most of the floristic, ecological and scientific studies and
Environmental Impact Assessments (EIAs) for setting up of major projects.
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