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. Rahangdale holds 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 Syzygium species.  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 reticosa amidst 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 and Pancratium 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 and Atalantia 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 indica and 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 Durgadevi has 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 and Heterophragma 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. rariflora along 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 and Exacum lawii are found in the flowering state.

September–October is the period of the greatest changes in the vegetation on the ROs. Smithia sp. 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 purpurea and 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 saxicolous conditions, 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., Senecio sp., 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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