RASINGAM & PARATHASARATHY 89

Tropical Ecology 50 (1): 89-102, 2009 ISSN 0564-3295 © International Society for Tropical Ecology www.tropecol.com Tree species diversity and population structure across major forest formations and disturbance categories in Little Andaman Island,

L. RASINGAM & N. PARATHASARATHY*

Department of Ecology and Environmental Sciences, Pondicherry University, Puducherry 605 014, India

Abstract: The Andaman and , located in the Indian ocean, are among the biodiversity rich localities in India. Several islands in the southern part were severely affected by a recent cyclone ‘ tsunami ’. We compared patterns of tree species diversity and extent of damage by tsunami at eight sites in Little Andaman island within eight one ha plots. The study sites were located at relatively undisturbed and disturbed Evergreen (UE, DE), Semi- evergreen (US, DS), Deciduous (UD, DD) and Littoral (UL, DL) forests. A total of 4252 trees ≥30 cm girth at breast height, covering 186 species in 125 genera and 56 families were recorded within these sites. Of these, 23 species (12.4%) were endemic to these islands. Tree species richness was lowest (18 species ha -1) in the tsunami affected littoral forest and highest (84 species ha -1) in the UE. Tree density (79 to 935 trees ha -1) and basal area (41 to 59.10 m 2 ha -1) were greater in all the undisturbed forests as compared to disturbed forests. In all the eight sites, tree species richness and density decreased with increasing girth class and the stand structure of the forests displayed a reverse J-shaped curve, with the exception of the DL. Importance Value Index of three endemic species viz. , Manilkara littoralis, Canarium euphyllum and Terminalia bialata has been compared across the forest types and tsunami hit areas. Management implications are discussed.

Resumen: Las islas Andamán y Nicobar, localizadas en el Océano Índico, figuran entre las localidades ricas en biodiversidad de la India. Varias islas de su parte sur fueron afectadas severamente por un reciente tsunami. Comparamos patrones de diversidad de especies arbóreas y la magnitud del tsunami en ocho sitios en la isla Pequeña Andamán, en ocho parcelas de 1 ha. Los sitios de estudio se localizaron en bosques perennifolios (UE, DE), subperennifolios (US, DS), caducifolios (UD, DD) y de litoral, tanto relativamente no perturbados como perturbados. En estos sitios se registró un total de 4252 árboles ≥ 30 cm de perímetro a la altura del pecho, los cuales incluyeron 186 especies distribuidas en 125 géneros y 56 familias. De éstas, 23 especies (12.4%) resultaron ser endémicas de las isla. La riqueza de especies arbóreas tuvo su mínimo (18 especies ha -1) en el bosque de litoral afectado por el tsunami y su máximo (84 especies ha -1) en el UE. La densidad arbórea (79 a 935 árboles ha -1) y el área basal (41 a 59.10 m 2 ha -1) tuvieron valores mayores en los sitios no perturbados que en los bosques perturbados. En los ocho sitios, la riqueza y la densidad de especies arbóreas y su densidad decrecieron hacia las clases perimétricas mayores, y las estructuras de rodal de los bosques mostraron una curva en forma de J invertida, con excepción del de DL. Los Índices de Valor de Importancia de tres especies endémicas, Manilkara littoralis, Canarium euphyllum y Terminalia bialata , fueron comparados entre tipos de bosque y áreas afectadas por el tsunami. Se discuten las implicaciones para el manejo.

Resumo : As ilhas de Andaman e Nicobar, localizadas no oceano Índico, estão entre as

* Corresponding Author ; e-mail: [email protected]

90 TREE DIVERSITY IN LITTLE ANDAMAN ISLAND

localidades com maior riqueza em biodiversidade na Índia. Várias ilhas na parte sul foram severamente afectadas por um ciclone “ tsunami ” recente. Comparam-se os padrões de diversidade arbórea e a extensão dos estragos pelo tsunami em oito parcelas de um hectare localizadas na pequena ilha de Andaman. As estações de estudo foram localizadas em locais perturbados e não perturbados na floresta sempreverde (EU e DE), na floresta semi- sempreverde (US e DS), na floresta decídua (UD, DD) e Litoral (UL, DL). Um total de 4252 árvores com perímetro à altura do peito ≥ 30 cm, cobrindo 186 espécies em 125 géneros e 56 famílias foram registadas nestas estações. Destas, 23 espécies (12,4%) eram endémicas nestas ilhas. A riqueza nas espécies arbóreas era mais baixa (18 espécies ha -1) nas florestas litorâneas afectada pelo tsunami e mais alta (84 espécies ha -1) na EU. A densidade arbórea (79 a 935 arvores ha -1) e uma área basal (41 a 59,10 m 2 ha -1) foi maior em todas as florestas não disturbadas quando em comparação com as disturbadas. Em todas a oito estações, a riqueza arbórea e a densidade decresceu com o aumento da classe de perímetro e a estrutura da parcela das florestas apresentavam uma curva do tipo J invertido, com excepção da DL. O índice do Valor de Importância de três espécies endémicas viz. Manilkara littoralis , Canarium euphyllum e Terminalia bialata foi comparado ao longo dos tipos florestais e nas áreas atingidas pelo tsunami. As implicações para a gestão são discutidas.

Key words: Conservation, human disturbance, Little Andaman, stand structure, selective logging, tree diversity.

Introduction insular flora is, therefore, very vital to understand the patterns of speciation, extent of diversity Insular biology has always drawn the across the small islands and to draw long term attention of a number of ecologists (e.g., plans for their conservation and management. Balakrishnan & Rao 1983; Renvoize 1979). It has The flora of A&N islands is insufficiently contributed much to our knowledge of speciation, known as compared to other parts of India and adaptability, invasion, colonization and evolution. nearly 20% of the area remains unexplored. Islands tend to have higher percentage of Earlier studies have mainly focused on the endangered species than other areas due to small qualitative assessment of the forest wealth and geographical area available for each species. only few efforts have been made to quantify the Presently, a vast majority of the island biota are vegetation structure and composition (Padalia et severely threatened due to incessant al. 2004; Tripathi et al . 2004). This study was anthropogenic pressures (Bramwell 1979). Rapid undertaken, to determine tree species diversity loss of tropical forests is recognized as one of the and stand structure in relatively undisturbed and serious environmental and economic problems all disturbed evergreen, semi-evergreen, deciduous over the world (Hare et al . 1997). A number of and littoral forests in Little Andaman. Major conservation biologists have raised concern over findings of the study with reference to floristic loss of biodiversity in tropical forests owing to the composition, species diversity and population deforestation and imprudent infra-structure structure of tree layer across disturbed and development in the name of modernization. It is undisturbed categories of these forests are doubtful whether modern man will arrive even at discussed. the stage of alpha taxonomy of some of the insular floras before they vanish in catastrophic events. Material and methods This situation may hold true for islands such as Andaman and Nicobar (A&N), where nearly 17% Study area of the are endemic (Reddy et al. 2004). The study was carried out in Little Andaman, Information on the distribution and abundance of which forms a part of A&N group of islands, India RASINGAM & PARATHASARATHY 91

Fig. 1. Map showing the location of Little Andaman Island, east of Indian mainland and eight study sites in the island. The complete names of study sites are mentioned in the text.

(10° 30’ - 10° 54' N latitudes and 92° 20’ - 92° 35' E and are mostly dominated by endemic tree longitudes; Fig. 1). It is the third largest island in Manilkara littoralis , in association with A&N and covers an area of 733 km 2. The terrain is Terminalia catappa, Gyrocarpus americanus, more or less flat with undulations in the northern Guettarda speciosa and Pongamia pinnata. The parts. The central and western portions are hilly deciduous forests are located beyond littoral and the highest elevation is about 210 m asl. forests and extend up to 400-600 m inland, Perennial streams are numerous which run both characterized by Terminalia bialata, T. procera, T. in the east-west and west-east directions. citrina, Tetrameles nudiflora and Pterocymbium Geologically, the island comprises thick tinctorium . The semi-evergreen forests, distributed sedimentary deposits of Eocene period deposited in the south-eastern part of the island harbour on pre-Tertiary fine grey sandstone, shales and silt dominant trees such as Oroxylum indicum, stones. Coral reef formations are found in the Canarium euphyllum, Neonauclea gageana and south-western portion. The soils are loose in Tetrameles nudiflora . The evergreen forests are texture and low in water holding capacity. The distributed from shore up to 210 m in the interior climate is warm and the temperature ranges from side of the island and are mostly dominated by 22° - 32°C. The island receives rains from southwest Pometia pinnata, spp. and Euodia and northeast monsoon (April-December). The glabra . All forest types were subjected to some mean annual rainfall ranges from 3000-3500 mm level of selective felling from 1983-2001. Timber and humidity is 85-90% throughout the year. extraction was banned by the order of Supreme The major vegetation types in the island are Court of India in 2002. Andaman Tropical Evergreen, Andaman Semi- evergreen, Andaman Moist Deciduous and Littoral Field methods forests (Champion & Seth 1968). The littoral Eight 1 ha plots were established, one each in forests extend up to 150-200 m from the seashore undisturbed (site code prefixed with ‘U’) and 92 TREE DIVERSITY IN LITTLE ANDAMAN ISLAND disturbed (site code prefixed with ‘D’) evergreen disturbance was ranked as none (0), very low (1), (UE, DE), semi-evergreen (US, DS), deciduous low (2), medium (3) and high (4) (Table 1). (UD, DD) and littoral (UL, DL) forests. Plots DE Each of the hectare plot was divided into 10 x and UE are located ~ 8 km northwest from Hut 10 m quadrats for systematic enumeration. All Bay, the capital town of Little Andaman island. trees ≥30 cm girth at breast height (gbh, 1.3 m) The inter-distance between these plots was ~ 1 were enumerated. For multi-stemmed trees the km. Semi-evergreen forest plots (US, DS) are bole girth was measured separately, basal area situated in southwestern part of Hut Bay. Plot DS calculated and summed following Mueller-Dombois is 2 km away from site US and is located near a & Ellenberg (1974). The voucher specimens were metal quarry and subjected to disturbance by the collected for each species to confirm their identity. quarry workers and domestic animals. Plot DD is Identification of specimens was carried out in the located close to human settlements and disturbed herbarium of Botanical Survey of India, Port Blair by tourism activity, cattle grazing and illegal (PBL) and Department of Ecology and timber extraction for household materials. The two Environmental Sciences, Puducherry, using the littoral forest plots were selected based on the Forest Flora of Andaman Islands (Parkinson 1923) destruction of tsunami and human disturbance. and the Flora of Andaman & Nicobar Islands Site DL was totally damaged by tsunami in (Hajra et al. 1999). The voucher specimens are December 2004, and four months later A&N Forest deposited in the Department of Ecology and Plantation and Development Corporation Environmental Sciences, Pondicherry University. extracted all the dead trees. Plot UL is located 10 km away from DL, where the sea level increased Data analysis up to 5 m during the tsunami , but did not damage Species diversity indices such as Shannon – the arborescent flora of the site. The altitude of all Wiener index and Simpson’s index were calculated the forest plots ranged from sea shore up to 70 m following Magurran (1988). Relative density, above sea level and all the sites experience various relative dominance, relative frequency and levels of human disturbances. Site disturbance Importance Value Index (IVI), a measure of scores were arrived based on the observation relative prominence of various species in the forest through questionnaire survey made during the were calculated following Cottam & Curtis (1956). field work by inquiring from the local people. The The species-area curve was plotted by sequential qualitative assessment of various types of

Table 1. Site disturbance scores (rank: 0 – none; 1 – rare; 2 – low; 3 – medium; 4 – high) of undisturbed and disturbed evergreen (UE, DE), semi-evergreen (US, DS), deciduous (UD, DD) and littoral forests (UL, DL) of Little Andaman Island, India .

Evergreen Semi- Deciduous Littoral forest Disturbance forest evergreen forest forest UE DE US DS UD DD UL DL Plantation 0 0 0 2 0 0 0 2 Tourism activity 0 0 0 0 1 2 2 0 Illegal timber extraction 1 3 1 3 3 4 2 4 Removal of dead and fallen wood 1 3 0 3 2 4 1 4 Past logging 4 4 3 3 3 3 2 4 Livestock grazing 1 3 0 4 2 4 2 4 Presence of exotics 0 0 0 1 1 4 0 4 Foot paths 1 3 0 2 2 3 1 4 Pipelines 0 0 0 0 1 0 0 0 Medicinal plant collection 1 2 0 2 1 1 2 3 Tsunami-affected 0 0 0 0 0 0 2 4 Quarry 0 0 0 2 0 0 0 0 Total score 9 18 4 22 16 25 14 33

RASINGAM & PARATHASARATHY 93 arrangement of 10 x 100 m sub-plots. The patterns multi-stemmed individuals was higher in UL of tree species composition were examined in the forest (31), followed by UD forest (17) and lowest eight sites using non-metric multidimensional in DL (1). Of the total 186 tree species and 44 scaling (NMS) ordination. The ordination was species (23%) were represented by just one performed based on the data of species richness individual. The species-area curves for all eight and disturbance scores, using PC-ORD package. sites did not reach an asymptote at the hectare To examine the species similarity among the ten plot scale. The species increment was steep in sites an agglomerative hierarchical clustering was forests UE (30) and US (22) at 0.1 ha level and low performed, using Sorensen’s index (Magurran in the DL (4) and DD (9), and 1 to 15 species were 1988). regularly added up at every 0.1 ha increment. Thus, 1 ha sample plots were insufficient to Results capture the species richness of these forests (Fig. 2). Species richness and diversity A total of 186 species of trees ≥ 30 cm gbh belonging to 125 genera and 56 families were recorded in all the plots of undisturbed and disturbed evergreen, semi-evergreen, deciduous and littoral forests (Table 2). Of these, two species could be identified only to genus level and 12 species remained unidentified. The species richness was highest in UE forest (84) followed by US forests (83), DE (73), UD (58), UL (43), DS (43), DD (41) and DL forest (18). Sites UE and US harboured higher diversity of genera and family among all the forests. The species diversity indices varied greatly across eight study sites as influenced by the disturbance level. Highest value of Shannon index (3.6) was obtained for US forest. DL forest yielded low score of Shannon index (1.6) Fig. 2. Species-area curves of tree species in the and high Simpson index (0.42). The number of eight study sites .

Table 2. Summary of tree diversity inventory ( ≥ 30 cm gbh) in eight 1 ha plots, distributed respectively one each in undisturbed and disturbed evergreen (UE, DE), semi-evergreen (US, DS), deciduous (UD, DD) and littoral (UL, DL) forests of Little Andaman Island, India. (Total number of species, genera and families in all the forests are 186, 125 and 56 respectively) .

Evergreen forest Semi-evergreen forest Deciduous forest Littoral forest Variables UE DE US DS UD DD UL DL Species richness 84 73 83 43 58 41 43 18 No. of genera 63 58 64 39 50 39 38 18 No. of families 35 33 36 28 29 25 26 15 Diversity indices (i) Shannon 3.4 3.5 3.6 2.7 3.1 1.7 2.7 1.6 (ii) Simpson 0.06 0.05 0.05 0.13 0.07 0.44 0.12 0.42 Density (stems ha -1) 488 410 935 543 519 623 655 79 Basal area (m 2 ha -1) 47.7 41.0 55.3 44.7 57.5 49.4 59.7 51.1 No. of multi-stemmed individuals 2 3 17 7 5 9 31 1 Maximum tree gbh (cm) 412 421 593 325 487 352 541 610 Average tree gbh (cm) 91.2 91.7 71.5 89.9 92.6 86.5 80.7 250.2

94 TREE DIVERSITY IN LITTLE ANDAMAN ISLAND

Table 3. Density of all tree species ≥30 cm gbh encountered in the eight study plots (stems ha -1) of Little Andaman forests (Abbreviations as in Table 1).

Density Species (and family) UE DE US DS UD DD UL DL Total

Terminalia bialata Stued. (Combretaceae) 4 2 7 14 47 409 11 0 494 Tetrameles nudiflora R.Br.ex Benn.(Datiscaceae) - 20 31 166 90 10 - - 317 Pterocymbium tinctorium (Blanco) Merr. (Sterculiaceae) 2 14 122 35 23 17 8 1 222 Gyrocarpus americanus Jacq. (Hernandiaceae) ------182 1 183 Bombax insigne Wall. (Bombacaceae) 4 2 46 29 27 9 34 3 154 Knema andamanica (Warb.) de Willde (Myristicaceae) 44 56 35 1 - - 2 - 138 Manilkara littoralis (Kurz) Dubard (Sapotaceae) ------78 51 129 Pometia pinnata J.R.Forst & G.Forst (Sapindaceae) 48 59 10 2 10 - - - 129 Terminalia procera Roxb. (Combretaceae) - 4 43 23 40 11 - - 121 Canarium euphyllum Kurz (Burseraceae) 2 8 97 4 2 - 2 - 115 Dipterocarpus alatus Roxb. () 58 11 8 5 21 - - - 103 Dipterocarpus gracilis Bl. (Dipterocarpaceae) 30 1 2 5 44 7 - - 89 Guettarda speciosa L. (Rubiaceae) ------88 - 88 Lagerstromia hypoleuca Kurz (Lythraceae) - - 6 61 12 3 - - 82 Terminalia citriana King (Combretaceae) 2 - 5 10 52 5 - - 74

Neolamarkia cadamba (Roxb.) Bosser (Rubiaceae) - - - 42 23 6 - - 71 Neonauclea gageana (King) Merr. (Rubiaceae) - - 30 38 - - - - 68

Celtis philippensis Blanco var. wightii (Planch.) Scop. (Ulmaceae) 5 15 30 10 5 1 - - 66 Drypetes longifolia (Bl.) Pax. & Hoffm. (Euphorbiaceae) 24 15 14 - 3 3 3 - 62 Planchonia valida (Bl.) Bl. (Lecythidaceae) 4 7 27 17 2 3 1 - 61 Oroxylum indicum (L.) Kurz (Bignoniaceae) 2 4 46 1 5 - - - 58 Dipterocarpus grandiflorus (Blanco) Blanco (Dipterocarpaceae) 31 3 4 15 - - - - 53 Chukrasia tabularis Andr. (Meliaceae) 1 - - - - 42 - - 43 Dracontomelon dao (Blanco) Merr.& Rolfe (Anacardiaceae) 2 11 18 8 3 1 - - 43 Terminalia catappa L. (Combretaceae) ------40 1 41 Semecarpus prainii King (Anacardiaceae) - - 30 - 1 - 9 - 40 Ficus hispida L.f. (Moraceae) 3 6 12 3 7 - 5 - 36 Ryparosa javanica (Bl.)Kurz ex Koord.& Val. (Flacourtiaceae) 4 1 27 3 1 - - - 36 Ficus racemosa Jack (Moraceae) - - 33 - - - - - 33 Streblus asper Lour. (Moraceae) - - 12 3 3 1 14 - 33 Garuga pinnata Roxb. (Burseraceae) - - 26 - 2 1 - 1 30 Aglaia spectabilis Bl. (Meliaceae) 11 13 - 5 - - - - 29

Morinda citrifolia L. var. bracteata Hook.f. (Rubiaceae) - - - - - 1 26 2 29 Sterculia rubiginosa Vent. var. glabrescens King (Sterculiaceae) 1 1 - - - - 21 4 27

Elaeocarpus rugosus Roxb. (Elaeocarpaceae) 15 11 ------26 Mallotus peltatus (Gies) Muell.-Arg. (Euphorbiaceae) 2 3 21 - - - - - 26 Dysoxylum arborescens (Bl.) Miq. (Meliaceae) 7 13 2 2 1 - - - 25 Pterospermum acerifolium (L.) Willd. (Sterculiaceae) 1 3 16 3 2 - - - 25 Aglaia argentea Bl. (Meliaceae) 2 8 1 - - 10 3 - 24 Canarium denticulatum Bl. ssp. denticulatum (Burseraceae) 14 1 3 - 6 - - - 24 Baccaurea ramiflora Lour. (Euphorbiaceae) 14 3 4 2 - - - - 23 Alphonsea ventricosa Hook.f & Thoms. (Annonaceae) - - - - - 22 - - 22 Others 151 115 167 36 87 61 128 15 760 Total 488 410 935 543 519 623 655 79 4252

RASINGAM & PARATHASARATHY 95

Richness of major plant families total basal area of DE forest was low (40.9 m 2 ha -1) as compared to UL forest (59.6 m 2 ha -1). Manilkara A total of 56 families were recorded within the littoralis , the predominant tree in littoral forests study plots (total area of 8 hectares). UL and DL, contributed 75.9 m 2 to basal area. The Euphorbiaceae formed the most speciose family other dominant trees in the study sites that with 11 genera and 17 species (9.14%). However, contributed to greater basal area include Moraceae (4 genera, 12 species, 6.5%), Rubiaceae Terminalia bialata (39.4 m 2), Pterocymbium (9 genera, 11 species, 5.9%), Meliaceae (6 genera, tinctorium (24.2 m 2), Tetrameles nudiflora (22.3 11 species, 5.9%), Anacardiaceae (7 genera, 8 m2) and Pometia pinnata (21.2 m 2). The stem species, 4.3%) and Annonaceae (6 genera, 6 species density of different tree species varied and 3.22%) were the other well represented considerably across sites (Table 4). Terminalia families. Apocynaceae, Bignoniaceae, Fabaceae, bialata had highest number of stems (494 stems) Hernandiaceae, Lechythidaceae, Malvaceae, followed by Tetrameles nudiflora (317 stems). 44 Pandanaceae, Ulmaceae and Verbenaceae had two species were represented by just one individual. species each (9.67%), while 26 families (46.4%) had Two species viz. Pterocymbium tinctorium and single species in all the forests. Five families Bombax insigne were distributed in all the forests Combretaceae (730 individuals, 17.23%), with 222 (5.2%) and 154 (3.6%) stems respectively. Datiscaceae (317, 7.48%), Sterculiaceae (291, Dipterocarpus gracilis (89), Celtis philippensis var. 6.87%), Dipterocarpaceae (287, 6.77%) and wightii (66), Dracontomelon dao (43) and Rubiaceae (283, 6.67 %) were abundant in terms of Diploknema butyracea (17) were encountered at all density, contributing ca. 45 % of the forest stand. the sites except littoral forest. The rare tree Eighteen families were represented by one Alphonsea ventricosa was encountered only in DD individual each (Table 3). with 22 stems (0.5%). The evergreen and semi- evergreen forests had 51 tree species common Tree density, basal area and dominance between them and 47 species were common The stand density was highest (935 ha -1) in US between semi-evergreen and moist deciduous forest and lowest (79 ha -1) in the tsunami affected forests. Neonauclea gageana was recorded only in forest i.e., DL and moderate in other forests. The semi-evergreen forest. It is a rare endemic species

Table 4. Contribution of families to tree genera, species, density (stems ha -1), basal area (BA m 2 ha -1) and family importance value (FIV) for the total eight study plots .

Family Genera Species Density BA FIV Combretaceae 1 4 730 61.9 34.9 Datiscaceae 1 1 317 22.4 13.6 Sterculiaceae 4 6 291 28.0 17.1 Dipterocarpaceae 2 6 287 27.5 16.9 Rubiaceae 9 11 283 22.2 18.2 Hernandiaceae 2 2 187 9.5 7.9 Sapotaceae 5 6 181 81.8 28.0 Euphorbiaceae 11 17 177 6.2 14.9 Burseraceae 2 3 169 16.8 9.8 Myristicaceae 3 4 163 7.2 7.8 Sapindaceae 4 4 162 23.2 11.8 Meliaceae 6 11 160 6.6 11.3 Bombacaceae 1 1 154 12.9 7.4 Moraceae 4 12 154 13.0 13.3 Anacardiaceae 7 8 111 11.2 9.7 Others 63 78 726 49.75 71.4

96 TREE DIVERSITY IN LITTLE ANDAMAN ISLAND reported only from middle A&N islands so far stand structure, except for the largest size class (Hajra et al. 1999). Its occurrence in the present (> 210 cm) in forests DL and UL (Fig. 3). The locality is a range extension. It was found that this smallest girth class of 30-60 cm contributed 44.20% species had higher density in disturbed plot DS (38 trees ha -1) and lower in undisturbed plot US (30 trees ha -1). Two species Dendrocnide sinuata (Urticaceae) and Elaeocarpus serratus (Elaeocarpaceae) recorded within UE and DE are mainly known from the forests of Western Ghats and other forest areas of northeast India (Rao 1986). Hence they form new additions to the flora of A&N Islands. As expected, tree density decreased with increasing girth class, exhibiting a reverse J-shaped

Fig. 3. Size-class distribution of tree density in the Fig. 4. Size-class distribution of basal area in the undisturbed and disturbed evergreen, semi-evergreen, undisturbed and disturbed evergreen, semi-evergreen, deciduous and littoral forest plots. deciduous and littoral forest plots. RASINGAM & PARATHASARATHY 97 of the stems and this proportion decreased with moderate species richness and human increasing size class. Tree density in smaller girth interference. Site DL placed in the bottom left of class (30-60 cm) was greater in UL (55.9%) and US the ordination due to the poor species richness and (53.26%) forests and lowest in DL (6.32%) forest. the high disturbances such as human interference Density of trees in higher girth class (>210 cm) was and the recent tsunami effects. higher in DL (50 trees ha -1), followed by UL (43 trees ha -1) and least in US forest (11 trees ha -1). The Discussion basal area distribution is typically J-shaped in the study sites, with the exception of sites US, DS and Tree species richness at defined study sites DD (Fig 4). Density of various size classes is given and in minimum diameter class gives a reliable in Table 5. The species richness in smaller girth instrument to indicate diversity level of a forest class (30-60 cm gbh) was maximum in forest US site (Wattenberg & Breckle 1995). Plant species (59) and lowest in DL forest (4). diversity is mostly influenced by human impacts Manilkara littoralis, a species of littoral forest and natural disturbances. Clear differences in had highest IVI value (217.5) at disturbed site stand structure and species diversity among (DL) while it had rather low IVI (72.2) at UL. undisturbed and disturbed sites of evergreen, Tetrameles nudiflora, an emergent tree, had semi-evergreen, deciduous and littoral forests were higher IVI (69.64) at DS than UD (45.8). discernible in this study. The stand density of Terminalia bialata (170.4) at DD forest, Pometia Little Andaman forests (mean 531 trees ha -1, range pinnata (50.4) at DE, Dipterocarpus gracilis (40.6) 79-935) is lower as compared to densities reported at UE and Canarium euphyllum (39) at US had from Saddle Peak (459 - 2681 trees ha -1) of North higher IVI values (Fig. 5). Of all the forests, DD Andaman Islands and Great Andaman groups (946 was unique as it was dominated by one species i.e., - 1137 trees ha -1, Padalia et al. 2004). However, the Terminalia bialata (Combretaceae) which tree density is comparable with other tropical contributed 65.7% of the stems (409), 170.4 to the forests e.g., Kalakad, Western Ghats (575 - 855 total IVI and 68.9% (34 m 2 ha -1) to basal area. trees ha -1, Parthasarathy 1999), Costa Rica (448 - Most of the individuals of this species were 617 trees ha -1, Heaney & Proctor 1990), Brazil (420 invariably represented by large trees. - 777 trees ha -1, Campbell et al. 1992), Sulawesi (408 trees ha -1, Whitmore & Sidiyasa 1986) and Species richness and intensity of disturbance Danum Valley, Sabah (431 trees ha -1, Kamarudin 1986). The tree density was low in DL forest (79 The non-metric multidimensional scaling trees ha -1), wherein maximum destruction was (NMS) ordination, based on the species richness, caused by tsunami. All trees in the lower girth and disturbance score is shown in Fig. 6. The class died due to the high salinity and tidal force. analysis revealed that the sites UE and US were In the deciduous forests, the stand density of UD distinctly placed on the positive coordinates of the (519 trees ha -1) was less than that of DD forest NMS axis, mainly because of high species richness (623 trees ha -1), but the basal area was and low level of human disturbance. Sites UL, UD, compensated by the mature and large trees. DD, DS and DE placed in the middle due to the

Table 5. Species richness of trees by girth class in eight study sites of Little Andaman Island .

Girth class Species richness (cm) UE DE US DS UD DD UL DL 30-60 57 54 59 34 49 38 48 4 61-90 36 29 33 24 28 21 26 7 91-120 28 22 24 20 21 7 17 8 121-150 24 17 14 18 14 7 9 4 151-180 12 11 8 10 8 6 11 4 181-210 11 11 7 6 13 3 4 0 >210 16 13 7 7 14 8 6 2

98 TREE DIVERSITY IN LITTLE ANDAMAN ISLAND

Fig. 5. Important value indices of top five tree species in UE, DE, US, DS, UD, DD, UL and DL forests. (rD-relative density, rF-relative frequency and rBA-relative dominance). Six- letter codes are used for species names, drawing three from generic name and three from species name, for full names of species refer Table 3. RASINGAM & PARATHASARATHY 99

The species richness of the present study Nicobar Islands and well represented in all girth forests (range 18 to 84 species ha -1) ranks low to classes. Ho et al . (1987) found that in moist forests moderately high when compared to other forests of of Jengka, Malaysia, Euphorbiaceae formed bulk Andaman islands (25 - 61 species ha -1 in Saddle of tree population (24.6%). Melastomataceae (22%), peak of North Andaman Islands, Tripathi et al. Oleaceae (26.6%) and Lauraceae (28%) formed 2004 and 58 - 59 species ha -1 in Great Andaman bulk of the tree population in Kolli hills, groups, Padalia et al. 2004), and those of Western Shervarayan hills of Eastern Ghats and Kalakad Ghats in south India (80 - 85 species ha -1 in Forest respectively (Parthasarathy 1999). In Kalakad-Mundanthurai Tiger Reserve, Parthasarathy African forest, Gilbertiodendron dewevrei 1999; 64 - 82 trees ha -1 in Sengaltheri-Kakachi, (Caesalpiniaceae) achieved dominance by Parthasarathy 2001; and 52 - 79 species ha -1 in inhibiting the growth of other understory plants by Varagalaiar, Ayyappan & Parthasarathy 2001). various ways (Torti et al . 2001). Monodominant The tree species richness in neotropical forests forests were dominated by different tree species in showed a wide variation, ranging from 20 species each and every geographical area. Celaenodendron ha -1 in Varzea forest of Rio Xingu, Brazil mexicanum in Mexico (Martijena & Bullock 1994), (Campbell et al. 1992) to 307 species ha -1 in the Nothofagus aequilateralis (Fagaceae) in New Amazonian Equator (Valencia et al. 1994). In the Caledonia (Read et al . 1995), Peltogyne gracilipes old world tropics species richness ranged from 26 (Caesalpiniaceae) in Maraca Island, Brazil species ha -1 in Kolli hills of India (Chittibabu & (Nascimento et al. 1997) and Memecylon Parthasarathy 2000) to 231 species ha -1 in Brunei umbellatum (Melastomataceae) in Pudukottai, Darussalam of (Poulsen et al. India (Mani & Parthasarathy 2005). At the family 1996). level, Leguminosae dominated the neotropics and The basal area of trees in Little Andaman Africa (Richards 1996), Dipterocarpaceae in forests (mean 50.8 m 2 ha -1, range 41 - 59.1) is much Malaysia (Manokaran et al . 1991; Whitmore 1984) higher than mean pantropical average of 32 m 2 and Melastomataceae in Pudukottai, India (Mani ha -1 (Dawkins 1959) and slightly higher than the & Parthasarathy 2005). value reported from Great Andamans (28 - 44 m 2 The most speciose families were ha -1, Padalia et al. 2004), Malaysia (24.2 m 2 ha -1, Euphorbiaceae (17 species), Moraceae (12), Poore 1968) and Brazilian Amazon forests (27.6 - 32 m 2 ha -1, Campbell et al. 1986). The values are more or less comparable with those reported from Saddle Peak forests of North Andaman islands (48 - 75 m 2 ha -1, Tripathi et al. 2004), Kalakad, Western Ghats (53.3 - 94.6 m 2 ha -1, Parthasarathy et al. 1992), New Caledonia (47 - 49.5 m 2 ha -1, Jeffre & Veillon 1990) forests and less than that of Monteverde of Costa Rica (62 m 2 ha -1, Nadkarni et al. 1995) and Kalakad forests of southern Western Ghats (61.7 - 94.6 m 2 ha -1, Parthasarathy 1999). The greatest basal area of 59.1 m 2 ha -1 obtained in UL forest was largely due to the contribution from the endemic tree Manilkara littoralis , which alone scored 47.8% (28.2 m 2 ha -1) of basal area. Lower value of basal area at DE (41 m 2 ha -1), is due to selective logging of timber species during recent past. In the present study, disturbed moist deciduous forests (DD) had the dominance of

Terminalia bialata (17.22% of all the trees), followed by Dastiscaceae (7.48% individuals). The Fig. 6. Non-metric multidimensional scaling (NMS) former is an endemic species to Andaman & ordination of the eight sites based on species richness and disturbance scores in the study forests. 100 TREE DIVERSITY IN LITTLE ANDAMAN ISLAND

Rubiaceae (11) and Meliaceae (11) in Little million years (Halle 1990). The conversion of Andaman. Kadavul & Parthasarathy (1999) also tropical rain forests into various land use systems reported that the family Euphorbiaceae (8) as the created so many impacts on island flora. As the most speciose family followed by Rubiaceae (5) in study sites are composed of high percentage of the semi-evergreen forests of Shervarayan hills of species rarity (34%) and endemic species (12%) Eastern Ghats. Moraceae (10), Lauraceae (8) and they increase our concern for species conservation Rubiaceae (8) in the Kolli hills (Chittibabu & of insular flora. A few decades before the eastern Parthasarathy 2000) and Lauraceae (14), parts of the Little Andaman was deforested for Euphorbiaceae (10) and Myrtaceae (10) in the rehabilitation of people and Kalakad Tiger Reserve, Western Ghats repatriates from Sri Lanka and under (Parthasarathy 1999). various rehabilitation schemes. Simultaneously The species rarity of the present study is 34%, the Andaman and Nicobar Islands Forest which is very close to the forests of Plantation and Development Corporation Limited Kuzhanthaikuppam of Coromandel Coast (31%, also cleared ~1593 hectare forest area in the Parthasarathy & Karthikeyan 1997), Malaysia northeastern parts for oil palm cultivation. In (38%, Poore 1968) and Barro Colorado island of December 2004 the east coast of the island was Panama (40%, Thorington et al. 1982); but less affected by the tsunami and damaged portions of than those of other tropical forests, such as Java littoral forest. Notably, the disturbed littoral forest (50%, Meijer 1959), New Guinea (55.4%, Paijmans recorded two and a half times lower tree diversity 1970) and Jengka forest of Malaysia (59%, Ho et and ten times lower tree density as compared to al. 1987). the undisturbed littoral forest. Later the Tree size class distribution can be used as Government of India allotted the land for indicators of changes in population structure and construction permanent shelters for tsunami- species composition (Newbery & Gartlan 1996). affected people in the inland forest. These Distribution curves that drop exponentially with activities exert more pressure on the island flora. increasing gbh (reverse J-shaped) are Thus in situ conservation of the insular flora of the characteristic for species with continuous Little Andaman Island which harbours moderate regeneration (Khamyong et al. 2004). Curves plant diversity but rich in local endemic species is showing little or no drop in the lower gbh classes emphasized because the endemics occur in small indicate the requirement is unsustainable and the population and in scattered localities. We long term change in species composition of the recommend long-term monitoring of the species- plant community studied is to be expected (Hall & rich evergreen forests and the littoral forest which Bawa 1993). Most species in the study plots harbours the endemic tree Manilkara littorallis for followed reverse J-shaped distribution with biodiversity changes and forest dynamics. greater number of individuals in small size classes. Such a trend has been reported from the forests of Acknowledgements Great Andaman groups (Padalia et al. 2004), Saddle peak of North Andaman islands (Tripathi We thank the Director, Botanical Survey of et al. 2004), Malaysia (Poore 1968), India, Kolkata and Deputy Director, Botanical (Khamyong et al. 2004), Sungei Menyala in Survey of India, Andaman & Nicobar Circle, Port Malaysia (Manokaran & Kochummen 1987) and in Blairs, for allowing us to consult the herbaria and Monteverde of Costa Rica (Nadkarni et al. 1995). officials of Andaman & Nicobar Islands Forest The lack of J-shaped structure for basal area in Plantation and Development Corporation Limited, the plot DL indicates past disturbance by the Port Blair, for field support. tsunami . References Conclusions Ayyappan, N. & N. Parthasarathy. 2001. Patterns of There is no doubt that primary rain forests are tree diversity within a large-scale permanent plot of vanishing and that we are now living through the tropical evergreen forest. Western Ghats, India. last decades of vegetation dating back as far as 30 Ecotropica 5: 197-211. RASINGAM & PARATHASARATHY 101

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