RASINGAM & PARATHASARATHY
Tropical Ecology 50(1): 89-102, 2009
© International Society for Tropical Ecology
www.tropecol.com
89
ISSN 0564-3295
Tree species diversity and population structure across major forest
formations and disturbance categories in Little Andaman Island, India
L. RASINGAM & N. PARATHASARATHY*
Department of Ecology and Environmental Sciences, Pondicherry University,
Puducherry 605 014, India
Abstract: The Andaman and Nicobar islands, 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), Semievergreen (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 m2 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 m2 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 semisempreverde (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 m2 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 biology has always drawn the
attention of a number of ecologists (e.g.,
Balakrishnan & Rao 1983; Renvoize 1979). It has
contributed much to our knowledge of speciation,
adaptability, invasion, colonization and evolution.
Islands tend to have higher percentage of
endangered species than other areas due to small
geographical area available for each species.
Presently, a vast majority of the island biota are
severely
threatened
due
to
incessant
anthropogenic pressures (Bramwell 1979). Rapid
loss of tropical forests is recognized as one of the
serious environmental and economic problems all
over the world (Hare et al. 1997). A number of
conservation biologists have raised concern over
loss of biodiversity in tropical forests owing to the
deforestation and imprudent infra-structure
development in the name of modernization. It is
doubtful whether modern man will arrive even at
the stage of alpha taxonomy of some of the insular
floras before they vanish in catastrophic events.
This situation may hold true for islands such as
Andaman and Nicobar (A&N), where nearly 17%
of the plants are endemic (Reddy et al. 2004).
Information on the distribution and abundance of
insular flora is, therefore, very vital to understand
the patterns of speciation, extent of plant diversity
across the small islands and to draw long term
plans for their conservation and management.
The flora of A&N islands is insufficiently
known as compared to other parts of India and
nearly 20% of the area remains unexplored.
Earlier studies have mainly focused on the
qualitative assessment of the forest wealth and
only few efforts have been made to quantify the
vegetation structure and composition (Padalia et
al. 2004; Tripathi et al. 2004). This study was
undertaken, to determine tree species diversity
and stand structure in relatively undisturbed and
disturbed evergreen, semi-evergreen, deciduous
and littoral forests in Little Andaman. Major
findings of the study with reference to floristic
composition, species diversity and population
structure of tree layer across disturbed and
undisturbed categories of these forests are
discussed.
Material and methods
Study area
The study was carried out in Little Andaman,
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
longitudes; Fig. 1). It is the third largest island in
A&N and covers an area of 733 km2. The terrain is
more or less flat with undulations in the northern
parts. The central and western portions are hilly
and the highest elevation is about 210 m asl.
Perennial streams are numerous which run both
in the east-west and west-east directions.
Geologically,
the
island
comprises
thick
sedimentary deposits of Eocene period deposited
on pre-Tertiary fine grey sandstone, shales and silt
stones. Coral reef formations are found in the
south-western portion. The soils are loose in
texture and low in water holding capacity. The
climate is warm and the temperature ranges from
22° - 32°C. The island receives rains from southwest
and northeast monsoon (April-December). The
mean annual rainfall ranges from 3000-3500 mm
and humidity is 85-90% throughout the year.
The major vegetation types in the island are
Andaman Tropical Evergreen, Andaman Semievergreen, Andaman Moist Deciduous and Littoral
forests (Champion & Seth 1968). The littoral
forests extend up to 150-200 m from the seashore
and are mostly dominated by endemic tree
Manilkara
littoralis,
in
association
with
Terminalia catappa, Gyrocarpus americanus,
Guettarda speciosa and Pongamia pinnata. The
deciduous forests are located beyond littoral
forests and extend up to 400-600 m inland,
characterized by Terminalia bialata, T. procera, T.
citrina, Tetrameles nudiflora and Pterocymbium
tinctorium. The semi-evergreen forests, distributed
in the south-eastern part of the island harbour
dominant trees such as Oroxylum indicum,
Canarium euphyllum, Neonauclea gageana and
Tetrameles nudiflora. The evergreen forests are
distributed from shore up to 210 m in the interior
side of the island and are mostly dominated by
Pometia pinnata, Dipterocarpus spp. and Euodia
glabra. All forest types were subjected to some
level of selective felling from 1983-2001. Timber
extraction was banned by the order of Supreme
Court of India in 2002.
Field methods
Eight 1 ha plots were established, one each in
undisturbed (site code prefixed with ‘U’) and
92
TREE DIVERSITY IN LITTLE ANDAMAN ISLAND
disturbed (site code prefixed with ‘D’) evergreen
(UE, DE), semi-evergreen (US, DS), deciduous
(UD, DD) and littoral (UL, DL) forests. Plots DE
and UE are located ~ 8 km northwest from Hut
Bay, the capital town of Little Andaman island.
The inter-distance between these plots was ~ 1
km. Semi-evergreen forest plots (US, DS) are
situated in southwestern part of Hut Bay. Plot DS
is 2 km away from site US and is located near a
metal quarry and subjected to disturbance by the
quarry workers and domestic animals. Plot DD is
located close to human settlements and disturbed
by tourism activity, cattle grazing and illegal
timber extraction for household materials. The two
littoral forest plots were selected based on the
destruction of tsunami and human disturbance.
Site DL was totally damaged by tsunami in
December 2004, and four months later A&N Forest
Plantation
and
Development
Corporation
extracted all the dead trees. Plot UL is located 10
km away from DL, where the sea level increased
up to 5 m during the tsunami, but did not damage
the arborescent flora of the site. The altitude of all
the forest plots ranged from sea shore up to 70 m
above sea level and all the sites experience various
levels of human disturbances. Site disturbance
scores were arrived based on the observation
through questionnaire survey made during the
field work by inquiring from the local people. The
qualitative assessment of various types of
disturbance was ranked as none (0), very low (1),
low (2), medium (3) and high (4) (Table 1).
Each of the hectare plot was divided into 10 x
10 m quadrats for systematic enumeration. All
trees ≥30 cm girth at breast height (gbh, 1.3 m)
were enumerated. For multi-stemmed trees the
bole girth was measured separately, basal area
calculated and summed following Mueller-Dombois
& Ellenberg (1974). The voucher specimens were
collected for each species to confirm their identity.
Identification of specimens was carried out in the
herbarium of Botanical Survey of India, Port Blair
(PBL)
and Department of
Ecology
and
Environmental Sciences, Puducherry, using the
Forest Flora of Andaman Islands (Parkinson 1923)
and the Flora of Andaman & Nicobar Islands
(Hajra et al. 1999). The voucher specimens are
deposited in the Department of Ecology and
Environmental Sciences, Pondicherry University.
Data analysis
Species diversity indices such as Shannon –
Wiener index and Simpson’s index were calculated
following Magurran (1988). Relative density,
relative dominance, relative frequency and
Importance Value Index (IVI), a measure of
relative prominence of various species in the forest
were calculated following Cottam & Curtis (1956).
The species-area curve was plotted by sequential
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
forest
Disturbance
Plantation
Tourism activity
Illegal timber extraction
Removal of dead and fallen wood
Past logging
Livestock grazing
Presence of exotics
Foot paths
Pipelines
Medicinal plant collection
Tsunami-affected
Quarry
Total score
Semievergreen forest
Deciduous
forest
Littoral forest
UE
DE
US
DS
UD
DD
UL
DL
0
0
1
1
4
1
0
1
0
1
0
0
9
0
0
3
3
4
3
0
3
0
2
0
0
18
0
0
1
0
3
0
0
0
0
0
0
0
4
2
0
3
3
3
4
1
2
0
2
0
2
22
0
1
3
2
3
2
1
2
1
1
0
0
16
0
2
4
4
3
4
4
3
0
1
0
0
25
0
2
2
1
2
2
0
1
0
2
2
0
14
2
0
4
4
4
4
4
4
0
3
4
0
33
RASINGAM & PARATHASARATHY
arrangement of 10 x 100 m sub-plots. The patterns
of tree species composition were examined in the
eight sites using non-metric multidimensional
scaling (NMS) ordination. The ordination was
performed based on the data of species richness
and disturbance scores, using PC-ORD package.
To examine the species similarity among the ten
sites an agglomerative hierarchical clustering was
performed, using Sorensen’s index (Magurran
1988).
Results
93
multi-stemmed individuals was higher in UL
forest (31), followed by UD forest (17) and lowest
in DL (1). Of the total 186 tree species and 44
species (23%) were represented by just one
individual. The species-area curves for all eight
sites did not reach an asymptote at the hectare
plot scale. The species increment was steep in
forests UE (30) and US (22) at 0.1 ha level and low
in the DL (4) and DD (9), and 1 to 15 species were
regularly added up at every 0.1 ha increment.
Thus, 1 ha sample plots were insufficient to
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)
and high Simpson index (0.42). The number of
Fig. 2. Species-area curves of tree species in the
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).
Variables
Species richness
No. of genera
No. of families
Diversity indices
(i) Shannon
(ii) Simpson
Density (stems ha-1)
Basal area (m2 ha-1)
No. of multi-stemmed individuals
Maximum tree gbh (cm)
Average tree gbh (cm)
Evergreen forest
Semi-evergreen forest
Deciduous forest
Littoral forest
UE
DE
US
DS
UD
DD
UL
DL
84
63
35
73
58
33
83
64
36
43
39
28
58
50
29
41
39
25
43
38
26
18
18
15
3.4
0.06
488
47.7
2
412
91.2
3.5
0.05
410
41.0
3
421
91.7
3.6
0.05
935
55.3
17
593
71.5
2.7
0.13
543
44.7
7
325
89.9
3.1
0.07
519
57.5
5
487
92.6
1.7
0.44
623
49.4
9
352
86.5
2.7
0.12
655
59.7
31
541
80.7
1.6
0.42
79
51.1
1
610
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).
Species (and family)
Density
UE DE
US
DS
UD DD UL DL Total
7
14
47
409
11
0
494
31 166
122 35
46 29
35
1
10
2
43 23
97
4
8
5
2
5
6
61
5
10
42
30 38
30 10
14
27 17
46
1
4
15
18
8
30
12
3
27
3
33
12
3
26
5
90
23
27
10
40
2
21
44
12
52
23
5
3
2
5
3
1
7
1
3
2
-
10
17
9
11
7
3
5
6
1
3
3
42
1
1
1
-
8
1
182 1
34 3
2
78 51
2
88
3
1
40 1
9
5
14
1
-
317
222
183
154
138
129
129
121
115
103
89
88
82
74
71
68
66
62
61
58
53
43
43
41
40
36
36
33
33
30
29
1
2
6
87
1
10
22
61
26 2
21 4
3
128 15
29
27
26
26
25
25
24
24
23
22
760
Terminalia bialata Stued. (Combretaceae)
4
2
Tetrameles nudiflora R.Br.ex Benn.(Datiscaceae)
Pterocymbium tinctorium (Blanco) Merr. (Sterculiaceae)
Gyrocarpus americanus Jacq. (Hernandiaceae)
Bombax insigne Wall. (Bombacaceae)
Knema andamanica (Warb.) de Willde (Myristicaceae)
Manilkara littoralis (Kurz) Dubard (Sapotaceae)
Pometia pinnata J.R.Forst & G.Forst (Sapindaceae)
Terminalia procera Roxb. (Combretaceae)
Canarium euphyllum Kurz (Burseraceae)
Dipterocarpus alatus Roxb. (Dipterocarpaceae)
Dipterocarpus gracilis Bl. (Dipterocarpaceae)
Guettarda speciosa L. (Rubiaceae)
Lagerstromia hypoleuca Kurz (Lythraceae)
Terminalia citriana King (Combretaceae)
Neolamarkia cadamba (Roxb.) Bosser (Rubiaceae)
Neonauclea gageana (King) Merr. (Rubiaceae)
Celtis philippensis Blanco var. wightii (Planch.) Scop. (Ulmaceae)
Drypetes longifolia (Bl.) Pax. & Hoffm. (Euphorbiaceae)
Planchonia valida (Bl.) Bl. (Lecythidaceae)
Oroxylum indicum (L.) Kurz (Bignoniaceae)
Dipterocarpus grandiflorus (Blanco) Blanco (Dipterocarpaceae)
Chukrasia tabularis Andr. (Meliaceae)
Dracontomelon dao (Blanco) Merr.& Rolfe (Anacardiaceae)
Terminalia catappa L. (Combretaceae)
Semecarpus prainii King (Anacardiaceae)
Ficus hispida L.f. (Moraceae)
Ryparosa javanica (Bl.)Kurz ex Koord.& Val. (Flacourtiaceae)
Ficus racemosa Jack (Moraceae)
Streblus asper Lour. (Moraceae)
Garuga pinnata Roxb. (Burseraceae)
Aglaia spectabilis Bl. (Meliaceae)
2
4
44
48
2
58
30
2
5
24
4
2
31
1
2
3
4
11
20
14
2
56
59
4
8
11
1
15
15
7
4
3
11
6
1
13
Morinda citrifolia L. var. bracteata Hook.f. (Rubiaceae)
Sterculia rubiginosa Vent. var. glabrescens King (Sterculiaceae)
Elaeocarpus rugosus Roxb. (Elaeocarpaceae)
Mallotus peltatus (Gies) Muell.-Arg. (Euphorbiaceae)
Dysoxylum arborescens (Bl.) Miq. (Meliaceae)
Pterospermum acerifolium (L.) Willd. (Sterculiaceae)
Aglaia argentea Bl. (Meliaceae)
Canarium denticulatum Bl. ssp.denticulatum (Burseraceae)
Baccaurea ramiflora Lour. (Euphorbiaceae)
Alphonsea ventricosa Hook.f & Thoms. (Annonaceae)
Others
1
1
15 11
2
3
21
7
13
2
1
3
16
2
8
1
14
1
3
14
3
4
151 115 167
Total
488 410 935 543 519 623 655 79 4252
2
3
2
36
RASINGAM & PARATHASARATHY
Richness of major plant families
A total of 56 families were recorded within the
study plots (total area of 8 hectares).
Euphorbiaceae formed the most speciose family
with 11 genera and 17 species (9.14%). However,
Moraceae (4 genera, 12 species, 6.5%), Rubiaceae
(9 genera, 11 species, 5.9%), Meliaceae (6 genera,
11 species, 5.9%), Anacardiaceae (7 genera, 8
species, 4.3%) and Annonaceae (6 genera, 6 species
and 3.22%) were the other well represented
families. Apocynaceae, Bignoniaceae, Fabaceae,
Hernandiaceae,
Lechythidaceae,
Malvaceae,
Pandanaceae, Ulmaceae and Verbenaceae had two
species each (9.67%), while 26 families (46.4%) had
single species in all the forests. Five families
Combretaceae
(730
individuals,
17.23%),
Datiscaceae (317, 7.48%), Sterculiaceae (291,
6.87%), Dipterocarpaceae (287, 6.77%) and
Rubiaceae (283, 6.67 %) were abundant in terms of
density, contributing ca. 45 % of the forest stand.
Eighteen families were represented by one
individual each (Table 3).
Tree density, basal area and dominance
The stand density was highest (935 ha-1) in US
forest and lowest (79 ha-1) in the tsunami affected
forest i.e., DL and moderate in other forests. The
95
total basal area of DE forest was low (40.9 m2 ha-1)
as compared to UL forest (59.6 m2 ha-1). Manilkara
littoralis, the predominant tree in littoral forests
UL and DL, contributed 75.9 m2 to basal area. The
other dominant trees in the study sites that
contributed to greater basal area include
Terminalia bialata (39.4 m2), Pterocymbium
tinctorium (24.2 m2), Tetrameles nudiflora (22.3
m2) and Pometia pinnata (21.2 m2). The stem
density of different
tree species varied
considerably across sites (Table 4). Terminalia
bialata had highest number of stems (494 stems)
followed by Tetrameles nudiflora (317 stems). 44
species were represented by just one individual.
Two species viz. Pterocymbium tinctorium and
Bombax insigne were distributed in all the forests
with 222 (5.2%) and 154 (3.6%) stems respectively.
Dipterocarpus gracilis (89), Celtis philippensis var.
wightii (66), Dracontomelon dao (43) and
Diploknema butyracea (17) were encountered at all
the sites except littoral forest. The rare tree
Alphonsea ventricosa was encountered only in DD
with 22 stems (0.5%). The evergreen and semievergreen forests had 51 tree species common
between them and 47 species were common
between semi-evergreen and moist deciduous
forests. Neonauclea gageana was recorded only in
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 m2 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
(Hajra et al. 1999). Its occurrence in the present
locality is a range extension. It was found that this
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
stand structure, except for the largest size class
(> 210 cm) in forests DL and UL (Fig. 3). The
smallest girth class of 30-60 cm contributed 44.20%
Fig. 3. Size-class distribution of tree density in the
undisturbed and disturbed evergreen, semi-evergreen,
deciduous and littoral forest plots.
Fig. 4. Size-class distribution of basal area in the
undisturbed and disturbed evergreen, semi-evergreen,
deciduous and littoral forest plots.
RASINGAM & PARATHASARATHY
of the stems and this proportion decreased with
increasing size class. Tree density in smaller girth
class (30-60 cm) was greater in UL (55.9%) and US
(53.26%) forests and lowest in DL (6.32%) forest.
Density of trees in higher girth class (>210 cm) was
higher in DL (50 trees ha-1), followed by UL (43
trees ha-1) and least in US forest (11 trees ha-1). The
basal area distribution is typically J-shaped in the
study sites, with the exception of sites US, DS and
DD (Fig 4). Density of various size classes is given
in Table 5. The species richness in smaller girth
class (30-60 cm gbh) was maximum in forest US
(59) and lowest in DL forest (4).
Manilkara littoralis, a species of littoral forest
had highest IVI value (217.5) at disturbed site
(DL) while it had rather low IVI (72.2) at UL.
Tetrameles nudiflora, an emergent tree, had
higher IVI (69.64) at DS than UD (45.8).
Terminalia bialata (170.4) at DD forest, Pometia
pinnata (50.4) at DE, Dipterocarpus gracilis (40.6)
at UE and Canarium euphyllum (39) at US had
higher IVI values (Fig. 5). Of all the forests, DD
was unique as it was dominated by one species i.e.,
Terminalia
bialata
(Combretaceae)
which
contributed 65.7% of the stems (409), 170.4 to the
total IVI and 68.9% (34 m2 ha-1) to basal area.
Most of the individuals of this species were
invariably represented by large trees.
Species richness and intensity of disturbance
The non-metric multidimensional scaling
(NMS) ordination, based on the species richness,
and disturbance score is shown in Fig. 6. The
analysis revealed that the sites UE and US were
distinctly placed on the positive coordinates of the
NMS axis, mainly because of high species richness
and low level of human disturbance. Sites UL, UD,
DD, DS and DE placed in the middle due to the
Table 5.
Girth class
(cm)
30-60
97
moderate
species
richness
and
human
interference. Site DL placed in the bottom left of
the ordination due to the poor species richness and
the high disturbances such as human interference
and the recent tsunami effects.
Discussion
Tree species richness at defined study sites
and in minimum diameter class gives a reliable
instrument to indicate diversity level of a forest
site (Wattenberg & Breckle 1995). Plant species
diversity is mostly influenced by human impacts
and natural disturbances. Clear differences in
stand structure and species diversity among
undisturbed and disturbed sites of evergreen,
semi-evergreen, deciduous and littoral forests were
discernible in this study. The stand density of
Little Andaman forests (mean 531 trees ha-1, range
79-935) is lower as compared to densities reported
from Saddle Peak (459 - 2681 trees ha-1) of North
Andaman Islands and Great Andaman groups (946
- 1137 trees ha-1, Padalia et al. 2004). However, the
tree density is comparable with other tropical
forests e.g., Kalakad, Western Ghats (575 - 855
trees ha-1, Parthasarathy 1999), Costa Rica (448 617 trees ha-1, Heaney & Proctor 1990), Brazil (420
- 777 trees ha-1, Campbell et al. 1992), Sulawesi
(408 trees ha-1, Whitmore & Sidiyasa 1986) and
Danum Valley, Sabah (431 trees ha-1, Kamarudin
1986). The tree density was low in DL forest (79
trees ha-1), wherein maximum destruction was
caused by tsunami. All trees in the lower girth
class died due to the high salinity and tidal force.
In the deciduous forests, the stand density of UD
(519 trees ha-1) was less than that of DD forest
(623 trees ha-1), but the basal area was
compensated by the mature and large trees.
Species richness of trees by girth class in eight study sites of Little Andaman Island.
Species richness
UE
DE
US
DS
UD
DD
UL
DL
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
The species richness of the present study
forests (range 18 to 84 species ha-1) ranks low to
moderately high when compared to other forests of
Andaman islands (25 - 61 species ha-1 in Saddle
peak of North Andaman Islands, Tripathi et al.
2004 and 58 - 59 species ha-1 in Great Andaman
groups, Padalia et al. 2004), and those of Western
Ghats in south India (80 - 85 species ha-1 in
Kalakad-Mundanthurai Tiger Reserve, Parthasarathy
1999; 64 - 82 trees ha-1 in Sengaltheri-Kakachi,
Parthasarathy 2001; and 52 - 79 species ha-1 in
Varagalaiar, Ayyappan & Parthasarathy 2001).
The tree species richness in neotropical forests
showed a wide variation, ranging from 20 species
ha-1 in Varzea forest of Rio Xingu, Brazil
(Campbell et al. 1992) to 307 species ha-1 in the
Amazonian Equator (Valencia et al. 1994). In the
old world tropics species richness ranged from 26
species ha-1 in Kolli hills of India (Chittibabu &
Parthasarathy 2000) to 231 species ha-1 in Brunei
Darussalam of Southeast Asia (Poulsen et al.
1996).
The basal area of trees in Little Andaman
forests (mean 50.8 m2 ha-1, range 41 - 59.1) is much
higher than mean pantropical average of 32 m2
ha-1 (Dawkins 1959) and slightly higher than the
value reported from Great Andamans (28 - 44 m2
ha-1, Padalia et al. 2004), Malaysia (24.2 m2 ha-1,
Poore 1968) and Brazilian Amazon forests (27.6 32 m2 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 m2 ha-1, Tripathi et al. 2004), Kalakad,
Western Ghats (53.3 - 94.6 m2 ha-1, Parthasarathy
et al. 1992), New Caledonia (47 - 49.5 m2 ha-1,
Jeffre & Veillon 1990) forests and less than that of
Monteverde of Costa Rica (62 m2 ha-1, Nadkarni et
al. 1995) and Kalakad forests of southern Western
Ghats (61.7 - 94.6 m2 ha-1, Parthasarathy 1999).
The greatest basal area of 59.1 m2 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 m2 ha-1) of basal area. Lower
value of basal area at DE (41 m2 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
former is an endemic species to Andaman &
99
Nicobar Islands and well represented in all girth
classes. Ho et al. (1987) found that in moist forests
of Jengka, Malaysia, Euphorbiaceae formed bulk
of tree population (24.6%). Melastomataceae (22%),
Oleaceae (26.6%) and Lauraceae (28%) formed
bulk of the tree population in Kolli hills,
Shervarayan hills of Eastern Ghats and Kalakad
Forest respectively (Parthasarathy 1999). In
African
forest,
Gilbertiodendron
dewevrei
(Caesalpiniaceae)
achieved
dominance
by
inhibiting the growth of other understory plants by
various ways (Torti et al. 2001). Monodominant
forests were dominated by different tree species in
each and every geographical area. Celaenodendron
mexicanum in Mexico (Martijena & Bullock 1994),
Nothofagus aequilateralis (Fagaceae) in New
Caledonia (Read et al. 1995), Peltogyne gracilipes
(Caesalpiniaceae) in Maraca Island, Brazil
(Nascimento et al. 1997) and Memecylon
umbellatum (Melastomataceae) in Pudukottai,
India (Mani & Parthasarathy 2005). At the family
level, Leguminosae dominated the neotropics and
Africa (Richards 1996), Dipterocarpaceae in
Malaysia (Manokaran et al. 1991; Whitmore 1984)
and Melastomataceae in Pudukottai, India (Mani
& Parthasarathy 2005).
The
most
speciose
families
were
Euphorbiaceae (17 species), Moraceae (12),
Fig. 6. Non-metric multidimensional scaling (NMS)
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
Andaman. Kadavul & Parthasarathy (1999) also
reported that the family Euphorbiaceae (8) as the
most speciose family followed by Rubiaceae (5) in
the semi-evergreen forests of Shervarayan hills of
Eastern Ghats. Moraceae (10), Lauraceae (8) and
Rubiaceae (8) in the Kolli hills (Chittibabu &
Parthasarathy 2000) and Lauraceae (14),
Euphorbiaceae (10) and Myrtaceae (10) in the
Kalakad
Tiger
Reserve,
Western
Ghats
(Parthasarathy 1999).
The species rarity of the present study is 34%,
which is very close to the forests of
Kuzhanthaikuppam of Coromandel Coast (31%,
Parthasarathy & Karthikeyan 1997), Malaysia
(38%, Poore 1968) and Barro Colorado island of
Panama (40%, Thorington et al. 1982); but less
than those of other tropical forests, such as Java
(50%, Meijer 1959), New Guinea (55.4%, Paijmans
1970) and Jengka forest of Malaysia (59%, Ho et
al. 1987).
Tree size class distribution can be used as
indicators of changes in population structure and
species composition (Newbery & Gartlan 1996).
Distribution curves that drop exponentially with
increasing
gbh
(reverse
J-shaped)
are
characteristic for species with continuous
regeneration (Khamyong et al. 2004). Curves
showing little or no drop in the lower gbh classes
indicate the requirement is unsustainable and the
long term change in species composition of the
plant community studied is to be expected (Hall &
Bawa 1993). Most species in the study plots
followed reverse J-shaped distribution with
greater number of individuals in small size classes.
Such a trend has been reported from the forests of
Great Andaman groups (Padalia et al. 2004),
Saddle peak of North Andaman islands (Tripathi
et al. 2004), Malaysia (Poore 1968), Thailand
(Khamyong et al. 2004), Sungei Menyala in
Malaysia (Manokaran & Kochummen 1987) and in
Monteverde of Costa Rica (Nadkarni et al. 1995).
The lack of J-shaped structure for basal area in
the plot DL indicates past disturbance by the
tsunami.
million years (Halle 1990). The conversion of
tropical rain forests into various land use systems
created so many impacts on island flora. As the
study sites are composed of high percentage of
species rarity (34%) and endemic species (12%)
they increase our concern for species conservation
of insular flora. A few decades before the eastern
parts of the Little Andaman was deforested for
rehabilitation
of
Bangladesh
people
and
repatriates from Sri Lanka and Myanmar under
various rehabilitation schemes. Simultaneously
the Andaman and Nicobar Islands Forest
Plantation and Development Corporation Limited
also cleared ~1593 hectare forest area in the
northeastern parts for oil palm cultivation. In
December 2004 the east coast of the island was
affected by the tsunami and damaged portions of
littoral forest. Notably, the disturbed littoral forest
recorded two and a half times lower tree diversity
and ten times lower tree density as compared to
the undisturbed littoral forest. Later the
Government of India allotted the land for
construction permanent shelters for tsunamiaffected people in the inland forest. These
activities exert more pressure on the island flora.
Thus in situ conservation of the insular flora of the
Little Andaman Island which harbours moderate
plant diversity but rich in local endemic species is
emphasized because the endemics occur in small
population and in scattered localities. We
recommend long-term monitoring of the speciesrich evergreen forests and the littoral forest which
harbours the endemic tree Manilkara littorallis for
biodiversity changes and forest dynamics.
Acknowledgements
We thank the Director, Botanical Survey of
India, Kolkata and Deputy Director, Botanical
Survey of India, Andaman & Nicobar Circle, Port
Blairs, for allowing us to consult the herbaria and
officials of Andaman & Nicobar Islands Forest
Plantation and Development Corporation Limited,
Port Blair, for field support.
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