Angiosperms of North Andaman , Andaman and Nicobar Islands , India

The present paper focus on the phytosociological survey carried out in North Andaman part of Andaman and Nicobar islands and enlists the plant species with their habit and forest types they belong. The study area showed five important forest types viz., evergreen, semi-evergreen, moist deciduous, mangroves and littoral. The survey in these islands encountered 241 tree species, 119 climbers, 45 shrubs and 49 herbs from 62, 41, 24 and 23 families respectively from a sample of 203 quadrats of 0.1 ha size. Euphorbiaceae is found to be dominant family represented by 34 species belong to 21 genera. The result of the survey indicates the potential species richness of the study site that encompasses a vivid biodiversity. It also provides a data base on North Andaman plant species which can be utilized in the context of species conservation and future inventories. Introduction Tropical rain forests are one of the nature’s most complicated landscapes and deserve special attention as they harbor high species richness and diversity and function as invaluable gene banks. Within Indian sub continent these forest are found in the Andaman and Nicobar islands (A&N), the Western Ghats and the greater Assam region in the North east. A&N islands popularly known as Bay islands, located between 10° 13' and 13° 30' N latitudes and 92°15' and 93°10' E longitude, stretching over 800 km in Bay of Bengal comprise 572 islands, reefs and rocks (Figure 1). These islands are one of the national wealthy forest regions enriched with variety of flora, structuring from tall canopy trees to the under ground herb forming distinct layers or synusiae. The flora shows affinities towards the Burmese and Malaysian type (Hajra et al. 1999) and the isolated island ecosystem nature favored these forest in maintaining high endemism, rarity and flora distinct from the neighbouring land. Due to the inaccessibility in approaching these islands as well as due to the presence of primitive tribes much study was not carried out in these areas related to phytodiversity. However in the recent past considerable floristic and ecological studies (Balakrishnan and Rao 1983; Ananda and Chakraborti 1987; Dagar 1989; Pradeep 1998; Hitendra et al. 2004; Roy et al. 2005; Prasad et al. 2007; 2008; Reddy et al. 2008) Check List 5(2): 254–269, 2009. ISSN: 1809-127X


Introduction
Tropical rain forests are one of the nature's most complicated landscapes and deserve special attention as they harbor high species richness and diversity and function as invaluable gene banks.Within Indian sub continent these forest are found in the Andaman and Nicobar islands (A&N), the Western Ghats and the greater Assam region in the North east.A&N islands popularly known as Bay islands, located between 10° 13' and 13° 30' N latitudes and 92°15' and 93°10' E longitude, stretching over 800 km in Bay of Bengal comprise 572 islands, reefs and rocks (Figure 1).These islands are one of the national wealthy forest regions enriched with variety of flora, structuring from tall canopy trees to the under ground herb forming distinct layers or synusiae.The flora shows affinities towards the Burmese and Malaysian type (Hajra et al. 1999) and the isolated island ecosystem nature favored these forest in maintaining high endemism, rarity and flora distinct from the neighbouring land.Due to the inaccessibility in approaching these islands as well as due to the presence of primitive tribes much study was not carried out in these areas related to phytodiversity.
However in the recent past considerable floristic and ecological studies (Balakrishnan and Rao 1983;Ananda and Chakraborti 1987;Dagar 1989;Pradeep 1998;Hitendra et al. 2004;Roy et al. 2005;Prasad et al. 2007;2008;Reddy et al. 2008) were initiated to reveal the species richness and diversity of these islands.Under the Jaivigyan science and technology mission project a study was carried out in these emerald islands, entitled "Biodiversity characterization at landscape level in Andaman and Nicobar islands using remote sensing and GIS".The primary objective of the project is to prepare a vegetation cover type and density map of the A&N islands along with detailed assessment of biodiversity and its distribution at community level.The present paper focus on the phytosociological survey carried out in North Andaman Islands of A&N and enlists the plant species encountered during the study belonging to various habit and forest types.

Study area
North Andaman is the northern most islands and form one of the major divisions of Andaman region (Figure 1).The showers from the dual monsoons keep the forest in wet evergreen condition and house different species belonging to trees, shrubs, herbs, climbers, etc. Champion and Seth (1968) classified vegetation of North Andaman into Andaman tropical evergreen, Andaman semi evergreen, Andaman moist deciduous, Mangroves and Littoral forest (Figure 2).The study of Prasad et al. (2007;2008) concluded these islands as repository of high species richness and phytodiversity.A considerable extent of islands species richness is also contributed by the Saddle peak national park with an altitude of 732 m above m.s. l. (Reddy et al. 2008).

Data collection
As the part of project, a field inventory was carried out to collect phytosociological data within different forest types of North Andaman Islands.Keeping in view of time and accessibility to the plot, quadrats were sampled covering all the vegetation types in different disturbance regimes and micro climatic conditions.The size of the quadrat was determined using species area curve and finally 0.1 ha size was considered as optimum unit for sampling.About 203 quadrats of 0.1 ha size were sampled distributed in different vegetation types viz., evergreen (62 plots), semi evergreen (58), moist deciduous (75), mangrove (5) and littoral (3).Within each plot all the life forms encountered were listed.Species were identified with the help of field botanist, literature and from the authentic specimens of Botanical survey of India, Port Blair, South Andaman.

Results and discussion
Ecosystem integrity of an island ecosystem depends on plant cover which inturn influenced by the type of vegetation and its stability.The North Andaman forest showed typical tropical forest physiognomy represented by top, middle and lower canopy of trees entangled with lianas and climbers along with under ground shrub and herb strata.The floristic survey in these islands encountered about 241 tree species, 119 climbers, 45 shrubs and 49 herbs from 62, 41, 24 and 23 families respectively (Appendix 1).Euphorbiaceae is found to be species rich family with 34 species represented by 21 genera.Out of 34 species, 30 belong to tree storey, 3 to shrubs and one climber.Rubiaceae (22 species and 18 genera) and Annonaceae (18 species and 12 genera) were observed to be the dominating family next to Euphorbiaceae.The result of the survey indicates the potential species richness of the study site that encompasses a vivid biodiversity with in an area of 1458 km 2 .This can be attributed, mainly to the existence of a broad range of ecological habitats and high diverse set of ecosystems varying from sandy beaches / littoral to dense humid evergreen forest.
The present survey provides a data base on North Andaman plant species which can be utilized in the context of species conservation and future inventories.Conservation of rare, endangered and endemic species is necessary for preservation of species diversity.Currently forests of these islands are also prone to various anthropogenic activities resulting in the fragmentation of forest into patches.Fragmentation process shows effect on species, especially on unique, rare and endemic, threatening their survival and resulting in the extinction of species (Prasad et al. 2009).Apart from anthropogenic interferences forest loss also occurs because of natural causes like soil erosion and displacement of organic matter due to high tides and much more by hazards like tsunami (Roy and Krishnan 2005).Continuous field studies that updates the data base to know the status of species and conservation policies and programmes to certain extent may help in understanding and protecting the unique ecosystem of these islands.

Figure 1 .
Figure 1.Location map of North Andaman Islands.

Figure 2 .
Figure 2. Forest types of North Andaman Islands.