Coastal Dune Flora , Nallavadu Village , Puducherry , India

198 Check List | Volume 6 | Issue 2 | 2010 Introduction Coastal sand dunes (CSD) are natural structures which protect the coastal environment by absorbing energy from wind, tide and wave action. Despite geographical differences, sand dunes have been considered as a specific ecosystem due to several common environmental features. CSD constitute a variety of microenvironments due to substrate mobility and physical processes. Plants establishing on coastal sand dunes are subjected to several environmental fluctuations which affect their growth, survival and community structure. CSDs are dynamic but fragile buffer zones of sand and vegetation where the following three characteristics can be found: large quantities of sand; persistent wind capable of moving the sand; suitable locations for sand to accumulate. Sand dunes occur throughout the world, from coastal and lakeshore plains to arid desert regions. In addition to the remarkable structure and patterns of sand dunes, they also provide habitats for a variety of life which is marvelously adapted to this unique environment. CSD formations ultimately depend on embayment size and prevailing wind energy (Kumar et al.1993). Their heights differ in response to adequate sand supply, climate and local topographic features (Barbour et al. 1985). Plants on coastal dunes are specially adapted to withstand various environmental stresses which allow them to grow, establish and to trap sand in such harsh conditions of coastal zones, so they are mostly represented by herbs, shrubs, creepers or runners (Sridhar et al. 2007). The role of vegetation in dune formation is critical and is that of a wind trap, sand binder and dune stabilizer (Wagner 1964; Dahm et al. 2005). The foliage of dune plants breaks wind activity leading to less erosive activity on the lee side (Chapman 1976). Pioneer zone, intermediate zone and back zone / forest zone were recognized earlier in coastal dunes and later several workers found shore, fore dune, main dune with wind ward and lee ward slopes, wet dune slacks and back dunes with plateaus, holes Abstract: Coastal sand dunes (CSD) are sensitive and fragile ecosystems with variety of specific floral species. Though there are few confined studies on coastal sand dunes in temperate regions, the coastal dunes of tropics, especially the Indian coramandal coast has received scanty attention. Hence, a detailed vegetation survey of 10 belt transects (5 × 100m) along coastal dune in December 2008 was done. A total of 41 species belonging to 35 genera and 20 families were identified at different distances from the shoreline towards inland where various edaphic factors decline facilitating more floral colonization. Thus, the coastal dune systems are rich and diverse in their floral composition, even over a small area. CSD constitute a variety of habitats and gather vital ecological and economic importance. Such unique sensitive systems have to be protected from habitat degradation in order to protect their native diversity and ecological functioning. 1 Pondicherry University. Department of Ecology and Environmental Science. Puducherry, 605014, India 2 Auroville Herbarium, Shakti, Auroville, Tamilnadu 605 101, India * Coressponding author. E-mail: ecopadma@gmail.com K. Padmavathy 1*, G. Poyyamoli 1 and N. Balachandran 2 Coastal Dune Flora, Nallavadu Village, Puducherry, India


Introduction
Coastal sand dunes (CSD) are natural structures which protect the coastal environment by absorbing energy from wind, tide and wave action. Despite geographical differences, sand dunes have been considered as a specific ecosystem due to several common environmental features. CSD constitute a variety of microenvironments due to substrate mobility and physical processes. Plants establishing on coastal sand dunes are subjected to several environmental fluctuations which affect their growth, survival and community structure. CSDs are dynamic but fragile buffer zones of sand and vegetation where the following three characteristics can be found: large quantities of sand; persistent wind capable of moving the sand; suitable locations for sand to accumulate.
Sand dunes occur throughout the world, from coastal and lakeshore plains to arid desert regions. In addition to the remarkable structure and patterns of sand dunes, they also provide habitats for a variety of life which is marvelously adapted to this unique environment.
CSD formations ultimately depend on embayment size and prevailing wind energy (Kumar et al.1993). Their heights differ in response to adequate sand supply, climate and local topographic features (Barbour et al. 1985). Plants on coastal dunes are specially adapted to withstand various environmental stresses which allow them to grow, establish and to trap sand in such harsh conditions of coastal zones, so they are mostly represented by herbs, shrubs, creepers or runners (Sridhar et al. 2007).
The role of vegetation in dune formation is critical and is that of a wind trap, sand binder and dune stabilizer (Wagner 1964;Dahm et al. 2005). The foliage of dune plants breaks wind activity leading to less erosive activity on the lee side (Chapman 1976). Pioneer zone, intermediate zone and back zone / forest zone were recognized earlier in coastal dunes and later several workers found shore, fore dune, main dune with wind ward and lee ward slopes, wet dune slacks and back dunes with plateaus, holes Abstract: Coastal sand dunes (CSD) are sensitive and fragile ecosystems with variety of specific floral species. Though there are few confined studies on coastal sand dunes in temperate regions, the coastal dunes of tropics, especially the Indian coramandal coast has received scanty attention. Hence, a detailed vegetation survey of 10 belt transects (5 × 100m) along coastal dune in December 2008 was done. A total of 41 species belonging to 35 genera and 20 families were identified at different distances from the shoreline towards inland where various edaphic factors decline facilitating more floral colonization. Thus, the coastal dune systems are rich and diverse in their floral composition, even over a small area. CSD constitute a variety of habitats and gather vital ecological and economic importance. Such unique sensitive systems have to be protected from habitat degradation in order to protect their native diversity and ecological functioning.  (Koske and Gemma 1997;Sridhar and Bhagya 2007) as compared to studies on tropical coastal dunes (Kulkarni et al. 1997;Sridhar and Bhagya 2007).
The Ecological roles and functions of coastal dunes include: essential store of sediments, protecting the land behind them from storm erosion and potential sea level rise; filter for rainwater and groundwater and in some situations, provided aquatic habitats such as dune lakes; protection of islands from storm surges, hurricanes and erosion; trapping of the windblown sand and prevention of sand being blown further inland by the vegetation; habitats for specially adapted plants, birds, and animals -several of which are now rare or endangered; a range of unique landforms and processes which have intrinsic value and are of scientific interest; and nesting sites for sea turtles and birds.
This paper aims to generate a baseline data on coastal sand dune vegetation in the coramendal coast, with special reference to Puducherry coastline. Apparently, very few publications are available on the floral diversity of Indian sand dunes (Sridhar and Bhagya 2007).

Study site
Puducherry is located on the Coramandal coast between 11°52'56" and 11°59'53" N, 79°45'00" and 79°52'43" E. It is limited on the East by the Bay of Bengal and on the other three sides by the Cuddalore and Villupuram district of Tamil Nadu State. Nallavadu is a coastal village with sand dune coverage of about 6 km 2 extent, present at a distance of about 14 km towards south on the way to Cuddalore from the Puducherry main town (Figure 1).
The coastal border has a length of 22 km and a breadth ranging from four to six hundred meters. Superficially, the coast is flat and sandy. The coastal zone of Puducherry comprises newer and older dunes including saline areas of clayey texture. The study area experiences mean annual temperature of 30.0 °C and mean annual rainfall about 1,311-1,172 mm. The mean number of annual rainy days is 55, the mean monthly temperature ranges from 21.3°-30.2°C. The climate is tropical dissymmetric with the bulk of the rainfall during northeast monsoon October-December (Indian Meteorological Department -Chennai).

Data collection
A total of 10 belt transects of about 5 × 100m were laid randomly (wherever the vegetation cover was predominantly found) in 10 different regions at different distance gradients from shoreline till the lagoon boundary begins. Every plant species found along the 10 transects are recorded by observation while walking. Species are identified then and there. Species list is given in Table 1.
As several authors have pointed out in various parts of the world, many dune ecosystems support high plant richness and diversity values (e.g. Musila et al. 2001;Grootjans et al. 2004;Fontana 2005;Celsi and Monserrat 2008). In this sense, the present work also indicates that the study area preserves a rich flora with high number of native dune plants. Moreover, the different vegetation formations together with the dune field geomorphologic heterogeneity provide a wide variety of environmental conditions and habitat types that support a diverse native fauna like Crabs, Dune Lizards etc. The conservation of the native vegetation of the CSD is a priority to conserve the integrity of the natural communities in coastal regions.     Table 1. List of coastal dune flora from Nallavadu Village, Puducherry, India. * Native species; ** Invasive species.

Scientific name
Family