Floral composition and vegetation structure of Nara Mangrove Reserve, Kadolkele, Sri Lanka and guidelines for conservation

Abstract

This study was conducted to understand vegetation structure and floral composition to develop suitable protocols for the conservation of NARA mangrove reserve, Kadolkele which is 10 ha in extent and located on the right bank of the northern part of Negombo Estuary (7011’ N, 79050’ E). The ecological value of mangroves is the least concern of people in the surrounding area and this mangrove patch is frequently under threat due to high land demand and its high economic value. Therefore,it is essential to understand ecological and other relevant features in order to determine strategies to conserve this mangrove forest. Knowledge of the vegetation structure and plant composition of this mangrove reserve is an important prerequisite, not only to understand all the aspects of structure and function of this reserve, but also to formulate guidelines for their conservation and management.

Vegetation data were collected in 100 m2 (10 m x 10 m) plots along three transects. Each transects extended inland from the shoreline. A quantitative study of the vegetation (true mangroves, mangrove associates, other trees and shrubs, seedlings and saplings) was conducted and species identified. The anthropogenic activities carried out in the area were also noted.

In total, 29 mangrove species were recorded, out of which 18 were considered true mangroves. Thirty three other types of vegetation were noted. Families with highest abundance of mangroves were Rhizophoraceae, Avicenniaceae and Combretaceae with identical zonal distribution towards the inland, respectively. Lumnitzera racemosa andAvicennia marina were most prominent among the families of Combretaceae and Avicenniaceae, respectively. Rhizophora apiculata and R. mucronata were the most abundant in family Rhizophoraceae while other members included Bruguiera gymnorhiza,B. sexangula and Ceriops tagal. Mangrove associates were found towards landside with high abundance of Premna integrifolia, Derris scandens and Acanthus ilicifolius. Out of the 20 species of true mangroves along the Sri Lankan south-western coast, present study recorded 17 species and an additional species Avicennia alba, which was recently introduced to the reserve from Thailand.

The results of the study indicate Kadolkele Mangrove Reserve consists of high biological diversity of mangroves and therefore it is extremely valuable as a living mangrove forest site readily accessible for education and research, being only 40 km north from Colombo. Destructive activities of the surrounding low income population, increasing of invasive alien floral species and deposition of the garbage such as polythene and plastics due to tidal activities of the lagoon were found to be the severe threats. In order to conserve this reserve, it is necessary to develop a management plan and detail studies should be carried out to improve the knowledge on the faunal diversity of mangrove reserve to provide information required to declare the mangrove reserve of Kadolkele as a conservation zone. Action should be taken to enhance the awareness of the surrounding community on mangroves to achieve sustainable conservation including utilization. The preliminary results of this study can be used as baseline data to monitor environmental change if further development activities continue at Negombo, and for comparison with other more degraded or rehabilitated habitats in western coast of Sri Lanka.