Salim Ali School of Ecology and Environmental Sciences, Pondicherry University, Pondicherry 605 014, INDIA.
In Pichavaram. where the present study has been conducted, there has been a shift in the coastline due to geomorphic changes in the configuration of the terraln (Kerrest, 1980; Tissot, 1987). These natural changes coupled together with increased anthropogenic pressures on the ecosystem have caused species such as Sonneratia apetala, Xylocarpus mekongensis and Xylocarpus granatum to become rare.
Other major threat to the mangrove ecosystem is, increased build up of CO2 and other green house gases, sea level rise and climate change. Rise in sea level and the extent of its impact on mangroves are debatable topics. However, many experts have predicted that the global mean temperature will increase from 1.5 to 2.5°C leading to a rise in sea level of 0.2 to 1.4 m by mid 21st century and. that between 1990 and 2020. species extinction caused by deforestation will account for the loss of 5 to 15% of the world's species (Hopley & Kinsey, 1988; WRI, IUCN & UNEP, 1992). UNEP (1994) has put forward the following predictions and responses of mangroves to the changing climate.
6.0 cm rise in global mean sea level per decade, causing erosion of seaward margins of mangroves, progress of mangrove communities to landward regions. increase in secondary productivity due to increase in nutrient input caused b) erosion;
0.5% increase in the level of atmospheric CO2, per year, causing increase in water use efficiency of mangroves;
0.3°C increase in global mean temperature per decade, migration of mangroves to higher altitudes. change in phenological patterns and plant and animal composition, increase in overall net and gross productivity and acceleration of mangrove microbial process; and
Changes in precipitation patterns, causing changes in soil water content and soil salinity; increase in primary productivity if there is an increase In precipitation to evapotranspiration ratio, and change in the distribution pattern of stenohaline species.
The International Society for Mangrove Ecosystems (ISME) has adopted a Charter for Mangroves in 1992, "that complements a World Charter for Nature that the General Assembly of the UN proclaimed in October 1982 affirming that nature shall be respected genetic viability) on earth shall not be compromised conservation shall be practiced, sustainable management shall be adopted by man. and nature shall he secured against degradation" (ISME. 1992).
The major objectives of the present study was to
1. Carry out a detailed vegetation analysis. establish the major elements of thu zones, examine phytosociological aspects and, Interpret the status ol present vegetation. and, compare the present status with the satellite imageries of Pichavaram mangroves of the years 1986 and 1994.
2. Study the status and distributional and vegetative and reproductive phenology of the fringing species which belong to the genus Rhizophora; this is crucial for the survival of the Pichavaram mangroves; and an attempt to describe the resource allocation mechanism of these species:
3. Measure reproductive fitness by means of seedling recruitment. establishment and survival rates of the fringing species, and
4. Identify major impacts, natural and man-made, and develop conservation strategies based on the results obtained from the above studies.