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Impact of Climate Change on the Sundarbans : Nipa palm under threat

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Saturday, February 2, 2013


A Nipa stand captured from Harbouria by the writer

Dr. Md. Mizanur Rahman



NIPA Palm (Golpata) is an indicator plant species of the Sundarbans biome albeit it is neither a true littoral nor a high saline resistant species. It grows in the mudflat and fertile riparian habitats where the water slowly rises up and then slowly falls back again. It can grow inland where the tide deposits the seeds.

Nipa can tolerate infrequent inundation, as long as the soil does not dry out. It occurs mostly in the fresh swamp and in the mixed fresh-brackish swamp forests. It also grows on low lands and depressions, at the base of eroding slopes and cliffs, or on sandy ridges or embankments of Mongla, Rampal, Morelganj, Shoronkhola, BagerhatSadar, Koyra, Paikgachha, Dacope, Sheyamnagar, Ashashuni, PirojpurSadar, Mathbaria, Pathorghata, Khepupara, Galachipa and AmtaliUpazila. It is an undershrub in the riparian zones and the ecological climax of Nipa or its associates occurs in pure stands on islets in the main channels or on depressions of the interior river meanders having silt loam soil texture. These deposits are enriched frequently by floods or surface run-off from nearby rivers during the monsoon.

The feathery leaves of the Nipa look like the coconut leaves. They are used as a roof material by the coastal inhabitants for their thatched houses and dwellings. The leaves are also widely used in the basket industry. Young leaf is used in the cigar industry to wrap the tobacco. It produces double biofuel compared to maize which is almost equal to sugarcane. The sap and the young fruits can be decomposed to produce biogas. Sometimes large stems are used as a life buoy in water.

The sap of Nipa is fed to pigs to improve the flavour of meat. The inflorescence is tapped to capture the sweet sap in the Patuakhali coastal areas. The collected sap is boiled down to produce jaggery and sweet syrup (gur). The sap is also used to produce local alcoholic beverage called “Cholai Mod”. Vinegar can be produced from this liquor by storing for several weeks. Young shoots are consumed as vegetable and the flower petals have aromatic value. Immature fruit is used to prepare dessert in many countries. The petals of the flower are also used as an aromatic tea.

They are important in preserving water quality and controlling the river erosion. They provide habitat for wildlife refuges especially for amphibians and reptiles. It provides shelter, shade and food for many aquatic animals. Nipa increases biodiversity, and provides wildlife corridors enabling aquatic and riparian organisms to move along river systems avoiding isolated communities. They provide forage for wildlife. It lowers nitrate contamination in surface runoff from agricultural fields. It works as windbreaks or shelterbelts to protect crops, water sources, soils and settlements. They are essential for dune stabilization as well. Nipa vegetation is the home of Crabs, Snails, Oysters, Mollusks, Brittle Star, Algae, Tortoises and Snakes. They provide excellent nurseries for Shrimps, Hilsha Fish, Zebra Fish, Hamilton Fish, Asian Sea Bass, Black Sea Bass, Silver Pomfret, Crocodile and Dolphins. They are very important habitats for Fishing Cat, Bengal Monitor, Black Lizard, Yellow Monitor, Water Monitor, Grey Mongoose, Ring Lizard, Pangolin, and other threatened species. The Royal Bengal Tiger uses Nipa patches for resting, sleeping and dining spaces.

The biodiversity of Sundarbans is exposed to threats of deforestation and climate change impacts. Declining trend of Nipa is one of the major threats to the mangrove ecosystem. The abundance of Nipa depends largely on soil type, salinity, duration and frequency of inundation and accretion of silt. The environmental parameters with the direct influences on Sundarbans in terms of global climate change are sea-level rise, natural calamities like cyclones, rising temperature, salinity and drought.

The obvious impacts of relative sea-level rise in the ecosystems of Sundarbans are permanent inundation, salinization and coastal erosion. One-metre rise of sea level will destroy the whole ecosystem of Sundarbans. Nipa vegetation will be submerged under water. The shift in the position of the land/sea boundary in the Sundarbans territory is complicated by high sedimentation rates in some areas and extensive coastal erosion in others. The coastal sediments are mobilized by tides and currents to the canals and the rivers. High siltation occurs in the dry season due to low flow of water. The water bodies are being silted quickly and the Nipa is losing the habitat day by day.

Nipa is very sensitive to hydrological conditions and occur in areas of low water salinity (<10ppm), where the mean daily inundation period does not exceed 3 hours. Low flow of water from the upper stream of the Ganges also has a major impact on salinity conditions and hence on the distribution of Nipa. The factors which contribute to the increase of salinity are tidal flooding during monsoon, direct inundation by brackish water, and horizontal movement of brackish ground water during dry season. The ecosystems of Sundarbans react with the increase of salt concentrations. Salinity is more devastating than any other parameter in this territory. It is very difficult to manage salinity because of the lasting nature of its effects on terrestrial and aquatic ecosystems. Saline water tides are highly crucial for Nipa's seed dispersal and germination. Predictions from the Sundarbans territory show that salinity may be double over the next few decades posing risks for survival of Nipa. Nipa is found only in the fresh swamp and the mixed fresh-brackish swamp.

Karamjal, Jongra, Mora Passur, Nandobala, Harbouria, Choraputia, Andharmanik, Tamulbunia, Supoti and Kochikhali forest areas are considered as the paradise habitats for Nipa. But declining trends in Nipa abundance has been observed in these areas over time. The inland Nipa is being disappeared rapidly. Due to increased salinity fresh water swamp is being converted into mixed fresh-brackish swamp while mixed fresh-brackish swamp into brackish swamp and brackish swamp into mangrove scrub. The littoral forests are becoming degraded forests due to higher mortality caused by higher salinity. With this change in the vegetation type the Nipa is being disappeared from the past mixed fresh-brackish swamp. Salinity causes a major threat to the succession of Nipa. Salinity weakens the potentiality of natural regeneration by reducing the viability of seeds, seedling germination and seedling recruitment. The Nipa mortality rate is being accelerated due to increased salinity. The production of new leaves, leaf longevity and the leaf area, net photosynthesis rate, stomata conductance and transpiration rate of leaves are being reduced.

The changes in the composition and abundance of this sensitive indicator species provide the specific biological signal of the climate change impacts.



The writer, a biodiversity specialist, is UNO, Mongla, Bagerhat (mizan_peroj @yahoo.com)



Source: thedailystar






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