Mangroves of Sunderbans - A Pristine Forest in Nature

Gautam Kumar Das

The famous resilient and salt-tolerant mangrove forests of the Sunderbans with abundant occurrences of 64 mangroves and its associated species including dominant species like Rhizophora, Avicennia, Heritiera and Sonneratia. Among those species, very recently, the age of Rhizophora mucronata is determined from the counting of annual growth rings. The oldest, recently fallen tree in the riverine forest displayed an average of 89 years with a height of 12 meter and a diameter of 28.6 cm. A tree of 34 cm diameter with an equal growth rate and a similar growth history is 106 years old. Age of mangrove species like Avicennia or others, lacking annual growth rings, thus barring from dendrochronological studies. But the periodic growth layer allows accurate age determination only in trees with radical growth rates about 0.5 mm/year. Age determination of the largest trees collected in the primary forests revealed the relatively young age of the trees about 100 years, though age is one of the factors in the formation of a primary pristine forest. All forests grow to maturity at different rates based on their environment. But the term old growth is highly relative and it is certainly not applicable for the mangroves forest of the Sunderbans.

Though pristine and primary forest in nature, the evergreen mangrove forest of the Sunderbans, as a whole, is considerably disturbed over centuries. The British East India Company rulers cleared major portions of the mangrove forest in order to earn more revenue from agricultural practices. Again, that British people first worked out the management plan for the Sunderbans in 1893 as it served as the saviour to Calcutta, the then capital of the British India from the storm surges or severe super cyclonic storms. In independent India, Sunderbans further disturbances during 1977- 80 because of Marichjhapi refugee problem. As a result of such disturbances over centuries, Sunderbans has lost its areas for mangrove forests, though size and intact areas are also the factors in defining a primary forest. The intact primary forest again, separated politically into two, Indian and Bangladesh parts of Sunderbans, is divided into two smaller ones. And the human settlements in the isolated islands of the Sunderbans do the same again and again, shortening the areas into smaller and smaller slices and all these causes end up with primary forest patches so small they no longer deserve the name of the Sunderbans as with the earlier 25,500 sq km of intact areas.

In 2019, the Indian part of Sunderbans is covered with only 2108.11 sq km mangrove forest areas, although there is no official threshold of size for primary forests, the cut off is usually considered in of whether the size of the forest allows for native species assemblages of 1586 species of fauna including Royal Bengal tiger, estuarine crocodiles, spotted deer and rhesus monkeys, and its natural structure with 64 mangrove and associated species leading to estuarine ecosystem functions to remain intact. Sunderban’s pristine nature does not mean that this primary forest must be completely devoid of human presence. Many indigenous communities particularly wood cutters, fishermen and honey collectors have entered within primary forests for years, using forest resources sustainably to support their occupational and traditional livelihoods. Indigenous community can be highly effective protectors of the Sunderbans, though the permit-holders fishermen, wood cutters and honey collectors disturb this forest of pristine nature off and on.

Succession is also an important factor to term Sunderbans a pristine forest. Floral succession changes the ecosystem within the forest from one state to another following disturbance especially for the mangroves that occur in patches for a particular species. But when cyclonic storms ravage the Sunderbans, it destroys mangroves miles after miles. After days, nature starts to work through regeneration of the saplings from the dirt up biomass stored upon the substratum. Like such regeneration of mangroves, in Sunderbans, formation of new vegetation upon a newly built-up island, the first organisms to grow are called pioneer species, typically fast-growing Dhani grasses (Porteresia coarctata), then Kaora (Sonneratia sp) and Kali Bain (Avicennia marina) plants that can take quick advantage of loose silty substrates with plenty of nutrients, supplied by the tidal water inundated the islands twice daily. These pioneer species promote the abundant occurrence of vegetation succession allowing for a new guard of species to move in by trapping nutrients from the inundated sediment-laden tidal waters during flood tide. This generation of species assemblages repeats itself with the progress of years that helps to introduce ecosystem in the island-forest land. From the bushy grasses to quick-growing mangroves like Avicennia and Sonneratia trees and finally becomes a dense mangrove forest covering the newly built-up island in the Sunderbans. The ultimate grown up is often referred to as a climax community and it’s these communities that are considered primary forests making the Sunderbans a pristine in nature.

As a pristine forest, Sunderbans management plan have been worked out annually. The working plan is followed up since 1949 that moderates selection-cum-improvement felling. No other normal forestry practices are carried out in the Sunderbans for years. Since 1999-2000, no coupe operation has been taken up. Extraction of minor produce like honey, bee-wax, Golpata (Nypa fruticans), Hental (Phoenix paludosa) etc are collected by the locals annually during a short span of period duly permitted by the forest department, though Golpata collection has been stopped since 1978 and collection of Hental has been discontinued since 1991. As a whole, Sunderbans management, at present, is running beyond any large-scale anthropogenic interference. Of late, Sunderbans in the South 24 Parganas district of West Bengal alone accounts for 41.85% mangrove cover of the country. India State of Forest Report 2019 shows the West Bengal has 42.45% of India’s mangrove cover. The report states that the Sunderbans has lost 1.89 sq km of mangrove forest areas in 2019 with respect to 2017 forest assessment.

Mangroves forest cover of Sunderbans in 2019

Worldwide, mangrove substrate soils store more than 6.4 billion tons of blue carbon. Blue carbon refers to the carbon captured and stored in estuarine and coastal ecosystems. It’s blue because it is formed underwater. Mangrove forest can play an important role in such carbon removals. The trees uptake carbon dioxide from the atmosphere as they grow and store it in their trunks, leaves and soil. Once a forest reaches primary status it can continue to carbon for centuries. Mangrove ecosystems, if kept undisturbed, mangrove forest soils act as long-term carbon sinks. But over the past two decades alone, almost 100,000 hectares, or 6% of the world’s mangrove forests have been lost - IUCN reported. Mangroves forests of the Sunderbans too have been lost over the centuries through deforestation for conversion of the agricultural land. Inclusive of such loss, another danger signals at the door that the rapid sea level rise could drown mangroves forests by 2100 globally. Scientists said that the sea level is rising globally at an average rate of 3.4 mm/year, and over the next few decades that rate is projected to enhance in between 5 mm/year and 10 mm/year by 2100. This could drown the mangroves forests with twisty trees of resilient nature in the worldwide estuarine and coastal environments including Sunderbans.

Frontier
Jun 11, 2020