The prevalence of top-dying disease in Sundari trees in the Sundarbans is declining gradually while their carbon storage capacity has increased.
The total amount of carbon, stored in Sundari trees in the world's largest mangrove forest, has increased by 21 percent or 1.4 million tonnes over the past four decades, according to a recent study published here.
During the same period, the number of diseased Sundari trees declined by six percent, while the total population of the species increased by around 15 million, or five percent, the research said.
Forest Department sources said top-dying disease or disorder, which causes the gradual death of the upper branches and leaves of Sundari trees, has been a longstanding ecological problem in the Sundarbans, it said, adding, "The disease causes the upper parts of affected trees to dry out and die, stunting their growth."
Historical records of Sundarbans, the world's largest mangrove forest, show that British forestry expert RS Troup first mentioned the death of Sundari trees from disease in 1921.
British-era forest survey reports from the 1920s identified around 13 to 17 percent of Sundari trees in the Sundarbans as diseased or affected by top-dying.
Later in 1931, SI Curtis documented the death of some Sundari trees for unknown reasons in the forest's working plan.
The disease became particularly severe after the 1970s. The construction of the Farakka Barrage around 1975 reduced freshwater flows into the Sundarbans region, contributing to increase soil salinity and the spread of top-dying disease among Sundari trees.
Prof Dr Swapan Kumar Sarkar of the Department of Forestry and Environmental Science at Shahjalal University of Science and Technology, a Sundarbans expert, said the prevalence of top-dying disease in Sundari trees had declined compared with previous periods.
Research shows that the total carbon stored in Sundari trees has increased by 21 percent, or 1.4 million tonnes, over the past 40 years. The number of diseased trees has fallen by six percent, while the overall population of Sundari trees across the Sundarbans has increased by
approximately 15 million, or five percent, it added.
Although increased salinity, fungi and pathogens, disrupted water drainage and soil aeration, climate change and cyclones are considered possible contributing factors, scientific research has yet to establish the precise cause of top-dying disease.
Professor Sarkar said controlling the disease requires more than identifying affected trees. Determining its actual causes, conducting long-term monitoring, improving forest management and ensuring the natural regeneration of Sundari trees are also essential, he continued.
He stressed that research on the disease should be treated as an important programme for forest management in Bangladesh, as Sundari trees are not only a major species in the Sundarbans but also play a vital role in maintaining the forest's structure, biodiversity and carbon storage capacity.
Talking to BSS, Divisional Forest Officer (DFO) of the Sundarbans West Forest Division in Khulna Md Hasanur Rahman said the prevalence of top-dying disease had declined significantly.
He said Sundari seeds and seedlings were now frequently visible during forest patrols, indicating that new stands of the species were developing naturally.
DFO of the Sundarbans East Forest Division in Bagerhat Md Rezaul Karim Chowdhury told BSS that the Sundarbans was in better condition than in previous years, with new Sundari stands emerging and forest greenery increasing.
However, he noted that top-dying disease was still observed in a few naturally affected areas of the Chandpai Range under the East Forest Division.
Contacted, Forest Conservator for the Khulna region Imran Ahmed also confirmed that carbon storage in Sundari trees had increased and the prevalence of top-dying disease had declined considerably.
He said several research activities under the Forest Department's Sundarbans Protection Project had been completed, while others were still underway.
Continuous research and evidence-based forest management are essential to protecting the Sundarbans' ecosystem and biodiversity, he added.
