A 700 to 800 metres stretch of mangroves to the west of Pakhiraloy ferry ghat on an island in the Indian Sundarbans, part of a plantation project in 2020, was reportedly washed away by the Gomor river in March this year. At another 1,200-1,300 metres stretch right next to it, part of the same project, the mangroves survived the waves, but not the grazing pressure from cattle.
As stipulated by the authorities, the plantation had been protected with nylon nets to keep cattle away. However, only scant traces of those barriers were found during Mongabay-India’s visit. The mangroves had grown up to two to three feet tall, but local communities said that the plantations looked only as thick as when they were planted first.
“Many of the trees that have survived now, may not last another couple of years if cattle grazing is not restricted, and fresh barricades of nylon nets are not put up,” local resident Jogesh Mondal told Mongabay-India.
The two plantation sites covering 10 hectares of land lie in the Rangabelia panchayat area on the Gosaba island of the Indian Sundarbans, in the Bay of Bengal delta. The Indian Sundarbans mangroves straddle the South-24-Parganas district in the state of West Bengal.
The plantation in 2020 was part of a targeted drive by the West Bengal government to plant five crore mangrove propagules (seeds) over 2,500 hectares in the South-24-Parganas district during that year.
Since the government’s agenda was to sow 20,000 propagules or seeds per hectare, a total of two lakh seeds may have been planted in this 10-hectare plot in 2020. The residents now estimate the number of surviving mangroves to be no more than 30,000.
The South 24 Parganas district accounts for 2,083.82 square kilometres, or 41.74% of India’s total mangrove cover, according to the State of Forests in India report 2021, and is also home to the royal Bengal tiger.
In 2020, the heavy damage to the Sundarbans mangroves from cyclone Amphan prompted West Bengal Chief Minister Mamata Banerjee to announce a mega plantation drive of five crore mangroves under the Mahatma Gandhi National Rural Employment Guarantee Act.
In the South 24 Parganas district, 3.2 lakh person-days of work were generated, and 6.52 crore rupees had been credited to the beneficiaries, according to a government report. The 2,500 hectares, of which 1,725 hectares were non-forest areas, were spread over 60-gram panchayats, with Rangabelia being one of them.
“It’s true that the river has washed away one stretch of the plantation, but the growth has been satisfactory at the adjacent stretch,” corroborated Debaprasad Sarkar, deputy chief of the Rangabelia panchayat.
The incident raises the possibility that mangrove plantations in erosion-prone areas are not surviving. Moreover, without appropriate maintenance of fencing to restrict the entry of cattle, plantations may degrade. Wide intertidal spaces with gentle slopes may be ideal for plantations along riversides.
This correspondent’s visits to Bali island in Gosaba block, G-plot in Patharpratima block and Jharkhali in Basanti block revealed a similar pattern.
Drastic decline in mangrove cover
The State of Forests in India report over the years show that between 1987 and 2021, Sundarbans’s mangrove cover varied between 2,076 square kilometres and 2,155 square kilometres.
However, in the 15 years between 2007 and 2021, Sundarbans’ very dense mangrove cover (canopy density of more than 70%) has come down from 1,038 square kilometres to 994 square kilometres, while moderately dense cover (canopy density of 70%-40%) suffered a greater loss – down from 881 square kilometres to 692 square kilometres. In contrast, open forest cover grew from 233 square kilometres to 428 square kilometres.
Scientists largely attribute the growth in open forest cover to afforestation initiatives. According to a study published in December 2021, about 110 square kilometres of mangroves disappeared within the Reserve Forest (Sundarbans Tiger Reserve) area due to erosion between 2000 and 2020. During the same time, the inhabited part of the Sundarbans Biosphere Reserve gained 81 square kilometres through plantation and regeneration.
“The gains are all outside the contiguous mangroves. However, they partially compensate for the losses of the contiguous mangroves in terms of carbon,” the report said.
In recent decades, there has been a significant level of enthusiasm among government officials, politicians and non-government organisations in planting mangroves on earthen embankments to create a shield against the encroaching sea and cyclonic storm surges. These initiatives are often supported by funding from international institutions.
However, a closer look at the data shows that West Bengal’s open mangrove cover increased by 71 square kilometres between 2003 and 2013, but it grew by only 17 square kilometres between 2013 and 2021.
Trial and error
Mangrove plantations for protecting coastline from cyclones, storm surges and erosion became a popular theme worldwide after the 2004 Asian tsunami. In the Sundarbans region, it gained popularity, particularly after cyclone Aila in 2009.
Millions of mangroves have been planted along suitable coastal areas worldwide since then, the Sundarbans included. They are widely acknowledged for their carbon sequestration potential to mitigate climate change.
A 2014 document published by Wetlands International and The Nature Conservancy stressed the point that existing mangrove forests could reduce erosion by lowering the impact of wind and waves. However, it also said, “In areas with erosion, mangrove restoration may require more active intervention such as protecting individual seedlings or restoring the sediment balance and hydrology.”
A number of studies in recent years have shown mangroves’ poor resistance to erosion, even though they may contribute to reducing the impacts of cyclones and storm surges. A 2019 paper said, in the context of Gujarat, “The results show that mangrove plantation did not decrease erosion.”
Speaking to Mongabay-India in the context of the Sundarbans, Sunando Bandyopadhyay, a professor of geography at Calcutta University, said: “The evidence of Sundarbans’ mangrove islands eroding at a faster rate than human-inhabited islands, busts the myth about the role of mangroves in preventing erosion.”
Sugata Hazra, a professor at Jadavpur University’s School of Oceanographic Studies says that in areas where the wave velocity is high, and erosion is rapid, mangrove plantations wouldn’t survive unless the saplings are protected from the waves.
“Mangroves are growing well in areas of accretion, where the wave velocity is less. But for frontal sides eroding fast, saving the plantations is difficult without a layer of protection. This could be an earthen embankment behind which such a plantation could be planned. We have to first allow the mangroves to grow before they can start preventing further erosion,” he told Mongabay-India.
Hazra said that selection of plantation sites was very important for a better success rate, and so was the timing. “Plantations after September can have a better success rate because the wave velocity reduces, while different methods are required for erosional and accretional areas.”
A July 2021 report by an expert committee constituted by the West Bengal state’s environment department states: “Mangroves cannot germinate and hold ground in open, eroding sections of the coast. Mangrove plantation in these localities would not be able to reverse the erosion, it will only work in protected, enclosed sections or where the offshore gradient is gentle.”
It agreed that “the impact of waves is more dominant along concave banks where there is no mangrove on intertidal spaces, which could at least absorb a part of the kinetic energy of the rolling waves.” In other words, they are effective in minimising the impact of cyclonic storm surges but not in preventing erosion.
Mongabay India’s visit revealed that in G-plot, one of the islands facing the Bay of Bengal, plantations along the southeastern shore have mostly been washed away due to erosion. However, a kilometre-long plantation inland at Buroburir Tat, initiated by NGOs in collaboration with the Gram Panchayat, has largely survived.
All-women groups at the Sundarbans – Srijani and Sabuj Sathi, planted about 40,000 saplings on a mudflat along a canal bordering Gobardhanpur and Buroburir Tat mouzas in G-plot Gram Panchayat, a kilometre inland, in 2017-2018. According to Bulurani Das, one of the coordinators, “More than 20,000 (saplings) have survived.”
“The plantation in this plot has been successful because it is a mudflat and an enclosed space. However, every attempt to plant mangroves in the erosion-affected Chhata area in the southeast of Gobindapur proved futile,” said Bimal Das, a member of G-plot Gram Panchayat, representing Gobardhanpur sansad or locality.
Similar trends were observed in the southern and southeastern parts of Bali Island, where only remnants of plantations could be spotted at several stretches, as well as in southern Paschim Sripatinagar, western Sridharnagar and south K-Plot.
According to Bali island resident Anil Mistry, principal field officer of Wildlife Protection Society of India, identifying the right time and location is important for higher survival rates of mangrove saplings.
He says low spring tides (when the moon is full and new) retreat more than the low neap tides (between the seventh and tenth day of the lunar cycle), exposing more mudflats along the riverbank.
However, the additional space revealed by the low spring tide is unfit for plantation. “During the low spring tides, planting agencies often use the entire available stretch, without considering that some part of it will constantly remain under water for several days every lunar cycle and will die,” he told Mongabay-India.
Saurav Moni, a Bengali folk singer and archivist who is originally from the village of Madhabkati in the northeastern part of the Sundarbans, bordering Bangladesh, led plantation drives in and around his village after flooding caused by cyclone Amphan devastated their neighbourhood in 2020. He observed that the biggest challenge was maintenance.
“Waves keep toppling the fencing again and again. The protective barricades will have to be repaired/ reinstalled repeatedly for a period of two to three years to get a higher survival rate. Maintenance will often require more financial support than the original plantations,” said Moni.
On Mousuni island, Mirza Saheb Baig, an internet cafe owner, showed how the ideal location for the plantation was changing, with sand replacing silt and clay at some points while silt replaced sand at others.
Near the confluence of Chinai, another delta river, with the Bay of Bengal, plantation drives carried out between five and 10 years ago visibly yielded results. However, beside that stretch, last year’s plantations were buried under depositions of sand.
In Jharkhali island’s Vidyasagar Colony No. 3, Tumpa Dakua of the women-led group Sabuj Bahini stressed the need for moderate slopes on the intertidal space.
“The waves seem to have become more intense over the past few years. Plantations are often washed away, but the survival rate is higher when the intertidal space is wide, and the slope is gentle,” she said. In the village of Prajagheri, another volunteer of the same group said the survival rate had been 30 percent on average.
As investigated by this visiting correspondent, most sites do not have a regular monitoring system. Some non-profits do engage one or two people to keep a watch. For the government-initiated plantations, after the whole stretch is covered with boundary nets following planting, site visits are only made once in three to six months.
The 2014 report of Wetlands International and The Nature Conservancy mentioned earlier spoke of protecting individual seedlings in erosional areas. No such practice existed here.
Local grasses
According to Krishna Ray, an assistant professor of Botany at the West Bengal State University, growing locally available grass varieties on the land identified for plantation must ideally be a prerequisite for plantations in erosion-affected areas.
With grants from the department of biotechnology of the Union government, she spearheaded a pilot project on three hectares of land at Ramganga Gram Panchayat area in Patharpratima block between 2014 and 2018.
“Our experience shows that if locally available, salt-tolerant grasses can be grown before and simultaneous to planting the propagules, the grass helps stabilise the soil and serves as a trapping for propagules that would come floating thereafter,” she said.
She added that the existing forest that was planted has more species and has grown in higher numbers. This success was attributed to the grasses, which trapped propagules. Four types of locally-available salt-tolerant grasses that grow in the intertidal space – Porteresia coarctata, Myriostachya wightiana, Paspalum vaginatum, and Sporobolus virginicus – can be effective in this way, she suggested.
Ray, however, believes that this would require more effort during the plantation period than what is devoted at present, as the plantation of grasses and propagules will have to be done repeatedly for the first few years. “Between 2014 and 2018, extensive efforts were required. But since 2018, the forest is growing on its own,” she said.
Whether the government will adopt this path remains to be seen. Meanwhile, in May this year, the state forest department announced that another 12.5 crore ‘mangroves and other associated species’ were planted in the district during 2021-22.
This article was first published on Mongabay.