Vanishing giants: Extinction threatens Bangladesh’s tallest tree

Being the tallest in the country, Boilam tree carries a strong symbolism for Bangladesh. Standing over 200 feet tall or a 20-30-storey building, the tree towers above all others in small forests in the country.

Now ravaged by years of climate change impacts and habitat encroachment, the tree stands on the brink of total extinction within its native Bangladesh.

Only 40-45 mature trees remain in small pockets of forests in Chattogram, Chittagong Hill Tracts, and Cox's Bazar, according to the Institute of Forestry and Environmental Sciences at Chittagong University. 

Boilam trees were a common sight even 30 years ago, locals said. A huge number of trees were in 1996 to make room for human habitats. Again, the cutting spree was expedited when Rohingya refugees began to arrive in Cox's Bazar from neighbouring Myanmar.

Unplanned slash-and-burn cultivation by locals is also a major contributor to the tree's disappearance, Dr Rafiqul Haider, director, Bangladesh Forest Research Institute, told The Business Standard. 

Furthermore, the Boilam tree's 30-year flowering cycle and 50-year timber harvesting timeline contributes to its disregard among locals. 

Atiqur Rahman, former professor of the Botany Department at Chattogram University, noted that Boilam has poor natural regeneration. "Naturally, its reproduction is constrained. As its population is not increasing in Bangladesh it has become critically endangered."

This is why the tree faces similar peril in its other habitats in Malaysia, Laos, Myanmar, Thailand and Vietnam, said the botanist. The International Union for Conservation of Nature (IUCN) in 2017 enlisted Boilam as critically endangered.

Boilam wood was once in high demand for its distinguishing feature of being long and lightweight, he mentioned. 

"In Cox's Bazar, it was once heavily used for making boats and people used to indiscriminately log Boilam trees for timber, causing its thinning numbers," said Atiqur.

Environmental impact 

Boilam trees can tolerate 15°C to 38°C temperature and prefer a mean annual rainfall in the range of 2,000mm-3,000mm, according to experts. 

However, the average rainfall in the Cox's Bazar region, the primary habitat of the tree, declined by about 234mm in the last three decades, said Dr Md Akhtar Hossain, professor and lead researcher of Boilam, Institute of Forestry and Environmental Sciences at Chittagong University, citing climate data from the Bangladesh Meteorology Department.

At the same time, average minimum temperature increased by about 1.4°C in the last 40 years and average maximum temperature by 1.5°C, he added.

According to a World Bank study, titled "Hotter and more humid with erratic rainfall: Climate change in Bangladesh", maximum temperature in Dhaka increased by 0.5°C whereas the increase for Chattogram was 0.9°C between 1980 and 2019."

These environmental shifts denote that the climate has changed drastically in the last 40 years which contributed to the fall of the Boilam population, researchers said.

Impacts on flowering 

According to a 2020 study named "Phenological Traits of Recalcitrant Seed-bearing Trees in Bangladesh," the peak flowering time for the Boilam tree is from March to April, while the peak seed collection time is from April to May.

However, Bangladesh experiences heat waves and less rainfall usually from April and May during the yielding time of the tree. 

Professor Akhtar Hossain said the Boilam's habitat is experiencing a "micro-climate change" disrupting its seed germination and making its seedlings difficult to survive. 

"We have very few mother trees left, which are over-aged and seedless. The remaining exhibit irregular seed cycles and poor yield," he said.

Moreover, the species requires at least fifty years for its maturity and that is why people are not interested in planting the species for timber. 

Cleaning forest floors by people (bush cleaning and litter removal) is another cause behind the poor regeneration of the species because during the period of fruit ripening the forest floor must be moist with litter, he mentioned. 

Revival Efforts

Professor Akhtar Hossain suggested artificial regeneration and restoration as well as people's awareness to help maintain the existence of the species.

A team led by Professor Mohammad Akhtar Hossain developed the country's first germplasm at Chittagong University to return this highly endangered tree back to the forests.  

Hundreds of Boilam seedlings have been planted in the floor germplasm at Chittagong University to preserve the Boilam tree gene. About 10,000 Boilam seedlings have been produced in the institute's nursery in two years.  

About 8,000 saplings have been planted in various forests of Sylhet, Chattogram, Cox's Bazar and Chittagong Hill Tracts through the Forest Department and various private development organisations.  

Professor Akhtar Hossain expressed the hope that the species will be saved from extinction if the trees mature and start producing flowers and seeds in the next 10-20 years.

A hall block of the Chittagong University has been named after the tree to raise awareness of the Boilam among the public.