The green canopy is shrinking in parts of the capital. More than 550 trees have died while many have fallen into decay in several areas in the last four years.
Nearly 500 trees died in the Bashundhara residential area, 20 around the Baridhara Lake, 25 near the Sher-e-Bangla Agricultural University and ten more at the Farmgate Park.
Botanists and soil experts still remain clueless about the reasons behind the death or decay of the trees.
Md Jasim Uddin, associate professor of botany department, Dhaka University, said an extensive study should be conducted to find out the reasons behind the decay of the plants and also the solutions.
Raintrees in some city areas might be decaying due to lack of proper environment or soil problems, he said.
The DU teacher said prior to planting trees in any place experts' opinions should be sought about the appropriate variety of trees.
Prof Shah Mohammad Ullah of soil science department of the university said soil problems or air pollution might be responsible for the deaths of the trees.
Trees could die, if the level of metals such as copper, nickel, lead, cadmium and zinc goes up in the soil, he said. Besides, a rise in sulphuric, nitric, hydrochloric and other types of acid in the air could also cause the leaves of trees to decay.
Trees grow under constraint in industrial areas where air remains highly polluted, he said.
The soil used for filling up lowlands for the Bashundhara Housing Project needs to be analysed to find the reasons behind the death of the trees there, he said.
Prof Mihir Lal Saha of botany department said vascular disease might have caused the deaths of the trees.
Prof Imdadul Hoque of the same department said he along with some other teachers might form a team to conduct a study on it.
Abdul Aziz, a welder working in under-construction buildings in Bashundhara residential area, said around 500 trees including raintrees, eucalyptus, akashmoni and krisnachura died there in the last four years.
Plenty of trees were there on the North South Road in Bashundhara but most of them died in the last six months, said Rafiq, a chauffeur, who used to drive on the road almost every day.
About 25 raintrees died in the last nine months on both sides of the road to the Sher-e-Bangla Agricultural University from the Second Gate in Agargaon. Nine more trees (four raintrees, four ekashia and one mango tree) died on the university campus.
Kartik Chandra Bhoumik, a security guard of the university, said some trees on the campus started to decay early this year.
Md Lutfor Rahman, assistant superintendent of the university's farm division, said it is alarming that a significant number of trees have died on the campus.
Promananda Baroi, an employee of the Planning Commission, said a lot of trees were in the area when he settled there 30 years ago. Many of them began to decay in the beginning of this year.
Superintending Engineer of the Dhaka City Corporation Abdur Razzak said roots of some trees do not go deep into the soil. These trees might not get adequate water during the lean period and decay slowly.
The DCC is yet to conduct any study on it, he said.