When the program was launched in late 2015, the Hanoi Green Trees Park Company was asked to study tree planting methods and techniques from China and Singapore.

Several tree species were brought to the capital city, including jacarandas, Madagascar almonds, date palms and maples.

At the end of 2018, officials announced that the program’s target of planting a million trees had already been met and that they planned an additional 600,000 trees by 2020. That goal was also achieved.

"The planting rate was increased by 40-50 times compared to previous periods, creating green belts and green spaces, which help regulate the atmosphere, increase moisture, limit noise and air pollution," a city report said.

Dang Van Ha, head of the College of Landscape Architecture and Urban Greening under the Vietnam National University of Forestry, said the program was a "groundbreaking idea," not just for the capital but also for the whole country.

Many of Hanoi’s streets, including Lang, Hoang Dieu, Vo Chi Cong, Van Cao and Hoang Quoc Viet have become much "greener," thanks to the program, said Ha. The program also helped reorganize pavements and other relevant structures to create flower bushes and rows of trees, he added.

He also acknowledged that there were limitations to the program, including a lack of diversity with tree species as also the use of some tree species not suited to the capital city’s climate and soil conditions.

Ha said the city should have chosen trees appropriate for different city landscapes beforehand.

"Due to the lack of prior planning and the time pressure to plant a million trees, the city found it difficult to find appropriate tree species and their suppliers," he said, adding that the city probably tried to resolve that by introducing a large number of tree species into the program.

While the city had said the introduction of some tree species into the program was "experimental," it is not a method adopted by other countries, who typically experimented with tree species inside greenhouses and similar spaces first, before actually planting them on the street, he said.

On Monday, Hanoi’s Department of Construction said the municipal People’s Committee has approved a proposal to replace rows of maples along the Nguyen Chi Thanh-Tran Duy Hung streets with Madagascar almonds as the maples were dying. Even when the maples were first planted in 2018, Ha had considered them not suitable for northern Vietnam.

The program has also used certain tree species with wide trunk radius, which is no longer popular in developed countries because of high costs and safety risks, Ha added.

Therefore, Hanoi should have policies to determine an appropriate trunk radius for its trees, and consider trees with branches and canopies that can have an immediate impact on the urban landscape, he said.

"With large cities like Hanoi and HCMC, there should be specialized, independent agencies to monitor the planting and maintenance of trees, not depending on construction departments and other divisions as they do currently," Ha said.

On Monday, former PM Nguyen Xuan Phuc approved a government program developed by the Ministry of Agriculture and Rural Development to plant a billion more trees until 2025, with 690 million in urban and rural areas and the rest in forests.

"A billion more trees would help increase the tree-per-person rate while improving forest quality and forest coverage. They would also help combat climate change, protect the environment and alleviate natural disasters," said Nguyen Quoc Tri, head of the Vietnam Administration of Forestry.