Urban tree-planting efforts are gathering pace in Bangkok, underpinned by aspirations to boost climate resilience, mitigate dust pollution, and conserve biodiversity. However, a recent study warns that the Thai capital continues to rapidly lose tree cover from its existing green spaces.
The study used satellite data and field surveys to analyse patterns of tree cover loss in Bangkok between 2018 and 2022, finding a 10.5 per cent drop in tree cover across the whole city, with larger areas of urban woodland losing more than 20 per cent of their canopy cover.
“This is a rapid rate of tree loss in just four years,” Phakhawat Thaweepworadej, a biodiversity researcher at Mahidol University in Bangkok and lead author of the study, told Mongabay. “The greater rate of loss in larger blocks of tree cover that have been shown to support more biodiversity and provide important ecosystem services is particularly concerning.”
The stark results indicate that without a strategic shift in policy and practice, the city risks losing its green spaces that could otherwise help it adapt to climate change, the authors note. This is a significant concern, given that the latest assessment of the Global Climate Risk Index ranks Thailand among the world’s top 30 countries most at risk of climate change.
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Combined strategies for preserving existing large trees and planting new trees are necessar. However, I might focus more on preserving green spaces with the existing large trees as a priority.
Vudipong Davivongs, associate professor, Kasetsart University
Incentivise tree preservation, not loss
Trees are increasingly recognised as vital components of climate adaptation plans in tropical megacities across the world. City parks and green roofs are among the mitigation strategies recommended in the World Bank’s 2024 policy guidelines for enhancing Thailand’s climate change resilience, for instance.
By casting shade and filtering the air, trees help to ameliorate the effects of harsh heat waves and the urban heat island effect created by heat-storing concrete environments. Their root systems also boost the capacity of urban soils to absorb rainwater, reducing the risk of flooding.
Yet Bangkok lags well behind global standards on urban parks. While estimates vary, the city’s green space to resident ratio falls significantly short of the World Health Organization’s recommended 9 square meters (97 square feet) per inhabitatant by most calculations. Its urban tree canopy, estimated at only 8.6 per cent of its total area in 2013, is also much lower than other major cities like New York, which has 20.9 per cent, and Beijing, which has 24 per cent canopy cover.
The authors point to recent legislative amendments to Thailand’s Forest Act as likely driving the urban tree loss trend. The original version of the law prohibited developers and landowners from cutting down 158 species of trees on private land.
However, changes made in 2019 now allow landowners to clear and sell these trees. While the rationale was to reduce illegal logging within the country’s protected areas, in reality it likely stimulated more tree loss outside of protected areas, the study notes.
Phakhawat said policies that incentivise the preservation of mature trees over their felling will be vital to improve the city’s environmental outlook.
Rules that allow landowners to use trees as collateral against financial loans hold some promise, he added. Prioritising the preservation of intact blocks of woodland that provide habitat connectivity across the city will also be crucial: “These larger woodlands generally support greater bird diversity, store more carbon and can absorb more rainwater,” he said.
Heritage and utilitarian value
Besides their ecological role, urban trees also carry cultural significance, Phakhawat said. Several areas of Bangkok are named for the types of trees that once flourished there, including the central business district hubs of Chong Nonsi and Sathon.
The study found, however, that trees valued by local communities — for their heritage or as food sources — aren’t afforded special protections in the city’s urban planning system. This means relatively green and biodiverse areas like the Bangkok Inner Orchard, an expanse of fruit groves cultivated along flood dikes on the city’s western margins, risk being converted should market prices shift.
“These traditional mixed fruit orchards consist of large and diverse fruit trees, [which] provide ecosystem services, environmental mitigation, and recreational functions to people and the city,” said Vudipong Davivongs, an associate professor at Kasetsart University in Bangkok, who was not involved in the recent study. “Conserving these fruit orchards could be an alternative way to increase green space in Bangkok.”
The study authors recommend more integration of urban agriculture initiatives, such as community gardens and agroforestry projects, into city plans as a way of simultaneously improving tree cover and urban food security. Planting edible fruit trees in the city’s expanding network of “pocket parks” and tree-planting campaigns could also extend their many benefits.
Plant new trees, but protect old ones too
In an effort to boost the city’s green space, the Bangkok Metropolitan Administration (BMA) launched a “One Million Trees” initiative in 2022, aiming to plant trees throughout the city’s 50 districts by 2026. The campaign hit its million-tree target in mid-2024, with the BMA announcing further plans for another million trees to be planted in nine districts on the eastern fringes of the city through 2026.
Although the One Million Trees campaign has met its initial planting goals, the long-term survival and value of its plantings remains uncertain, the study notes, especially given that many of the newly planted species were nonnative small trees and climbers, such as yellow elder (Tecoma stans) and Bougainvillea spectabilis.
“Most of the trees planted are seedlings, not saplings. They’re very small,” Phakhawat said. “So it will take 10 to 20 years for them to grow to a size where they’re giving shade or substantially storing carbon.” He urged the initiative to plant larger trees as well, to make up for the delay and to replace natural losses of mature trees across the city.
Scientific evidence shows that tree planting must be followed up by rigorous aftercare and follow-up monitoring programs. While planting a few fast-growing species may give an initial appearance of success, if programs aren’t invested in the long term, new plantings quickly die out.
Phakhawat said more studies are needed to assess the outcomes of the One Million Trees initiative, to probe the survival rates of the new trees as well as their contribution to urban canopy cover, biodiversity and ecosystem services. He also urged the BMA to include more native species of tree that can better support local biodiversity in future iterations of the campaign.
Without such improvements, funds risk being wasted on tree-planting projects with uncertain outcomes, while the city’s existing green spaces and mature trees dwindle.
Ultimately, an urban planning approach that explicitly prioritises the preservation of existing trees and green spaces, while encouraging well-managed planting of new trees, will be the most effective way forward, Vudipong said.
“Combined strategies for preserving existing large trees and planting new trees are necessary,” he said. “However, I might focus more on preserving green spaces with the existing large trees as a priority.”
This story was published with permission from Mongabay.com.