Tree-cover dynamics in a rapidly urbanising tropical mega-city – Are trees of greater biodiversity and ecosystem service value less likely to be lost?

Abstract

Urban trees are crucial for biodiversity and providing ecosystem services. It is unclear if sites where trees support more biodiversity and have greater contributions to ecosystem service provision have greater rates of tree loss, or are better protected. We assess this in an expanding tropical mega-city (Bangkok, Thailand), using data from 150 1-km2 cells, selected across the urbanisation gradient. We quantify rates of tree-cover loss/gain between 2018 and 2022, and associations with sites’ biodiversity value (native tree and avian species richness), ecosystem services (carbon storage, human food production capacity) and economic value (following regulations enabling trees to be used as collateral in financial loans – which may incentivise landowners to retain trees). Surveys were conducted at randomised points and in the largest woodland within each cell. Randomised points lost ∼10 % tree-cover with greater loss at more urbanised sites. Woodland points lost ∼20 % tree-cover, with the greater loss at sites with intermediate urbanisation intensity. Loss was lower at sites with higher native tree, but not bird, species richness. Sites where trees stored more carbon tended to lose less tree-cover (randomised points, marginally significant) or have a lower probability of losing tree-cover (woodland points). Tree-cover loss was not related to site’s capacity to provide food for people. Sites where trees had greater value as collateral for financial loans lost slightly less tree-cover at randomised, but not woodland, points. Without this policy tree-cover loss rates may thus be even higher. Bangkok is rapidly losing tree-cover, including at sites with high biodiversity and ecosystem service values. These losses reverse gains in urban tree-cover earlier in the 21st century, and coincide with 2019 changes in the Forest Act enabling private landowners to remove trees on their land. Without effective policy change, the rapid loss of urban tree-cover will continue to negatively impact Bangkok’s biodiversity and people.