Urban green space, street tree and heritage large tree assessment in Bangkok, Thailand

Three inventories were conducted to quantify Bangkok's green infrastructure for future planning and improvement in the context of a seasonal monsoonal dry climate. Total green space was quantified by extracting surface cover areas from remotely sensed data in a geographical information system (GIS) environment, and this information was used to designate suitable sites for future green spaces such as parks. Street trees were inventoried for species identification and size. Trees of heritage value were identified through a public awareness campaign, and then were subsequently surveyed for species identification, height and trunk diameter. GIS green space analysis showed that per capita park space was approximately 1.8 m², but a master plan proposed increasing per capita park area to 4 m² within 25 years. The increased park area will be largely in the form of lower cost, semi-naturalized tree parks. The inventoried street tree population, approximately 200,000, was skewed somewhat towards a monoculture, as 42% were the facultative evergreen Pterocarpus indicus Wild. By contrast, none of the other species exceeded 7% of the total. That most of the other species consisted of smaller trunk diameters than P. indicus, and therefore younger, suggests that Bangkok's street tree plantings are becoming more diverse. The heritage large tree inventory was dominated by evergreen tree species, particularly exceptionally large Ficus species, found largely on Buddhist temple grounds, followed by Albizia saman (Jacq.) Merr. The slower growing evergreen heritage species are worth careful appraisal and preservation because they are less likely to be commonly planted. Careful species selection balancing drought deciduous and dry evergreen species can achieve adaptation to the monsoonal dry season with diverse aesthetic quality in both Bangkok's street tree population and in its semi-naturalized tree parks.