Bangkok's existing mixed fruit orchards are tree diversity hotspots for city greening

Bangkok's Inner Orchard (BIO), located in the west peri-urban area of the city, provides both fresh products and ecological benefits to its inhabitants. Although this unique forest-like cultivation of mixed fruit trees growing on dikes has the potential to become an urban forest, it has never been thoroughly investigated. Urban expansion is a threat to this orchard. Sustainable cities must maintain a balance between development and the environment. In this study, six orchards were surveyed by collecting data on tree species, plant height, crown width, and location and analyzed to identify the orchard areas covered by forest canopy and clarify the forest structure and tree species diversity in the orchards. Overall, 98.64% of the forest canopy within the orchard area was evaluated using cover analysis. Analysis of the forest structure of the BIO revealed that the average tree height was greater than that of common orchard trees. Tree diversity analysis showed an average Shannon index value of 2.53, indicating mid-range diversity. Older orchards showed a greater diversity of fruit tree species, whereas newer orchards, replanted after major flood and drought events, showed a lesser diversity of fruit tree species. In order to protect BIO on the long-term, it is essential to identify and apply appropriate conservation strategies. Including BIO areas in the Bangkok greening scheme would cause rapid increases in the green area per capita ratio. Both urban food forest and urban agriculture concepts could be applied to existing BIO orchards, which represent new urban green area types. BIO thus has the potential to act as an urban forest and tree diversity hotspot for Bangkok.