Microclimate regulating service of preserved urban remnant forests in Tokyo, Japan

Tokyo, Japan, is one of the world’s most densely populated cities, with much of its land converted into impervious urban structures. Historically, the western part of the city was dominated by farmland and forests, some of which have persisted despite urban expansion. Many of the remnant forests are fragmented and isolated within the urban landscape yet continue to provide habitats for native species and deliver various ecosystem services. Recognizing their ecological value, the government has designated such areas as Tokyo Metropolitan Conservation Areas.

This study focuses on the microclimate regulating service of the preserved forests, particularly those surrounded by residential areas. The aim is to assess their role in mitigating summer heat and benefiting residents, as well as to provide quantitative evidence of the service to enhance public recognition of the forests' ecological value, which remains underappreciated.

We selected two preserved forests (~2.5 ha each) and conducted fixed-point and mobile temperature observations in September 2024. Fixed-point measurements were taken over one month within and surrounding the forests, while mobile observations were performed at noon and night over three days by cycling around the forests.

Results show that, on sunny and calm days, forest temperatures averaged 0.75°C lower than surrounding areas. The difference was most pronounced at noon, with an average temperature difference of 2.1°C, while nighttime difference was negligible. Mobile observations revealed that at noon, the cool air within the forests remained largely confined, causing the pronounced temperature difference. At night, however, cooler temperatures were observed in the forests’ surroundings and temperatures increased gradually with distance, suggesting that the cool air had dispersed into the surrounding residential areas. In addition, other regulating services, such as air purification and flood regulating services, will also be discussed to provide a comprehensive understanding of the forests’ ecosystem services.