都市を冷やすための「強い木」を植える

Planting Strong Urban Tree Communities to Cool Our Cities

Cities often experience higher temperatures than surrounding rural areas. This occurs because asphalt and buildings trap heat, a phenomenon known as the urban heat island effect. As global warming progresses, this problem is becoming more severe. Over half the world’s population lives in cities, and the heat can cause health problems.

One method to cool cities is “planting trees.” Trees create shade and lower surrounding temperatures by releasing moisture through their leaves. However, trees also suffer stress from high temperatures. If temperatures continue to rise in the future, trees currently planted may not survive.

Researchers conducted a study in Miami, USA. This is because temperatures there are predicted to rise by approximately 4°C by the end of this century. The study examined 249 tree species planted throughout the city, analyzing each species’ heat tolerance. It then calculated the difference between current and projected future temperatures.

The results revealed that a 4°C temperature increase would expose over 40% of tree species to the risk of heat stress. Native species (those originally native to the region) were predicted to be more vulnerable than non-native species (those introduced from other regions). However, some native species are “highly resilient,” exhibiting strong resistance to heat, drought, strong winds, and salt damage.

Researchers emphasize the importance of selecting and planting these robust trees while considering future climate conditions. Since urban trees live for decades, planning must account not only for current climates but also for future environments. Choosing appropriate trees contributes to protecting the health and quality of life for city dwellers.