TOEFLリスニング

🎧 リスニング原文

Narrator: Listen to part of a lecture in an environmental science class. Professor: Today we're going to talk about a surprising ecosystem service provided by forests: the cooling effect of trees. While we often focus on carbon absorption, trees also release water vapor through transpiration, which cools the air, similar to sweating in humans. But this effect is not uniform; it depends on the forest's location and species composition. For example, a study in the Amazon found that large-leafed trees with high transpiration rates can lower local temperatures by up to two degrees Celsius. In contrast, coniferous forests in boreal regions have a lower cooling effect because their needle-like leaves reduce water loss, especially in winter. Moreover, the cooling effect is most significant near the forest canopy, but it can extend to surrounding areas via wind patterns. This has practical implications: planting urban trees can reduce the heat island effect, but only if we choose species with high water use and ensure adequate irrigation. Otherwise, stressed trees may actually emit more volatile organic compounds, which can worsen air quality. So, when designing green infrastructure, we must consider not just carbon, but also water and temperature dynamics.