Today in our environmental science lecture, we're discussing urban green spaces. A recent study in Melbourne found that adding trees to city streets can reduce local temperatures by up to 3 degrees Celsius during summer. However, the researchers noted that this cooling effect depends on tree species. Broad-leaf trees with dense canopies, like oaks, provide more shade than narrow-leaf varieties such as eucalyptus. The study also highlighted that green roofs, while effective for insulation, have less impact on street-level heat. Interestingly, the data showed that parks larger than two hectares are significantly cooler than smaller pocket parks, which tend to be warmer due to surrounding buildings.
❓ According to the lecture, which factor most significantly influences the cooling effect of urban trees?
A. The size of the park where the trees are planted
B. The type of tree species and its canopy density