- and it's all down to the number of TREES The analysis, put together by environmental group Friends of the Earth (FOE) and mapping experts TerraSulis, found that neighbourhoods with more tree cover, green space, or both were much cooler than those lacking such vegetation. It is the first time that the cooling abilities of trees and green spaces in built-up areas has been modelled, according to FOE. The research covered five English cities - London, Birmingham, Bristol, Newcastle and Manchester.