A short review of previous studies dealing with the effects of tree planting in urban areas is presented with a focus on CFD modelling of tree-atmosphere interaction and assessment of air quality in street canyons. Several tree planting/street canyon configurations were analysed. In general, results show that the RSM models performs better when used to simulate flow and pollutant dispersion in street canyons with tree planting, even though extra investigations would be required. The general suggestion is that more complex turbulence models should be employed and most probably Large Eddy Simulations models would be more appropriate.