Urban reforestation efforts compete for money and urban land that could be used for other purposes. For example, effort placed in planting new trees can take away from maintenance of already established trees.
^Hall, Justine M.; John F. Handley; A. Roland Ennos (15 March 2012). "The potential of tree planting to climate-proof high density residential areas in Manchester, UK". Landscape and Urban Planning. 104 (3–4): 410–417. doi:10.1016/j.landurbplan.2011.11.015.
^Taha, Halder (May 2008). "Urban Surface Modification as a Potential Ozone Air-quality Improvement Strategy in California: A Mesoscale Modelling Study". Boundary-Layer Meteorology. 127 (2): 219–239. doi:10.1007/s10546-007-9259-5.