Indirect carbon reduction by residential vegetation and planting strategies in Chicago, USA

Concern about climate change has evoked interest in the potential for urban vegetation to help reduce the levels of atmospheric carbon. This study app lied computer simulations to try to quantify the modifying effects of exist ing vegetation on the indirect reduction of atmospheric carbon for two resi dential neighborhoods in north-west Chicago. The effects of shading, evapot ranspiration, and windspeed reduction were considered and were found to hav e decreased carbon emissions by 3.2 to 3.9% per year for building types in study block I where tree cover was 33%, and -0.2 to 3.8% in block 2 where f ree cover was 11%. This resulted in a total annual reduction of carbon emis sion averaging 158.7 (+/-12.8) kg per residence in block I and 18.1 (+/-5.4 ) kg per residence in block 2. Windspeed reduction greatly contributed to t he decrease of carbon emission. However, shading increased annual carbon em ission from the combined change in heating and cooling energy use due to ma ny frees in the wrong locations, which increase heating energy use during t he winter The increase of carbon emission from shading is somewhat specific to Chicago, due in part to the large amount of clean, nuclear-generated co oling energy and the long heating season. In Chicago, heating energy is req uired for about eight months from October to May and cooling energy is used for the remaining 4 months from June to September If fossil fuels had been the primary source for cooling energy and the heating season had been shor ter, the shading effects on the reduction of carbon emission would be great er. Planting of large frees close to the west wall of buildings, dense plan ting on the north, and avoidance of planting on the south are recommended t o maximize indirect carbon reduction by residential vegetation, in Chicago and other mid and high-latitude cities with long heating seasons. (C) 2001 Academic Press.