The Variation of Air Purification Benefit Provided by Street Tree Assemblages in Shenyang, China

Street tree assemblages are a widespread natural component in cities and provide a range of ecosystem services. The spatial distribution of street tree assemblages within cities, however, is not uniform. We assessed the air purification benefits provided by street trees in Shenyang, China, to examine how urban form, urban geography and drivers of vegetation management affect this ecosystem service. The i-Tree Street Model was utilized to evaluate air purification benefits provided by street trees. We analyzed the results using two indices, with values expressed in US dollars (USD, $): the per kilometer benefit (PKB) and average tree benefit (ATB). Neither index displayed a consistent trend across the human population density gradient or along the urban-suburban continuum. The district with the highest PKB and ATB is neither the oldest nor the newest one to develop, but rather the one that began to develop around 2002. We conclude that public policy is a main driver of vegetation management, especially for street trees, because street tree abundance is closely related to road construction, which, in turn, is closely tied to economic development in a region. We also discovered no significant difference in the benefit of street tree assemblages along the urban-suburban continuum. That's probably because all areas within the different beltways contain mature street trees, the time-lag effect for growth is inconsequential. We recommend that the dynamic variations of street tree assemblages over a certain time span be taken into consideration when examining the effects of urban sprawl on ecosystem services provided by street tree assemblages.