Abstract
Abstract. Cities represent a key space for a sustainable society in a changing environment, and our society is steadily embracing urban green space for its role in mitigating heat waves and anthropogenic CO2 emissions. This study reports 2 years of surface fluxes of energy and CO2 in an artificially constructed urban forest measured by the eddy covariance method to examine the impact of urban forests on air temperature and net CO2 exchange. The urban forest site shows typical seasonal patterns of forest canopies with the seasonal march of the East Asian summer monsoon. This study shows that the urban forest reduces both the warming trend and urban heat island intensity compared to the adjacent high-rise urban areas and that photosynthetic carbon uptake is large despite relatively small tree density and leaf area index. During the significant drought period in the second year, gross primary production and evapotranspiration decreased, but their reduction was not as significant as those in natural forest canopies. We speculate that forest management practices, such as artificial irrigation and fertilization, enhance vegetation activity. Further analysis reveals that ecosystem respiration in urban forests is more pronounced than for typical natural forests in a similar climate zone. This can be attributed to the substantial amount of soil organic carbon due to intensive historical soil use and soil transplantation during forest construction, as well as relatively warmer temperatures in urban heat domes. Our findings suggest the need for caution in soil management when aiming to reduce CO2 emissions in urban areas.
Highlights
Cities make up only 2 % of the Earth’s land surface but hold more than 55 % of the world’s population
This study reported 2-year surface fluxes of energy and CO2 measured by the eddy covariance method in order to examine the role of artificially generated urban forests in mitigating air temperature and anthropogenic CO2 emissions
The study area is an urban park with an artificially planted forest in the Seoul Metropolitan Area redeveloped from a racetrack and factory in the mid-2000s, where it is influenced by a lengthy summer rainy season during the East Asian summer monsoon
Summary
Cities make up only 2 % of the Earth’s land surface but hold more than 55 % of the world’s population. It remains an urgent issue to implement integrated policies for climate change mitigation and adaption toward sustainable cities against global warming and related natural disasters Urban green infrastructures, such as urban forests, have been recognized as a key solution toward alleviating climatic and environmental disasters (e.g., Chiesura, 2004; Haaland and van den Bosch, 2015; Oke et al, 2017; Kroeger et al, 2018). When green spaces replace gray infrastructures during urban redevelopment, it remains unclear whether their benefits emerge in real conditions and thereby overcome their maintenance cost and other harmful effects (e.g., allergy and ozone increase). To leverage their full potential benefits, it is necessary to assess the biophysical effects of urban forests based on direct long-term monitoring in urban areas
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