Arboriculture & Urban Forestry 46(2): March 2020 was US $228, PM2.5 was US $22, PM10 was US $1,877, and carbon sequestration was US $601. The carbon storage value by all of the heritage trees was US $76,019. The average value provided by heritage trees was US $10.2/tree/yr from air purification, US $0.8/tree/yr from carbon sequestration, and US $96.2/ tree/yr from carbon storage. The monetary values were much lower than expected. Calculation of monetary values depended on the cost of pollutant removal or the market price of car- bon emission. Regarding the monetary values of eco- system services, the relevant information is lacking for Macau and rather inadequate in the literature. Nowak et al. (2008) calculated the values of ecosys- tem services of urban forests for the United States. Other similar studies have been conducted. For exam- ple, in China, the economic benefits of NO2 reduction reduction were estimated to be CNY 4,757/t in 2010 (Pedersen et al. 2014). Converted by the exchange rate (exchange rate at USD : CNY = 1 : 6.8 in 2010) and adjusted by inflation (8.8% in 2010 through 2012 in Macau), NO2 were estimated to be CNY 21,383/t, and the benefits of SO2 mated value of US $3,421/t and SO2 and SO2 reduction had an esti- an estimated value of US $761/t. Based on these values, the heri- tage trees in Macau only provided one-fourth to one- third of the benefits of NO2 removal on a monetary basis because of a lower monetary value projection for air-pollutant removal in China, partly due to the considerable discrepancy in price indices between China and western countries. However, the air purification ability of trees subsi- dized the cost of air-pollution reduction or created economic benefits to the society such as reduction of health-care costs. The benefits were proportional to the population density. The per-tonne values of NO2 SO2, O3 , , and PM2.5 were calculated by regression equations in conjunction with population density for urban areas in the United States by Hirabayashi (2014). With Macau’s high population density, which reached 19,000 people/km-2 (Statistics and Census Service 2013), the monetary values were US $10,564/t, US $2,838/t, US $74,008/t, and US $2,821,256/t, respectively, for NO2 PM2.5 , SO2 , O3 , and . The monetary value of air purification by the heritage trees would be about 3.5 times the calculated values from Nowak et al. (2008). A similar situation was found for the cost of carbon removal. For exam- ple, the economic benefits of CO2 reduction in China 129 were CNY 130/t in 2010 (Pedersen et al. 2014). Mean- while, the Carbon Pricing of Guangdong Emissions Trading Scheme was only set at US $10/t in 2013 (The World Bank 2014). The differences in the carbon reduction price could be as large as 13 times the current literature. The monetary benefit gained from carbon sequestration and storage of the heritage trees in Macau depended not only on the tree size and carbon seques- trating ability; it also depended on the market’s mon- etary value for CO2 reduction using technological means. Different monetary values of the heritage trees could be estimated due to widely divergent costs of abatement for pollutants and carbon, which may dif- fer by 10 times. The benefits of air-pollutant reduc- tion should be unusually large in Macau in comparison with other cities, due to the inordinately high average population density, which is the second highest in the world (The World Bank 2017c). Adverse impacts of air pollution have affected millions of residents in dense urban areas. Reducing pollution concentration can significantly depress the total medical expenses of a community and generate a huge economic value to the society. Trees in urban areas with a large human population can bestow an exceptionally valuable health service on more citizens on a sustainable basis. This study estimated the value of the removal of five air pollutants and gross carbon sequestration by the heritage trees without addressing additional local and direct ecosystem services of trees, such as micro-climate regulation, noise abatement, rainwater drainage, groundwater recharge, flood prevention, sewage treatment, and recreational and cultural val- ues (Bolund and Hunhammar 1999). Cooling due to urban greening can contribute to potential carbon avoidance from energy saving of buildings, which could be four times larger than the direct carbon sequestration rate of vegetation (Nowak and Crane 2000). The 309 park trees in Toronto, Canada, were estimated to provide US $29,251 in total (US $95/ tree/yr)(Millward and Sabir 2011), which contributed 61% of services in relation to local property value, energy savings, and stormwater reduction. Air-quality improvement and CO2 reduction only accounted for 5% and 1% of total benefits, respectively. The poten- tial values of the heritage trees will be much higher if the monetary value computation can include more ecosystem services. Under such estimation, the heri- tage trees in Macau would provide up to US $221,905 (US $281/tree) annually. ©2020 International Society of Arboriculture
March 2020
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