Arboriculture & Urban Forestry 46(2): March 2020 The concept of the urban forest originated during the 1960s in North America and during the 1980s in Europe (Konijnendijk et al. 2005). Cordell et al. (1984) identified urban forestry in parks or squares, both commercial and residential pathways, green belts, and other urban sites. Urban forestry is also defined in terms of maintaining healthy and func- tional vegetation and associated systems that provide long term benefits desired by the community, with an emphasis on the role of people who manage and use the urban forest in providing for its sustainability (Dwyer et al. 2003). In recent years, it has been recognized that the main contribution of urban forestry is the impact on human health. These benefits to human health include the shade that trees provide (Nowak et al. 2006; Smargiassi et al. 2009), the reduction of the effect of the so-called urban heat island (Li et al. 2013; Haase et al. 2014), and the reduction of ultraviolet radiation, among others. The urban heat island effect can be defined as the occurrence of higher temperatures in central areas of the city compared to the adjacent peri-urban and rural areas; urban heat islands even generate micro-climates as a result of the combina- tion of urban morphology and the heat released by human activities (Colunga et al. 2015; Coronel et al. 2015). Furthermore, relative humidity converges to comfortable levels for human habitation (approxi- mately 55% to 60%), even though the gradients and oscillations depend on grey infrastructure (number of buildings and their height) and the distribution of trees, bushes, grass, and pavement (Weng et al. 2004; Petralli et al. 2006; Hamstead et al. 2016). This is because materials like concrete and asphalt are unable to absorb and retain water like plants can; however, these materials can absorb and retain solar radiation (Bowler et al. 2010). Another relevant variable linked to urban forestry is ultraviolet radiation (UV), especially in latitudes where there is a worrying reduction in the ozone layer as is the case for countries in the southern part of South America. Na et al. (2014) modeled functions to predict the mitigating effects of trees on UV radiation at ground level. Grant et al. (2002) developed a three-dimensional model to measure UV radiation for different tree canopy coverage, the results of which showed that cities located between latitudes 15° S and 30° S have identical exposures, while cities between latitudes 15° S and 60° S and with less than 50% coverage have an ultraviolet protection factor 85 (UPF) lower than 2. For other latitudes with a 90% coverage, the UPF was 10. As a result, the mitigation of the temperature, convergence of relative humidity to comfortable levels, and the reduction of UV radia- tion in public spaces is relevant for public policy making, particularly in a climate change context. Exposure to particulate matter is known to be asso- ciated with health problems in the population. Trees play an active role in the reduction of particulate mat- ter as with other atmospheric contaminants common in cities (Scott et al. 1999; Escobedo et al. 2006; Nowak et al. 2006; Bealey et al. 2007; McDonald et al. 2007; Litschke and Kuttler 2008; Escobedo et al. 2011; Vos et al. 2013; Irga et al. 2015). Hence, trees contribute to improving the health of the population by reducing rates of respiratory illness (Escobedo et al. 2011). However, the role that each different com- ponent of the phenotype of the tree plays in these pro- cesses, such as leaf size, stoma, density, meteorological conditions, among others, has yet to be set out in detail. Tiwary et al. (2009) were able to estimate in a quantity of 0.009 tons per hectare/year the particulate matter (PM10 ) retention capacity of grass, conifer, and broadleaf trees, which would be equivalent to a reduc- tion of two deaths and two hospital admissions in the same time period. Currently, air quality is monitored in contaminated cities so that restrictive measures can be taken against the polluting sources. The most com- monly measured particle sizes are PM10 and PM2.5 , as is the case in various cities in Chile (MMA 2011). Urban noise, also referred to as environmental noise, produces effects on the health of the population and can be catalogued in three different ways: physi- opathological, psychological changes, and physical harm. The effect of trees and green areas on reducing health and psychological well-being has been previ- ously studied (Gidlöf-Gunnarsson and Öhrström 2007). Fang and Ling (2003) estimated the effect of a belt of evergreen trees, concluding that trees are able to reduce negative health effects and calling it effec- tive reduction. Along highways, Pudjiwati et al. (2013) estimated a reduction of about 10% at a dis- tance of 20 meters from the road, while Samara and Tsitsoni (2007) determined that the most appropriate distance was 10 meters, taking into account a pine plantation for the same effect. Van Renterghem et al. (2013) studied the effect of hedges on the reduction of noise that comes from vehicles in cities, finding that high and dense hedges provide a noise reduction from light or slow moving vehicles. Furthermore, it ©2020 International Society of Arboriculture
March 2020
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