The ecosystem services and environmental benefits of urban green spaces are sometimes overlooked though constantly perceived. This happens because the common appreciation of services normally relates to their monetary value, especially when it comes to political decisions and priorities, even in the face of residents expressing their appreciation of the amenity of green spaces as priceless.
2.5.5.1. Appreciating and valuing the benefits
Although science has clearly confirmed the role of natural processes in providing the essential life-support services from which humans gain benefit and on which they are highly dependent (Daily et al., 1997), such processes tend to be neglected because their values have not been clearly priced or sufficiently measured by commercial markets (Costanza et al., 1997). Additionally, most of the time the role of nature is undervalued as people never have to pay for its benefits (Gregory Mc Pherson, 1992).
One obstacle to valuing environmental services is the fact they are difficult to quantify (Gregory Mc Pherson, 1992). Their contribution to people's prosperity cannot be measured by conventional macroeconomic indicators as these ignore non-market services and the costs of natural capital depletion for the next generation (Howarth &
Farber, 2002). Despite the difficulties in measuring benefits in monetary terms, much research has been aimed at attempting to disclose their economic value because when it comes to the political agenda, before any funding for natural capital investment can be
made, everything has to be economically convincing. Therefore, research into market value equivalence is necessary to help authorities and political powers give more attention to and make more provision for natural settings and ecosystems in their decision making (Daily et al., 1997). This is because an evaluation method of urban green space benefits is important in justifying their significance relative to other types of infrastructure development in monetary terms (Gregory Mc Pherson, 1992).
Likewise the ecological and economic benefits of urban green space can be divided into direct and indirect benefits. Direct economic benefits are obtained under the economic value of the environmental service functions of any components of the green space. The indirect economic benefits are derived from the economic value gained due to the presence of the green space in an area. The direct economic value of urban green space can be estimated by employing marginal cost as a way to price the benefit. It means the cost of producing or generating one benefit or one substance (for instance air pollution abatement) is used to estimate the economic value of the service. This method was used by Jim & Chen (2008) for evaluating the air pollution removal service of urban trees.
Three methods have been proposed for evaluating indirect benefits (Gregory Mc Pherson, 1992) as listed below.
1. Travel cost method
This method assesses the benefit by using the money people have to spend to visit the features. This is only effective when evaluating the benefit of distant parks and urban green spaces.
2. Contingent valuation
Here the valuation is based on people’s willingness to pay, which is compared to the real amount people are paying.
3. Hedonic pricing method
This method is believed to be most effective because people’s preferences are influenced by and reflect some of the off-site external benefits, such as pollution abatement, noise reduction, attractive view, and presence of wildlife. The hedonic pricing method assumes the value of the benefits by correlating costs and prices of market transactions.
Howarth & Farber (2002) have suggested the three methods could be used to generate a shadow price that represents the marginal contribution of the green space to human satisfaction in monetary units.
2.5.5.2. How much is gained?
In terms of appreciating the benefits of environmental services, they have to show an attractive economic profit to gain attention (Gregory Mc Pherson, 1992). Therefore, it is very important to document the value of all benefits in order to gain up front funding for green investment, rather than it being only given what is left over in the budget (Benedict & McMahon, 2002).
The role of natural capital should not be underestimated. One study estimated, the value of environmental services on average was 183% more than total global GDP (Costanza, et. al. 1997). However, this claim is debatable and has led to the accusation there has been an overvaluation of people’s willingness to pay for the services and an underestimation of compensation from the loss of ecosystem services (Pearce, 1998). In addition, the method and specific data are provisional and open to criticism (Howarth &
Farber, 2002).
Despite the debate regarding the magnitude of ’real monetary value‘,benefits do have economic value. A study in Ghuangzou, China estimated the annual value of air pollution removal by urban trees at US$744,969.4 (Jim & Chen, 2008), compared with US$3.3 million each year by the 6 million trees of Sacramento’s urban forest (Mc Pherson, 1998) and the $3.8 billion value of pollutant removal by various US urban trees (Nowak et al., 2006). Another study identified 1675kg of air pollutants were removed by 19.8ha of green roofs in one year in Chicago (Yang, Yu, & Gong, 2008).
The annual monetary value of pollutant removal by urban trees in the same city reached US$9.2 million.
The benefit of pollutant removal by trees in urban green space would also have significant economic value in cities in the developing world, as these cities usually have a limited budget for pollution abatement efforts.
In conclusion, most of the benefits of urban green space described above can also be explained as ecosystem services beneficial for humans within their living environment
(Costanza et al., 1997; De Groot, Wilson, & Boumans, 2002). In turn, the level of these benefits depends on the state of a green space in terms of its ecological richness and biodiversity (Fuller, Irvine, Devine-Wright, Warren, & Gaston, 2007).