Furthermore, research supports the idea that social capital is increased through community involvement in neighborhood parks (Gies 2006).
Environmental Health Parks and green spaces significantly improve environmental conditions in urban areas. Trees and plants improve air quality by producing oxygen and absorbing pollutants (Nowak and Crane 2006). Parks and green space also have the potential to benefit urban water by treating stormwater and increasing infiltration. Green surfaces are more permeable than pavement, and this has the effect of reducing stormwater runoff and increasing the amount of water that infiltrates the soil to groundwater basins and aquifers (Davis 2005). In addition, vegetation is important for removing pollutants from runoff, improving the quality of stormwater before it reaches waterways (Davis 2005). Numerous best management practices are available for implementation in parks and public spaces, which are directed at managing runoff and improving water quality (Davis 2005). These solutions can be of significant benefit to cities by helping to meet water quality standards and improving the safety and availability of public waters. Trees and green space also reduce the heat island effect by reducing the amount of urban surfaces that store solar heat, and by cooling the air through evapotranspiration (United States Environmental Protection Agency 2009). Tree canopies can reduce mid-day air temperatures above ground by 1.26 to 2.34 degrees F (Souch and Souch 1993).
Providing habitat for native species can also be an important function of parks and green space. Urban development displaces native species of plants and animals, many of which have become endangered or extinct (Murphy 1986). In southern California, whole ecosystems are now marginalized and endangered that once thrived in the lowlands, riparian corridors and coastlines where cities have developed (Haslam 1990). According to the field of landscape ecology, patches and corridors in the urban matrix such as parks and greenbelts can play an important role in providing habitat connectivity, thereby increasing the chances of survival for native species (Snep, Opdam, Baveco, Wallis, DeVries, Timmermans, Kwak and Kuypers 2006). Global warming is expected to threaten human health with more frequent and more intense heat waves and increased prevalence of infectious diseases (National Assessment Synthesis Team 2000, Patz 2000, Epstien 2000, Patz et al. 2000). Current measured environmental impacts of global warming include ice melting, especially at the poles; decline in arctic species populations; increase in sea level rise; increase in precipitation; and outbreaks of certain pest insect species (National Geographic 2011). Predicted impacts include continued sea level rise and ice melting, more erratic and catastrophic weather, floods and drought, less available fresh water, as well as extinctions and ecosystem changes (National Geographic 2011). Vegetative growth in parks and other green infrastructure counteracts global warming by taking carbon dioxide out of the atmosphere and storing it as woody tissue and soil organic matter (Billups 2001).
Figure 2–6.  Rio de Los Angeles State Park, Los Angeles; parks contribute to social and environmental health.
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Red Fields to Green Fields Los Angeles