55% of the world’s population now live in urban areas – in Europe, that number soars to almost 75% (The World Bank, 2020). These cities can be extremely densely packed, making green spaces difficult to preserve, and even harder to squeeze into established areas (Haaland & van Den Bosch, 2015). When gardens, parks and fields are replaced with more housing, the loss of green space is not made up for elsewhere – with increased urban densification (high population in a small area), green space is often the first casualty (Haaland & van Den Bosch, 2015). This post will look at why green space is important, but why creating more is not always as simple as just planting trees along a road.
Examples of urban green spaces include parks, forests, green roofs on buildings, community gardens, urban trees and even the vertical application of turf (Haaland & van Den Bosch, 2015; Cameron et al., 2012). As you might expect, these areas and features can provide a range of benefits to both local biodiversity and human health – from filtering air, providing food and cooling temperatures, to improving the local bird species diversity and reducing habitat fragmentation (Tzoulas et al., 2007). In fact, it was found that for the UK city of Manchester, a 10% in green spaces would negate the 4 degree C increase in temperature predicted by 2090 (Cameron et al., 2012).
“Based on a study of five major UK cities, if 20% of the population within 2 km of an 8–20 ha green space used that space to reach a target of 30 min activity on 5 days a week, the saving to the UK’s National Health Service would be more than £1.8 million (€2.7 million) a year.” – Tzoulas et al. 2012
But creating urban green space is not as easy as you might think. There are a range of social, cultural and economic factors to consider when building a green network in a city. The first question to ask yourself might be, “what kind of green space do we want to create?” Research has found that though green space like parks can make healthier neighbourhoods, they also increase house prices, which can lead to property becoming unavailable for the people who need it in the area (Wolch et al., 2014). For example, when New York’s High Line, a disused train line now completely covered in plants, was created, it led to property values within the region increasing by 103% between 2003 and 2011 (Wolch et al., 2014). These changes are evidence of a process of “ecological gentrification”, whereby the infrastructure and affordability of an area is impacted to the point where local people are disadvantaged (Wolch et al., 2014).
In many countries, inner cities are home to a large proportion of people of colour and low-income earners (Wolch et al., 2014). In US cities for example, it is these people most likely to be affected by ecological gentrification, since wealthier (predominantly white) households tend to live on the outskirts (Wolch et al., 2014). Low-income earners already have less access to green space than more affluent communities (Aronson et al., 2017), and are more likely to be affected by inner city infrastructure changes. This theory has been shown in a number of examples – in some towns of the Eastern Cape, South Africa, street trees are more diverse in wealthier neighbourhoods, and in Phoenix, Arizona, wealthier neighbourhoods support the largest number of lizard species (Aronson et al., 2017). Clearly, wealth and race influences access to biodiversity.
“Negative relationships among biodiversity, access to green space, and occurrence of racial minorities have been documented in both northern and southern hemisphere cities, primarily driven by socioeconomics and segregation legacies” – Aronson et al. 2017
Management of current green spaces is another issue for consideration. An increase in gardens for example, might be associated with improved food provision, carbon offsetting or biodiversity gains. But it could equally be tied to an increase in fertiliser and pesticide use, invasive ornamental species and increased water consumption (Cameron et al., 2012). Common management practices such as pruning, removal of leaf litter (dead leaves) and growing turf lawns instead of woodlands could do more harm than good on an environmental level (Aronson et al., 2017). And when management is not coordinated across areas, the full biodiversity benefits of management activities cannot be gained – For example in Chicago, USA, collective wildlife-friendly management across many individual gardens had a far greater benefit on native bird population, compared to single gardens considered alone (Aronson et al., 2017).
Aronson et al. (2017) suggested the first steps in improving urban biodiversity are to improve what is already present in urban areas, through enhancing biodiversity and coordinated management. And to mitigate ecological gentrification, a “just green enough” approach has been suggested – this is a way which puts the concerns of local communities central to the planning process, rather than prioritising the ecology or aesthetics of an area (Wolch et al., 2014). Focusing on smaller projects is also more likely to benefit local people, since it avoids the creation of large features that property developers could capitalise on. There is evidence that urban green spaces can improve city life – in the “Garden City” of China, Hangzhou, dilapidated factories, canals and other neglected areas have been transformed to green spaces, leading to temperature reductions of 4-6oC in some parts of the city (Wolch et al., 2014). Green infrastructure presents a huge opportunity for urban developers to improve millions of lives – I remain hopeful that our cities will be a lot greener in the future.
Aronson, M.F., Lepczyk, C.A., Evans, K.L., Goddard, M.A., Lerman, S.B., MacIvor, J.S., Nilon, C.H. & Vargo, T. (2017) Biodiversity in the city: key challenges for urban green space management. Frontiers in Ecology and the Environment, 15(4), pp.189-196
Cameron, R.W., Blanuša, T., Taylor, J.E., Salisbury, A., Halstead, A.J., Henricot, B. & Thompson, K. (2012) The domestic garden–Its contribution to urban green infrastructure. Urban forestry & urban greening, 11(2), pp.129-137
Haaland, C. & van Den Bosch, C.K. (2015) Challenges and strategies for urban green-space planning in cities undergoing densification: A review. Urban forestry & urban greening, 14(4), pp.760-771.
The World Bank (2020) Urban Population. [online] Available at: https://data.worldbank.org/indicator/SP.URB.TOTL.IN.ZS (Accessed: 07/10/2020)
Tzoulas, K., Korpela, K., Venn, S., Yli-Pelkonen, V., Kaźmierczak, A., Niemela, J. & James, P. (2007) Promoting ecosystem and human health in urban areas using Green Infrastructure: A literature review. Landscape and urban planning, 81(3), pp.167-178
Wolch, J.R., Byrne, J. & Newell, J.P. (2014) Urban green space, public health, and environmental justice: The challenge of making cities ‘just green enough’. Landscape and urban planning, 125, pp.234-244
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