Learning to Live in Cities: Challenges of Urban Green Spaces

Sonali Chauhan

My work as a researcher in the field of ecology doesn’t always mean spending several hours in forested areas but it also means spending long hours in front of a computer doing regular administrative work. While I enjoy being in the field collecting data and working on plants, I am not particularly enthusiastic about sitting in front of a computer for several hours every day, although it is an essential part of my work. So, recently, I started growing some succulents and low light plants on my work desk to give me company while attending to mundane office work. Growing plants is very similar to conducting experiments in a Lab, and it is something that keeps me motivated. My new green companions are neither demanding nor do they require much time or attention (i.e. once you have identified their basic needs for survival and growth), instead they somehow manage to keep me calm while I scramble to finish routine office work each day. I am still intrigued by how such small plants, growing in a small space, can have such a calming effect on me and keep my spirits high.

Studies have shown that exposure to nature in cities is linked to not just better physical but also mental health. Scholars believe that experiences of nature are important for the urban population for they better a person’s “cognitive functioning, emotional well-being and other parameters of mental health” (Cox et al., 2018). The health benefits of green spaces are highlighted by WHO in a brief review report. The urban green spaces are also a priority area of the WHO Health 2020 policy framework. In the UK, it is a policy recommendation that every house should have access to “natural” green space within 300 meters. The call for green cities is becoming more and more vocal in policy domains. As a result, many cities have strict rules and regulations to maintain the green cover of the city.

However, creating and maintaining green spaces in cities is not an easy task. Take a moment to think about this: how do the harsh environmental conditions and increased pollution levels of cities affect plant populations? It is important to dwell upon this question if we are to maintain a healthy population of our green companions and ensure the conservation of urban green spaces. At this juncture, I would like to point out to an important study to further explain the need for us to ask such questions. Contrary to our thinking, researchers have concluded that planting more and more trees might not be a sustainable solution. This they found out is due to the fact that growth in urban trees is much faster than rural trees, although they have comparatively shorter lifespans. The result is negative carbon storage by urban street trees (Smith et al., 2019). Thus, the study calls for more attention to be given to the health of urban trees instead of investment of resources in planting more. This highlights the point that plantation drives without a scientific plan to monitor plant health are neither an environmentally sound nor an economically feasible solution. In the following sections, I wish to list out some other challenges that make conserving and managing urban woodlands a difficult and complicated task.

Where is the land?

Green spaces in cities can be categorised into two groups – patch and corridor. Examples of patches are gardens or remnants of forests while examples of corridors are roadside plantations and waterways. Whether patch or corridor, both require land that must be kept aside for greening. Further, when we talk of creating or preserving an urban forest, it means the setting aside of a large continuous space for non-human residents. Land in the city is not only a scarce resource but is also a valuable commodity.

There is always a constant demand for more and more land for housing, roads, industries, etc. Thus, conserving forests or large green spaces in the city becomes a difficult task. The demand for land has resulted in fragmentation and in most cases, complete decimation of important green spaces in cities. Recalling the recent protests in Delhi, the state government, the central government and several environmental activists were involved in a tussle over the cutting of more than 10,000 trees for construction and renovation of government housing colonies in Delhi (Mishra, 2018). Thus, green spaces in cities are not just ecological but also sociopolitical entities. Understanding this dimension of urban green spaces requires a completely different lens altogether and I might discuss this separately in a future blog post.

Overview of Bosco Verticale, Milan, Italy
A Moss Wall in Oslo, Norway

Recently, there have been some very innovative solutions being put forward by urban planners and architects in an effort to create green spaces that do not actually require land. Some of the interesting and popular examples are the Bosco verticale, a vertical forest residential building, and moss walls – green walls that are capable of capturing carbon much like trees. The concept of vertical gardening is now becoming very popular in cities. In Delhi, one might come across vertically lined plants on metro pillars or under flyovers. Although the scientific community has not yet actively studied the effectiveness of these novel interventions, such initiatives are indicative of the fact that people are thinking about countering the challenge of space while also seeing the need to incorporate greenery in the design of built spaces.

New Environmental Conditions and New Green Companions

Now, let’s talk about environmental and ecological challenges faced by urban green spaces. Even if we do manage to conserve green spaces in the city, they may lose their integrity over time due to changes in abiotic elements such as temperature, light, soil, as well as increased biotic pressure of predation and competition from invasive species.

It is well known that cities have a higher temperature than their rural counterparts. This difference in temperature is known as the “heat island effect”. Temperature plays an important role in plant physiology. Similarly, the activities of some plants are synchronous with the daily variation of light. For instance, some plants open their flowers at a particular time of the day. Light is a source of energy for plants, but it also provides important cues for flowering, germination and growth. Increased use of artificial lighting in cities affects plant phenology and interactions such as pollination and dispersal (refer to my previous blog post for details). Urban soils are also found to be different in their concentration of organic carbon. An urban-rural gradient-based study conducted in the city of Baltimore, USA found that urban soils have relatively high organic carbon densities compared to suburban and rural areas (Pouyat et al., 2002). This study concluded that changes associated with increasing urbanization have impacts on “soil chemistry, composition and nutrient fluxes”.

All these environmental changes are likely to threaten the survival of native plant communities that have adapted to certain environmental parameters. These altered home conditions in the urban may also positively affect new companions or alien species and promote their invasion. In a previous blog post, I used the example of the Delhi Ridge forest to highlight the threat of invasive species that urban forests have to constantly contend with. In another study of an urban forest (Tifft Nature Preserve) on the western shore of Lake Erie in the City Buffalo, USA, researchers concluded that in the absence of a proper management plan, the existing urban forest may eventually be converted into an “invasive species dominated urban shrub land”.  This study highlights the failure in native tree seedling recruitment (i.e. germination of a new individual, survival and growth into a young plant)as a result of factors such as limitedseed dispersal, increased rate of predation by herbivores, and competition posed by understory invasive plants (Labatore et al., 2017).

In order to survive, plants have to overcome both abiotic and biotic filters. In an urban scenario, the range of these filters keeps expanding, posing serious threats to the survival of plant communities. This complex hierarchy of filters creates new challenges and research opportunities that need to be addressed by scientists, architects and planners for the conservation of urban green spaces and the creation of resilient cities.

References

  • Cox, D. T., Shanahan, D. F., Hudson, H. L., Fuller, R. A., & Gaston, K. J. (2018). The impact of urbanisation on nature dose and the implications for human health. Landscape and urban planning, 179, 72-80.
  • Labatore, A. C., Spiering, D. J., Potts, D. L., & Warren, R. J. (2017). Canopy trees in an urban landscape–viable forests or long-lived gardens?. Urban ecosystems20(2), 393-401.
  • Mishra, Alok (2018, July 04). Revoke Tree Cutting Nod for 3 projects: Govt to LG. Times of India.
  • Pouyat, R., Groffman, P., Yesilonis, I., & Hernandez, L. (2002). Soil carbon pools and fluxes in urban ecosystems. Environmental pollution116, S107-S118.
  • Smith, I. A., Dearborn, V. K., & Hutyra, L. R. (2019). Live fast, die young: Accelerated growth, mortality, and turnover in street trees. PloS one14(5).

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