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Why everyone should get on the Urban Greening bandwagon

The mitigation of urban heat island effect is one of the most significant impacts of the abundance of flora in Melbourne Gardens, and it's all down to urban greening – the cooling capacity of just one small tree has been likened to two residential air conditioners. Here's why we should all get on the urban greening bandwagon.

Did you know that on a hot summer’s day, the temperature in Fern Gully is significantly lower than the temperature in the middle of the city, even though it’s less than 1 km away?

But how?

The 'urban heat island' effect is a fascinating phenomenon which results in urban areas being generally warmer than surrounding green areas, due to their high concentration of roadways and industrial building materials. Concrete, steel and other hard surfaces capture and store heat which is released at night in conjunction with waste heat from cars and buildings.  The lack of permeability and vegetation in urban areas results in less cooling capacity from evapotranspiration and shading.

The mitigation of urban heat island effect is one of the most significant impacts of the abundance of flora in Melbourne Gardens, which forms the largest and most varied collection of urban vegetation in the city. The cooling capacity of just one small tree has been likened to two residential air conditioners.

The Gardens has been conducting a microclimate monitoring/mapping project since 2012 to determine whether specific locations within the gardens could act as microclimates to protect future vegetation from increasing temperatures as climate change escalates. The project revealed that certain irrigated areas within the Gardens, most notably Oak Lawn and Fern Gully, were significantly cooler than the city - in some cases by up to 6° C. Fern Gully is the beacon of cooling capacity in the Gardens— typically most days Fern Gully is 2 °C cooler, and a little under half the days 3 °C  cooler than the city. This supports the theory that vegetation can reduce urban heat island effect, and makes Fern Gully the perfect place to take a moment to relax and reflect on a hot day. 

Research has shown that establishing greener infrastructure has a wide range of positive impacts on our environment and could be vital in helping mitigate the effects of climate change, particularly rising temperatures.

Aside from the mental and physical health benefits we experience when we spend time in nature, green spaces have a range of positive effects on the environment, including improving air quality, enabling carbon sequestration, reducing flooding (greenspaces act like sponges during flooding – slowing runoff and absorbing water), and providing habitats for rare and threatened remnant flora and fauna, as well as increasing the energy efficiency and liveability of buildings.

Urban greening refers to all forms of vegetation in urban environments, including street trees, lawns, green walls/rooves, and open parks and gardens. While 24% of Melbourne is covered by trees or shrubs, the majority of this coverage occurs within residential areas, leaving our urban spaces decidedly lacking in vegetation, and escalating housing development projects and the predicted impact of climate change and population growth on our environment mean we must do everything we can now to ‘green’ our urban spaces.

If you're living in an urban area and want to 'green-ify' your space, it's worth noting that the cooling potential of green spaces relies on the plants having ready access to a water supply. Cacti and succulents, for example, have little cooling capacity despite being optimum water-saving plants. The ideal plants are those that are resilient to drought conditions, will readily use sustainable sources of water when available to cool the air by evapotranspiration, and provide overhead shade. There are numerous Australian species that have a high potential for urban greening - Peter Symes, Curator Horticulture at Melbourne Gardens, suggests that if you have some space that dry rainforest species such as the vibrant Brachychiton acerifolius (Illawarra flame tree) could be ideal. They have drought tolerance but are also able to utilise water when it's present and make for a beautiful addition to a landscape.

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