Research in the 1990s and 2000s began to quantify the benefits of urban trees beyond aesthetics, with cooling and slowing of stormwater recognised as particularly important, as well as many others (McPherson et al., 1997). More recently, urban trees have been identified as integral ecological structures in cities supporting a wide variety of wildlife (Stagoll et al., 2012), a key mechanism to help cities adapt to climate change (Gill et al., 2018) and mitigate the urban heat island effect (Livesley et al., 2016).

Urban forests support improved human health and wellbeing via a number of pathways – encouraging physical activity such as walking, reducing extreme heat, reducing stress, encouraging social interactions, and exposing people to diverse ‘microbiomes’ (Flies et al., 2017). Trees also contribute to the ‘sense of place’ of cities and the character of neighborhoods (Pearce et al., 2015). More recently, the importance of urban forests in supporting the cultural practices of Indigenous people is being recognised (Marin, 2019).

In the future Melbourne will experience a changing climate, becoming increasingly warm, dry and liable to more frequent extremes of heat and inundation.

Trees are a really important way that cities can adapt to climate change. They help cool the city through shading and ‘evapotranspiration’ where trees move water from the soil to their leaves where it evaporates - like an evaporative air conditioner. This makes trees much cooler than roads or buildings. Perhaps more importantly, this makes areas with trees ‘feel’ much cooler for the people nearby. This can lessen the impact of predicted temperature increases and heat waves from climate change. Trees also help avoid the ‘urban heat island’, where heat is stored in roads and buildings during the day and released overnight, increasing overall temperature.

We now know that the urban forest itself also needs to be adapted to climate change. Many tree species in Melbourne are already at the upper limit of temperatures where they are known to grow well – if average temperatures get warmer, these trees will struggle to thrive. A key to managing the forest in the face of change and uncertainty is to increase diversity – to plant new species and reduce reliance on a small number of widely planted species where future performance is uncertain.

Over the last 20 years, there has been a great deal of research showing that cities are important for biodiversity. Cities are often found in biodiversity hotspots, including Melbourne which is at the intersection of grassland, highlands and plains bioregions that have very different natural vegetation communities.

In Australia, many threatened species are found in cities, and rely on cities for their survival (Ives et al., 2016). Biodiversity in cities is also an important component of people’s connection to nature, and sense of place – as local species and ecosystems are found nowhere else (Threlfall and Kendal, 2018). The City of Melbourne is home to many native wildlife species – birds (239), reptiles (12), mammals (18), frogs (7), insects (over 1500), and fish (31).

Contemporary approaches to urban biodiversity extend this focus on species diversity to ecosystem ‘function’ such as nutrient and energy cycling, the ability of plants and animals to reproduce and disperse to different parts of the city, and that support important services such as pollination and cooling.

The urban forest is a critical part of Melbourne’s biodiversity – it extends across the whole municipality connecting different natural ecosystems, provides habitat for many species of wildlife, contains and supports many native plant species, and is accessible by everyone living in and visiting the city.

Another contemporary approach to biodiversity conservation and natural resource management is to respect and incorporate Indigenous knowledge into management, empowering Traditional Owners to care for country and building capacity and capability within Aboriginal and Torres Strait Islander communities. The City of Melbourne is located on the lands of the Wurundjeri Woi-wurrung and Bunurong Boon Wurrung peoples. Traditional Owners have a special relationship with many plant and animal species in the city, and urban forest management aims to respect and maintain these relationships in the way the urban forest is managed.

Important places for Traditional Owners can be found on a map of Aboriginal Melbourne. There are also many Aboriginal and Torres Strait Islander people, and other First Nations people from around the world, in Melbourne. Urban forests are a key opportunity for these peoples to maintain connections with nature and traditional cultural practices.

The diversity of the urban forest itself is also important for its own health. Having a diverse forest provides some protection against catastrophic tree loss from climate change or pests and diseases. Using a wider range of species, reducing reliance on a few dominant species, and using seed grown rather than genetically uniform clonal trees can all increase the resilience of the urban forest to catastrophic loss (Lohr et al., 2016). Having different species that provide the same functions and services and that respond in different ways to pressures such as climate change means that the urban forest will continue to provide benefits to people despite an uncertain future.

There has been a great deal of research on the benefits of urban forests in Melbourne over the last 15 years. Local research has shown that Melbourne’s trees can:

• cool streets by 1.5°C, and increase human thermal comfort by up to 5°C (Sanusi et al., 2017)
• remove AUD$200/tree of nitrogen runoff (Baptista et al., 2020)
• are an important contributor to sense of place and the cultural life of residential areas (Pearce et al., 2015)
• promote diverse native bird (White et al., 2005) and bee (Threlfall et al., 2015) communities when structurally diverse native species are used.

There are a few key challenges that must be addressed in urban forest management plans. Cities have limited space for trees, and many streets have restrictions overhead and underground where many services (water, sewerage, telecommunication and electricity wires) can be found, and on the ground where trees must coexist with footpaths, roads, parking and buildings.

The City of Melbourne has been working closely with planners and engineers to make sure that trees are considered when infrastructure development occurs. Nonetheless, finding adequate space for trees, particularly large trees is a challenge for increasing canopy cover and biodiversity in cities.

Another current challenge is managing urban forests equitably. Research has found that many urban forests are distributed inequitably – that disadvantaged areas have less access to the benefits urban forests provide, and are less involved in decision-making around the urban forest (Threlfall et al., 2022). A key challenge for urban forest managers is not to reinforce this inequity – to make sure that diverse voices are heard in urban forest planning and management, and that the benefits from urban forests are available to everyone in the city.

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