For most people in cities, contact with nature comes through highly curated environments such as gardens, parks and nature reserves. Yet, scattered throughout cities there are many ‘informal’ and unmanaged green spaces that go unnoticed. Informal green spaces include abandoned lots, overgrown pavements, and fenced off railway corridors - all ubiquitous sights of urban landscapes. While these sites are often perceived negatively, recent insights in urban ecology suggest that these spaces might be important biodiversity hotspots.

Research suggests that managed green spaces alone cannot support the full range of biodiversity within cities, especially when it comes to less charismatic species such as insects or spiders whose populations are already in decline. Additionally, many barriers to creating new managed spaces exist such as high competition for land that results in green space creation often being a low priority for councils. In the absence of committed management or funding, then, could informal green spaces help contribute to maintaining biodiversity in urban areas?

Perhaps unsurprisingly, informal green spaces have a broad diversity in size, species, and structural characteristics. Some appear nascent, occurring on recently abandoned plots, while other spaces have been left untouched for years, often with a wealth of both invasive and native species uneasily co-existing.

One third of vegetation in these spaces were native species, especially trees, suggesting that informal green spaces are contributing to canopy cover, which not only provides habitat but also helps to cool urban areas. Around 40 percent of recorded species are invasive, including dense stands of Lantana camara, which can outcompete native flora and is generally considered problematic. However, studies show that lantana thickets provide important understorey shelter for many species such as superb fairy-wrens and brush turkeys by protecting them from predators like cats and foxes. While gradual restoration that phases out lantana is preferable, many councils may lack the financial resources or the willingness to prioritise remediation of these neglected places and care should be taken to ensure that vegetation structures are not disrupted in a way that risks wildlife that use it for shelter.

Due to their ubiquitous presence, informal green spaces also have the remarkable potential to connect Sydney’s isolated patches of managed green space together. Highly connected webs of green space increase resilience of their hosted species through the ability to migrate and replenish lost populations. Similarly, informal green spaces are sometimes the only avenues for heavily industrialised areas to retain wildlife, especially in areas where councils do not have the maintenance of managed parks as a priority.

Ultimately, informal green spaces are the result of ecological succession— the process of self-establishing, competing against other species, and proliferating— and while this may act as form of resilience for native species, this same process can also drive weedy species to thrive within urban cities such as Sydney. It is impossible to generalise all informal green spaces as ‘bad’ or ‘good’— instead, they should be evaluated within the context of their surroundings and history, before deciding if it should be retained as-is, remediated, or cleared.

There is much to be gained from recognising the ecological value of these overlooked spaces. By shifting how we perceive them, we can expand our understanding of urban nature and identify new opportunities for supporting biodiversity across the city. These informal green spaces should be researched further to more efficiently utilise urban areas and increase nature interactions with urban residents.

This article was written by Catherine Gunawan, whose work in urban ecology continues to deepen our understanding of how novel ecosystems support biodiversity in Sydney.