Playbook for Urban Biodiversity

1. Small habitat patches don't matter

Myth

Small patches of habitat come in many forms including bushland remnants, backyards, nature strips, rain gardens, green roofs and many more. New research quantifying the Single Large or Several Small (SLOSS) debate is turning old ideas about the importance of large patches on their head and showing that cumulative loss or gain of small patches can have far-reaching consequences.

Counter arguments

Challenging traditional perspectives

Diamond provided original theories on the significance of habitat patch size, denoting that a single large patch of habitat (SL) is better than several smaller habitat patches (SS). It was believed that a SL habitat can host more species, thus mitigating the risk of species extinction. This theory has since been popularised in practice, where large natural areas, for example state and national parks, are prioritised for action and management, whilst smaller habitats are deemed unimportant for conservation.

Recent and emerging research has since identified that small habitat patches are in fact important for biodiversity conservation and serve many benefits. Multiple small habitat patches frequently foster greater species diversity across a wider range of taxonomic groups than a single large patch of equal size. Further, migratory birds and pollinating species often benefit from having access to many small patches of habitat.

Within cities, small persisting habitat patches have been deemed essential for the survival of urban species. Australian cities are biodiversity rich, harbouring greater species diversity and threatened biodiversity than non-urban environments, highlighting the important role these spaces play in saving species from extinction. Small patches of remnant habitat are distributed across a landscape of human modified environments, increasing overall landscape diversity and presenting novel habitats to urban species. Evidently, current research highlights the need for policy and practice to shift the focus from minimum patch size and prioritise minimum total area of all patches.

Patch composition, arrangement and distance matter

Although the narrative is changing, habitat composition and distance between patches continue to play important roles when determining habitat value. Small habitat patches need to be size- and site-specific, for example, grass and vegetation cover, presence of old trees and size of a city square influence the diversity and abundance of urban birds. In other taxa groups, insect diversity has been strongly linked to understorey vegetation cover.

Further, there is evidence suggesting that patches situated within the urban landscape, amongst other patches, has the strongest positive effect on biodiversity. Therefore, future urban planning should focus, not only on preserving and enhancing small habitat patches, but also in creating a network of corridors with these small patches.

What are these urban habitat patches? And what do they look like?

Urban habitat patches are and can be anything from road verges, median strips, roundabouts, green roofs, backyards, rain gardens, bushland remnants and so forth. As practitioners of the urban environment, it is crucial to expand our knowledge on what we know and believe habitats are and can be, as there is much potential to explore the untapped value of small patches in cities. By identifying these spaces as potential habitat patches, we can then consider the possibility, appropriateness and pathways to transform into a space that species may use.