Maintaining biodiversity in the city: The role of local-government planning

Contrary to popular perception, urban environments in Australia still support significant biodiversity, including more than 400 nationally listed threatened species [1].

Urban-dwelling species come in all shapes and sizes, from delicate orchids in Canberra to towering gum trees in Hobart, secretive bandicoots in Melbourne or brazen parrots in Perth [2]. Cities also support populations of endangered lilies, grevilleas, frogs, flying-foxes, tortoises and lizards

Intriguingly, 39 of these species are now found only in urban areas: cities are literally our last chance to save them from extinction [3]. Conservation actions can help our city-dwelling native plants and animals overcome many of the challenges they face in the urban landscape.

A growing body of research supports the value of urban biodiversity for city-dwelling humans. Interaction with nature in cities can reduce stress levels, blood pressure, cardiovascular disease, anxiety, depression, frustration and anger, while improving mood, self-esteem, cognitive function, academic performance and productivity [4]. Access to these benefits diminishes as urban biodiversity is lost and as people in cities become increasingly disconnected from nature over time [5].

With all this at stake, local-government planners face pressure to balance many competing interests in urban landscapes, including a trade-off between actions that will benefit people and nature in the short and long term. In a recent essay, The seven lamps of planning for biodiversity in the city, we presented seven ecological principles (or lamps) to metaphorically bridge the gap between planning for the human and the more-than-human in cities.

Here, we discuss three sets of actions to 'turn on these lamps' to help maintain biodiversity in the city.

Maintaining or restoring movement across the landscape

Wildlife in cities needs freedom to move, in just the same way that human residents do. All animals explore their surroundings to find food, water, mates and safe places to rest or nest.

Cities can be hard places for animals to thrive, as the resources they need for survival may be sparse and isolated in small pockets (or patches) of habitat. These valuable fragments are often separated by major roads, railways or high-rise buildings that form a barrier to animal movement. Adding new habitat resources and connecting existing habitat patches can help make our cities more hospitable for urban wildlife. However, councils often need to trade off the costs of providing biodiversity-focused resources with other infrastructure requirements.

Ecological connectivity theory describes how easy or difficult it is for an animal to travel across a landscape. Measures of ecological connectivity can be used to identify places where adding new habitat or removing barriers to movement will give us the greatest gains, maximising the biodiversity benefits of linking nature within the city.

We worked with the City of Melbourne to develop a simple, step-by-step Framework for measuring ecological connectivity for seven species groups of animals with diverse habitat requirements: insect pollinators, aquatic insects, amphibians, reptiles, woodland birds, hollow-using birds and hollow-using bats [6]. The framework guides a user through the selection of appropriate habitat and potential barriers to movement for each target group. Once these have been identified, the connectivity of the landscape is measured by mapping the area of habitat that the animal can access, given how far it can move.

The map below shows how this framework was used to measure ecological connectivity in the City of Melbourne for insect pollinators such as the dainty swallowtail butterfly or blue-banded bee, and to identify the priority road barriers to remove. These species can only travel relatively short distances (<1 km) so finding ways to connect habitat patches across road barriers becomes especially important.

Local government and conservation practitioners can use this publicly available framework to plan biodiversity actions, assess the impact of different developments, identify landscape features that create barriers for our target species (such as roads), and prioritise conservation actions at locations that would improve connectivity the most. While focused on animals, this approach can also benefit many species of native plants that rely on animals for pollination of their flowers or dispersal of their seeds.

Recognising and protecting the conservation value of urban wetlands

Urban environments in Australia are critical for the conservation and management of many wetland species [7]. Urban wetlands provide water, food and shelter: resources that might otherwise be scarce and are particularly important for nomadic and migratory species that rely on these spaces during critical times within their life cycle. More than one-quarter of urban-occurring EPBC-listed species use urban wetlands [8]. Ultimately, urban wetlands provide key refuge habitat, or stepping-stone habitat, in a landscape that may be otherwise inhospitable.

Urban wetlands take a variety of forms and often include artificial or unconventional habitats that were not originally intended to support biodiversity [8]. For example, retention basins, disused quarries, rain gardens and swales, wastewater-treatment plants, backyard ponds and even concreted drainage lines have all been shown to support native wetland-dependent species. Conservation opportunities are therefore not restricted to more ‘natural’ looking wetlands; we should also consider the potential value of unconventional spaces. The removal of wetland habitats, particularly those that are small, informal, ephemeral or artificial, is a common threat to wetland-dependent species in urban environments. Causes of wetland loss include draining, infilling or land reclamation for development. Wetland loss can also occur as an incidental consequence of nearby development or land-use change, as hydrological flows are altered.

Other threats to urban wetlands and their biodiversity result from processes occurring in the broader urban landscape, such as reduced connectivity due to urban infrastructure, increased pollutant and nutrient loads and reduced water quality from stormwater run-off. Urban wetland conservation can be achieved by recognising the value of water retention for both city-dwelling humans and nature. Creating small-scale, novel wetlands like rain gardens, ponds and ephemeral basins within urban developments can provide environmental cooling and create focal attractions for both people and wildlife within the landscape. Where possible, wetlands designed to support wildlife should receive rainwater rather than stormwater, to reduce the impacts of chemical pollution on freshwater species and avoid the creation of ecological traps [9]. Ephemeral wetlands are particularly important for frogs, as introduced fish and other predators are excluded when the wetlands dry out over the warmer months of the year.

Engaging the community with nature in the city

Connecting with neighbourhood nature, including through outdoor recreation in parks and reserves and activities such as bird watching, grew in popularity during the lockdowns of 2020. However, some members of the community are more engaged than others. The involvement and support of local communities is key to developing strategies to improve urban biodiversity [10]. Citizen science offers an opportunity to connect more people with biodiversity in their local landscapes and can also contribute to research.

An example of citizen science in action is the CAUL Urban Wildlife App which allows citizens to contribute data on the distribution and behaviour of wildlife in cities. We developed the app in consultation with wildlife experts, urban ecologists, land managers and decision-makers to identify key information gaps in urban-wildlife management around Australia.

The app has four modules, each focusing on a different group of species: flying-foxes, frogs, beneficial insects, and possums and gliders. More than 300 users have contributed over 3,500 records to date [11]. Citizen scientists have recorded two species of flying-fox, three species of bell frog, eight species of possum (including the critically endangered western ringtail possum) and more than 40 different types of insect pollinators including the blue-banded bee, yellow admiral and meadow argus.

The data collected through this, and other citizen science processes is helping researchers and urban wildlife managers address gaps in knowledge of the ecology, behaviour and distribution of native species in urban environments.

Local-government planners help shape public and private spaces in a variety of ways across a range of spatial scales, and have a key role to play in the shift towards planning for the more-than-human. Maintaining existing urban biodiversity and encouraging the return of additional native species to our neighbourhoods through a variety of actions, will provide significant benefits for both people and nature – in cities all around Australia and the world.

AUTHOR ACKNOWLEDGEMENT

We acknowledge the Traditional Owners of the lands and waters where this research took place, all around Australia, and pay our respects to Elders past and present. We acknowledge that all cities in Australia were built on Indigenous land and that this land was never ceded. This research was supported by funding from the Australian Government’s National Environmental Science Program through the Clean Air and Urban Landscapes Hub and the Threatened Species Recovery Hub, and by the University of Queensland and the City of Melbourne. The possum and glider module is a collaboration between the TSR and CAUL Hubs and the National Landcare Program through the South West Catchments Council (Western Australia). The CAUL Urban Wildlife App was developed by Gaia Resources.