Dunedin’s inner-city greening project shows even small spaces can be wildlife havens

Even small green spaces can bring nature back into cities, as our project in Otepoti Dunedin has shown.

Over the past two years, Dunedin’s city centre has become greener and more biodiverse thanks to the installation of street-side planters.

This change, though modest, proves popular with a range of insects that have moved in even though the city centre remains dominated by grey non-permeable surfaces.

This real-world example shows that urban dwellers with limited green spaces can still have a positive impact on urban biodiversity through the use of planters and raised garden beds.

Since most New Zealanders live in urban areas, these are the places where people frequently interact with and experience nature. The way we design cities shapes our experience of the natural world, and it should include habitat for our native flora and fauna.

As housing pressure rises, stand-alone homes with private gardens are increasingly replaced by medium-density housing with limited greenspace. If we want to keep our living environments green, we have to find ways to enhance biodiversity in increasingly smaller spaces.

Opportunities to connect with nature are linked to increased mental and physical wellbeing, sense of place and pro-environmental behaviours. In fact, having a connection to nature was deemed equally important as income in a recent Australian survey that ranked life satisfaction.

Planning with biodiversity in mind

Amid the growing recognition of biodiversity’s importance, the Dunedin City Council has started weaving it into city planning, despite the absence of national policies for modified urban habitats.

The council partnered with local agency Aukaha to incorporate mana whenua values of environmental guardianship into the design of the city’s main shopping street.

The upgrade of Dunedin’s George Street comprises three consecutively installed blocks, each with a slightly different theme. The first block is dominated by native plants, the second features more flowering species, and the third has a mixture of both.

In total, the planters include more than 2,500 plants representing close to 60 species, of which more than half are native. These offer a variety of resources for wildlife, from food (pollen, nectar, fruit) to habitat niches created through the plants’ varying heights and physical structures. Each block’s planters have either loose stone or bark as the ground medium.

Urban insect colonisation

To test whether George Street’s planters actually do enhance biodiversity we conducted a two-year study of insect colonisation.

We used pitfall traps buried in the ground and hand-held vacuuming of plants to catch insects and assessed whether the planters act as stepping-stone habitats – small patches that connect fragmented urban landscapes to more natural ones, thus enhancing biodiversity and ecosystem health.

Our results are promising. As expected in a harsh, disturbed urban environment, we found the insect communities in the George Street planters differ from those found in more extensive natural areas such as the Town Belt or Ross Creek, which tend to have more specialised species.

However, several groups have successfully colonised the planters, including spiders, flies, native wasps, beetles and other insects.

Beetles, New Zealand’s largest insect group, are good indicators of ecosystem health. We found a small population of Scopodes fossulatus, a native ground-dwelling carnivorous beetle, also present in the surrounding natural areas. Its presence indicates sufficient food resources (other smaller insects) and a functioning micro-ecosystem.

Gardening for wildlife

The George Street planters offer practical guidance for urban dwellers on how to enhance biodiversity in their own outdoor spaces, regardless of size.

Bark was found to be more successful in attracting insects than loose stone as the planter medium. Planting vegetation of varying heights is one of the best ways to enhance urban biodiversity.

This can be achieved by planting a native ground cover such as Aceana microphylla (bidibid), together with a variety of structurally complex plants between 30 centimetres and more than two metres in height.

Plants with more leaf surface area and complex shapes and forms, such as Polystichum vestitum (prickly shield fern), are more likely to offer habitat, and thus attract insects, compared to structurally simple plants like Libertia (New Zealand iris) species.

While non-native plants add colour, including native plants will attract native insects as they have co-evolved.

George Street demonstrates that even in a small space, staggering flowering times throughout the year to provide continuous food resources is achievable: native Veronica (formerly Hebe) “Beverly Hills”, for instance, produces bright purple flowers throughout spring and summer, while non-native Lenten roses flower from late winter to spring.

When sourcing native plants for pots, planters or gardens, growers should consider supporting local nurseries. They often offer a greater genetic diversity and in-depth knowledge on local climatic preferences.

Most importantly, it’s good to take time to connect with nature, be it on a balcony, backyard or the seats around the George Street planters, and enjoy the species these small but mighty green spaces can attract.

Jacqueline Theis receives funding from the Ministry of Business, Innovation and Employment. She is affiliated with the Entomological Society of New Zealand.

Barbara I.P. Barratt receives funding from the Ministry of Business, Innovation and Employment for research on border biosecurity, risk assessment for biological control agents and native grassland ecology; from the Department of Conservation for research on endangered insect species; and from Environment Canterbury for expert advice on terrestrial invertebrates.

Connal McLean is affiliated with the Entomological Society of New Zealand and a trustee of the Moths and Butterflies of NZ Trust.

Yolanda van Heezik receives funding from the Ministry of Business, Innovation and Employment.