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Ecologists create new tool for scoring biodiversity of private gardens

A new tool to rate gardens on their level of biodiversity could have key implications for building more ecologically sustainable cities in an increasingly urbanized world.

Ecologists create new tool for scoring biodiversity of private gardens
Photo: “A different perspective” by Noelle Bennett. The tūī, an endemic honeyeater, are attracted to New Zealand gardens with nectar-rich native plants.

Researchers at the University of Otago created a tool to rate gardens on their level of biodiversity, which could have key implications for building more ecologically sustainable cities in an increasingly urbanized world. 

The intention is that the use of the tool to evaluate gardens would support a garden certification scheme named GardenStar (after the HomeStar system used for rating building sustainability in New Zealand).  

The researchers – Professors Yolanda van Heezik and Phil Seddon – believe that a garden certification scheme might incentivize New Zealanders to create more biodiverse gardens. Increasing the biodiversity of private gardens would create more habitat for native birds and other animal species in urban environments, and could increase the capacity of gardens to contribute to ecosystem services.

The evaluation tool was created by pooling together an interdisciplinary group of 20 experts to identify features that are key to promoting biodiversity. Then, a 1000minds conjoint analysis survey was used to elicit the experts’ judgements regarding the relative importance of these indicators. 

GardenStar was piloted on 89 properties in Dunedin and the Whakatipu Basin, which were examined and scored to identify their level of biodiversity. The distributions of the scores for the four main categories contributing to the overall score – habitat extent, habitat quality, habitat management, and landscape context – identified the extent to which various actions by householders might improve their scores, while the distribution of the overall score helped to determine how stars could be allocated. Habitat quality and habitat management were identified as the areas most lacking in people’s garden, but are also the categories that householders have the most potential to improve.

The results highlight areas of potential improvement for creating more biodiverse greenspaces, which is facilitated by the expert feedback provided to each homeowner on how they could make their gardens more biodiverse. Informing homeowners of their garden’s relative ranking compared to other gardens can further encourage them to improve their score.

As private gardens make up a significant proportion of urban areas in many cities worldwide, improving their biodiversity can make a significant contribution to urban biodiversity, sustainability and livability. Currently, most residential developments fail to address biodiversity, which Professors van Heezik and Seddon hope to change.


Y van Heezik, B Barratt, B Burns et al (2023), “A rapid assessment technique for evaluating biodiversity to support accreditation of residential properties”, Landscape and Urban Planning 232, 104682.

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