New Ways to Characterise the 3D Structure of Urban Vegetation

If you go to the public parks around where you live, you will likely find that the structure of the vegetation differs substantially among parks. Some parks may have wide open gassy areas, some may have forested areas with a grassy understory, while others may have forested areas with a dense understory. If you think about it, you may even go to certain parks to undertaken particular activities because of the type of vegetation structure present. In fact, you are unlikely to go to a park that is completely covered by dense forest to kick a football about, but you may go there to bird watch. Despite the importance of vegetation structure for how we use and value urban green spaces, until recently we have had only limited capacity to map the 3D structure of urban vegetation across whole cities.

In a recent paper, led by Rhiannon Caynes, we developed a new approach to achieve this type of 3D mapping and illustrated its application in Brisbane, Australia. In the paper we demonstrate, using LiDAR data, a new way of characterising the spatial and vertical structure of vegetation across an entire city at a high resolution. Our novel approach uses functional metrics that are able to characterise the structure of vegetation in terms of: land cover (e.g., amount of tree cover), spatial structure (e.g., fragmentation of tree cover), and vertical structure (e.g., canopy heights, and vertical complexity).We illustrate the approach by applying it to all public parks in Brisbane at a 5m mapping resolution, revealing detailed information about the 3D structure of vegetation in each park. In doing so, we were able to show that parks varied in terms of the amount of tree cover and tree cover fragmentation (i.e., spatial structure), but also in terms of vegetation vertical structure, including vertical complexity, but that this was largely independent of spatial structure. The independence between spatial and vertical structure indicates that these two components of the 3D structure of vegetation may be being managed separately in Brisbane’s public parks.

Our approach to characterising vegetation in urban greenspace opens up a wide range of new possibilities for understanding patterns of green space provision and the value of green space for urban residents. For example, linking spatial data on green space use and our vegetation metrics provides an opportunity for a much more nuanced understanding of how people interact with the 3D structure of parks. It could also provide opportunities for monitoring fine scale changes in urban parks over time, beyond what is achievable with standard vegetation mapping approaches. Consequently, our work presents some exciting new areas of potential discovery for urban ecological research and application to urban planning.