University Square (Impact Site), Melbourne, Australia.

By Camilo Ordóñez, Caragh Threlfall, Dave Kendal, Jessica Baumann, Cherese Sonnkila, Dieter Honchuli, Rodney van der Ree, Richard Fuller, Melanie Davern, Alex English, Kelly Hertzog, and Stephen Livesley.

Read the full paper here.

Urban trees are vital to healthy urban environments. However, current research does not capture the direct and combined, social and ecological, effects of urban trees. This is because most research focuses on city-wide correlations between tree abundance and social and ecological indicators. Such an approach assumes that wildlife and human contact with trees occurs, does not collect in-situ and combined ecological and social data, and poorly accounts for factors that co-vary with tree abundance.

To understand the social-ecological effect of urban trees, research must transition from generating understanding of the spatial correlation between trees and social-ecological factors, to gaining an understanding of the processes that connect trees with the wider ecological and social community.

Field experiments can help researchers achieve this understanding, but few examples exist. In this study we have developed an innovative approach to examine two key questions: 1) how does the removal of urban trees affect the abundance and diversity of ecological communities?; and 2) how does the removal of urban trees affect people’s perceptions of urban trees?

To answer these questions we designed two experiments, one in an urban park, and one in a residential street, where tree removals were occurring. We collected ecological and social data from these field sites as well as from similar sites for control. We analysed these data to determine the combined effect of before/after urban tree removal at impact/control sites on changes in wildlife abundance and diversity, as well as people’s perceptions.

In our park experiment we observed a reduction in bird biodiversity and mammal abundance; an increase in predation due to the smaller amount of habitat remaining after tree removal (i.e., “refuge effect”); a decrease in the importance people assigned to the site and the trees at the site; and an increase in people’s positive attitude towards urban tree planting at the sites. However, we did not observe any changes in our street experiment.

With this study we generate complementary evidence that urban trees provide critical habitat to urban wildlife and are of critical importance to people’s nature experiences and demonstrate how these social-ecological effects are place-dependent.