Who's behind urban tree sponsorship? Lessons learned from the spatial analysis of public engagement in a tree-planting programme about justice and motivations for participation

For those living in urban areas, street trees offer a range of benefits, including clean air, cooling and recreational space. While previous studies have examined urban green space and urban tree canopy cover, there is still a knowledge gap on distributive aspects of participatory tree planting programmes in cities. Therefore, this study examines the spatial distribution of trees planted through the "Strong Trees" sponsorship programme in the city of Leipzig, with a particular focus on the relationship between the trees’ spatial distribution and socio-demographic patterns of the city. A combined regression and cluster analysis revealed that the proportion of assigned tree sponsorships is extraordinal high in central Leipzig compared to the periphery. We found a negative correlation between assigned sponsorships and several socio-demographic variables, including household net income, recreational area, average age, and households with children. Conversely, a positive correlation was observed between the possession of a high school degree and tree sponsorships. By accounting for the spatial variation of the way these factors play out for tree sponsorships, we identified three clusters: A central one with below average income, high education and undersupply of public green; a sub-central cluster with below average income, low education and better green supply; and a sub-urban cluster exhibiting high income, average education and large private green supply. This study clearly establishes a link between the spatial distribution of tree sponsorships and socio-demographic variables of a city, proposing that tree sponsorship programmes may serve to offset limited access to urban green, particularly in areas characterised by high levels of education, average to low income, and far too little green. The clustering uncovers distributive injustice including low sponsorship numbers coupled with limited recreational area shares, low net household income and lower education. • We examine the tree’s spatiality of the "Strong Trees" programme in Leipzig. • A combined regression and cluster analysis show the highest number of sponsorships in central Leipzig. • We found low shares of tree sponsors in the periphery. • We found a negative correlation between tree sponsorships and household net income, age, and having children. • A positive correlation is observed between high school degree and tree sponsoring.