More trees, more naturalness, and greater willingness to engage in physical activity: an image-based study

Urban green spaces may promote health partly by encouraging physical activity, but it remains unclear which visible vegetation elements most strongly shape perceived naturalness and activity-related responses. This image-based study examined whether visible vegetation, particularly visible tree proportion, was associated with perceived naturalness and willingness to engage in physical activity in urban environments.

An online image-based questionnaire was conducted among 337 university students in Ya'an, China. Participants evaluated 40 photographs of typical urban streets and open spaces in Yucheng District. A DeepLabv3 semantic segmentation model pretrained on the ADE20K dataset was used to quantify the pixel proportions of three vegetation-related labels: Tree, Grass, and Other plant. Participants rated perceived naturalness on a 4-point scale and willingness to engage in physical activity on an 11-point scale. Analyses included image-level Pearson correlations, generalized estimating equations, receiver operating characteristic analysis, mediation analysis, and image-level sensitivity analyses.

Perceived naturalness was strongly correlated with physical activity willingness (r = 0.949, p < 0.001). Tree, Grass, and Other plant proportions were positively associated with perceived naturalness, whereas only Tree and Other plant showed significant positive associations with physical activity willingness in the main GEE models. Tree proportion showed the most consistent pattern of associations across the main and sensitivity analyses. ROC analysis indicated that Tree proportion had good ability to identify spaces perceived as natural (AUC = 0.90), with an exploratory optimal cut-off of 27.7%. Mediation analysis further showed that perceived naturalness significantly mediated the associations of Tree and Other plant proportions with physical activity willingness.

Visible vegetation, especially visible tree proportion, may contribute to stronger perceived naturalness and greater willingness to be physically active in urban spaces. These findings highlight the potential importance of visible trees in urban greening and active-living design. However, because this study used static images and measured willingness rather than actual behavior, the results should be interpreted as preliminary evidence concerning environmental perception and activity tendency.