Rapid urbanization has led to a series of environmental problems that are harmful to the physical and mental health of residents. Not only can increasing urban tree canopy (UTC) improve sustainable city development, but it can also effectively promote the quality of life for residents; however, the uneven spatial distribution of UTC can also bring about social justice problems. Currently, there are few studies related to the justice of UTC distribution in China. Based on this, the paper adopts object-oriented image classification technology to interpret and extract UTC data from satellite images, and it uses house price to explore the justice of the spatial distribution of UTC in the main urban area of Guangzhou from the perspective of environmental justice by ANOVA, Pearson correlation coefficient, and bivariate local spatial autocorrelation. The results show that: (1) There is a significant positive correlation between UTC and house price in the main urban area of Guangzhou, and there are regional differences in the distribution of UTC, with the UTC in the “very high” house price group being significantly higher than that in other groups. (2) The spatial clustering of UTC and house price in the main urban area of Guangzhou is found to be “low-low” and “high-high”; thus, it can be concluded that the spatial distribution of UTC in the main urban area of Guangzhou is uneven. This is an environmental injustice, as the areas with low UTC are spatially clustered in old residential areas, while the areas with high UTC are spatially clustered in commercial housing estates with high house prices. The study shows that urban tree planting should not only focus on quantitative improvement but also on equitable spatial layouts to promote social equity and justice thereby improving the urban ecological environment and promoting healthy urban development.

Over the past two decades, mental health has become a global public health concern. Although existing research suggests that the urban living environment is closely related to mental health changes, it remains unclear how this relationship evolves when the urban living environment undergoes sudden, citywide changes due to public health measures. To address this issue, we conducted a three-wave longitudinal survey in Shanghai during and after periods of citywide restriction and reopening, with data collected in May 2022 (during the lockdown), November–December 2022 (prior to the lifting of citywide restrictions), and May–June 2023 (the onset of the second infection wave). Out of 810 responses, 276, 215, and 195 participants provided valid responses in the first, second, and third waves, respectively, yielding a total of 686 valid questionnaires. We calculated the difference scores between each pair of waves and built linear regression models to analyze the determinants of mental health change across two transition periods. Results show that participants’ mental health improved overall. From the lockdown to reopening, improvements were driven by reduced individual stressors, lower family conflict, and higher housing and institutional satisfaction. From the reopening to the onset of the second infection wave, mental health changes were related to changes in individual stressors, housing satisfaction, and social connection. These findings reveal that the determinants of mental health differ across distinct phases of environmental change. The study contributes to understanding how individual stress and social connection jointly shape psychological resilience during crises. Beyond the pandemic, our results highlight the importance of integrating mental health and urban resilience into urban renewal and neighborhood governance agendas. Such integration is crucial for fostering adaptive, inclusive, and sustainable urban development in the face of future social or environmental disruptions.