Advances on the Influence of Vegetation and Forest on Urban Air Quality and Thermal Comfort—2nd Edition

Urbanisation has intensified environmental challenges, particularly the deterioration of air quality and the amplification of heat stress, both of which directly affect public health and urban liveability. Vegetation- and forest-based strategies, often framed as nature-based solutions (NBS), have consequently gained relevance as key tools to mitigate these problems by reducing air pollutant concentrations, improving thermal comfort, and delivering a wide range of co-benefits. Their influence, however, is neither uniform nor linear, since aerodynamic, deposition, shading, and evapotranspiration processes interact in complex ways with urban morphology, atmospheric pollutants, and meteorological conditions. As a result, understanding the role of vegetation in shaping urban environments requires interdisciplinary approaches and evidence from both experimental and modelling studies. Building on the first edition of this Special Issue (https://www.mdpi.com/journal/forests/special_issues/urban_air_thermal, accessed on 24 November 2025), the present collection (https://www.mdpi.com/journal/forests/special_issues/M488RLLI1L, accessed on 24 November 2025) offers new insights into the multiple mechanisms through which vegetation affects air quality, microclimate, and thermal comfort, while also highlighting the challenges of designing context-sensitive green infrastructures that carefully account for the specific environmental, urban, and social conditions in which they are embedded.

This Special Issue comprises 11 papers, including the editorial [1], authored by researchers from various regions (China, Bulgaria, Canada, Italy, Australia, and Spain) and diverse scientific backgrounds, reflecting a broad spectrum of approaches to the study of vegetation in urban contexts. Some contributions focused on the health and climate impacts of large-scale revegetation strategies, demonstrating through mesoscale meteorological simulations that increasing green cover can reduce temperature-related mortality in Southern European cities [2]. Other studies examined the interplay between vegetation and atmospheric pollutants, such as the role of canopy structure in shaping PM2.5 variability in subtropical zones, the dust-retention capacity of urban parks, and the pollutant-filtering efficiency of evergreen and deciduous ornamental tree species [3,4,5]. The broader biofiltering potential of vegetation was further explored by comparing the pollutant accumulation capacities of mosses, lichens, herbs, and trees, underscoring the value of combining different plant types for effective urban air quality management [6]. Wind comfort was also addressed through a campus-scale case study showing how plant configurations influence local airflow and pedestrian comfort [7]. Regarding the thermal environment, the application of the three-dimensional Green Plot Ratio (GPR) demonstrated the effectiveness of urban greenery in reducing heat stress in residential areas [8], while a complementary study revealed the seasonal trade-offs of street canyon greening, where vegetation that improves summer cooling may compromise winter comfort [9]. In addition, a long-term field experiment combined with microenvironment simulations on an individual Ficus concinna tree quantified the relative contributions of shading and transpiration to urban cooling, showing that transpiration accounted for nearly half of total cooling and dominated under high-temperature conditions, while shading effects peaked under strong solar radiation but could increase nighttime and winter temperatures due to longwave radiation reflection [10]. Finally, a study on garden plants in Suzhou (China) showed how different life forms adopt distinctive functional strategies to cope with air pollution, providing criteria for species selection in stressed urban environments [11].

The papers in this collection reaffirm the complexity of vegetation–atmosphere interactions in cities, while also offering concrete evidence of the benefits of NBS for air quality, thermal comfort, and climate resilience. At the same time, previous research has emphasised that local factors, including plant traits, urban design, and meteorological conditions, strongly influence the impact of vegetation. Vegetation can act simultaneously as a sink and a barrier for pollutants, or as a source of biogenic emissions, while also exerting both cooling and insulating effects that vary seasonally. This underscores the importance of designing green infrastructures not merely as aesthetic additions, but as functional systems capable of balancing ecosystem services and potential disservices. By advancing both theoretical understanding and practical methodologies, the contributions gathered here provide valuable knowledge for researchers, policymakers, and urban planners aiming to create greener, healthier, and more sustainable cities. Ultimately, this Special Issue aspires to serve as a reference point for interdisciplinary research and decision-making on the integration of vegetation into urban environments in the context of ongoing climate change.