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In the context of escalating global temperatures and intensified heat waves, the Mediterranean region emerges as a noteworthy hotspot, experiencing a surge in the frequency and intensity of these extreme heat events. Nature-based solutions, particularly management of urban green infrastructure (UGI) areas, have shown promising outcomes in adapting urban areas to the challenges posed by heat waves. The objective of the current study is twofold: firstly, to identify the compositional patterns of strategically distributed small public green spaces, demonstrating their enhanced capacity to mitigate the impact of heat waves in the Mediterranean region; secondly, to assess the association, direction, and explanatory strength of the relationship between the composition elements of the UGI areas and area typology, specifically focusing on the variation in land surface temperature (LST) values during heat wave episodes spanning from 2017 to 2023. The methodology involved obtaining land surface temperature (LST) values from satellite images and classifying green areas based on composition, orientation, and typology. Ordinal multiple regressions were conducted to analyze the relationship between the considered variables and LST ranges during heat wave episodes that occurred from 2017 to 2023. The findings indicate an increase in LST ranges across many areas, emphasizing heightened thermal stress in a Mediterranean medium-sized compact city, Granada (in the southeast of the Iberian Peninsula). Traditional squares, pocket parks and gardens, and pedestrian areas with trees and impervious surfaces performed better in reducing the probability of exceeding LST values above 41 °C compared to other vegetated patches mainly occupied by herbaceous vegetation and grass. The study concludes by advocating for the strategic incorporation of vegetation, especially trees, along with traditional squares featuring semipermeable pavement with trees and shrubbery, as a potential effective strategy for enhancing resilience against extreme heat events. Overall, this research enhances our understanding of LST dynamics during heat waves and offers guidance for bolstering the resilience of urban green spaces in the Mediterranean region.

Atmospheric conditions, as well as pollutants, can induce changes in the viability and germinability of the pollen grain. This process frequently occurs in cities due to the high rate of air pollution that can alter the quality of pollen, affecting its biological functions. In this work, the effect of different environmental stress factors, mainly UV-B radiation and polluting gases (CO, NO2 and SO2), on the viability and maturity of the pollen of four ornamental tree-species present in the green infrastructure of Granada, namely Acer negundo, Carpinus betulus, Olea europaea and Cupressus spp. is analyzed. Differential staining techniques were used with fresh pollen collected in areas with different exposure to environmental stress to detect intact cell membranes (Trypan blue) and the state of maturity (Pyrogallol red). It was observed that the species from sectors more exposed to environmental stress registered a low viability and were affected by factors such as UV-B radiation and atmospheric pollutants. On the contrary, the pollen from tree species growing in peri-urban forests presented a higher rate of viability and less effect of pollutant factors. Differences were also observed according to the species/genus and according to the sampling area. This modification in the morphological and/or organic composition of the pollen wall may cause a loss of quality in the reproductive processes of plants, and it may be bioindicator of the process of progressive degradation that plant species can experience in urban environments under conditions of environmental stress, and prevent the impacts that can affect other species.

Urban Forests (UFs) are key elements in Mediterranean compact cities, as they provide numerous ecosystem benefits and increase the resilience of cities against the anticipated impacts of climate change. It is, thus, necessary to review all the aspects that may have a negative effect on their ecosystem functions and the services that they provide. In this paper, a set of indicators is proposed that allow for a preliminary evaluation of some of the main disservices and factors that Mediterranean UFs present and the ways to maximize their benefits for users. For this purpose, 20 indicators, divided into three categories—Biodiversity, Accessibility/Facilities, and Infrastructure—were selected. Within these three categories, a range of values was established, from low to high or absence/presence. The indicators were tested in 24 urban forests of different types, all of which are representative of a medium-sized compact Mediterranean city. The results highlight that the UFs have adequate species richness and diversity, but among the species present are quite a few that emit BVOCs and allergens, as well as some that have invasive behavior. Poor cleaning, absence of night lightning, and scarcity of water points are aspects to improve in a good number of UFs; while a high surface area of impermeable soil, low tree cover, and extensive areas of grass that require large amounts of water for maintenance are the main issues of the infrastructure block that need medium-term planning to be addressed. It can be concluded that the proposed set of indicators allows for a general assessment of the readiness of UFTs in Mediterranean cities for the upcoming climatic, social, and ecological challenges.

Present-day dense cities are increasingly affected by the impacts associated with climate change. The recurrence of extreme climate events is projected to be intensified in cities in the next decades, especially in the most vulnerable areas of the world, such as the Mediterranean region. In this context, the urban green infrastructure (UGI) is presented as a nature-based solution that directly contributes to climate change mitigation in Mediterranean compact cities and improves health, social, welfare, and environmental conditions for inhabitants. This research sets out a manageable framework to define, locate, and categorize more functional green urban and peri-urban areas in a dense Mediterranean city. It takes spatial distribution, extension, and the capacity to improve inhabitants’ wellbeing through the provision of ecosystem services as classification criteria. Results show a scenario with a greater functional green surface available for the citizens to be managed. Identified areas have been categorized as cores, nodes, links, and green spaces defined as “other” areas. In particular, the latter play a significant role at social, structural, and ecological levels. The study showcases that rethinking urban design and strategic decision-making around these areas can enhance green equity in Mediterranean dense cities, their capacity to better deal with environmental extremes, and the inhabitants’ engagement with a culture of sustainability and wellbeing.

Green planning focusses on specific site requirements such as temperature tolerance or aesthetics as crucial criteria in the choice of plants. The allergenicity of plants, however, is often neglected. Cariñanos et al. (2014; Landscape and Urban Planning, 123: 134–144) developed the Urban Green Zone Allergenicity Index (IUGZA) that considers a variety of plant characteristics to calculate the allergenic potential of urban green spaces. Based on this index, we calculated an index for the individual-specific allergenic potential (IISA) that accounts for a varying foliage volume by accurate measurements of crown heights and surface areas occupied by each tree and only included mature individuals. The studied park, located in Eichstätt, Germany, has an area of 2.2 ha and consists of 231 trees. We investigated the influence of species composition using six planting scenarios and analysed the relationship between allergenic potential and species diversity using Shannon index. Only a small number of trees was female and therefore characterised as non-allergenic, 9% of the trees were classified as sources of main local allergens. The allergenic potential of the park based on literature values for crown height and surface was IUGZA = 0.173. Applying our own measurements resulted in IISA = 0.018. The scenarios indicated that replacing trees considered as sources of main local allergens has the strongest impact on the park’s allergenic potential. The IUGZA offers an easy way to assess the allergenic potential of a park by the use of a few calculations. The IISA reduces the high influence of the foliage volume but there are constraints in practicability and in speed of the analysis. Although our study revealed that a greater biodiversity was not necessarily linked to lower index values, urban green planning should focus on biodiversity for ameliorating the allergenic potential of parks.