Applying the concept of niche breadth to understand urban tree mortality in the UK.

Accelerated climate change has raised concerns about heightened vulnerability of urban trees, spurring the need to reevaluate their suitability. The urgency has also driven the widespread application of climatic niche-based models. In particular, the concept of niche breadth (NB), the range of environmental conditions that species can tolerate, is commonly estimated based on species occurrence data over the selected geographic range to predict species response to changing conditions. However, in urban environments where many species are cultivated out of the NB of their natural distributions, additional empirical evidence beyond presence and absence is needed not only to test the true tolerance limits but also to evaluate species' adaptive capacity to future climate. In this research, mortality trends of Acer and Quercus species spanning a 21-year period (2000-2021) from tree inventories of three major UK botanic gardens - the Royal Botanic Gardens, Kew (KEW), Westonbirt, the National Arboretum (WESB), and the Royal Botanic Garden Edinburgh (RBGE) - were analyzed in relation to their NB under long-term drought stress. As a result, Acer species were more responsive to drought and heat stress. For Acer, positioning below the lower limits of the precipitation of warmest quarter led to an increase in the probability of annual mortality by 1.2 and 1.3 % at KEW and RBGE respectively. In addition, the mean cumulative mortality rate increased corresponding to an increase in the number of niche positions below the lower limits of the selected bioclimatic variables. On the other hand, Quercus species in general exhibited comparable resilience regardless of their niche positions. Moreover, Mediterranean oaks were most tolerant, with cumulative mortality rates that were lower than those of native oaks in the UK. These findings further highlight the importance of incorporating ecological performance and recognizing species-specific adaptive strategies in climatic niche modeling.

'Green barriers' for air pollutant capture: Leaf micromorphology as a mechanism to explain plants capacity to capture particulate matter.

Finding ways to mitigate atmospheric particulate matter (PM) is one of the key steps towards fighting air pollution and protecting people's health. The use of green infrastructure is one option that could help improving urban air quality and promoting more sustainable cities. Detailed knowledge of how plants capture particulate matter can support plant selection for this purpose. Previous studies have primarily focused on 2D techniques to assess the micromorphology of plant leaves. Here, 3D optical profilometry and SEM imaging (2D) are used to quantify leaf roughness and other micromorphological leaf traits of three contrasting plant species (Hedera helix 'Woerner', Thuja occidentalis 'Smaragd', and Phyllostachys nigra) located within a mixed-species green barrier. These techniques have allowed us to identify the relative distribution of adhered atmospheric PM with respect to the surface topography of leaves, with high spatial resolution. Leaf surface roughness did not show a direct relationship with PM deposition; however, the descriptors width, depth and frequency of the grooves are important to explain PM capture by the leaves. Additionally, the presence of wax on leaves was relevant for PM adherence. All species captured PM, with their overall PM capture efficiency ranked from highest to lowest as follows: Thuja occidentalis > Hedera helix > Phyllostachys nigra. All green barrier species contributed to air quality improvement, through PM capture, regardless of their location within the barrier. Having multiple species in a green barrier is beneficial due to the diverse range of leaf micromorphologies present, thus offering different mechanisms for particulate matter capture.

Green infrastructure and ecosystem services - is the devil in the detail?

BACKGROUND: Green infrastructure is a strategic network of green spaces designed to deliver ecosystem services to human communities. Green infrastructure is a convenient concept for urban policy makers, but the term is used too generically and with limited understanding of the relative values or benefits of different types of green space and how these complement one another. At a finer scale/more practical level, little consideration is given to the composition of the plant communities, yet this is what ultimately defines the extent of service provision. This paper calls for greater attention to be paid to urban plantings with respect to ecosystem service delivery and for plant science to engage more fully in identifying those plants that promote various services. SCOPE: Many urban plantings are designed based on aesthetics alone, with limited thought on how plant choice/composition provides other ecosystem services. Research is beginning to demonstrate, however, that landscape plants provide a range of important services, such as helping mitigate floods and alleviating heat islands, but that not all species are equally effective. The paper reviews a number of important services and demonstrates how genotype choice radically affects service delivery. CONCLUSIONS: Although research is in its infancy, data are being generated that relate plant traits to specific services, thereby helping identify genotypes that optimize service delivery. The urban environment, however, will become exceedingly bland if future planting is simply restricted to monocultures of a few 'functional' genotypes. Therefore, further information is required on how to design plant communities where the plants identified (1) provide more than a single benefit (multifunctionality), (B) complement each other in maximizing the range of benefits that can be delivered in one location, and (3) continue to maintain public acceptance through diversity. The identification/development of functional landscape plants is an exciting and potentially high-impact arena for plant science.