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

Green infrastructure design for the containment of biological invasions. Insights from a peri-urban case study in Rome, Italy

Secondary shrublands and transitional woodland/shrub formations are recognised to be particularly susceptible to plant invasions, one of the main global threats to biodiversity, especially in dynamic peri-urban landscapes. Urban fringes are in fact often the place for the sprawl of artificial surfaces, fragmentation of habitats, and complex land transitions (including both agriculture intensification and abandonment), which in turn increase propagule pressure of exotic species over residual semi-natural ecosystems. Within this framework, the present study was aimed at analysing i) how landscape composition and configuration affect the richness of woody exotic species in shrubland and transitional woodland/shrub patches, and ii) how this threat can be addressed by means of green infrastructure design in a peri-urban case study (Metropolitan City of Rome, Italy). Accordingly, the occurrence of exotic plants was recorded with field surveys and then integrated with landscape analyses, both at patch level and over a 250 m buffer area around each patch. Thus, the effect of landscape features on exotic plant richness was investigated with Generalised Linear Models, and the best model identified (pseudo R-square = 0.62) for inferring invasibility of shrublands throughout the study area. Finally, a Green Infrastructure (GI) to contain biological invasion was planned, based on inferred priority sites for intervention and respective, site-tailored, actions. The latter included not only the removal of invasive woody alien plants, but also reforestation and planting of native trees for containment of dispersal and subsequent establishment. Even though specifically developed for the study site, and consistent with local government needs, the proposed approach represents a pilot planning process that might be applied to other peri-urban regions for the combined containment of biological invasions and sustainable development of peripheral complex landscapes.

Quantifying the impacts of future shoreline modification on biodiversity in a case study of coastal Georgia, United States

People often modify the shoreline to mitigate erosion and protect property from storm impacts. The 2 main approaches to modification are gray infrastructure (e.g., bulkheads and seawalls) and natural or green infrastructure (NI) (e.g., living shorelines). Gray infrastructure is still more often used for coastal protection than NI, despite having more detrimental effects on ecosystem parameters, such as biodiversity. We assessed the impact of gray infrastructure on biodiversity and whether the adoption of NI can mitigate its loss. We examined the literature to quantify the relationship of gray infrastructure and NI to biodiversity and developed a model with temporal geospatial data on ecosystem distribution and shoreline modification to project future shoreline modification for our study location, coastal Georgia (United States). We applied the literature-derived empirical relationships of infrastructure effects on biodiversity to the shoreline modification projections to predict change in biodiversity under different NI versus gray infrastructure scenarios. For our study area, which is dominated by marshes and use of gray infrastructure, when just under half of all new coastal infrastructure was to be NI, previous losses of biodiversity from gray infrastructure could be mitigated by 2100 (net change of biodiversity of +0.14%, 95% confidence interval -0.10% to +0.39%). As biodiversity continues to decline from human impacts, it is increasingly imperative to minimize negative impacts when possible. We therefore suggest policy and the permitting process be changed to promote the adoption of NI.

Modelling the potential of rainwater harvesting to improve the sustainability of landscape and public garden irrigation

Access to water for irrigating amenity landscape and public gardens is under intense pressure due to the rising competition for water between different sectors, exacerbated by increased drought risk and climate change. Rainwater harvesting (RWH) has the potential to reduce the economic impacts of restrictions on irrigation abstraction in dry years and to build resilience to future water shortages. This study investigated the hydrological viability of RWH for the landscape and public garden sector based on an analysis of five Royal Horticultural Society gardens. A RWH model was developed and combined with on-site observations, key informant interviews and GIS analyses, to estimate irrigation demands and the volumes of harvested rainfall for contrasting agroclimatic years. The results showed that gardens located in wetter regions and with low irrigation water demand to harvestable area ratio had a higher RWH potential and could almost exclusively rely on rainwater to meet irrigation demand, even in dry years. RWH potential is more limited for gardens in drier regions where they would require larger areas to harvest rainwater and for storage. Appropriately designed rainwater harvesting systems offer the potential to remove most of the risk of irrigation abstraction restrictions during dry years and associated impacts on amenity planting quality and visitor experience.

Motivations for urban front gardening: A quantitative analysis

Private gardens in urban settings offer multiple benefits for the environment and society. In addition to benefits to people's health and well-being, planting in front gardens in particular can mitigate local flooding and urban heat islands. To encourage more front garden planting, greater understanding of householders' motivations for front gardening is needed. Addressing research gaps on gardening for reasons other than food production and on motivations for gardening in front gardens, a large-scale online survey (n = 1,000) was conducted with urban/suburban dwellers in England. Exploratory factor analysis identified three factors of motivation: enjoyment, meaning and benefit (intrinsic), creating something beautiful (aesthetic) and functional outcomes (utilitarian). A multiple regression model incorporating the three factors and sociodemographic variables explained 11% of variance of time spent front gardening, with intrinsic motivations the strongest predictor. Intrinsic motivations were stronger for women than for men. The study provides a quantitative categorisation of motivational factors as a basis for comparative research and design of interventions and policy to increase front gardening.

Mapping Peer-Reviewed Scientific Studies on Plant Trait–Service Linkages Across Ecosystems: A Bibliometric Analysis

The concept of ‘ecosystem service’ has gained momentum in the twenty-first century to bridge the gap between human–nature interactions. However, the challenge remains to map the flow of ecosystem services (ES) for their efficient management. Among the multiple existing methods, biophysical assessments provide better knowledge of the state of the ecosystem and its mapping for complimentary services. Trait–service linkage is one of the tools to reliably link biodiversity with ES if we better understand the role functional traits play in the underlying ecosystem processes. In this paper, we have performed a bibliometric analysis of published literature on ES and plant functional traits to identify the current state of knowledge on trait–service linkage, biases, research gaps, and challenges. There was a skewed geographical basis for trait–service linkage studies; most studies were conducted in Europe and North America. The majority of the research focused on supporting and regulating ES, mainly carbon sequestration, biomass production, and climate regulation, using a particular set of vegetative traits, such as leaf, root, and plant height, and ignored most regeneration traits, except for a few flower traits. A matrix to quantify the association between ES and selected plant traits (specific leaf area, leaf dry matter content, leaf area, leaf nitrogen content, vegetation height, wood density, canopy density, root length, root density, flowering time, flower color and flower size) revealed that the two leaf traits (specific leaf area and leaf dry matter content) in the linkage have contrasting associations with multiple ES. The study illustrated that there is still a considerable research gap in linking plant traits with essential ES (biomass production, climate and water regulation). Thus, suggest future studies on ES should focus more on trait–service linkage across major ecosystems to underpin key ecosystem processes for better sustenance of ES and human well-being.

Encouraging planting in urban front gardens: a focus group study

AIMS

Encouraging planting in front gardens offers mental and physical health benefits, as well as positive local environmental impacts such as reducing flood risk and improving air quality. However, urban front garden greenery has reduced in recent years. We aimed to explore adults' views regarding planting greenery in front gardens, barriers and facilitators, and their understanding of health and environmental impacts, to identify appropriate intervention mechanisms for behaviour change.

METHODS

We carried out five online focus groups with 20 participants aged 20-64 in England, purposively sampled for variation according to age, gender, home ownership, income, ethnicity and residing in an urban or suburban area. We audio recorded each focus group, transcribed it verbatim and analysed transcripts using thematic analysis.

RESULTS

Front gardening was a relaxing activity that provided benefits including increased wellbeing, fresh air and vitamin D. Planting in front gardens depended heavily on available time and space, garden orientation, local security and the weather. Front gardens could be a place for social interaction. Participants tended to prioritise neatness and tidiness over greenery. Lack of knowledge and low self-efficacy were key barriers. There was little awareness of the environmental benefits of front garden greenery; however, reducing flood risk and encouraging biodiversity were viewed positively.

CONCLUSION

Initiatives to encourage front garden planting should focus on plants that require little knowledge to acquire and care for, are suitable to the local environmental conditions and with a visual impact of neatness and bright colour. Campaigns should draw attention to local flood risk reduction and increasing biodiversity, in addition to personal health benefits.

Tree Effects on Coffee Leaf Rust at Field and Landscape Scales

Although integrating trees into agricultural systems (i.e., agroforestry systems) provides many valuable ecosystem services, the trees can also interact with plant diseases. We demonstrate that a detailed understanding of how plant diseases interact with trees in agroforestry systems is necessary to identify key tree canopy characteristics, leaf traits, spatial arrangements, and management options that can help control plant diseases at different spatial scales. We focus our analysis on how trees affect coffee leaf rust, a major disease affecting one of the world's most significant crop commodities. We show that trees can both promote and discourage the development of coffee leaf rust at the plot scale via microclimate modifications in the understory. Based on our understanding of the role of tree characteristics in shaping the microclimate, we identify several canopy characteristics and leaf traits that can help manage coffee leaf rust at the plot scale: namely, thin canopies with high openness, short base height, horizontal branching, and small, dentate leaves. In contrast, at the edge of coffee farms, having large trees with high canopy volume and small, thick, waxy leaves is more useful to reduce throughflow wind speeds and intercept the airborne dispersal of urediniospores, an important consideration to control disease at the landscape scale. Seasonal pruning can help shape trees into the desired form, and trees can be spatially arranged to optimize desired effects. This case study demonstrates the added value of combining process-based epidemiology studies with functional trait ecology to improve disease management in agroforestry systems.

Macro-Morphological Traits of Leaves for Urban Tree Selection for Air Pollution Biomonitoring: A Review

Urban trees provide different ecosystem benefits, such as improving air quality due to the retention of atmospheric particulate matter (PM) on their leaves. The main objective of this paper was to study, through a systematic literature review, the leaf macro-morphological traits (LMTs) most used for the selection of urban trees as air pollution biomonitors. A citation frequency index was used in scientific databases, where the importance associated with each variable was organized by quartiles (Q). The results suggest that the most biomonitored air pollutants by the LMTs of urban trees were PM between 1-100 µm (Q1 = 0.760), followed by O₃ (Q2 = 0.586), PM_2.5 (Q2 = 0.504), and PM₁₀ (Q3 = 0.423). PM was probably the most effective air pollutant for studying and evaluating urban air quality in the context of tree LMTs. PM_2.5 was the fraction most used in these studies. The LMTs most used for PM monitoring were leaf area (Q1) and specific leaf area (Q4). These LMTs were frequently used for their easy measurement and quantification. In urban areas, it was suggested that leaf area was directly related to the amount of PM retained on tree leaves. The PM retained on tree leaves was also used to study other f associated urban air pollutants associated (e.g., heavy metals and hydrocarbons).

Vertical Greenery as Natural Tool for Improving Energy Efficiency of Buildings

The European Construction Sector Observatory outlined that green building envelopes as green roofs and walls contribute to the reduction of energy demand and CO2 emissions due to the air conditioning in summer periods, and the mitigation of heat islands in urban areas. For this reason, the understanding about the contribution of urban greening infrastructures on buildings to sustainable energy use for air conditioning is urgent. This paper focuses on the analysis of a vertical surface provided with a Parthenocissus quinquefolia (L.) Planch., a winter deciduous species, as green cover of a building, assessing the reduction of the solar radiation energy absorbed by the façade and, consequently, the heat flux (HF) transmitted into the internal ambient. This research shows that, in July, surface temperatures (STs) on the vegetated façade were up to 13 °C lower than on the unvegetated (bare) façade. Under the climate and environmental conditions of the green wall located at ENEA Casaccia Research Center, a saving of 2.22 and 1.94 kWhe/m2, respectively in 2019 and 2020, for the summer cooling electricity load, was achieved. These energy reductions also allowed the saving of 985 and 862 g CO2/m2 emissions, respectively, in 2019 and 2020. Ultimately, a green factor named Kv* was also elaborated to evaluate the influence of vegetation on the STs as well as on HFs transmitted into the indoor ambient and adapted to the case of a detached vertical green cover. Measurements of Kv* factor lasting three years showed the suitability of this index for defining the shading capacity of the vegetation on the building façade surfaces, which can be used to predict thermal gains and effects in a building endowed of a vertical green system.

Positive relationships among aboveground biomass, tree species diversity, and urban greening management in tropical coastal city of Haikou

Within urban green spaces, tree species diversity is believed to correlate with aboveground biomass, though there is some disagreement within the literature on the strength and directionality of the relationship. Therefore, we assessed the relationship between the biodiversity of woody species and the aboveground biomass of woody plant species in the tropical, coastal city of Haikou in southern China. To accomplish this, we obtained comprehensive tree and site data through field sampling of 190 urban functional units (UFUs, or work units) corresponding to six types of land uses governmental-institutional, industrial-commercial, park-recreational, residential, transport infrastructure, and undeveloped area. Based on our field data, we investigated the relationship between tree species diversity and aboveground biomass using multiple regression, which revealed significant relationships across all five types of land uses. Aboveground biomass in green spaces was also correlated with anthropogenic factors, especially time since urban development, or site age, annual maintenance frequency by human caretakers, and human population density. Among these factors, maintenance is the strongest predictor of aboveground biomass in urban green space. Therefore, this study highlights the critical role of maintenance of urban green space in promoting both aboveground biomass and woody biodiversity in urban ecosystems and, consequently, on urban ecosystem services. Our findings contribute to a deeper understanding of the ecosystem services provided by communities of woody plant species in urban areas.

A "plan bee" for cities: Pollinator diversity and plant-pollinator interactions in urban green spaces

Green infrastructure in cities is considered to serve as a refuge for insect pollinators, especially in the light of an ongoing global decline of insects in agricultural landscapes. The design and maintenance of urban green spaces as key components of green infrastructure play a crucial role in case of nesting opportunities and for foraging insects. However, only few research has explored the impact of urban green space design on flower visitor communities, plant-pollinator interaction and the provision of the ecosystem service of pollination in cities. We investigated the abundance and diversity of pollinator communities in different urban park types in designed, standardized vegetation units, linked the visitation rates to the structural composition of the park types and derived indices for implemented pollination performances. The study was performed in two different structural park elements, flower beds and insect-pollinating trees. To gain a comprehensive understanding of the interaction between plants and pollinators, we calculated a plant-pollinator network of the recorded community in the investigation area. Visitation rates at different park types clearly showed, that the urban community gardens in comparison to other urban park types had a significantly higher abundance of pollinator groups, comparable to results found on a rural reference site. Tilia trees contributed significantly to the ecosystem service of pollination in investigated green spaces with a high supply of nectar and pollen during their flowering period. Calculations of pollination performances showed that recreational parks had comparably low visitation rates of pollinators and a high potential to improve conditions for the ecosystem service of pollination. The results indicated the strong potential of cities to provide a habitat for different groups of pollinators. In order to access this refuge, it is necessary to rely on near-natural concepts in design and maintenance, to create a wide range of flower diversity and to use even small green patches. Based on the findings, we encourage an integrated management of urban free spaces to consider parks as key habitats for pollinators in anthropogenic dominated, urban environments.

Transpiration by established trees could increase the efficiency of stormwater control measures

Evapotranspiration is an important aspect of the hydrological cycle in natural landscapes. In cities, evapotranspiration is typically limited by reduced vegetation and extensive impervious surfaces. Stormwater control measures (SCMs) seek, among other objectives, to move the urban hydrological cycle towards pre-development conditions, promoting processes such as infiltration and evapotranspiration. Yet, evapotranspiration is generally assumed to play a minor role in the water balance of stormwater control measures. Since established urban trees can use large quantities of water, their inclusion with stormwater control measures could potentially substantially increase evapotranspiration. We installed infiltration trenches alongside established Lophostemon confertus trees in the grassed verges of a typical suburban street to assess 1) whether redirecting stormwater to trees could increase their transpiration and 2) the contribution of transpiration to the water balance of stormwater control measures. We measured stormwater retention and transpiration for two spring-summer periods and estimated an annual water balance for the infiltration trenches. Although redirecting stormwater to trees did not increase their transpiration, these trees did use large volumes of water (up to 96 L d^-1), corresponding to 3.4 mm d^-1 per projected canopy area. Annually, stormwater retention was 24% of runoff and tree transpiration was equivalent to 17% of runoff. Our results suggest that streetscapes fitted with tree-based stormwater control measures, could increase the volumetric reduction of stormwater runoff by increasing the proportion of evapotranspiration in the water balance. Since public space is highly contested in cities and increasing canopy cover is a priority for many planners, integrating trees with stormwater control measures could provide dual benefits for a single management intervention, enabling a greater number of distributed stormwater control measures with smaller impervious catchments in the streetscape.

Mapping Functional Urban Green Types Using High Resolution Remote Sensing Data

Urban green spaces are known to provide ample benefits to human society and hence play a vital role in safeguarding the quality of life in our cities. In order to optimize the design and management of green spaces with regard to the provisioning of these ecosystem services, there is a clear need for uniform and spatially explicit datasets on the existing urban green infrastructure. Current mapping approaches, however, largely focus on large land use units (e.g., park, garden), or broad land cover classes (e.g., tree, grass), not providing sufficient thematic detail to model urban ecosystem service supply. We therefore proposed a functional urban green typology and explored the potential of both passive (2 m-hyperspectral and 0.5 m-multispectral optical imagery) and active (airborne LiDAR) remote sensing technology for mapping the proposed types using object-based image analysis and machine learning. Airborne LiDAR data was found to be the most valuable dataset overall, while fusion with hyperspectral data was essential for mapping the most detailed classes. High spectral similarities, along with adjacency and shadow effects still caused severe confusion, resulting in class-wise accuracies <50% for some detailed functional types. Further research should focus on the use of multi-temporal image analysis to fully unlock the potential of remote sensing data for detailed urban green mapping.

Is plant survival on green roofs related to their drought response, water use or climate of origin?

Green roofs are novel urban ecosystems with shallow substrate depths and low water availability. Hence, it is critical to select green roof plants that can survive water-deficits, particularly in climates with hot and dry summers. Shrubs are perennial plants which can be drought resistant and may be suitable for green roofs. However, studies about survival and health of shrubs are limited. The aim of this study was to determine whether plant climate of origin aridity, drought response and water use strategies could be used to select shrubs which can survive on green roofs that experience water-deficit. We selected 15 shrub species from a range of climates (dry, mesic and wet) and planted them together in 20 replicate green roof modules with 130 mm deep substrate. We monitored substrate water contents, plant minimum water potentials (ψ_min), health (visual score), percentage survival and related survival with their turgor loss point (ψ_tlp) and water use strategies (evapotranspiration rates in a related glasshouse experiment). We also determined whether plants could recover after dry periods by rewatering after the summer. Mean gravimetric soil water content decreased to approximately 5% after summer drought, which resulted in mortality. Overall, survival ranged between 10% and 100% for the 15 species. However, survival was not related to their ψ_tlp or water use strategies. While shrubs from more arid climates had lower ψ_min in response to dry substrates, this did not result in greater survival and health. Following rewatering, only four shrub species resprouted. Hence, as plant drought response, water use strategy and climate of origin were not strongly related to survival, we suggest survival on green roofs is likely to be determined by a combination of physiological traits. Emergency irrigation for shrubs growing on green roofs in hot and dry climates is recommended during summer to keep them alive.

Do non-native species contribute to biodiversity?

The Convention on Biological Diversity (CBD) emphasises the role of biodiversity in delivering benefits essential for all people and, as a result, seeks to safeguard all life-forms. The indices that are used to measure progress towards international conservation and sustainability goals, however, focus solely on the ‘native’ component of biodiversity. A subset of non-native species can cause undesirable economic, social, or biological effects. But non-native species also contribute to regional biodiversity (species richness and biotic interactions) and ecosystem services. In some regions and cities, non-native species make up more than half of all species. Currently, the contributions of these species to biodiversity and ecosystem services are overlooked. Here, I argue that biodiversity and sustainability indices should include all species. This is not only consistent with definitions of biodiversity but also will promote the idea that long-term, sustainable, human well-being is intricately tied to benefits derived from nature.

Modeling ozone uptake by urban and peri-urban forest: a case study in the Metropolitan City of Rome

Urban and peri-urban forests are green infrastructures (GI) that play a substantial role in delivering ecosystem services such as the amelioration of air quality by the removal of air pollutants, among which is ozone (O₃), which is the most harmful pollutant in Mediterranean metropolitan areas. Models may provide a reliable estimate of gas exchanges between vegetation and atmosphere and are thus a powerful tool to quantify and compare O₃ removal in different contexts. The present study modeled the O₃ stomatal uptake at canopy level of an urban and a peri-urban forest in the Metropolitan City of Rome in two different years. Results show different rates of O₃ fluxes between the two forests, due to different exposure to the pollutant, management practice effects on forest structure and functionality, and environmental conditions, namely, different stressors affecting the gas exchange rates of the two GIs. The periodic components of the time series calculated by means of the spectral analysis show that seasonal variation of modeled canopy transpiration is driven by precipitation in peri-urban forests, whereas in the urban forest seasonal variations are driven by vapor pressure deficit of ambient air. Moreover, in the urban forest high water availability during summer months, owing to irrigation practice, leads to an increase in O₃ uptake, thus suggesting that irrigation may enhance air phytoremediation in urban areas.

The health benefits of nature-based solutions to urbanization challenges for children and the elderly - A systematic review

Urban green and blue spaces promote health by offering areas for physical activity, stress relief, and social interaction, which may be considered as cultural ecosystem services. They also provide a number of regulating ecosystem services that can be regarded as nature-based solutions to mitigate impacts from urbanization-induced challenges. Urban trees and other vegetation provide cooling through shade and evapotranspiration, which reduce the impact of the urban heat island on hot summer days. Urban vegetation may improve air quality by removing air pollutants. Open areas in cities, such as parks, gardens, playgrounds and cemeteries, are unsealed spaces that also improve infiltration during extreme precipitation events providing water regulating functions. All these services have the potential to improve the health of urban residents, particularly of specific vulnerable groups such as children and the elderly. The aim of this paper is to provide an overview of the current state of evidence on the relationship between the health of children and the elderly and urban green and blue spaces that can account as nature-based solutions to urbanization-induced challenges. We discuss potential confounding factors and refer to the different green space metrics used to identify associations to health. From the results, we cannot conclude on a universal protective health effect of urban green and blue spaces for children and the elderly. While the association trend is positive, the results remain inconclusive, context dependent and are partly overridden by socioeconomic confounders. However, the research area is consistently increasing, and we advance important prospects for future research on urban green and blue spaces in the face of global challenges such as urbanization.