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Impervious surfaces that characterise urban areas can make them harsh, water-limited places for plants to grow. To help alleviate plant stress under these challenging drought conditions, a range of soil additives can be utilised. Although well-studied individually, our understanding of the interaction between different soil additives in alleviating drought stress in urban areas is rudimentary. The aim of this study was to (1) assess the growth of urban horticultural plant species under drought stress and (2) determine whether drought stress in these species is alleviated by the use of soil additives, both individually and in combination. We grew six plant species (three trees, three graminoids) commonly planted in Australian urban areas under two watering regimes (drought-stressed, well-watered) and four soil additive treatments (no additive, microbial additive only, biochar only, microbial additive and biochar), and assessed their performance. We found that drought stress significantly reduced the growth of the six study species. Surprisingly, this decrease in growth was not reduced with the use of soil additives, despite biochar increasing soil water content and mycorrhizal colonisation when used in combination with the microbial additive. However, the addition of biochar significantly delayed the visual onset of drought stress across all species. Our results show that soil additives can be used as a cost-effective management strategy to increase plant resilience to drought stress in urban areas.

Invertebrates comprise the most diversified animal group on Earth. Due to their long evolutionary history and small size, invertebrates occupy a remarkable range of ecological niches, and play an important role as “ecosystem engineers” by structuring networks of mutualistic and antagonistic ecological interactions in almost all terrestrial ecosystems. Urban forests provide critical ecosystem services to humans, and, as in other systems, invertebrates are central to structuring and maintaining the functioning of urban forests. Identifying the role of invertebrates in urban forests can help elucidate their importance to practitioners and the public, not only to preserve biodiversity in urban environments, but also to make the public aware of their functional importance in maintaining healthy greenspaces. In this review, we examine the multiple functional roles that invertebrates play in urban forests that contribute to ecosystem service provisioning, including pollination, predation, herbivory, seed and microorganism dispersal and organic matter decomposition, but also those that lead to disservices, primarily from a public health perspective, e.g., transmission of invertebrate-borne diseases. We then identify a number of ecological filters that structure urban forest invertebrate communities, such as changes in habitat structure, increased landscape imperviousness, microclimatic changes and pollution. We also discuss the complexity of ways that forest invertebrates respond to urbanisation, including acclimation, local extinction and evolution. Finally, we present management recommendations to support and conserve viable and diverse urban forest invertebrate populations into the future.

Residential yards are a significant component of urban socio‐ecological systems; residential land covers 11% of the United States and is often the dominant land use within urban areas. Residential yards also play an important role in the sustainability of urban socio‐ecological systems, affecting biogeochemical cycles, water and the climate via individual‐ and household‐level behaviours. Spatial contagion has been observed in yard vegetation in several cities, potentially due to social norms that compel neighbours to emulate or conform to specific aesthetic qualities or management regimes. Residents may feel obliged to mow their front yards or prune their trees, creating patterns of spatial autocorrelation in residential neighbourhoods. In this study, we examined the spatial autocorrelation of several yard vegetation characteristics in both front and backyards in Boston, MA, USA. Our study area included 1,027 Census block groups (sub‐neighbourhood areas) and 175,576 parcels with matched front‐backyard pairings (n = 351,152 yards in total) across Boston's metropolitan area. We spatially defined ‘neighbours’ in five ways to better account for the potentially variable nature of how conformity or contagion manifests in empirical terms. We anticipated front yards to have stronger spatial autocorrelation due to the more publicly visible nature of these green spaces. We found positive and significant spatial autocorrelation in all measured vegetation variables, in both front and backyards. Unexpectedly, spatial autocorrelation tended to be higher in backyards for tree canopy variables but higher in front yards for turf grass cover. Among block groups, different socio‐economic variables, such as median household income, predicted spatial autocorrelation of vegetation characteristics. Our results were sensitive to how neighbours were spatially defined. Our results further underscore the importance of backyards as critical areas for sustaining an urban tree canopy, and show that spatial patterns vary across different social groups. The importance of ‘neighbour’ definition indicates opportunities to think carefully about the mechanisms driving spatial autocorrelation and the scales at which patterns develop. The identification of these mechanisms will have important implications for scales of policy and implementation for urban and suburban greening. A free Plain Language Summary can be found within the Supporting Information of this article.

Nature-Based Solutions (NBSs) promise a future where natural, human and technical elements help solving many of the issues plaguing cities. Pollution reduction, increased human wellbeing and climate change adaptation are only some of the challenges targeted by NBSs. However, under the warming climate affecting many of the world’s cities, most of modern NBSs will be highly impacted by the same climate factors they hope to mitigate. As in the case of extreme temperatures or altered water availability, these factors can impact and cause the failure in the organisms, technical elements and governance structures that NBSs rely upon, thus decreasing performance, reliability and sustainability of these solutions. In this commentary we propose critical considerations related to designing, building and managing “climate-ready” NBSs – defined as local integrated solutions able to cope with or adapt to climate change. We do so by highlighting examples in heat- and drought-stricken areas across Australian cities as they sit at the global forefront of a hotter world. We discuss in detail i) tolerance and adaptability of NBS to new climates, ii) NBS design for weather extremes and climate-safety margins, iii) NBS trialing and prototyping, and iv) planning for “climate-ready” NBSs. In doing so, we highlight caveats and limitations to propose an implementation framework to make NBSs not only work, but succeed, in a hotter urban world; one that sees 50 °C as a critical limit to sustain urban life and nature.

Gardening has the potential to improve health and wellbeing, especially during crises. Using an international survey of gardeners (n=3743), this study aimed to understand everyday gardening experiences, perspectives and attitudes during early stages of the COVID-19 pandemic in 2020. Our qualitative reflexive thematic and sentiment analyses show that during the first months of the COVID-19 pandemic, gardening seemed to create a safe and positive space where people could socially connect, learn and be creative. Participants had more time to garden during the pandemic, which led to enhanced connections with family members and neighbours, and the ability to spend time in a safe outdoor environment. More time gardening allowed for innovative and new gardening practices that provided enjoyment for many participants. However, our research also highlighted barriers to gardening (e.g. lack of access to garden spaces and materials). Our results illustrate the multiple benefits of gardening apparent during COVID-19 through a lens of the social-ecological model of health.

Nature-based solutions (NBS) are increasingly recognised as a means to address critical urban sustainability problems such as heatwaves, flooding and biodiversity loss. Accordingly, cities around the world have committed to ambitious targets for urban greening. Meeting these targets will require large areas of land to be converted from existing uses to green space. However, finding this land is difficult in established urban areas, where space is already strongly contested. Here we show an approach by which cities can make substantial progress towards a range of sustainability targets: by converting redundant street parking into biodiverse green space. Significant areas of public land in dense cities are currently allocated to street parking, while off-street parking garages in urban areas are typically abundant and have high rates of vacancy. We demonstrate that vacancy in off-street garages is so substantial that up to half of street parking in our case study municipality (The City of Melbourne, Australia) could be accommodated in garages within 200 m, freeing up large areas for conversion to green space. Our modelling shows this would have significant benefits in terms of tree canopy cover, stormwater treatment and ecological connectivity in the city. These benefits would represent strong progress towards – and even meet – a number of the city’s ambitious NBS targets. As many cities allocate extensive areas to both street parking and off-street garages, this approach to freeing up space for nature in cities is widely applicable. Our findings indicate this is a practical means for municipalities with the required political will and public support to deliver their sustainability goals.

Australia is experiencing mounting pressures related to processes of urbanisation, biodiversity loss and climate change felt at large in cities. At the same time, it is cities that can take the leading role in pioneering approaches and solutions to respond to those coupling emergencies. In this perspective piece we respond to the following question: What are the required transformations for prioritising, valuing, maintaining and embracing nature in cities in Australia? We adopt the mission framework as an organising framework to present proposed pathways to transform Australian cities as nature-positive places of the future. We propose three interconnected pathways as starting actions to steer urban planning, policy and governance in Australian cities: First, cities need to establish evidence-based planning for nature in cities and mainstream new planning tools that safeguard and foreground urban nature. Second, collaborative planning needs to become a standard practice in cities and inclusive governance for nature in cities needs to prioritise Aboriginal knowledge systems and practices as well as look beyond what local governments can do. Third, for progressing to nature-positive cities, it is paramount to empower communities to innovate with nature across Australian cities. Whilst we focus on Australian cities, the lessons and pathways are broadly applicably globally and can inspire science-policy debates for the post COP15 biodiversity and COP26 climate change implementation processes.

Urbanization and its resulting environmental stressors are often managed within terrestrial, freshwater, or marine realms separately. This is problematic for the many cities situated at the intersection between these realms, because stressors and associated management actions can affect multiple realms simultaneously and impacts may be compounded at boundaries. Here, we describe management approaches operating within and across realms, and identify impediments to cross-realm urban management. We find that management that fails to consider connectivity either within or between realms at best delivers only small-scale benefits and at worst can produce large-scale unintended negative outcomes. In contrast, management that explicitly considers inter-realm connectivity can generate large benefits relative to the cost of interventions. Successful cross-realm management requires consideration of connectivity, scale (temporal and spatial), and ecological processes across more than two realms, and is underpinned by an integrated and collaborative approach that provides multiple benefits.

Tree mortality during global-change-type drought is usually attributed to xylem dysfunction, but as climate change increases the frequency of extreme heat events, it is necessary to better understand the interactive role of heat stress. We hypothesized that some drought-stressed plants paradoxically open stomata in heatwaves to prevent leaves from critically overheating. We experimentally imposed heat (>40°C) and drought stress onto 20 broadleaf evergreen tree/shrub species in a glasshouse study. Most well-watered plants avoided lethal overheating, but drought exacerbated thermal damage during heatwaves. Thermal safety margins (TSM) quantifying the difference between leaf surface temperature and leaf critical temperature, where photosynthesis is disrupted, identified species vulnerability to heatwaves. Several mechanisms contributed to high heat tolerance and avoidance of damaging leaf temperatures-small leaf size, low leaf osmotic potential, high leaf mass per area (i.e., thick, dense leaves), high transpirational capacity, and access to water. Water-stressed plants had smaller TSM, greater crown dieback, and a fundamentally different stomatal heatwave response relative to well-watered plants. On average, well-watered plants closed stomata and decreased stomatal conductance (gs ) during the heatwave, but droughted plants did not. Plant species with low gs , either due to isohydric stomatal behavior under water deficit or inherently low transpirational capacity, opened stomata and increased gs under high temperatures. The current paradigm maintains that stomata close before hydraulic thresholds are surpassed, but our results suggest that isohydric species may dramatically increase gs (over sixfold increases) even past their leaf turgor loss point. By actively increasing water loss at high temperatures, plants can be driven toward mortality thresholds more rapidly than has been previously recognized. The inclusion of TSM and responses to heat stress could improve our ability to predict the vulnerability of different tree species to future droughts.

Tree canopy connectivity is important for supporting biodiversity. In urban landscapes, empirical examinations of habitat connectivity often overlook residential land, though yards and gardens often comprise a large portion of urban forests. We quantify structural composition (patches and paths), connectivity and fragmentation of an entire tree canopy network spanning 1220 Boston’s neighborhoods to assess the configuration of the urban forest potentially affecting tree-dependent wildlife species, such as some birds and arboreal mammals. The urban landscape was classified by land use, and residential yards were further subdivided into front yards, backyards, and corner yards. Structural composition, connectivity and fragmentation of the tree canopy was assessed using morphological spatial pattern and network analysis. Canopy metrics were then related to the land use of 349,305 property parcels. Back yard tree canopy cover was 65.23%. The majority of canopy links were on residential land (60.95% total), and particularly in backyards. Back yards contained the highest number of canopy fragments (48.65% total). Fragmentation of the canopy network peaked at ~ 23% of total canopy cover. Canopy fragmentation, distance among patches and their shape complexity were lower in neighborhoods with more tree canopy. The important role that yards have in sustaining canopy connectivity across urban landscapes poses challenges and opportunities. Urban land management and planning need to protect connectivity links within urban forests when located on private residential realm. A prioritization strategy aimed at expanding urban tree cover could focus on yards to ensure that urban landscape connectivity is maintained and increased.

Residential yards comprise most land and green space across cities. Despite yards being ubiquitous, little comprehensive information exists on how vegetation varies between front and backyards. This hinders our ability to optimize greening interventions on private urban land. We devised an accurate GIS algorithm to locate and classify front and backyards within residential landscapes. By applying this method to the greater Boston area, we measured vegetation structure (i.e., canopy cover, height and volume) of front and backyards with LiDAR and multispectral imagery. We further investigated relationships between urban form, architectural style, socio-economics, and the structure of front and backyard vegetation across Boston’s residential landscapes. Among the 85,732 residential parcels that were not corner lots and had cadastral and architectural data available, backyards were twice as large as front yards on average and had significantly greater canopy cover, vegetation volume and taller trees. Parcel-level characteristics, including vegetation in the corresponding front or backyard, as well as morphological characteristics of parcels, were the best predictors of vegetation structure. House architectural style was related to vegetation structure. The neighborhood socio-economic characteristics were the least important factors in predicting yard vegetation structure. Our study highlights that urban greening in yards depends on urban form and morphology at the parcel scale, and as such, it could be enhanced through urban to provide opportunities for additional vegetation. Architectural style might represent a further filter by which residents manage vegetation in their home environment, making it possible to devise strategies to green our cities – in style.

Author(s): Ossola, A; Cadenasso, ML; Meineke, EK | Abstract: Cities and towns are complex ecosystems with features that can vary dramatically in space and time. Our knowledge of the spatial structure of urban land and ecological systems is expanding. These systems have been investigated across spatial scales, urban to rural gradients, networks of urban macrosystems, and global megalopolises. However, the temporal dimensions of urban ecosystems – such as those related to ecological cycles and historical legacies – are far less understood and investigated. Here, we outline the main dimensions of time that can shape how events in urban ecosystems unfold, which we categorize as: (i) time flows and duration, (ii) synchrony, lags, and delays, (iii) trends and transitions, (iv) cycles and hysteresis, (v) legacies and priming, (vi) temporal hotspots and hot moments, and (vii) stochastic vs. deterministic processes affecting our ability to forecast the future of cities and the species that live in them. First, we demonstrate the roles of these understudied dimensions by discussing exemplary studies. We then propose key future research directions for investigating how processes over time may regulate the structure and functioning of urban land and biodiversity, as well as its effects on and implications for urban ecology. Our analysis and conceptual framework highlights that several temporal dimensions of urban ecosystems – like those related to temporal hotspots/moments and stochastic vs. deterministic processes – are understudied. This offers important research opportunities to further urban ecology and a comprehensive research agenda valuing the “Urban Chronos” – the change of urban ecosystems through time.

A study of factors impacting landslide displacement rates was conducted on the Ripley Landslide within the Thompson River valley in British Columbia, Canada for the International Programme on Landslides’ project #202. Seasonal and multiyear changes in atmospheric factors cause cyclic fluctuation of matric suction in the vadose zone through changes to the in situ water content. The ingress of moisture is shown to contribute to multiyear and seasonal loss of stability causing increasing landslide displacement rates, often disregarded in slope stability calculations. However, the water content in the unsaturated zone is important, especially in semi-arid to arid climates where the water table is low and large portions of the slope are unsaturated. Additional tools for studying long-term variations in climate and seasonal changes in water content are presented. These tools are used to characterize historical climate and compare several factors that have resulted in changing landslide displacement rates and magnitude. Infiltration of precipitation and snowmelt directly contributes to matric suction loss in the head scarp and is exacerbated by the presence of tension cracks. While groundwater levels are often correlated to changing displacement rates, changes in matric suction can also influence the rates of displacement. Climatic trends over subsequent years alter the long-term soil water accumulation which impacts rates of landslide displacement. By accounting for additional strength, or potentially a loss in strength due to increasing water content, it is possible to develop a more complete understanding of the mechanisms of climate change which drive displacement rates in the translational, metastable earthen slides that dominate the Thompson River valley. These mechanisms can be applied to comparable river valleys around the world.

Increasing focus on Nature-Based Solutions (NBS) in cities has significantly expanded the range of applications in which urban nature is considered useful, as well as the range of NBS available. Traditional parks, gardens and street trees now sit alongside innovative approaches including rooftop pollinator habitats, constructed wetlands and hydroponic green facades, each of which has its own particular challenges and benefits. This variety of solutions introduces an important new decision-making challenge for cities wishing to implement NBS: choosing the right set of specific NBS interventions. Decision support tools such as Multi-Criteria Decision Analysis (MCDA) can help navigate complex decisions, but their application to urban NBS selection decisions has been limited. Current NBS assessment frameworks tend to either give highly aggregated results, or are tailored to only one specific ecosystem service. Here we demonstrate a novel application of MCDA to the practical challenge of selecting a set of NBS to address multiple urban challenges. The MCDA tool developed here was used in seven cities participating in the European Union project ‘Urban GreenUP’. We describe the development and use of the MCDA tool, and explore how cities used the tool to guide NBS selection. We also evaluate the tool using sensitivity analysis and feedback from users. We find that participating cities are seeking to balance a large number of possible benefits from NBS solutions, and the tool proved useful for navigating the selection decision. Users identified opportunities to improve the tool’s usability and clarity. They also noted a key strength of the tool as a prompt for co-production of knowledge and decisions. Collectively, these findings advance the design and application of tools to support complex decisions about selecting NBS to address diverse urban challenges.

Heterogeneity in quantity and quality of resources provided in the urban matrix may mitigate adverse effects of urbanization intensity on the structure of biotic communities. To assess this we quantified the spatial variation in butterfly richness and abundance along an impervious surface gradient using three measures of urban matrix quality: floral resource availability and origin (native vs. exotic plants), tree cover, and the occurrence of remnant habitat patches. Butterfly richness and abundance were surveyed in 100 cells (500 × 500 m), selected using a random-stratified sampling design, across a continuous gradient of imperviousness in Melbourne, Australia. Sampling occurred twice during the butterfly flight season. Occurrence data were analyzed using generalized linear models at local and mesoscales. Despite high sampling completeness, we did not detect 75% of species from the regional species pool in the urban area, suggesting that urbanization has caused a large proportion of the region's butterflies to become absent or extremely rare within Melbourne's metro-area. Those species that do remain are largely very generalist in their choice of larval host plants. Butterfly species richness and abundance declined with increasing impervious surface cover and, contrary to evidence for other taxa, there was no evidence that richness peaked at intermediate levels of urbanization. Declines in abundance appeared to be more noticeable when impervious surface cover exceeded 25%, while richness declined linearly with increasing impervious surface cover. We find evidence that the quality of the urban matrix (floral resources and remnant vegetation) influenced butterfly richness and abundance although the effects were small. Total butterfly abundance responded negatively to exotic floral abundance early in the sampling season and positively to total floral abundance later in the sampling season. Butterfly species richness increased with tree cover. Negative impacts of increased urbanization intensity on butterfly species richness and abundance may be mitigated to some extent by improving the quality of the urban matrix by enhancing tree cover and the provision of floral resources, with some evidence that native plants are more effective.

Le Roux et al. suggest that documented increases in local plant richness in response to climate change should consider the nature of 'new' species. They find that species responsible for increases in richness in areas that have experienced significant disturbance and climate change are often invasive and/or weedy species.

The use of functional information in the form of species traits plays an important role in explaining biodiversity patterns and responses to environmental changes. Although relationships between species composition, their traits, and the environment have been extensively studied on a case-by-case basis, results are variable, and it remains unclear how generalizable these relationships are across ecosystems, taxa and spatial scales. To address this gap, we collated 80 datasets from trait-based studies into a global database for metaCommunity Ecology: Species, Traits, Environment and Space; “CESTES”. Each dataset includes four matrices: species community abundances or presences/absences across multiple sites, species trait information, environmental variables and spatial coordinates of the sampling sites. The CESTES database is a live database: it will be maintained and expanded in the future as new datasets become available. By its harmonized structure, and the diversity of ecosystem types, taxonomic groups, and spatial scales it covers, the CESTES database provides an important opportunity for synthetic trait-based research in community ecology., Measurement(s)species abundance • species trait • environmental feature • latitude • longitudeTechnology Type(s)digital curationFactor Type(s)year of data collection • type of ecosystem • level of human disturbanceSample Characteristic - Environmentterrestrial natural environment • fresh water • marine biome • anthropogenic terrestrial biome • natural environment • area of mixed forest • cultivated environmentSample Characteristic - LocationEarth (planet) Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.11317790

The use of functional information in the form of species traits plays an important role in explaining biodiversity patterns and responses to environmental changes. Although relationships between species composition, their traits, and the environment have been extensively studied on a case-by-case basis, results are variable, and it remains unclear how generalizable these relationships are across ecosystems, taxa and spatial scales. To address this gap, we collated 80 datasets from trait-based studies into a global database for metaCommunity Ecology: Species, Traits, Environment and Space; “CESTES”. Each dataset includes four matrices: species community abundances or presences/absences across multiple sites, species trait information, environmental variables and spatial coordinates of the sampling sites. The CESTES database is a live database: it will be maintained and expanded in the future as new datasets become available. By its harmonized structure, and the diversity of ecosystem types, taxonomic groups, and spatial scales it covers, the CESTES database provides an important opportunity for synthetic trait-based research in community ecology., This work was funded by the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig (funded by the German Research Foundation; DFG FZT 118). We thank Jitendra Gaikwad for his precious help with the technical aspects of the database storage and management through the iDiv Biodiversity Portal (https://idata.idiv.de/, https://doi.org/10.25829/idiv.286-21-2695) and the iDiv IT Support for their help in the CESTES website development (https://icestes.github.io/). The datasets provided by A. Jeliazkov were collected with financial support from the Fédération d’Ile-de-France pour la Recherche en Environnement (FIRE FR-3020). The dataset provided by R. Carvalho and F.L. Tejerina-Garro had financial support from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq No. 471283/2006-1) granted to FLTG. The datasets provided by R. van Klink, J.-Y. Humbert, R. Arlettaz and M.H.M. Menz were collected with financial support from the Swiss National Science Foundation (grants 31003A_125398/2 and 31003A_149656) awarded to RA.

The COVID-19 pandemic has severely disrupted social life. Gardens and yards have seemingly risen as a lifeline during the pandemic. Here, we investigated the relationship between people and gardening during the COVID-19 pandemic and what factors influenced the ability of people to garden. We examined survey responses (n = 3,743) from gardeners who reported how the pandemic had affected personal motivations to garden and their use of their gardens, alongside pandemic-related challenges, such as food access during the first wave of COVID-19 (May-Aug 2020). The results show that for the respondents, gardening was overwhelmingly important for nature connection, individual stress release, outdoor physical activity and food provision. The importance of food provision and economic security were also important for those facing greater hardships from the pandemic. While the literature on gardening has long shown the multiple benefits of gardening, we report on these benefits during a global pandemic. More research is needed to capture variations in public sentiment and practice - including those who do little gardening, have less access to land, and reside in low-income communities particularly in the global south. Nevertheless, we argue that gardening can be a public health strategy, readily accessible to boost societal resilience to disturbances.

Extreme heatwaves and drought have been shown to significantly affect urban tree survival, with potentially substantial economic costs for urban managers and local governments. During the 2019–2020 austral summer, the western Sydney Local Government Area (LGA) of Penrith experienced unprecedented high temperatures with less than 60 % of average rainfall compared with the proceeding five summers. This culminated in the highest temperature ever recorded in greater Sydney, of 48.9 °C. It is increasingly important that trees for urban applications are selected to be able to withstand such conditions. In early 2020, we conducted a visual assessment of canopy damage on street trees found in the Penrith LGA following the 2019–2020 summer heatwaves. We assessed the health of over 5500 trees and classified them as undamaged, lightly damaged, heavily damaged or defoliated. We found that more than 10 % of all the trees assessed displayed some level of canopy damage, with exotic deciduous species showing the greatest proportion of canopy damage. A logistic regression revealed that for exotic deciduous species, the probability of having sustained no canopy damage was 79 % lower than that for native evergreen species. Using these data, the economic costs to replace damaged trees was calculated using two scenarios that incorporated costs of tree planting and maintenance: low cost (replacing all heavily damaged and defoliated trees with juvenile trees) and high cost (replacing all heavily damaged and defoliated trees with advanced trees), with costs ranging from $500,000 to $800,000 (AUD). We also calculated the cost of replacing all individuals of the most damaged species with more climate-resilient species in order to secure the urban forest and found that the cost would be over AUD$1,000,000. This research highlights the importance of careful planning to ensure urban forest resilience and economic sustainability in the face of climate change.

Water availability can be a major abiotic constraint for plant success in urban areas. To ensure resilient green spaces, understanding which species are able to cope with low water availability is paramount for plant selection. However, in the horticultural industry, descriptions of species’ responses to low water availability are oftentimes poorly defined, inconsistent across sources, and informed from the natural habitat of species, personal experience, or both. Therefore, a method to objectively assess tolerances of species to low water availability is needed. Using a multivariate approach, we characterised the drought strategies of 113 horticultural plant species spanning five different growth forms (graminoids, herbs, climbers, shrubs and trees) by using five leaf-level traits (leaf mass per area (LMA), leaf thickness, unit leaf area, leaf dry matter content (LDMC) and leaf water potential at turgor loss point (TLP)). Based on this approach, we found that species clustered into three distinct groups, which correspond to fundamental drought strategies based on previous ecological literature (i.e., ‘dehydration avoiders’ (species with high LMA and LDMC, thick leaves and low (more negative) TLP), ‘dehydration tolerators’ (species with low LMA and LDMC and high (less negative) TLP) and an ‘intermediate’ mixture of the two strategies). We found that the majority of species that were considered as ‘drought tolerant’ by the horticultural industry were classified as either ‘dehydration tolerators’ (31.9 %) or ‘dehydration avoiders’ (42.5 %) using our trait-based approach. We did not find any strong connections between the climate of origin of our species and our trait-based classifications. Distinguishing between dehydration avoidance and dehydration tolerance may help to enhance horticultural guidelines by better informing which species are suitable for particular biophysical and landscape contexts. This trait-based approach allows for evidence-based evaluation of drought strategies of new and emerging species and cultivars that may be suitable for urban landscapes.

Australia is currently grappling with a range of social and environmental challenges, many of which impact the way our public health system, and society more broadly, function. In this short communication paper we explore urban agriculture in Australia as a Nature-Based Solution (NBS) to address some of the ecological, social, economic and health challenges facing the continent. We argue that urban agriculture has the potential to mitigate the effects of climate change extremes while simultaneously providing multiple benefits such as improving wellbeing, people-nature connections, and food security. We present three exemplar case studies diverse in geography, context and governance from Queensland, Tasmania, and New South Wales exploring verge gardening, market gardening, and a community greening program respectively to highlight the benefits of urban agriculture as a NBS. We advocate that various forms of urban agriculture need to be researched and considered for their potential impacts and multiple benefits to be fully supported, governed, and understood in light of the social-ecological challenges Australian cities face.

As the global climate warms, cities worldwide face more frequent and extreme heatwaves. These events can affect human health and decrease liveability. While the mitigating effects of vegetation on land surface temperature (LST) are well characterised at large spatial scales and during typical weather conditions, the cooling benefits that urban greening can provide at local scales, particularly during summer heatwaves, are poorly quantified. We quantified LST variation across an urban landscape to assess relationships with land use and vegetation cover from land unit (average ~ 460 m2) to suburb scale (~1.66 km2) under extreme summer heat conditions. High resolution (2 m), day- and night-time LST was measured at the peak of a heatwave event, after three consecutive days with air temperature exceeding 40 ˚C, by flying an aircraft fitted with a thermal imager over 90 suburbs in Adelaide, Australia. Daytime, night-time, and diurnal range LST distributions were related to measures of land use, vegetation cover (i.e., tree, grass) and urban morphology at both the suburb and land unit scale. At the suburb scale, vegetation cover did not affect LST. However, at the land unit scale, tree canopy cover, and to a lesser extent grass cover, decreased local LST by up to 6 ˚C during the day, but not at night. Overall night-time LST was poorly predicted by the land use and land cover predictors. Moving inland from the coast, small vegetation patches, mostly contained in yards and gardens, was associated with the greatest localised LST reductions in the hotter inland suburbs. LST within land units was further decreased during the day when vegetation was present within 30 m buffers around each land unit, suggesting a moderate landscape cooling effect on LST. Our results suggest that even small urban vegetation patches can be managed to provide substantial heat mitigation during increasingly frequent summer heatwaves, particularly around the residential environments where people live.

Functional diversity and composition of soil bacterial communities affect important soil biogeochemical processes. In natural and semi-natural ecosystems, variations in habitat complexity have been shown to significantly impact both litter and soil bacterial communities. However, this remains largely untested in urban ecosystems, where human management can lead to habitat complexity combinations unobserved in rural ecosystems. We established 10 research plots in low-complexity park, high-complexity park, and high-complexity remnant habitat types (n = 30) in Melbourne, Australia. The use of organic carbon substrates by soil and litter bacteria was measured using EcoPlates to investigate the effects of habitat complexity upon metabolic functional diversity and functional composition of bacterial communities of i) soil and ii) one-year old litter. Direct and indirect effects of habitat complexity, microclimate and decomposition status upon litter microbial functional diversity and composition were also modelled using path analysis. Soil bacterial communities had significantly higher functional diversity compared to litter bacterial communities, but no significant effect of habitat complexity was apparent. The functional composition of soil bacterial communities was not affected by habitat complexity. In contrast, the functional composition of litter bacterial communities in high complexity parks and remnants was significantly different from that in low-complexity parks. The functional composition of litter bacterial communities, but not their diversity, was directly affected by habitat complexity and microclimate as well as their indirect effects upon the decomposition status of litter. Human management of urban habitat complexity can alter the functional composition of litter and soil bacterial communities without affecting their functional diversity. While this can have significant impacts on bacteria-regulated processes and ecosystem services, it also suggests that urban bacterial communities might be able to adjust to further environmental and climatic changes affecting urban ecosystems.

Globally, local governments are increasing investment in urban greening projects. However, there is little consideration of whether the species being planted will be resilient to climate change. We assessed the distribution of climatically suitable habitat, now and in the future, for 176 tree species native to Australia, commonly planted across Australia's Significant Urban Areas (SUAs) and currently grown by commercial nurseries. Species' occurrence records were obtained from inventories and herbaria, globally and across Australia, and combined with baseline climate data (WorldClim, 1960-1990) and six climate scenarios for 2030 and 2070 using climatic suitability models (CSMs). CSMs for each species were calibrated and projected onto baseline and future scenarios. We calculated changes in the size of climatically suitable habitat for each species across each SUA, and identified urban areas that are likely to have suitable climate for either fewer or more of our study species under future climate. By 2070, climatically suitable habitat in SUAs is predicted to decline for 73% of species assessed. For 18% of these species, climatically suitable area is predicted to be more than halved, relative to their baseline extent. Generally, for urban areas in cooler regions, climatically suitable habitat is predicted to increase. By contrast, for urban areas in warmer regions, a greater proportion of tree species may lose climatically suitable habitat. Our results highlight changing patterns of urban climatic space for commonly planted species, suggesting that local governments and the horticultural industry should take a proactive approach to identify new climate-ready species for urban plantings.

During the COVID-19 pandemic, many countries experienced something of a boom in interest in gardening. Gardens have long been considered as refuges into which we retreat to escape various struggles and challenges. In this study we examine the characteristics and functions of the garden as a refuge during the period of increased garden interest associated with the COVID-19 pandemic. Analysis of qualitative results about garden experiences from 3,743 survey respondents revealed intertwining garden and emotional geographies. Utilising non-representational and therapeutic landscape theories, we found multifarious and heightened experiences of non-material aspects of gardens; that is, the sensory and emotional aspects. People experienced, for example, a sense of joy, beauty, and reassurance, a greater attunement to the natural world and an increased sense of nature connection than they had at other times: birds felt louder. These heightened sensory and emotional experiences had therapeutic benefits, across age and geographical spectrums, during these difficult times. This research improves our understandings of the positive potential of non-material aspects of gardens in the creation of therapeutic landscapes in and beyond COVID-19.

To date, urban plant selection has mainly been focused on species-level characteristics such as aesthetics and suitability to form assemblages. In natural environments, however, plant species form natural assemblages based on positive (and negative) ecological interactions. Implementing an assemblage-level approach to plant selection in an urban context that utilises ecological interactions between species can not only look aesthetically pleasing but can also reduce common maintenance issues and improve plant performance and resilience. Agricultural practice has long since recognised the usefulness of utilising species interactions to improve plant and soil health, deter pests and increase resource use and diversity. However, the benefits of assemblage-level interactions have seldom been translated into the urban context. In this opinion piece, we advocate for the use of an assemblage-level approach for species selection in urban settings that draws on the interaction between species, based on key ecological principles. We suggest five such principles; facilitation, competition and niche separation, enemy avoidance and deterrence, plant-soil interactions and species diversity. We propose selected examples of how they have been utilised in agriculture and argue that these concepts can be adopted in urban landscapes.

As cities are largely private systems, recent investigations have assessed the provision of ecosystem services from the private realm. However, these assessments are largely based on the concept of ownership and fail to capture the complexity of service provision mediated by interactions between people and ecological structures. In fact, people interact with ecological structures in their role of land tenants and stewards, further modulating the provision of ecosystem services. We devise a theoretical framework based on the concepts of ownership, tenancy, and stewardship, in which people, as mediators of ecosystem services, regulate the provision of services throughout the private-social-public domain. We survey relevant literature describing these dimensions and propose a comprehensive framework focused on the private-social-public domain. Our framework can advance ecosystem service research and enhance the provision of ecosystems services. The inclusion of people’s individual, social and public roles in the mediation of ecosystem services could improve how benefits are planned for, prioritized, and optimized across cities.

The extent of urban ecological homogenization depends on how humans build, inhabit, and manage cities. Morphological and socio-economic facets of neighborhoods can drive the homogenization of urban forest cover, thus affecting ecological and hydrological processes, and ecosystem services. Recent evidence, however, suggests that the same biophysical drivers differentiating composition and structure of natural forests can further counteract the homogenization of urban forests. We hypothesize that climate can differentiate forest structure across residential macrosystems at regional-to-continental spatial scales. To test this hypothesis, forest structure (tree and shrub cover and volume) was measured using LiDAR data and multispectral imagery across a residential macrosystem composed 1.4 million residential parcels contained in 9 cities and 1503 neighborhoods. Cities were selected along an evapotranspiration (ET) gradient in the conterminous United States, ranging from the colder continental climate of Fargo, North Dakota (ET = 464.43 mm) to the hotter subtropical climate of Tallahassee, Florida (ET = 1000.47 mm). The relative effects of climate, urban morphology, and socio-economic variables on residential forest structure were assessed by using generalized linear models. Climate differentiated forest structure of the residential macrosystem as hypothesized. Average forest cover doubled along the ET gradient (0.39 – 0.78 m(2) m(−2)), whereas average forest volume had a threefold increase (2.50 – 8.12 m(3) m(−2)). Forest volume across neighborhoods increased exponentially with forest cover. Urban morphology had a greater effect in homogenizing forest structure on residential parcels compared to socio-economics. Climate and urban morphology variables best predicted residential forest structure, whereas socio-economic variables had the lowest predictive power. Results indicate that climate can differentiate forest structure across residential macrosystems and may counteract the homogenizing effects of urban morphology and socio-economic drivers at city-wide scales. This resonates with recent empirical work suggesting the existence of complex multi-scalar mechanisms that regulate ecological homogenization and ecosystem convergence among cities. The study initiates high-resolution assessments of forest structure across entire urban macrosystems and breaks new ground for research on the ecological and hydrological significance of urban vegetation at subcontinental scale.