Background and aims Green roofs are often installed to reduce urban stormwater runoff. To optimally achieve this, green roof plants need to use water when available, but reduce transpiration when ...limited to ensure survival. Succulent species commonly planted on green roofs do not achieve this. Water availability on green roofs is analogous to natural shallow-soil habitats including rock outcrops. We aimed to determine whether granite outcrop species could improve green roof performance by evaluating water use strategies under contrasting water availability. Methods Physiological and morphological responses of 12 granite outcrop species with different life-forms (monocots, herbs and shrubs) and a common green roof succulent were compared in well watered (WW) and water deficit (WD) treatments. Key results Granite outcrop species showed a variety of water-use strategies. Unlike the green roof succulent all of the granite outcrop species showed plasticity in water use. Monocot and herb species showed high water use under WW but also high water status under WD. This was achieved by large reductions in transpiration under WD. Maintenance of water status was also related to high root mass fraction. Conclusions By developing a conceptual model using physiological traits we were able to select species suitable for green roofs. The ideal species for green roofs were high water users which were also drought tolerant.
Green roofs are novel ecosystems that are increasingly common in cities. While their hydrologic and energy saving benefits are well‐established, green roofs have also been proposed as having ...significant value for conserving biodiversity. We evaluate six hypotheses that describe the purported biodiversity conservation benefits of green roofs. Green roofs largely support generalist species particularly insects, but their conservation value for rare taxa, and other taxonomic groups especially vertebrates, is poorly documented. Further, their ability to replicate biotic communities in the context of ecological restoration is largely untested, as is their potential to connect ground‐level habitats. Synthesis and applications. Given the evidence, green roof proponents should use restraint in claiming conservation benefits and it is premature for policymakers to consider green roofs equivalent to ground‐level urban habitats. Ecologists need to work with the industry to evaluate green roof biodiversity and help design green roofs based on ecological principles to maximize biodiversity gains.
The majority of humanity now lives in cities or towns, with this proportion expected to continue increasing for the foreseeable future. As novel ecosystems, urban areas offer an ideal opportunity to ...examine multi-scalar processes involved in community assembly as well as the role of human activities in modulating environmental drivers of biodiversity. Although ecologists have made great strides in recent decades at documenting ecological relationships in urban areas, much remains unknown, and we still need to identify the major ecological factors, aside from habitat loss, behind the persistence or extinction of species and guilds of species in cities. Given this paucity of knowledge, there is an immediate need to facilitate collaborative, interdisciplinary research on the patterns and drivers of biodiversity in cities at multiple spatial scales. In this review, we introduce a new conceptual framework for understanding the filtering processes that mold diversity of urban floras and faunas. We hypothesize that the following hierarchical series of filters influence species distributions in cities: (1) regional climatic and biogeographical factors; (2) human facilitation; (3) urban form and development history; (4) socioeconomic and cultural factors; and (5) species interactions. In addition to these filters, life history and functional traits of species are important in determining community assembly and act at multiple spatial scales. Using these filters as a conceptual framework can help frame future research needed to elucidate processes of community assembly in urban areas. Understanding how humans influence community structure and processes will aid in the management, design, and planning of our cities to best support biodiversity.
Urbanization contributes to the loss of the world's biodiversity and the homogenization of its biota. However, comparative studies of urban biodiversity leading to robust generalities of the status ...and drivers of biodiversity in cities at the global scale are lacking. Here, we compiled the largest global dataset to date of two diverse taxa in cities: birds (54 cities) and plants (110 cities). We found that the majority of urban bird and plant species are native in the world's cities. Few plants and birds are cosmopolitan, the most common being Columba livia and Poa annua. The density of bird and plant species (the number of species per km2) has declined substantially: only 8% of native bird and 25% of native plant species are currently present compared with estimates of non-urban density of species. The current density of species in cities and the loss in density of species was best explained by anthropogenic features (landcover, city age) rather than by non-anthropogenic factors (geography, climate, topography). As urbanization continues to expand, efforts directed towards the conservation of intact vegetation within urban landscapes could support higher concentrations of both bird and plant species. Despite declines in the density of species, cities still retain endemic native species, thus providing opportunities for regional and global biodiversity conservation, restoration and education.
Based on attention restoration theory we proposed that micro-breaks spent viewing a city scene with a flowering meadow green roof would boost sustained attention. Sustained attention is crucial in ...daily life and underlies successful cognitive functioning. We compared the effects of 40-s views of two different city scenes on 150 university students' sustained attention. Participants completed the task at baseline, were randomly assigned to view a flowering meadow green roof or a bare concrete roof, and completed the task again at post-treatment. Participants who briefly viewed the green roof made significantly lower omission errors, and showed more consistent responding to the task compared to participants who viewed the concrete roof. We argue that this reflects boosts to sub-cortical arousal and cortical attention control. Our results extend attention restoration theory by providing direct experimental evidence for the benefits of micro-breaks and for city green roofs.
•Neuroscience techniques provide direct empirical support for attention restoration theory.•A micro-break viewing a green, but not concrete roof city scene, sustains attention.•The green roof city scene perceived as more restorative than concrete roof city scene.•Results suggest city nature is valuable for healthy cities and workplaces.
AIM: Cities represent an ideal study system for assessing how intensive land‐use change and biotic interchange have altered beta diversity at broad geographic extents. Here we test the hypothesis ...that floras in cities located in disparate regions of the globe are being homogenized by species classified as invasive (naturalized species that have spread over a large area) or as a European archaeophyte (species introduced into Europe before ad 1500 from the Mediterranean Basin). We also test the prediction that the global influences of European activities (colonization, agriculture, commerce) have supported this outcome. LOCATION: One hundred and ten cities world‐wide. METHODS: We examined the richness and composition of urban floras among European (n = 85) and non‐European cities (n = 25) for species classified as native or non‐native, or further classified as European archaeophyte or invasive. We modelled how geographic, climatic and anthropogenic factors were related to compositional similarity between European and non‐European cities. RESULTS: We found that most plants in the cities we examined, particularly non‐European cities, were native and unique to each city. Non‐native species were similarly unique, but occurred in much lower proportions relative to natives. Although European archaeophytes and invasive species also occurred in lower proportions, they had similar compositions among cities. European archaeophytes were most prevalent in European cities, but were most similar among non‐European cities. Contrasting European and non‐European cities, geography and climate were most relevant for native and invasive species, whereas climate and agriculture were most relevant for European archaeophytes. MAIN CONCLUSIONS: Cities in disparate regions of the globe retain regionally distinct native and non‐native plant assemblages, while invasive species, and especially European archaeophytes, were associated with lower beta diversity among cities. These findings suggest that intensive land‐use change and biotic interchange, shaped through European influences, have had a world‐wide effect on the beta diversity of urban plant assemblages.
•We examine bee communities in three dominant urban green spaces.•Bee assemblages in residential neighbourhoods were dominated by Apis mellifera.•Suitable bee habitat was infrequently managed, and ...dominated by native vegetation.•Simple changes to green space management can assist native bee conservation.
Networks of urban green space can provide critical resources for wild bees, however it is unclear which attributes of green spaces provide these resources, or how their management can be improved to benefit a diversity of bee species. We examined bee communities in three dominant urban green space habitats: (1) golf courses (2) public parks and (3) front gardens and streetscapes in residential neighbourhoods in Melbourne, Australia and assessed which local and landscape attributes influenced bee communities. There was a greater abundance and richness of bee species in public parks compared to golf courses and residential neighbourhoods, where the latter habitat was dominated by European Honeybees (Apis mellifera). The occurrence of A. mellifera was positively associated with increases in flowering and native plants. Ground-nesting Homalictus species occurred more frequently in older golf courses and public parks surrounded by low impervious surface cover, and with a low diversity of flowering plants. Cavity nesting, floral specialists within the Colletidae family occurred more often in green space habitats with greater native vegetation, and occurred infrequently in residential neighbourhoods. The lack of appropriate nesting habitat and dominance of exotic flowering plants in residential neighbourhoods appeared to positively impact upon the generalist A. mellifera, but negatively affected cavity and ground nesting floral specialist bee species (e.g. Halictidae and Colletidae). Our results highlight the need to include urban areas in pollinator conservation initiatives, as providing resources critical to diverse bee communities can assist in maintaining these key pollinators in urban landscapes.
In order to mitigate areas of high urban air temperature (or ‘hotspots’), advice and tools are currently being sought to help inform urban planning and decision making around urban greening. One ...potential tool receiving growing interest is the use of thermal imagery for identifying hotspots, however this relies on the assumption that patterns in land surface temperature (LST) coincide with patterns in air temperature. This study explores the capacity of very high resolution (VHR), airborne thermal infrared (TIR) remotely sensed data to identify hotspots at a neighbourhood and street scale resolution. As such it assesses whether VHR TIR remote sensing is an appropriate tool for urban planning and urban greening decision making. In partnership with a local municipality in Melbourne, Australia, VHR (0.5m) daytime and night time TIR images were captured during warm summertime conditions in February 2012. We found that VHR TIR data certainly identified locations of high LST that could be prioritized for urban greening, however at very high resolutions, VHR TIR data could not identify hotspots because patterns in LST did not strongly correlate with patterns of high air temperature. When VHR TIR data was aggregated to a coarser resolution, it could be used at the neighbourhood-scale to identify hotspots due to greater confidence that areas of high LST do represent air temperature hotspots. Increased vegetation proportion was associated with a reduction in LST for both the day and night meaning urban greening can be used to mitigate hotspots and should be prioritized in wide, open streets where building shade is less. While VHR TIR remote sensing may be an attractive option, this study shows it is not a suitable tool to help inform urban planning and urban greening decision making as the capture, post-processing and interpretation requirements and costs of delivering a high quality product are prohibitive for many end users. We suggest that those seeking to use thermal imagery to identify hotspots in the urban landscape, strongly consider more accessible and cheaper satellite remote sensing products (such as Landsat). VHR TIR derived LST may be useful in designing urban spaces for improved human thermal comfort and focusing on a small region of interest, but the numerous complexities and limitations of the data must be recognized.
•Thermal infrared (TIR) remote sensing can identify urban hotspots at appropriate scales.•Increasing urban vegetation cover can reduce land surface temperatures (LST).•LST and air temperature broadly follow similar patterns at coarse spatial resolution.•TIR remote sensing is a useful tool for planning and informing urban greening.•Defining the scale of application should inform TIR remote sensing product selection.
1. Cities are rapidly expanding world-wide and there is an increasing urgency to protect urban biodiversity, principally through the provision of suitable habitat, most of which is in urban green ...spaces. Despite this, clear guidelines of how to reverse biodiversity loss or increase it within a given urban green space is lacking. 2. We examined the taxa- and species-specific responses of five taxonomically and functionally diverse animal groups to three key attributes of urban green space vegetation that drive habitat quality and can be manipulated over time: the density of large native trees, volume of understorey vegetation and percentage of native vegetation. 3. Using multi-species occupancy-detection models, we found marked differences in the effect of these vegetation attributes on bats, birds, bees, beetles and bugs. At the taxa-level, increasing the volume of understorey vegetation and percentage of native vegetation had uniformly positive effects. We found 30-120% higher occupancy for bats, native birds, beetles and bugs with an increase in understorey volume from 10% to 30%, and 10-140% higher occupancy across all native taxa with an increase in the proportion of native vegetation from 10% to 30%. However, increasing the density of large native trees had a mostly neutral effect. At the species-specific level, the majority of native species responded strongly and positively to increasing understorey volume and native vegetation, whereas exotic bird species had a neutral response. 4. Synthesis and applications. We found the probability of occupancy of most species examined was substantially reduced in urban green spaces with sparse understorey vegetation and few native plants. Our findings provide evidence that increasing understorey cover and native plantings in urban green spaces can improve biodiversity outcomes. Redressing the dominance of simplified and exotic vegetation present in urban landscapes with an increase in understorey vegetation volume and percentage of native vegetation will benefit a broad array of biodiversity.
•Review of cooling potential from green infrastructure in cities with hot, dry summers.•Presents a hierarchical process to prioritise urban areas for green infrastructure.•Framework to strategically ...select green infrastructure that is ‘fit-for-place’ and ‘-purpose’.•Case study of framework applied to local government planning scale.
Warming associated with urban development will be exacerbated in future years by temperature increases due to climate change. The strategic implementation of urban green infrastructure (UGI) e.g. street trees, parks, green roofs and facades can help achieve temperature reductions in urban areas while delivering diverse additional benefits such as pollution reduction and biodiversity habitat. Although the greatest thermal benefits of UGI are achieved in climates with hot, dry summers, there is comparatively little information available for land managers to determine an appropriate strategy for UGI implementation under these climatic conditions. We present a framework for prioritisation and selection of UGI for cooling. The framework is supported by a review of the scientific literature examining the relationships between urban geometry, UGI and temperature mitigation which we used to develop guidelines for UGI implementation that maximises urban surface temperature cooling. We focus particularly on quantifying the cooling benefits of four types of UGI: green open spaces (primarily public parks), shade trees, green roofs, and vertical greening systems (green walls and facades) and demonstrate how the framework can be applied using a case study from Melbourne, Australia.
PDF
