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... While replacing heavily damaged trees with another tree of the same species provides a short term solution to restoring tree benefits, these trees are likely to be damaged during future heatwave and drought conditions. Given that the frequency and intensity of heatwaves and drought are projected to increase under climate change (Sheffield and Wood, 2008;Perkins-Kirkpatrick and Gibson, 2017), it is imperative that we consider utilising climate-ready species in order to secure the urban forest (Yang, 2009;Burley et al., 2019). Extreme climate events have often had significant influence on shaping urban forests, which has been associated with behavioural changes in species selection (Roman et al., 2018). ...
... In light of the increasing impacts of climate change on the resilience of the urban forest, it is imperative that species selection shifts away from aesthetic appeal and towards climate suitability of species (Yang, 2009;Burley et al., 2019). By 2041, it is expected that the population of Penrith LGA will have increased by 76.5 % compared with current levels (NSW Department of Planning, Industry and Environment, 2019). ...
... Securing the urban forest by pre-emptively replacing all individuals of vulnerable species with more climate-resilient species represents an extreme form of management that may also not be within the budget capacity of many municipalities. Instead, current urban managers should proactively consider planting species suitable for future climates now in a bid to phase out unsuitable species (Yang, 2009;Burley et al., 2019). This will help ensure a healthy and resilient urban forest for the future while meeting ambitious tree canopy targets and ensuring economic sustainability in the present. ...
Article
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 5,500 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.
... However, NBSs are themselves vulnerable to the climate challenges they are meant to address (McPhearson et al., 2015;Calliari et al., 2019). Unlike natural ecosystems, often adapted to natural disturbance regimes (i.e., drought, wildfires), urban NBSs may be ill-equipped to cope with additional stressors (Burley et al., 2019). NBSs face a number of urban stressors, such as disturbance and pollution, before having to deal with climate extremes (Meineke et al., 2016). ...
... These urban species can tolerate a wide range of climates, thus potentially having higher adaptability to new climate conditions. However, many species in cities are predicted to shift their suitable climatic habitats pole-ward under future climate change (Burley et al., 2019). Likewise, some species might become less suitable under climate change (Ramage et al., 2013;Jenerette et al., 2016) with higher-latitude species being restricted to cooler regions, and low-latitude species becoming more suitable at higher latitudes. ...
... Local adaptation to climatic and environmental factors is often seen as a fundamental criterion for species-selection in most NBS applications (Nesshöver et al., 2017). Australian native species are evolutionarily or ecologically adapted to cope with high temperatures and prolonged drought periods and can generally perform better than many exotic species (Burley et al., 2019). Local governments have recognized that some exotic plant species might struggle in a 50 • C world, prompting a reconsideration of selection criteria. ...
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.
... While city residents and governing bodies are seeking SETS strategies to proactively improve the capacity to cope with and adapt to climate change [19][20][21] , SETS change is still often only identified as a driver, provoker, or a reinforcer of climate change impacts, rather than as an opportunity to ameliorate or mitigate impacts. For example, urbanization increases urban populations, energy consumption, and therefore exacerbates climate change 22 , setting in motion perverse reinforcing loops and vicious cycles 23 . In turn, climate change can cause massive migrations of people to and from urban areas, and population displacement and vulnerability, causing a further change in urban SETS now and in the future 24 . ...
... Climate change can trigger nonlinear positive tipping points from society and technology that, through feedback, create different-ideally improvedsystem states ( Fig. 2) 3,30 . For example, in urban forestry plans, forecasted future climate envelopes can offer an opportunity to redesign planting strategies around species more likely to withstand future temperature and rainfall extremes and replace those likely to struggle or fail 23 . For urban communities to acknowledge such changes and strategically steer SETS change requires systems' thinking to accelerate actions for sustainable urban transitions 29 . ...
... The rapid rates of projected climate change and particularly in cities mean that many plant and animal species will not be able to adapt to new conditions 23 . This warrants creative ecological climate change adaptation changes to support urban biodiversity and associated ecological functions, while ideally promoting climate change mitigation. ...
Article
Full-text available
Urban social–ecological–technological systems (SETS) are dynamic and respond to climate pressures. Change involves alterations to land and resource management, social organization, infrastructure, and design. Research often focuses on how climate change impacts urban SETS or on the characteristics of urban SETS that promote climate resilience. Yet passive approaches to urban climate change adaptation may disregard active SETS change by urban residents, planners, and policymakers that could be opportunities for adaptation. Here, we use evidence of urban social, ecological, and technological change to address how SETS change opens windows of opportunity to improve climate change adaptation.
... Strategic landscape plant selections have been shown to alleviate these issues, and improve the suitability and sustainability of cities to cope with global climate change (Norton et al., 2015;Grote et al., 2016;Espeland and Kettenring, 2018). Since the climatic suitability and sustainability (climatic sustainability means the sustainability of climatic suitability for landscape plants, under climate change) of landscape plants per se under global climate change are often neglected (Ordóñez and Duinker, 2015;Burley et al., 2019), these features need to be explored, especially in woody landscape plants, given the long lifespan of most trees (Burley et al., 2019;Jin et al., 2020). ...
... Strategic landscape plant selections have been shown to alleviate these issues, and improve the suitability and sustainability of cities to cope with global climate change (Norton et al., 2015;Grote et al., 2016;Espeland and Kettenring, 2018). Since the climatic suitability and sustainability (climatic sustainability means the sustainability of climatic suitability for landscape plants, under climate change) of landscape plants per se under global climate change are often neglected (Ordóñez and Duinker, 2015;Burley et al., 2019), these features need to be explored, especially in woody landscape plants, given the long lifespan of most trees (Burley et al., 2019;Jin et al., 2020). ...
... The geographical origin and accumulation of alien plants have attracted increasing attention and have been conducted at different spatial scales from regional to global (Jiang et al., 2011;Donaldson et al., 2014;Almeida et al., 2015;van Kleunen et al., 2015;Dawson et al., 2017). In any case, little attention has been paid to the climatic origin and/or accumulation of plants, and landscape plants are often ignored (with some exceptions like Jenerette et al., 2016;Burley et al., 2019). The inadequate knowledge base has hindered improvements for the present species composition and the climate-change resilience of landscape plants (Savi et al., 2015;Burley et al., 2019). ...
Article
Cities have become the main abodes for people, and landscape plants with their notable influence on quality of life, are important components of the urban ecosystem. The need to explore the climatic suitability and sustainability of landscape plants is especially relevant due to globalization and climate change. Nevertheless, this research area is constrained by the limited understanding of the biogeographical origin of landscape plants. We have compiled data on species lists, taxonomic information, and geographical and climatic origins for woody landscape plants in 36 major cities across China. We used climatic niche breadth (CNB) and climatic mismatched ratio (CMR) to assess the climatic suitability and sustainability of landscape plants. We found that 412 alien species had several hotspots of origin, mainly tropical regions in the Americas, Asia, and Australia. The 1,258 domestic species mainly originated from temperate southern China. Tropical species had a conspicuous geographical clustering in coastal cities of southern China, while the temperate species were abundant in all cities. The CNBs of domestic species were wider than those of alien species, and arid cities with harsher environmental stresses (mainly due to the limited precipitation) registered higher CMRs. In terms of sustainability, the response of landscape plants to climate change varied across climate zones, being influenced by a rich presence of temperate species. Overall, our findings emphasized that landscape plant selections should not only pay attention to the existing landscape needs, but also consider the climatic sustainability of landscape plant species to climate change, especially for long lifespan woody plants.
... Further, the urban tree inventories and species lists we collated reported trees planted only on public land, not private land, urban reserves and remnants, and botanic gardens -the inclusion of trees from these additional areas will likely increase estimates of urban tree species richness (Bush et al., 2018; Ossola & Hopton, F I G U R E 3 Examples of application of the Global Urban Tree Inventory (GUTI) dataset. (a) Trait distribution of average leaf length of the 176 common urban tree species native to Australia found to have suitable climate habitat across the 82 most populated significant urban areas (SUAs, in pink) across the continent (drawn from bioclimatic modelling data from Burley et al., 2019, andleaf trait data from ABRS, 2020;Cooper & Cooper, 2004;de Salas, 2009;Maslin, 2012;NT Government, 2014;RBGSYD, 2000;SHSA, 2014 andWheeler et al., 2002). Bars are standard errors of mean. ...
... Bars are standard errors of mean. (b) Example of precipitation and temperature niches for Allocasuarina torulosa and Allocasuarina verticillata, two congeneric trees species native to Australia but widely planted in cities and towns globally (drawn from Burley et al., 2019). A. torulosa has urban (GUTI) precipitation and temperature niches (grey) significantly different from those calculated from the species' natural occurrences [i.e., Global Biodiversity Information Facility (GBIF)/Atlas of Living Australia (ALA), in coral]. ...
Article
Motivation The Global Urban Tree Inventory (GUTI) is a compilation of datasets on tree species found in cities and towns throughout the world. GUTI data can be used to address a diverse range of theoretical and applied investigations related to species’ biogeography and distribution, ecological and physiological tolerance to climatic, biophysical and environmental parameters, as well as plant conservation and invasion. Main types of variables contained GUTI contains current taxonomic data for 4,734 tree species planted in urban areas, their conservation status [International Union for Conservation of Nature’s (IUCN’s) Red List of Threatened Species] and invasion potential (Global Register of Introduced and Invasive Species). Spatial location and grain Four hundred and seventy‐three urban areas in seventy‐three countries across five continents. The urban areas spanned 21 of 29 Koppen–Geiger climatic zones, and all 19 Food and Agriculture Organization of the United Nations global ecofloristic zones. Time period and grain GUTI is based on the most recent collections of urban tree inventories and species lists compiled by local authorities or reported in the scientific literature. Most data have been collected or updated since 2010. Major taxa and level of measurement Four thousand seven hundred and thirty‐four tree species (c. 8% of the global known arboreal flora). One‐tenth of these tree species face conservation risk in the wild, whereas 327 species are known to have invasion potential. Software format .xls file.
... Analysing the climate envelopes of urban tree species at a global scale has been suggested as an approach to identify tree species that may be better suited to future urban climates (Kendal and Baumann, 2016;Burley et al., 2019;Esperon-Rodriguez et al., 2019). Our aim was to determine whether the drought or thermal tolerance of a tree species can be predicted from variables derived from its climate envelope using exclusively open-source data (Kendal and Baumann, 2016). ...
... must be interpreted in this context, as they were clearly influenced by the source species data from the GBIF and how we summarised that data to represent species climate envelopes. Many studies have supplemented natural occurrence data with data from arboreta and urban tree inventories to better capture the fundamental climatic niche (Vetaas, 2002;Bocsi et al., 2016;Kendal et al., 2018;Burley et al., 2019;Esperon-Rodriguez et al., 2019). However, the only way to accurately describe the fundamental climatic niche is to plant and grow species across large climatic gradients. ...
Article
Analysing the climate envelope of plant species has been suggested as a tool to predict the vulnerability of tree species in future urban climates. However, there is little evidence that the climate envelope of a plant species directly relates to the drought and thermal tolerance of that species, at least not at the resolution required to identify or rank species vulnerability. Here, we attempted to predict drought and thermal tolerance of commonly used urban tree species using climate variables derived exclusively from open-source global occurrence data. We quantified three drought and thermal tolerance traits for 43 urban tree species in a common garden experiment: stomatal sensitivity to vapour pressure deficit, leaf water potential at the turgor loss point, and leaf thermal tolerance. We then attempted to predict each tolerance trait from variables derived from the climate envelope of each species, using occurrence data from the Global Biodiversity Information Facility. We found no strong relationships between drought and thermal tolerance traits and climatic variables. Across wide environmental gradients, plant tolerance and climate are inherently linked. But our results suggest that climate envelopes determined from species occurrence data alone may not predict drought or thermal tolerance at the resolution required to select tree species for future urban forests. We should focus on identifying the most relevant strategies and traits required to describe tolerance which in combination with climate envelope analysis should ultimately predict growth and mortality of trees in urban landscapes.
... Ideally, such assessments should consider how these relative contributions change along the urbanisation gradient. It is plausible, for example, that urban heat islands increase the risk that native species will face unfavourable climatic conditions in highly urbanised locations (Burley et al., 2019). Consequently, at least in temperate regions, where non-native species typically originate from warmer climates, non-natives may be more capable of providing ecosystem services (Walther et al., 2009). ...
... This complicates urban planning decisions given the growing debate regarding on the relative priority of biodiversity conservation and ecosystem service provisioning (e.g., Conway et al., 2019). Despite a positive relationship between total species richness and CS at the randomised points we generally find little evidence to support the theory that species diversity enhances ecosystem service provision (Burley et al., 2019;Slade et al., 2019), perhaps because of the very low abundance of most species (Winfree et al., 2015). That high level of ecosystem service provision is generated from a small number of tree species increased the vulnerability of future service provision to forthcoming environmental stresses in Bangkok, such as disease and insect pests (Bumrungsri et al., 2008), rising urban heat island intensity (Khamchiangta and Dhakal, 2020), and flooding (Leksungnoen et al., 2017). ...
Article
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We assess how tree species richness and ecosystem services vary along a tropical urbanisation gradient in a rapidly expanding mega-city (Bangkok, Thailand). We conduct tree surveys in 150 1 km cells selected by random stratification across an impervious surface cover gradient. In each cell, surveys were conducted at the centre (representing typical conditions) and in the largest patch of trees (assessing woodland retention impacts). We estimated trees’ contributions to i) carbon storage, ii) food production for people, iii) biodiversity support (production of food for frugivorous birds), and iv) economic value (assessed using regulations for using trees as collateral for financial loans). Surveys detected 162 species (99 natives) indicating substantial species loss relative to nearby natural forests. Despite this, and contrasting with typical patterns in temperate cities, tree species richness (including of natives) and ecosystem service provision is relatively stable across the urbanisation gradient. This finding has two important consequences. First, growing cities through high intensity developments that require less space may benefit regional biodiversity without compromising ecosystem services. Second, even the typically very small woodlands present in highly urbanised locations contribute to supporting biodiversity and providing ecosystem services; thus such woodlands require protection. Species richness is not strongly positively associated with most of our focal ecosystem services. Urban planners must therefore pay attention to both biodiversity and ecosystem services as these do not automatically accrue from each other, partly because non-native species contributed substantially to most ecosystem services except biodiversity support. Finally, trees provide substantial value as collateral for financial loans (averages of £643 ha at random locations and £2282 ha in wooded locations). Policies promoting such valuations may reduce tree removal and encourage tree planting, but the list of eligible species warrants revision to include additional species that enhance biodiversity support, ecosystem services, and resilience against future environmental instability.
... Furthermore, with increasingly dry climates in some urban regions predicted with climate change (Ripple et al., 2020), supplemental irrigation may become an unsustainable and expensive option to keep urban green spaces healthy and functional. Thus, it is increasingly important that plant species for urban applications be selected based on their tolerance of low water availability throughout their lifespan (Burley et al., 2019). ...
... Furthermore, as urban drought is often coupled with increased temperatures (Dale and Frank, 2017), the loss of leaves and canopy cover might reduce benefits provided by plants such as evaporative cooling and shade during extremely hot periods. While some of these effects could be mitigated through irrigation, this can result in greater environmental, sustainability and economic costs that may not be feasible during water use restrictions or under increasing temperatures with climate change (Burley et al., 2019). Instead, plants with a dehydration avoider strategy may be more appropriate for parks or gardens where restricted rooting space is less likely to be an issue (Sjöman et al., 2015(Sjöman et al., , 2018a. ...
Article
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.
... Large urban trees, especially street trees, are frequently removed, and replaced with smaller trees (Smith et al., 2019). The long-term effect of this fast turnover on the retention of microhabitats in the urban landscape is important to assess as the urban tree population is likely to decrease in size (Smith et al., 2019) with an expected rise in tree mortality rates (Burley et al., 2019). Additionally, many of these microhabitats might result in mechanical weakness that would require the removal of the tree at some point (Table 4). ...
Article
In addition to social and economic benefits, urban trees provide habitats for many different species and contribute significantly to urban biodiversity. To prevent harm to humans or infrastructure, tree risk assessment is conducted regularly in urban areas. Resultant pruning activities are often criticized as leading to unnecessary injuries and artificial tree shapes. In this study we compared different tree maintenance levels and the occurrence of biodiversity related structures, so-called tree microhabitats, to provide another perspective on the consequences of pruning urban trees. For a sample of urban street and park trees in Montreal, Quebéc, Canada, we found that the positive relationship between tree size (diameter at breast height) and microhabitat abundance and diversity was less steep than in a nearby forest with comparable species composition. Intensive tree maintenance in urban trees led to levels of certain microhabitats such as cavities and injuries that were comparable to natural, unmanaged forests. Light maintenance of urban trees encouraged more crown deadwood than typical and intensive maintenance levels. Tree species as well as cardinal direction of the nearest building played a minor role in the occurrence and development of microhabitats. Our results underline the importance of conserving and maintaining large living trees, especially in urban areas to provide tree microhabitats. These results also demonstrate the important role of intensive tree maintenance in stimulating tree microhabitat development in urban areas. However, new ways have to be found to reconcile the need for microhabitats and the maintenance of structurally healthy urban trees.
... In the near future, tree species composition in urban areas is likely to change towards climate-change resilient species, which can cope with increases in intensity, frequency, and severity of abiotic stresses (Burley et al., 2019). In particular, drought and heat resistance are primary selection criteria for urban greening programs (e.g., Roloff et al., 2009). ...
Article
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Nitrogen oxides (NO x), mainly a mixture of nitric oxide (NO) and nitrogen dioxide (NO 2), are formed by the reaction of nitrogen and oxygen compounds in the air as a result of combustion processes and traffic. Both deposit into leaves via stomata, which on the one hand benefits air quality and on the other hand provides an additional source of nitrogen for plants. In this study, we first determined the NO and NO 2 specific deposition velocities based on projected leaf area (sV d) using a branch enclosure system. We studied four tree species that are regarded as suitable to be planted under predicted future urban climate conditions: Carpinus betulus, Fraxinus ornus, Fraxinus pennsylvanica and Ostrya carpinifolia. The NO and NO 2 sV d were found similar in all tree species. Second, in order to confirm NO metabolization, we fumigated plants with 15 NO and quantified the incorporation of 15 N in leaf materials of these trees and four additional urban tree species (Celtis australis, Alnus spaethii, Alnus glutinosa, and Tilia henryana) under controlled environmental conditions. Based on these 15 N-labeling experiments, A. glutinosa showed the most effective incorporation of 15 NO. Third, we tried to elucidate the mechanism of metabolization. Therefore, we generated transgenic poplars overexpressing Arabidopsis thaliana phytoglobin 1 or 2. Phytoglobins are known to metabolize NO to nitrate in the presence of oxygen. The 15 N uptake in phytoglobin-overexpressing poplars was significantly increased compared to wild-type trees, demonstrating that the NO uptake is enzymatically controlled besides stomatal dependence. In order to upscale the results and to investigate if a trade-off exists between air pollution removal and survival probability under future climate conditions, we have additionally carried out a modeling exercise of NO and NO 2 deposition for the area of central Berlin. If the actually dominant deciduous tree species (Acer platanoides, Tilia cordata, Fagus sylvatica, Quercus robur) would be replaced by the species suggested for future conditions, the total annual NO and NO 2 deposition in the modeled urban area would hardly change, indicating that the service of air pollution removal would not be degraded. These results may help selecting urban tree species in future greening programs.
... As political and social pressure to increase tree planting intensifies (Forestry Commission, 2019), the familiar refrain of 'Right tree for the right place' is repeated. Burley et al. (2019) identify two challenges for the urban forestry industry in the selection process of trees for a future climate. Firstly, the selection of species based on hierarchical filters that identify climate as the pivotal biophysical limiting factor would substantially improve outcomes for cities and industry. ...
Article
The ecosystem services provided by urban trees make substantial contributions to the urban environments. However, many of these ecosystem services are strongly connected to tree size and health which means that right tree for site and climate is essential. Whilst most urban forestry literature focuses on finding "the right tree for the right place" by describing the variation in physiological traits at the species level, many species also show substantial intraspecific variation in their traits at the level of the organ, such as leaf economic traits or wood density. The question is how well do the nursery industry that support us with trees acknowledge this fact. The aim of this study was to investigate to what extent provenance and ecotypes is understood within the largest tree nurseries in Germany, Netherlands and the UK. We identified five tree species commonly planted within urban forests in central and northern Europe and carried out a brief analysis of the climatic envelopes experienced by them in their natural range. We then carried out short interviews with nursery representatives to examine whether it is possible to identify which ecotypes of these species are represented in commercial horticulture. The results show that in the large majority of cases (63 %), provenance knowledge was unknown. In some cases (11-12 %), the nurseries identified sources at the country level (e.g. Netherlands or Germany). None of the nurseries in the study hade any information from which ecotypes their material originated from. The principal finding of this study is that it is not currently possible for specifiers to select trees at an intra-specific level based on climate or ecological criteria since it is of the utmost importance that the plant material that is used is of the best possible fit with the target site.
... Analysis is based on data from the current study and supplemented by data from three other previously published studies to increase the power of analysis. The relationship is highly significant (p =< 0.001 R 2 = 0.3) n = 100 with establishing the urban forest (Burley et al., 2019;Hirons & Sjöman, 2019). ...
Article
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Diversification of urban forests is essential to enhance their resilience to future biotic threats as well as those posed by a changing climate. Arboreta and botanic gardens host a wide range of plant material that can be evaluated to inform tree selection policy. This study demonstrates that plant functional traits, such as the water potential at leaf turgor loss, can be highly instructive when developing evidence-based recommendations for urban environments. However, if botanic collections are to fulfil a critical role in understanding plant response to environment, they should not be managed solely as visitor attractions but must have scientific objectives at the forefront of management policy. Summary • Arboreta and botanic gardens host a multitude of species that can be utilized in research focused on improving diversity within urban forests. Higher tree species diversity will enhance the resilience of urban forests to abiotic and biotic threats and help deliver strategies that foster sustainable communities. Consequently, this study aims to demonstrate the value of botanic collections as a resource for research into tree species selection for more resilient urban landscapes. • As water stress is a major constraint for trees in urban environments, understanding the drought tolerance of species is essential for urban tree selection. This study evaluates a key functional trait relating to drought tolerance. Using vapor pressure osmometry, the water potential at leaf turgor loss was evaluated for 96 species using plant material from seven botanic collections in North America and Europe. • Leaf turgor loss contrasted widely in the temperate deciduous trees evaluated and, in summer, ranged from −1.7 MPa to −3.9 MPa. Significant differences in drought tolerance were also apparent across genera and closely related cultivars. Osmotic adjustment was shown to be a major physiological factor driving leaf turgor loss. A meta-analysis also demonstrated that leaf turgor loss was closely
... This species was been widely planted especially between the 20s and 50s of the last century [3], so that a great number of trees are now old or senescent. Various other issues bother this species in town, like the threats deriving from climate change [4], which undermine the static stability of plants and incite decline [5][6][7], from new pests and pathogens, such as Toumeyella parvicornis and Heterobasidion spp. [8][9][10], from mismanagement (especially road maintenance and management of underground facilities) [11]. ...
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The Italian Stone Pine (Pinus pinea L.) is one of the most employed ornamental trees in towns with Mediterranean climates. For example, in the city of Rome, Pinus is the most common genus, with more than 51,000 trees. This study investigates technical and economic features of maintenance operations of Stone Pines and evaluates the productivity and costs of the observed yards. Pruning and felling are the most frequent management operations of trees in towns and this study analyzes the features of these operations carried out in 14 work sites. The operations were carried out either with aerial platforms (19 trees) or ascending the crown by tree-climbing (6 trees). The operations were sampled with time studies (12 trees for pruning and 13 for felling). Work time was measured from the beginning of operations to the transport of the residual biomass to the collection and loading point, using centesimal stopwatches and video recording. The total residual biomass was weighed or assessed. Total observation time amounted to 63.1 hours. The evaluation of the costs of each work site considered the fixed and the variable costs and the costs for the labor force. A Multiple Linear Regression model (statistics: determination coefficient R2: 0.74, adjusted R2: 0.67, p-value < 0.001) which utilizes four regressors easily evaluable before the work, was adopted to predict the gross time of the operations. This paper can contribute to optimize trees maintenance methods in urban sites and to assess the potential residual wood biomass attainable from urban forestry maintenance in the city of Rome.
... Urban forests provide many essential ecosystem services, including carbon sequestration; decreasing air, water, and noise pollution; mitigating the urban heat island effect and flood risk; and providing recreational areas Kleerekoper et al. 2012;Roy et al. 2012;Nowak et al. 2013;Berland et al. 2017). Urban forests also provide an ideal system to study future climate, as they can be subject to more extreme and stressful conditions (Carreiro and Tripler 2005), and changes in climatic suitability may differ compared to trees growing in neighboring natural areas (Burley et al. 2019). Tree failures that result from more extreme conditions (e.g., wind events) can damage property, interrupt essential services, and injure people-sometimes fatally. ...
Article
While often considered “open grown,” urban trees are often found in relatively close proximity to neighboring trees, buildings, and other elements of urban infrastructure. These spatial arrangements may provide wind protection during severe weather events such as hurricanes. Beyond this very local scale, urban tree abundance and condition are often influenced by the greater sociodemographic context of the neighborhood or community where they are found. In an effort to assess the impact of these external factors on wind firmness after Hurricane Irma impacted Florida in 2017, we revisited three urban areas that had previously been inventoried using sample plots prior to the storm. At each plot we assessed storm damage and characterized surrounding protective elements (i.e., buildings and other trees) using a combination of ground-based and aerial approaches. This was then paired with block group level sociodemographic data derived from the United States Census. Logistic regression results confirmed previous research, showing that partial and whole tree failure were significantly more likely with a larger stem diameter (p = 0.001) and perceived/previously documented lower wind firmness (p = 0.004). However, our results disagreed with previous studies linking species diversity and resilience, showing tree failure was significantly more likely with higher Shannon Diversity Index (p = 0.008). A comparative geographically weighted logistic regression model also found that the higher proportions of African American residents and Hispanic residents, and the median age of residents were significant predictors of less likely tree failure in 30%, 36%, and 20% of plots, respectively. However, this evidence was weak, compared to that of tree- and plot-level effects. Despite being a key predictor of interest, we did not see any significant protective effect from neighboring trees or structures.
... The final conclusion concerning the tree species which are most suitable for the changing urban conditions requires, however, further research and observation (Burley et al., 2019;Núñez-Florez et al., 2019). In addition, the introduction of new species in northern European cities on a larger scale (Zander & Ulrichs, 2014;Böll, 2018), it may be worth considering species which have already been planted in southern cities of the continent, and which respond well to drought stress and the high levels of insolation. ...
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This study examined the impact of air pollution, and more specifically the impact of traffic, on the health of urban trees. Due to the lack of data sets, urban tree growth modeling often relies on the existing knowledge of forest. However, urban trees differ from forest trees. One of the aims of the study is to fill the lacunae in this field. It was hypothesized that in streets with higher traffic volume, both growth parameters and health status of trees would be decreased in comparison to trees growing in streets with lower traffic volume. Four of the most common tree species growing in Berlin were selected: Tilia cordata Mill., Acer platanoides L., Platanus acerifolia (Aiton) Willd., and Aesculus hippocastanum L. Apart from the tree age and stand position (high and low traffic volume), the height and circumference were measured and the following traits were analyzed: trunk condition, crown defoliation, leaf discoloration, the presence of hollows and nests. The streets that were selected for the analysis were located in the center of Berlin. For each species, four streets with high traffic volume and four streets with low traffic volume were chosen. The car traffic volume had a significant impact on growth parameters. Significant differences in height and circumference between trees growing on streets with low or high traffic volume were noticed; the higher the traffic volume, the lower the tree height and circumference. This tendency is particularly visible in P. acerifolia, T. cordata and A. platanoides. This relation was observed in all species except for A. hippocastanum. In the conditions of high-traffic volume, A. platanoides is thriving revealing the smallest differences in vitality and condition of the crown, trunk and leaves. The greatest differences in the health condition of the trees among the analyzed variants of traffic intensity were observed in the case of T. cordata. Lime trees seem to be most suitable for planting in the streets with lower traffic volume, whereas A. platanoides seems most suitable for planting in the streets with high traffic volume. P. acerifolia, despite its generally good health, is suffering from several progressing diseases. It is worth considering whether it should be gradually replaced with more resistant species. Aesculus, especially A. hippocastanum, are currently the most endangered ones. An alternative to this species can be A. carnea.
... This species was been widely planted especially between the 20s and 50s of the last century (Massari, 1991), so that a great number of trees are now old or senescent. Various other issues threat this species in town, such as the adverse effects deriving from climate change (Yang, 2009), which undermine the static stability of plants and incite decline (Burley et al., 2019;Costello et al., 2015;Gasperini et al., 2016), from new pests and pathogens, such as Toumeyella parvicornis and Heterobasidion spp. (Garonna et al., 2018;Moricca et al., 2018;D'Amico et al., 2007), from mismanagement (especially road maintenance and management of underground facilities) (Biocca et al., 2003). ...
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... 27 The resilience of urban vegetation must, therefore, be planned under alternative future climate change scenarios to ensure that the benefits can continue to be delivered. 28,29 Although gaining increasing attention from researchers and practitioners, it remains unclear to what extent nature-based solutions are comparable with, and thus can replace, grey infrastructure in terms of effectiveness. 30 Nature-based solutions, when implemented at scale, can have major financial and governance challenges. ...
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Record climate extremes are reducing urban liveability, compounding inequality, and threatening infrastructure. Adaptation measures that integrate technological, nature-based, and social solutions can provide multiple co-benefits to address complex socioecological issues in cities while increasing resilience to potential impacts. However, there remain many challenges to developing and implementing integrated solutions. In this Viewpoint, we consider the value of integrating across the three solution sets, the challenges and potential enablers for integrating solution sets, and present examples of challenges and adopted solutions in three cities with different urban contexts and climates (Freiburg, Germany; Durban, South Africa; and Singapore). We conclude with a discussion of research directions and provide a road map to identify the actions that enable successful implementation of integrated climate solutions. We highlight the need for more systematic research that targets enabling environments for integration; achieving integrated solutions in different contexts to avoid maladaptation; simultaneously improving liveability, sustainability, and equality; and replicating via transfer and scale-up of local solutions. Cities in systematically disadvantaged countries (sometimes referred to as the Global South) are central to future urban development and must be prioritised. Helping decision makers and communities understand the potential opportunities associated with integrated solutions for climate change will encourage urgent and deliberate strides towards adapting cities to the dynamic climate reality.
... The hardwood plantation estate (Eucalyptus and Corymbia species) rapidly expanded from the 1990s and has also plateaued at 1 million ha. In addition, a wide range of native and exotic genera have been planted as amenity trees in urban and peri-urban areas (Burley et al., 2019;Bennett, 2020;Nahrung and Carnegie, 2020), with key taxa including Eucalyptus, Pinus, Platanus, Populus, Quercus, and Ulmus. Urban and peri-urban trees can act as bridgeheads for the establishment and spread of invasive forest species (Paap et al., 2017;Branco et al., 2019), and thus can be used as sentinels for early detection of invasive alien species (Smith et al., 2010;Paap et al., 2017;Mansfield et al., 2019). ...
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... Identifying species and genotypes likely to be tolerant of future climates is an option for expanding the current palette of tree species within different locales (e.g. Brandt et al., 2017;Burley et al., 2019;Esperon-Rodriguez et al., 2019;McPherson et al., 2018;Sadeghabadi et al., 2020;Steenberg et al., 2017;Yang, 2009). Initiatives such as Citree database (Vogt et al., 2017) (Ramage et al., 2013;Roman et al., 2013). ...
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The management of urban forests is a key element of resilience planning in cities across the globe. Urban forests provide ecosystem services as well as other nature based solutions to 4.2 billion people living in cities. However, to continue to do so effectively, urban forests need to be able to thrive in an increasingly changing climate. Trees in cities are vulnerable to extreme heat and drought events, which are predicted to increase in frequency and severity under climate change. Knowledge of species' vulnerability to climate change, therefore, is crucial to ensure provision of desired ecosystem benefits, improve species selection, maintain tree growth and reduce tree mortality, dieback and stress in urban forests. Yet, systematic assessments of causes of tree dieback and mortality in urban environments are rare. We reviewed the state of knowledge of tree mortality in urban forests globally, finding very few frameworks that enable detection of climate change impacts on urban forests and no long-term studies assessing climate change as a direct driver of urban tree dieback and mortality. The effects of climate change on urban forests remain poorly understood and quantified, constraining the ability of governments to incorporate climate change resilience into urban forestry planning.
... There are numerous, well-recognized threats to UK habitats, including urbanization (United Nations, 2016;Watkins et al., 2020), climate change (Burley et al., 2019;S. Roy et al., 2012) and biosecurity (Kemp et al., 2021;van Kleunen et al., 2018). ...
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The contributions of constructed Green Infrastructure (GI) to biodiversity are often used to justify urban development projects, yet in many cases these contributions have been difficult to quantify. As a result, a wide range of GI features are designed and implemented, often without knowledge of whether these features contribute meaningfully to biodiversity or if there are biosecurity risks presented by their design or procurement. Our understanding of design practices could be significantly improved if researchers and policymakers were able to draw upon a data resource that recorded the specifications used in development projects and facilitated easy access to them. In the United Kingdom, planning Portals act as substantial and untapped repositories of grey literature, containing highly detailed data with a diverse spatial coverage, recording the diversity and extent of existing habitats and specifications for proposed species assemblages. However, they are difficult to navigate or query, making it challenging to use these resources to gain macro-level insights from the data held within the portals. In this paper, we present GIbase 1.0, a new dataset that incorporates plant specifications from development projects across England and Scotland along with trait data associated with each species. To demonstrate the utility of the dataset, in a separate exercise we tested whether these data could be used to inform policymakers and researchers about current procurement and planting practices. To this end, we assessed the proposed GI features that are submitted by developers to local planning authorities as part of the planning process and then carried out fieldwork to record the extent to which these specifications were delivered. The findings from this work are published separately (Karlsdottir et al., 2021).
... Further, recent studies have shown that drought is the main inciting factor impacting urban trees' health and survival [17,18], and climatic predictions forecast rising temperatures and more frequent heat and drought events. Therefore, there is a need for urban tree management to select tree species according to their future drought response [19]. In order to guarantee a good water supply for vital trees with high environmental ecosystem provision, the requirements of the individual tree species must be known. ...
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Urbanization and climate change are two inevitable megatrends of this century. Knowledge about the growth responses of urban trees to climate is of utmost importance towards future management of green infrastructure with the aim of a sustainable provision of the environmental ecosystem services. Using tree-ring records, this study analyzed growth response to climate by stem diameter at breast height (DBH) of 1178 trees in seven large cities worldwide, including Aesculus hippocastanum L. in Munich; Platanus × hispanica Münchh. in Paris; Quercus nigra L. in Houston; Quercus robur L. in Cape Town; Robinia pseudoacacia L. in Santiago de Chile, Munich, and Würzburg; and Tilia cordata Mill. in Berlin, Munich, and Würzburg. Climate was characterized following the de Martonne aridity index (DMI). Overall, trees showed an 8.3% lower DBH under arid than humid climate at the age of 100. Drought-tolerant tree species were overall not affected by climate. However, R. pseudoacacia showed a lower diameter when growing in semi-dry than humid climate. In contrast, drought-sensitive tree species were negatively affected by arid climate. Moreover, the effect of drought years on annual diameter increment was assessed. P. × hispanica and R. pseudoacacia appeared as the most drought-resistant species. The highest sensitivity to drought was detected in T. cordata and Q. robur. A. hippocastanum and Q. nigra showed a lower diameter growth during drought events, followed by a fast recovery. This study’s findings may contribute to a better understanding of urban tree growth reactions to climate, aiming for sustainable planning and management of urban trees.
... Recent research on nature-based solutions points to the importance of urban biodiversity conservation as well as to the importance of understanding 'which nature' will likely withstand extreme climate change in a warming planet . With its unique ecosystems and ecological knowledge on which species and ecological features are fit for the harsh Australian climate, Australian researchers can contribute with critical knowledge on how to best J o u r n a l P r e -p r o o f ecologically design, implement and maintain nature-based solutions to sustain their potential in delivering multiple benefits (Burley et al., 2019;Kirk et al., 2021). ...
... At the same time, they might be strongly affected by future climatic change to an extent that is species specific (Brandt et al., 2017). Such strong impact of future climate change suggests the inclusion of more drought-resistant tree species into urban green (Burley, 2019). Therefore, there is increasing awareness that urban green management needs to focus on the long-term sustainability of service provision by urban trees (Amini Parsa et al., 2019, Fongar et al., 2019, Phelan et al., 2019, Wolf et al., 2020, and managers will have to consider mixtures of potentially feasible tree species. ...
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Urban tree managers are challenged with sustainable ecosystem service provision in particular when urban tree populations become over mature. Therefore, managers have to quantify both future services and population stability. We exemplify an approach for estimating the tradeoff between cooling, CO2-fixation and crown volume development, and the time until the changing tree population becomes stable. Using a realistic distribution of age classes and functional groups, we evaluate the balance between service provision and stabilization over decades to centuries. Their tradeoff mainly depends on the proportion of functional groups used in the replacement of mortal trees. Moreover, managers may steer tradeoff through an intentional planting postponement and acquisition of additional space.
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Urbanization is a major driver of environmental change, which calls for multifunctional and comprehensive actions such as Nature-based Solutions (NbS). They are “inspired and supported by nature… and must benefit biodiversity and support the delivery of a range of ecosystem services”. But what nature should one aim for? We tested the hypothesis that local vegetation may not always be the best source of inspiration, as environmental changes impact both extant conditions and species suitability for restored ecosystems. We analyzed the megacity of São Paulo, where laws promote the use of species from the local Atlantic Forest biome. We trained a Linear Discriminant Analysis to classify the Brazilian biomes and predicted the biomes' correspondence considering city's vegetation cover and climate. With 80% accuracy, the model predicted correspondence with the Atlantic Forest in 57% of the city, while 43% is better represented by the Cerrado, a dense Tropical Savanna biome. Cerrado species are naturally adapted to higher insolation, temperature and more seasonal precipitation, and they can parallel the ecosystem services of the Atlantic Forest. To help guide NbS implementation, we consider four “urban biomes”: Atlantic Forest, Seasonally Flooded Atlantic Forest, Cerrado, and the Seasonally Flooded Cerrado, whose dynamics seem to depend mainly on changes in the proportion of dense vegetation cover. We then discuss possible examples of NbS in the city. Results According to the PCA (Tables S3-S6), the main difference between the classification of the green spaces classified is the higher proportion of forest cover in those classified as Mata Atlantica, with almost any influence from other vegetation cover types (Fig. 5E). This pattern is still consistent when vegetation cover is evaluated outside the largest green spaces where the presence of even small forest patches across the urban fabric results in the Mata Atlântica category Discussion The urban ecosystem restoration could benefit from such natural and dynamic processes in which the Cerrado could act as a transient urban biome in the way of restoring the urban forests through soil horizon development and species succession followed by the densification of the vegetation whenever this planting scheme is possible. Conclusions These transitions among urban biomes may occur as local conditions change with the implementation of NbS, and the results point to the effectiveness of increasing the vegetation density wherever possible.
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Urban forests and trees are affected by potential biotic and abiotic climate change impacts. To enhance urban forest adaptability and resilience to climate change impacts, tree species with high local climate adaptability and robust stress tolerance should be identified and selected. Climate events in the Shanghai area, such as late frost, chilling, heat waves, drought, typhoons, waterlogging, soil salinization, pests, and disease, directly or indirectly impact urban forests and trees. For urban tree species selection in the context of climate change, an assessment framework was proposed and applied to assess the climate change adaptability of 65 urban tree species in Shanghai using a method combined with quantitative data and qualitative descriptions. In this study, the climate types of tree species were divided into four groups according to annual mean temperature (AMT) and annual precipitation (AP): temperate, cool subtropical, warm subtropical, and moist subtropical species. The results showed that hardness, heat tolerance, chilling requirement, and drought tolerance were categorized as climate-related tolerances, while other tolerances were categorized as non-climate-related tolerances. The tree species’ optimal AMT and AP were significantly correlated with climate-related tolerances, but they did not respond to the non-climate-related tolerances. The warm subtropical species had higher stress tolerances than other climate types in the Shanghai area; therefore, the warm subtropical species with high tolerances were the most suitable alternatives for urban tree species selection with regards to Shanghai’s climate change impacts. This study also found that the AMT optimum is a better index to reflect tree species’ climate-related tolerances rather than the AP optimum. Finally, the adaptability assessment framework of climate change impact will offer guidance for future-oriented urban forest management and urban tree species selection in Shanghai.
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Urban forests in northern Europe are threatened by climate change and biosecurity risks, and in response, city planners are urged to select a wider portfolio of tree species to mitigate the risks of species die-off. However, selecting the right species is a challenge, as most guidance available to specifiers focuses on ecosystem service delivery rather than the information most critical to tree establishment: the ability of a species to tolerate the stresses found in a given place. In this paper, we investigate the potential of using ecological techniques to describe ecological traits at the level of species selection, and the potential of functional ecology theories to identify species that are not widely discussed or specified at present but might be suitable. We collected trait data on 167 tree species across 37 genera, including 38 species within a case study genus, Magnolia L., and tested four theories that posit ways in which traits trade off against each other in predictable ways. We found that at this scale, most species recommended for urban forestry tend to be ordinated along an axis of variation describing pace of life and stress tolerance, and that most Magnolia species are described as being fast-growing rather than stress-tolerant, although there is a degree of inter-specific variation. Further, we found that only one theory offers a succinct and reliable way of describing physiological strategies but translating ecological theory into a form appropriate for urban forestry will require further work.
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Many cities are increasing urban canopy cover to mitigate the impacts of urbanisation and climate change. Ambitious canopy cover targets are being implemented, with little consideration on how best to achieve them. The City of Bristol has recently published a One City Plan, which includes a target to double tree canopy cover by 2045. This study aims to investigate its feasibility, and explore different planting scenarios to achieve the target and maximise ecosystem service delivery. Using an existing i-Tree Eco assessment of the urban forest, i-Tree Forecast was used to project future urban forest growth under a number of different user-defined planting scenarios. Sixteen scenarios were forecasted over 27 years to test a variety of approaches. Tree stock size and number, timing of planting and annual mortality rates were varied to test the performance of each scenario. Planting 18,000 large tree stock, equivalent to ‘heavy standards’ every year for 27 years provided the most feasible scenario in balancing canopy cover, leaf area index and pollutant removal whilst providing a stable population. This increased to 44,000 trees per year assuming an annual mortality rate of 3% more typical of urban areas, demonstrating the importance of good stewardship. The size of planted tree and timing of planting had a strong impact on the development of canopy cover. It was concluded that the One City Plan target is feasible if the planting rate is increased to at least 18,000 large tree stock from the current 10,000 trees per year.
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In recent times, the global climate variation is mainly caused by the industrialization and developments of urban cities also; this can affect the hydrological circumstances of the environments that create vulnerability to the human society and surroundings. Therefore, the significant risk analysis of climate changes is essential for planning urban cities’ support systems. In earlier, most of the recent literature mainly focused on the effect of global variation but failed to validate the risk level of climate variation on an urban scale. Thus, the risk analysis of climate change in urban systems has tended to become highly challenging. For this reason, this article creates a potential literature review on the urban planning support system under climate change risk analysis. The review of this article is classified into different categories of investigations such as the landscape as well as urban planning, formation methods, adaptation methods, urban policies, and performance analysis towards the urban system risk calculation. The performance analysis of urban support system strategies is investigated and compared for validation in terms of resilience, reliability, sustainability, and vulnerability. On this basis, the investigation summarizes the efficient research developments and discusses the main problem to be overcome for the climate change impact in the urban planning system. From this, future guidelines can afford to the modern numerical estimation of urban system climatic variation risk, which is emphasized with the novel enhancing methodologies for climatic variation influence on urban and exploring finest process to the climate risk facility in urban cities.
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Research on nature-based solutions, green infrastructure, and ecosystem services to support climate action in cities has proliferated over the past decade. However, relatively little attention has been paid to the unique features of urban forests under climate change. This paper addresses this gap by providing an integrative critical review of 44 articles published during the 2000-2020 period. The review allowed to identify three key themes that require further research: (1) the need to strengthen the framing of urban forests under climate change in the light of other discourses; (2) the need to better understand the complexity of urban forest benefits and exposures, and (3) the need to facilitate further knowledge integration to support more informed and inclusive decision making. The paper concludes by highlighting prospects for collaboration across science, policy and practice contexts. © 2020, Bulletin of the Transilvania University of Braşov. All rights reserved
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Cities have been described as ‘heat islands’ and ‘dry islands’ due to hotter, drier air in urban areas, relative to the surrounding landscape. As climate change intensifies, the health of urban trees will be increasingly impacted. Here, we posed the question: Is it possible to predict urban tree species mortality using (1) species climate envelopes and (2) plant functional traits? To answer these, we tracked patterns of crown dieback and recovery for 23 common urban tree and shrub species in Sydney, Australia during the record-breaking austral 2019–2020 summer. We identified 10 heat-tolerant species including five native and five exotic species, which represent climate-resilient options for urban plantings that are likely to continue to thrive for decades. Thirteen species were considered vulnerable to adverse conditions due to their mortality, poor health leading to tree removal, and/or extensive crown dieback. Crown dieback increased with increasing precipitation of the driest month of species climate of origin, suggesting that species from dry climates may be better suited for urban forests in future climates. We effectively grouped species according to their drought strategy (i.e., tolerance versus avoidance) using a simple trait-based framework that was directly linked with species mortality. The seven most climate-vulnerable species used a drought-avoidance strategy, having low wood density and high turgor loss points along with large, thin leaves with low heat tolerance. Overall, plant functional traits were better than species climate envelopes at explaining crown dieback. Recovery after stress required two mild, wet years for most species, resulting in prolonged loss of cooling benefits as well as economic losses due to replacement of dead/damaged trees. Hotter, longer, and more frequent heatwaves will require selection of more climate-resilient species in urban forests, and our results suggest that future research should focus on plant thermal traits to improve prediction models and species selection.
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Modern cities are dominated by impervious surfaces that absorb, store and release heat in summer, create large volumes of runoff and provide limited biodiversity habitat and poor air quality can also be a health issue. Future climate change, including more frequent and extreme weather events will likely exacerbate these issues. Green infrastructure such as parks, gardens, street trees and engineered technologies such as green roofs and walls, facades and raingardens can help mitigate these problems. This relies on selecting plants that can persist in urban environments and improve stormwater retention, cooling, biodiversity and air pollution. However, plant selection for green infrastructure is challenging where there is limited information on species tolerance to heat and water variability or how these species can deliver multiple benefits. Therefore, we draw on research to illustrate how plant performance for green infrastructure can be inferred from plant attributes (i.e., traits) or from analysis of their natural distribution. We present a new framework for plant selection for green infrastructure and use a case study to demonstrate how this approach has been used to select trees and shrubs for Australian cities. We have shown through the case study and examples how plant traits and species’ natural distribution can be used to overcome the lack of information on tolerance to both individual and multiple stressors and how species contribute to the provision of benefits such as stormwater retention, cooling, biodiversity and air pollution mitigation. We also discuss how planting design and species diversity can contribute to achieving multiple benefits to make the most of contested space in dense cities and to also reduce the risk of failure in urban greening.
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Species occurrence records from online databases are an indispensable resource in ecological, biogeographical and palaeontological research. However, issues with data quality, especially incorrect geo-referencing or dating, can diminish their usefulness. Manual cleaning is time-consuming, error prone, difficult to reproduce and limited to known geographical areas and taxonomic groups, making it impractical for datasets with thousands or millions of records. Here, we present CoordinateCleaner, an r-package to scan datasets of species occurrence records for geo-referencing and dating imprecisions and data entry errors in a standardized and reproducible way. CoordinateCleaner is tailored to problems common in biological and palaeontological databases and can handle datasets with millions of records. The software includes (a) functions to flag potentially problematic coordinate records based on geographical gazetteers, (b) a global database of 9,691 geo-referenced biodiversity institutions to identify records that are likely from horticulture or captivity, (c) novel algorithms to identify datasets with rasterized data, conversion errors and strong decimal rounding and (d) spatio-temporal tests for fossils. We describe the individual functions available in CoordinateCleaner and demonstrate them on more than 90 million occurrences of flowering plants from the Global Biodiversity Information Facility (GBIF) and 19,000 fossil occurrences from the Palaeobiology Database (PBDB). We find that in GBIF more than 3.4 million records (3.7%) are potentially problematic and that 179 of the tested contributing datasets (18.5%) might be biased by rasterized coordinates. In PBDB, 1205 records (6.3%) are potentially problematic. All cleaning functions and the biodiversity institution database are open-source and available within the CoordinateCleaner r-package. © 2019 The Authors. Methods in Ecology and Evolution published by John Wiley & Sons Ltd on behalf of British Ecological Society.
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Cities are natural laboratories for studying vegetation responses to global environmental changes because of their climate, atmospheric, and biogeochemical conditions. However, few holistic studies have been conducted on the impact of urbanization on vegetation growth. We decomposed the overall impacts of urbanization on vegetation growth into direct (replacement of original land surfaces by impervious built‐up) and indirect (urban environments) components, using a conceptual framework and remotely‐sensed data for 377 metropolitan statistical areas (MSAs) in the conterminous United States (CONUS) in 2001, 2006, and 2011. Results showed that urban pixels are often greener than expected given the amount of paved surface they contain. The vegetation growth enhancement due to indirect effects occurred in 88.4%, 90.8% and 92.9% of urban bins in 2001, 2006 and 2011, respectively. By defining offset value as the ratio of the absolute indirect and direct impact, we obtained that growth enhancement due to indirect effects compensated for about 29.2%, 29.5% and 31.0% of the reduced productivity due to loss of vegetated surface area on average in 2001, 2006, and 2011, respectively. Vegetation growth responses to urbanization showed little temporal variation but large regional differences with higher offset value in the western CONUS than in the eastern CONUS. Our study highlights the prevalence of vegetation growth enhancement in urban environments and the necessity of differentiating various impacts of urbanization on vegetation growth, and calls for tailored field experiments to understand the relative contributions of various driving forces to vegetation growth and predict vegetation responses to future global change using cities as harbingers. This article is protected by copyright. All rights reserved.
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Climate change is driving global species redistribution with profound social and economic impacts. However, species movement is largely constrained by habitat availability and connectivity, of which the interaction effects with climate change remain largely unknown. Here we examine published data on 2798 elevational range shifts from 43 study sites to assess the confounding effect of land-use change on climate-driven species redistribution. We show that baseline forest cover and recent forest cover change are critical predictors in determining the magnitude of elevational range shifts. Forest loss positively interacts with baseline temperature conditions, such that forest loss in warmer regions tends to accelerate species’ upslope movement. Consequently, not only climate but also habitat loss stressors and, importantly, their synergistic effects matter in forecasting species elevational redistribution, especially in the tropics where both stressors will increase the risk of net lowland biotic attrition. Habitat change and warming each contribute to species' elevational range shifts, but their synergistic effects have not been explored. Here, Guo et al. reanalyze published data and show that the interaction between warming and forest change predicts range shifts better than either factor on its own.
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Growth in urban populations creates opportunities for urban forests to deliver ecosystem services critical to human wellbeing and biodiversity. Our challenge is to strategically expand urban forests and provide our international communities, particularly the vulnerable, with healthier, happier, and enriched lives.
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Urban trees are an essential component of urban ecosystems, and management of this resource constitutes an essential element of urban open space management. However, municipal tree inventories in Sweden and elsewhere have received limited attention. It is unknown how common municipal tree inventories are in Sweden, factors governing whether a municipality has an inventory and what the inventories are used for. This study therefore sought to: Create an overview of the state of Swedish municipal tree inventories and determine how municipality size, green space budget and management organisation affect the presence and scope of municipal tree inventories. The research questions examined were: What is the current state of Swedish municipal tree inventories? and what affects the status of these municipal tree inventories? A survey with questions related to strategic and operational perspectives of municipal tree inventories, e.g. how they are conducted and used, together with questions relating to budget and potential use of consultants, was sent to all 290 Swedish municipalities. The response rate was 55.5%. The main findings were that municipality size affects whether a municipality has an urban tree inventory and that the municipal organisation form affects how inventories are used. The existence of an inventory also increased the probability of the municipality having a tree management plan. Based on these results we recommend further research related to strategic management perspectives of tree inventories.
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Identification of refugia from climate change is increasingly considered important for biodiversity conservation, but the distribution of putative refugia may vary across alternative climate scenarios, impeding conservation decision-making. Based on 117 plant species representative of ecoregions within south-eastern Australia, we provide a case study identifying in situ refugia across a spectrum of plausible future climates. We define in situ refugia as areas that currently contain populations of the target species, and are projected to remain climatically suitable in the future. Refugia were identified across scenarios describing futures that are, relative to 1990–2009, warmer and wetter, warmer/drier, hotter/wetter, and hotter with little precipitation change. Despite substantial variation in the spatial extent and longevity of climate refugia across species, ecoregions and climate scenarios, clear patterns emerged. By 2070, refugia for species in i) deserts and xeric shrublands; ii) mediterranean forests, woodlands and shrublands; and iii) temperate and tropical grasslands are likely to be least extensive under a hotter/wetter future. Conversely, wetter conditions may lead to broader refugia for species in temperate forests. We identified areas of congruence where high richness refugia (refugia for ≥ 50% of representative species) were projected to occur irrespective of the climate scenario. These regions therefore appear robust to uncertainty about climate change, presenting clear targets for conservation attention. Our approach provides valuable information for decision-makers, enabling them to identify and visualise the spatial arrangement of refugia under contrasting scenarios of environmental change. This reveals management options in the context of climate uncertainty and facilitates informed prioritisation of conservation resources.
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Despite the importance of urban trees, their growth reaction to climate change and to the urban heat island effect has not yet been investigated with an international scope. While we are well informed about forest growth under recent conditions, it is unclear if this knowledge can be simply transferred to urban environments. Based on tree ring analyses in ten metropolises worldwide, we show that, in general, urban trees have undergone accelerated growth since the 1960s. In addition, urban trees tend to grow more quickly than their counterparts in the rural surroundings. However, our analysis shows that climate change seems to enhance the growth of rural trees more than that of urban trees. The benefits of growing in an urban environment seem to outweigh known negative effects, however, accelerated growth may also mean more rapid ageing and shortened lifetime. Thus, city planners should adapt to the changed dynamics in order to secure the ecosystem services provided by urban trees.
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Urban forests produce ecosystem services that can benefit city dwellers, but are especially vulnerable to climate change stressors such as heat, drought, extreme winds and pests. Tree selection is an important decision point for managers wanting to transition to a more stable and resilient urban forest structure. This study describes a five-step process to identify and evaluate the performance of promising but infrequently used tree species. The approach is illustrated for the Central Valley of California, USA and has been implemented in the Inland Empire and Southern Coastal regions of California. Horticultural advisors nominated 134 taxon for consideration. A filtering process eliminated taxon that were relatively abundant in a compilation of 8 municipal tree inventories, then those with low adaptive capacity when scored on habitat suitability, physiology and biological interactions. In 2015, 144 trees were planted, with 2 trees of each of 12 species planted in 4 Sacramento parks and 4 replicates planted in the Davis, California reference site. This approach can serve as an international model for cities interested in climate adaptation through urban forestry.
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1. Compilation of vegetation databases has contributed significantly to the advancement of vegetation science all over the world. Yet, methodological problems result from the use of plant names, particularly in data that originate from numerous and heterogeneous sources. One of the main problems is the inordinate number of synonyms that can be found in vegetation lists. 2. We present Taxonstand, an r package to automatically standardise plant names using The Plant List (http://www.theplantlist.org). The scripts included in this package allow connection to the online search engine of the Plant List and retrieve information from each species about its current taxonomic status. In those cases where the species name is a synonym, it is replaced by the current accepted name. In addition, this package can help correcting orthographic errors in specific epithets. 3. This tool greatly facilitates the preparation of large vegetation databases prior to their analyses, particularly when they cover broad geographical areas (supranational or even continental scale) or contain data from regions with rich floras where taxonomic problems have not been resolved for many of their taxa. Automated workflows such as the one provided by the taxonstand package can ease considerably this task using a widely accessible working nomenclatural authority list for plant species names such as The Plant List.
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Urban macroecology studies can provide important insights into the impacts of climate change and human intervention in ecosystems. Current theory predicts that urban trees are constrained by temperature in very cold climates but not in other climates. Here we predict the climatic niche variables of planted urban tree populations from the realized climatic niche of native populations and explore whether niches are constrained across all temperatures. Global (182 cities across six continents). Urban tree data: 1980–2016. Native tree data: 1950–2017. Two hundred and three tree species. We used urban tree inventory data and Global Biodiversity Information Facility occurrence data to compare the realized climatic niches of native and urban tree populations. Realized climatic niches are calculated by combining bioclimatic data with native tree and urban tree occurrence data. Regression is used to predict the climatic niche of urban tree populations from the climatic niche of native populations. The realized climatic niche of native tree populations was a good predictor of the realized climatic niche of urban tree populations, although climatic niches are attenuated in urban populations. Urban tree niches were 38–90% wider than native tree niches, with the mean annual temperature niche breath of urban tree populations 3.3 °C (52%) wider than native tree populations. Urban trees are planted in climates that are outside the realized climatic niche of native populations. Temperature remains a strong filter on urban tree populations across the full temperature range. Temperature increases attributable to the combined effect of the urban heat island and global climate change are likely to have a substantial impact on urban tree populations around the globe. This is particularly true for temperate cities, where cold climate trees are planted near the upper limits of their realized temperature niches.
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The method of cross validatory choice and assessment is applied to prediction of a multinomial indicator. The resulting predictor is compared with analogous expressions due to Good and Fienberg & Holland. Some numerical comparisons are made.
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The spatial arrangement of urban vegetation depends on urban morphology and socio-economic settings. Urban vegetation changes over time because of human management. Urban trees are removed due to hazard prevention or aesthetic preferences. Previous research attributed tree loss to decreases in canopy cover. However, this provides little information about location and structural characteristics of trees lost, as well as environmental and social factors affecting tree loss dynamics. This is particularly relevant in residential landscapes where access to residential parcels for field surveys is limited. We tested whether multi-temporal airborne LiDAR and multi-spectral imagery collected at a 5-year interval can be used to investigate urban tree loss dynamics across residential landscapes in Denver, CO and Milwaukee, WI, covering 400,705 residential parcels in 444 census tracts. Position and stem height of trees lost were extracted from canopy height models calculated as the difference between final (year 5) and initial (year 0) vegetation height derived from LiDAR. Multivariate regression models were used to predict number and height of tree stems lost in residential parcels in each census tract based on urban morphological and socio-economic variables. A total of 28,427 stems were lost from residential parcels in Denver and Milwaukee over 5 years. Overall, 7% of residential parcels lost one stem, averaging 90.87 stems per km2. Average stem height was 10.16 m, though trees lost in Denver were taller compared to Milwaukee. The number of stems lost was higher in neighborhoods with higher canopy cover and developed before the 1970s. However, socio-economic characteristics had little effect on tree loss dynamics. The study provides a simple method for measuring urban tree loss dynamics within and across entire cities, and represents a further step towards high resolution assessments of the three-dimensional change of urban vegetation at large spatial scales.
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The recent decline in the health of the City of Melbourne’s deciduous tree species to a recent drought event has led to concerns about the vulnerability of the city’s trees to future climate change. Understanding the response of tree growth to past climate is critical for determining the likely impacts of climate change on future growth and can provide insights into the suitability of current species to future climates. We used dendrochronogical approaches to determine the relationships between climate and tree radial growth for common deciduous tree species in Melbourne’s urban forest. Chronologies were successfully developed for Quercus robur, Ulmus procera, Ulmus L. and Platanus acerifolia with all found to be sensitive to past climatic variability. All four species showed radial growth in a given year was negatively impacted by arid conditions in the previous autumn and arid conditions in the spring orearly summer of that year. Interspecific differences in climate – growth relationships, consistent with xylem anatomy trait differences (ring vs. diffuse porous), were observed. Successive years of drought had a significant negative influence on radial tree growth. Future climate change scenario testing suggested that a shift towards a warmer, drier climate would exacerbate declines in radial growth, and thereby health, highlighting that the studied species are vulnerable to climate change. From a planning perspective, a balance between (a) conserving these vulnerable tree species through proactive management; and, (b) planting more drought and heat tolerant species is likely the best approach towards adapting Melbourne’s urban forest to climate change.
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Aim To synthesize the species distribution modelling (SDM) literature to inform which variables have been used in MaxEnt models for different taxa and to quantify how frequently they have been important for species’ distributions. Location Global. Methods We conducted a quantitative synthesis analysing the contribution of over 400 distinct environmental variables to 2040 MaxEnt SDMs for nearly 1900 species representing over 300 families. Environmental variables were grouped into 24 related factors and results were analysed by examining the frequency with which variables were found to be most important, the mean contribution of each variable (at various taxonomic levels), and using TrueSkill™, a Bayesian skill rating system. Results Precipitation, temperature, bathymetry, distance to water and habitat patch characteristics were the most important variables overall. Precipitation and temperature were analysed most frequently and one of these variables was often the most important predictor in the model (nearly 80% of models, when tested). Notably, distance to water was the most important variable in the highest proportion of models in which it was tested (42% of 225 models). For terrestrial species, precipitation, temperature and distance to water had the highest overall contributions, whereas for aquatic species, bathymetry, precipitation and temperature were most important. Main conclusions Over all MaxEnt models published, the ability to discriminate occurrence from reference sites was high (average AUC = 0.92). Much of this discriminatory ability was due to temperature and precipitation variables. Further, variability (temperature) and extremes (minimum precipitation) were the most predictive. More generally, the most commonly tested variables were not always the most predictive, with, for instance, ‘distance to water’ infrequently tested, but found to be very important when it was. Thus, the results from this study summarize the MaxEnt SDM literature, and can aid in variable selection by identifying underutilized, but potentially important variables, which could be incorporated in future modelling efforts.
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In an increasingly urbanized world, air pollution mitigation is considered one of most important issues in city planning. Urban trees help to improve air quality by facilitating widespread deposition of various gases and particles through the provision of large surface areas as well as through their influence on microclimate and air turbulence. However, many of these trees produce wind-dispersed pollen (a known allergen) and emit a range of gaseous substances that take part in photochemical reactions – all of which can negatively affect air quality. The degree to which these air-quality impacts are manifested depends on species-specific tree properties: that is, their “traits”. We summarize and discuss the current knowledge on how such traits affect urban air pollution. We also present aggregated traits of some of the most common tree species in Europe, which can be used as a decision-support tool for city planning and for improving urban air-quality models.
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AimWe propose and test a climate tolerance and trait choice hypothesis of urban macroecological variation in which strong filtering associated with low winter temperatures restricts urban biodiversity while weak filtering associated with warmer temperatures and irrigation allows dispersal of species from a global source pool, thereby increasing urban biodiversity. LocationTwenty cities across the USA and Canada. Methods We examined variation in tree community taxonomic diversity, origins and production of an aesthetic ecosystem service trait in a cross-section of urban field surveys. We correlated urban tree community composition indicators with a key climate restriction, namely mean minimum winter temperature, and evaluated alternative possible drivers: precipitation, summer maximum temperature, population size and the percentage of adults with a college education. ResultsSpecies accumulation curves differed substantially among cities, with observed richness varying from 22 to 122 species. Similarities in tree communities decreased exponentially with increases in climatic differences. Ordination of tree communities showed strong separation among cities with component axes correlated with minimum winter temperature and annual precipitation. Variation among urban tree communities in richness, origins and the provisioning of an aesthetic ecosystem service were all correlated with minimum winter temperature. Main conclusionsThe urban climate tolerance and trait choice hypothesis provides a coherent mechanism to explain the large variation among urban tree communities resulting from an interacting environment, species and human decisions. Reconciling the feedbacks between human decision making and biophysical limitations provides a foundation for an urban ecological theory that can better understand and predict the dynamics of other linked biotic communities, associated ecosystem dynamics and resulting services provided to urban residents.
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Choosing optimal and suitable trees and shrubs in urban areas can minimize the negative influences and increase the positive effects and the aesthetic acceptance by urban residents. Additional challenges in the selection of trees and shrubs are user requirements and growth conditions at urban sites. Therefore, the selection of planted trees and shrubs in cities has to incorporate these location-specific factors. Based on an extensive literature review, more than 390 woody plants were investigated to obtain a comprehensive assessment of specific characteristics by integrating specific urban aspects. Within this study, a database was developed that allows users to simultaneously consider site characteristics and natural distribution, tree appearance, ecosystem services, management activities, and the risks and interferences caused by urban woody plants. The developed Citree database is useful for preventing mistakes in planning, which would otherwise result in high ecologic and economic costs. Choosing the right species for the right location will also increase the floristic biodiversity within urban tree plantings and the sustainable uses of urban trees.
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Summary. Recent work by Reiss and Ogden provides a theoretical basis for sometimes preferring restricted maximum likelihood (REML) to generalized cross-validation (GCV) for smoothing parameter selection in semiparametric regression. However, existing REML or marginal likelihood (ML) based methods for semiparametric generalized linear models (GLMs) use iterative REML or ML estimation of the smoothing parameters of working linear approximations to the GLM. Such indirect schemes need not converge and fail to do so in a non-negligible proportion of practical analyses. By contrast, very reliable prediction error criteria smoothing parameter selection methods are available, based on direct optimization of GCV, or related criteria, for the GLM itself. Since such methods directly optimize properly defined functions of the smoothing parameters, they have much more reliable convergence properties. The paper develops the first such method for REML or ML estimation of smoothing parameters. A Laplace approximation is used to obtain an approximate REML or ML for any GLM, which is suitable for efficient direct optimization. This REML or ML criterion requires that Newton–Raphson iteration, rather than Fisher scoring, be used for GLM fitting, and a computationally stable approach to this is proposed. The REML or ML criterion itself is optimized by a Newton method, with the derivatives required obtained by a mixture of implicit differentiation and direct methods. The method will cope with numerical rank deficiency in the fitted model and in fact provides a slight improvement in numerical robustness on the earlier method of Wood for prediction error criteria based smoothness selection. Simulation results suggest that the new REML and ML methods offer some improvement in mean-square error performance relative to GCV or Akaike's information criterion in most cases, without the small number of severe undersmoothing failures to which Akaike's information criterion and GCV are prone. This is achieved at the same computational cost as GCV or Akaike's information criterion. The new approach also eliminates the convergence failures of previous REML- or ML-based approaches for penalized GLMs and usually has lower computational cost than these alternatives. Example applications are presented in adaptive smoothing, scalar on function regression and generalized additive model selection.
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The aesthetic value of trees in the avenues, boulevards and gardens of Australian cities is widely appreciated, but their economic significance is undervalued. Trees provide services and fulfill functional roles in cities. They are significant components of urban infrastructure and have a real and calculable economic value. An urban forest of 100,000 trees can save $ 1.5 million per annum because their shade reduces electricity consumption and saves water. Shade can prolong the life of tarmac, and carbon is sequestered as trees grow. A large tree growing in a school provides the equivalent shade of four shade sails, returning a value of about $ 2000 per annum, while five trees stabilize a steep suburban block which would otherwise require about $ 50,000 of engineered piling to secure building insurance. The shade provided by trees in mitigating the urban heat island effect is recognized, but what is its economic value? How many heatwave related excess deaths and ambulance callouts can be saved as a consequence of the urban forest? The urban forest improving human health outcomes by fostering a 1-2% increase in passive/active recreation can save $ 274 million per annum in one Australian State alone. Calculation of the economic contributions of trees can change the economic algorithms upon which decisions are made. Public utilities should be undergrounded and street trees properly maintained. At a time of climate change, high density housing and inner city renewal are leading to a significant reduction in tree cover in major cities, which comes at a significant economic cost to urban infrastructure.
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Many environmental challenges are exacerbated within the urban landscape, such as stormwater runoff and flood risk, chemical and particulate pollution of urban air, soil and water, the urban heat island, and summer heat waves. Urban trees, and the urban forest as a whole, can be managed to have an impact on the urban water, heat, carbon and pollution cycles. However, there is an increasing need for empirical evidence as to the magnitude of the impacts, both beneficial and adverse, that urban trees can provide and the role that climatic region and built landscape circumstance play in modifying those impacts. This special section presents new research that advances our knowledge of the ecological and environmental services provided by the urban forest. The 14 studies included provide a global perspective on the role of trees in towns and cities from five continents. Some studies provide evidence for the cooling benefit of the local microclimate in urban green space with and without trees. Other studies focus solely on the cooling benefit of urban tree transpiration at a mesoscale or on cooling from canopy shade at a street and pedestrian scale. Other studies are concerned with tree species differences in canopy interception of rainfall, water uptake from biofilter systems, and water quality improvements through nutrient uptake from stormwater runoff. Research reported here also considers both the positive and the negative impacts of trees on air quality, through the role of trees in removing air pollutants such as ozone as well as in releasing potentially harmful volatile organic compounds and allergenic particulates. A transdisciplinary framework to support future urban forest research is proposed to better understand and communicate the role of urban trees in urban biogeochemical cycles that are highly disturbed, highly managed, and of paramount importance to human health and well-being.
Article
Canopy size control is one of the major purposes of summer pruning. However, reducing canopy size might also result in less light interception, consequently decreasing canopy photosynthetic efficiency and carbohydrate production, which might lead to the imbalance of carbohydrate supply and fruit demand. To document the effectiveness of summer pruning on canopy control and the impact on canopy gas exchange, pruning treatments at four levels of intensity (unpruned, light, moderate, and severe) were carried out on mature 'Empire'/M.9 slender spindle apple trees (Malus domestica Borkh.) on 30 July 1998 and 4 August 1999. Changes in canopy leaf area after summer pruning were estimated. Canopy net carbon exchange rate (NCER) and canopy transpiration before and after summer pruning were monitored. Canopy growth was suppressed by summer pruning and the post-pruning regrowth was insignificant. Canopy NCER was reduced in proportion to the amount of leaf area removed by summer pruning. The result suggests that commercial pruning intensity similar to the moderate to severe treatments in this study could cause a significant reduction in canopy NCER and carbohydrate production. In addition, canopy transpiration was reduced in proportion to pruning intensity. Lower water consumption and improved water status during the growing season after summer pruning might benefit fruit growth and relieve the potential detriment due to carbohydrate shortage.
Article
Road density and proportion of urban area are considered to be useful indicators of invasion risk from non-native plants. However, the mechanisms behind the relationship between these indicators and establishment of non-native species have rarely been addressed explicitly. To identify these mechanisms, we used a species distribution model (MaxEnt) for an invasive ornamental weed Rudbeckia laciniata using road density and proportion of urban area as explanatory variables, along with soil moisture and solar radiation. Overall model performance is relatively high (AUC = 0.91). Road density explained most R. laciniata occurrence, followed by the proportion of urban area. The occurrence probability of R. laciniata increased monotonically with road density, but the rates of increase constantly fell. The occurrence probability also increased with urban area when the proportion of urban area was small, but started to decrease when the proportion of urban area reached 0.2. Our results suggest that both road density and proportion of urban area are important factors in determining R. laciniata establishment but work differently.
Article
Climate change is a likely addition to the unpredictable challenges urban communities will face. Enhancing urban forests has gained prominence as a climate adaptation tool in cities. The fact that urban forests are also vulnerable is now starting to emerge. Many urban forest management professionals do not know how to take climate change into account and what aspects of urban forest vulnerability to climate change to prioritize. Bringing climate change to the forefront of the decision-making process in urban forest management, and urban forests to the forefront of urban climate issues, is important to urban forest success. This paper presents an exploratory assessment of vulnerability to climate change in the Canadian urban forests of Halifax, London, and Saskatoon. The objectives of the assessment were to: 1) identify the elements of urban forest exposure and sensitivity to climate change, the nature of the expected impact, and the adaptive capacities that exist in these three urban forests; 2) assess which of these elements contributes more to urban forest vulnerability to climate change; and, 3) elicit adaptive strategies based on this information. The method used was participatory and expert-based and allowed for a systematic evaluation of vulnerability. Exposures related to drought, heat stress, and wind, susceptibility of urban trees to insects and diseases, and the sensitivity of young trees and tree species with specific temperature and moisture requirements, are the main concerns regarding the vulnerability of urban forests to climate change in these three cities.
Article
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.
Article
Urban trees help towns to cope with climate warming by cooling both air and surfaces. The challenges imposed by the urban environment, with special reference to low water availability due to the presence of extensive pavements, result in high rates of mortality of street trees, that can be increased by climatic extremes.We investigated the water relations and xylem hydraulic safety/efficiency of Quercus ilex trees growing at urban sites with different percentages of surrounding impervious pavements. Seasonal changes of plant water potential and gas exchange, vulnerability to cavitation and embolism level, and morpho-anatomical traits were measured.We found patterns of increasing water stress and vulnerability to drought at increasing percentages of impervious pavement cover, with a consequent reduction in gas exchange rates, decreased safety margins toward embolism development, and increased vulnerability to cavitation, suggesting the occurrence of stress-induced hydraulic deterioration.The amount of impermeable surface and chronic exposure to water stress influence the site-specific risk of drought-induced dieback of urban trees under extreme drought. Besides providing directions for management of green spaces in towns, our data suggest that xylem hydraulics is key to a full understanding of the responses of urban trees to global change.
Article
Trees provide ecosystem services that counter negative effects of urban habitats on human and environmental health. Unfortunately, herbivorous arthropod pests are often more abundant on urban than rural trees, reducing tree growth, survival, and ecosystem services. Previous research where vegetation complexity was reduced has attributed elevated urban pest abundance to decreased regulation by natural enemies. However, reducing vegetation complexity, particularly the density of overstory trees, also makes cities hotter than natural habitats. We ask how urban habitat characteristics influence an abiotic factor, temperature, and a biotic factor, natural enemy abundance, in regulating the abundance of an urban forest pest, the gloomy scale, (Melanaspis tenebricosa). We used a map of surface temperature to select red maple trees (Acer rubrum) at warmer and cooler sites in Raleigh, North Carolina, USA. We quantified habitat complexity by measuring impervious surface cover, local vegetation structural complexity, and landscape scale vegetation cover around each tree. Using path analysis, we determined that impervious surface (the most important habitat variable) increased scale insect abundance by increasing tree canopy temperature, rather than by reducing natural enemy abundance or percent parasitism. As a mechanism for this response, we found that increasing temperature significantly increases scale insect fecundity and contributes to greater population increase. Specifically, adult female M. tenebricosa egg sets increased by approximately 14 eggs for every 1°C increase in temperature. Climate change models predict that the global climate will increase by 2–3°C in the next 50–100 years, which we found would increase scale insect abundance by three orders of magnitude. This result supports predictions that urban and natural forests will face greater herbivory in the future, and suggests that a primary cause could be direct, positive effects of warming on herbivore fitness rather than altered trophic interactions.
Article
Species distribution modeling (SDM) links ecological theory of species–environment relationships with statistical learning methods and geospatial data to understand and predict the distributions of species and their habitats. Also called ecological niche modeling, SDM is widely used for biodiversity assessment and to predict the impacts of environmental change on biodiversity in terrestrial and aquatic habitats. It can also provide insight and understanding about ecological relationships.
Article
The MaxEnt software package is one of the most popular tools for species distribution and environmental niche modeling, with over 1000 published applications since 2006. Its popularity is likely for two reasons: 1) MaxEnt typically outperforms other methods based on predictive accuracy and 2) the software is particularly easy to use. MaxEnt users must make a number of decisions about how they should select their input data and choose from a wide variety of settings in the software package to build models from these data. The underlying basis for making these decisions is unclear in many studies, and default settings are apparently chosen, even though alternative settings are often more appropriate. In this paper, we provide a detailed explanation of how MaxEnt works and a prospectus on modeling options to enable users to make informed decisions when preparing data, choosing settings and interpreting output. We explain how the choice of background samples reflects prior assumptions, how nonlinear functions of environmental variables (features) are created and selected, how to account for environmentally biased sampling, the interpretation of the various types of model output and the challenges for model evaluation. We demonstrate MaxEnt’s calculations using both simplified simulated data and occurrence data from South Africa on species of the flowering plant family Proteaceae. Throughout, we show how MaxEnt’s outputs vary in response to different settings to highlight the need for making biologically motivated modeling decisions.
Article
With the rise of new powerful statistical techniques and GIS tools, the development of predictive habitat distribution models has rapidly increased in ecology. Such models are static and probabilistic in nature, since they statistically relate the geographical distribution of species or communities to their present environment. A wide array of models has been developed to cover aspects as diverse as biogeography, conservation biology, climate change research, and habitat or species management. In this paper, we present a review of predictive habitat distribution modeling. The variety of statistical techniques used is growing. Ordinary multiple regression and its generalized form (GLM) are very popular and are often used for modeling species distributions. Other methods include neural networks, ordination and classification methods, Bayesian models, locally weighted approaches (e.g. GAM), environmental envelopes or even combinations of these models. The selection of an appropriate method should not depend solely on statistical considerations. Some models are better suited to reflect theoretical findings on the shape and nature of the species’ response (or realized niche). Conceptual considerations include e.g. the trade-off between optimizing accuracy versus optimizing generality. In the field of static distribution modeling, the latter is mostly related to selecting appropriate predictor variables and to designing an appropriate procedure for model selection. New methods, including threshold-independent measures (e.g. receiver operating characteristic (ROC)-plots) and resampling techniques (e.g. bootstrap, cross-validation) have been introduced in ecology for testing the accuracy of predictive models. The choice of an evaluation measure should be driven primarily by the goals of the study. This may possibly lead to the attribution of different weights to the various types of prediction errors (e.g. omission, commission or confusion). Testing the model in a wider range of situations (in space and time) will permit one to define the range of applications for which the model predictions are suitable. In turn, the qualification of the model depends primarily on the goals of the study that define the qualification criteria and on the usability of the model, rather than on statistics alone.
Article
AimTo investigate the velocity of species-specific exposure to climate change for mid- and late 21st century and develop metrics that quantify exposure to climate change over space and time. LocationCalifornia Floristic Province, south-western USA. Methods Occurrences from presence/absence inventories of eight Californian endemic tree species (Pinus balfouriana [Grev.&Balf.], Pinus coulteri [D.Don], Pinus muricata [D.Don.], Pinus sabiniana [D.Don], Quercus douglasii [Hook.&Arn.], Quercus engelmannii [Greene], Quercus lobata [Nee] and Quercus wislizeni [A.DC.]) were used to develop eight species distribution models (SDMs) for each species with the BIOMOD platform, and this ensemble was used to construct current suitability maps and future projections based on two global circulation models in two time periods [mid-century: 2041–2070 and late century (LC): 2071–2100]. From the resulting current and future suitability maps, we calculated a bioclimatic velocity as the ratio of temporal gradient to spatial gradient. We developed and compared eight metrics of temporal exposure to climate change for mid- and LC for each species. ResultsThe velocity of species exposure to climate change varies across species and time periods, even for similarly distributed species. We find weak support among the species analysed for higher velocities in exposure to climate change towards the end of the 21st century, coinciding with harsher conditions. The variation in the pace of exposure was greater among species than for climate projections considered. Main conclusionsThe pace of climate change exposure varies depending on period of analysis, species and the spatial extent of conservation decisions (potential ranges versus current distributions). Translating physical climatic space into a biotic climatic space helps informing conservation decisions in a given time frame. However, the influence of spatial and temporal resolution on modelled species distributions needs further consideration in order to better characterize the dynamics of exposure and species-specific velocities.
Article
This paper explores emerging forms for the system and practice of British planning, set in the context of managing conflicts over the use and development of land, and promoting particular qualities of places. In some periods, these two purposes came together, at other times, they drifted apart. Economic, environmental, social and political pressures in the 1990s encourage reintegration. This presents a demanding challenge requiring both the invention of new ways of working and changes in the formal arrangements of the planning system. It promises a more sustainable approach to addressing contemporary concerns with qualities of place in a 'stakeholder society'.
Article
Current circumstances — that the majority of species distribution records exist as presence-only data (e.g. from museums and herbaria), and that there is an established need for predictions of species distributions — mean that scientists and conservation managers seek to develop robust methods for using these data. Such methods must, in particular, accommodate the difficulties caused by lack of reliable information about sites where species are absent. Here we test two approaches for overcoming these difficulties, analysing a range of data sets using the technique of multivariate adaptive regression splines (MARS). MARS is closely related to regression techniques such as generalized additive models (GAMs) that are commonly and successfully used in modelling species distributions, but has particular advantages in its analytical speed and the ease of transfer of analysis results to other computational environments such as a Geographic Information System. MARS also has the advantage that it can model multiple responses, meaning that it can combine information from a set of species to determine the dominant environmental drivers of variation in species composition. We use data from 226 species from six regions of the world, and demonstrate the use of MARS for distribution modelling using presence-only data. We test whether (1) the type of data used to represent absence or background and (2) the signal from multiple species affect predictive performance, by evaluating predictions at completely independent sites where genuine presence–absence data were recorded. Models developed with absences inferred from the total set of presence-only sites for a biological group, and using simultaneous analysis of multiple species to inform the choice of predictor variables, performed better than models in which species were analysed singly, or in which pseudo-absences were drawn randomly from the study area. The methods are fast, relatively simple to understand, and useful for situations where data are limited. A tutorial is included.