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• We used an urban tree inventory and high-resolution climate projections to identify species and locations at risk from climate change in Melbourne, Australia. • The climate safety margin, an indicator of species' climatic tolerance, was used as a metric of climate risk. • Presently, 218 species (46%) are exceeding their temperature safety margins; this number is predicted to increase to 322 species (68%) by 2050. • Similarly, 255 species (54%) are exceeding their precipitation safety margins; this number is predicted to increase to 257 species (54%) by 2050. • Our approach provides spatial information on climate risk at local scales appropriate for management decisions. Climate change represents a threat to the performance and persistence of urban forests and the multiple benefits they provide to city dwellers. Here, we use a novel approach to identify species and areas at high risk of climate change using the city of Melbourne, Australia, as a case study. We derive a safety margin, calculated based on climatic tolerance to two extreme climate variables (maximum temperature of the warmest month, MTWM; precipitation of the driest quarter, PDQ), for 474 tree species recorded in Melbourne for baseline (average for 2011–2020) and future (2041–2070) climatic conditions. For MTWM, 218 species (46%) are exceeding baseline climatic safety margins; this number is predicted to increase to 322 species (68%) by 2055 under the Shared Socioeconomic Pathway 5–8.5. For PDQ, 255 and 257 species (54%) are identified as at risk for baseline and future climates, respectively. Using georeferenced locations of trees and high-resolution climate data, we map spatial patterns in climate risk, showing high risk areas across the city. We demonstrate how using urban tree inventories and climate risk metrics can aid in the identification of vulnerable species and locations at high climate risk to prioritise areas for monitoring and assist urban planning. [ABSTRACT FROM AUTHOR]

Urban warming affects many millions of city dwellers worldwide. The current study evaluated the extent to which trees reduce air and surface temperatures in urban settings across Greater Sydney, Australia. Summertime air and surface temperatures were measured directly in the shade of 470 individual trees planted in three contrasting contexts (parks, nature strips, asphalt) and compared with temperatures in paired adjacent areas receiving full sunlight. Differences between shade and sunlit temperatures were evaluated against measured morphological traits (leaf area index [LAI], clear stem height, crown depth, height and diameter at breast height) for all trees. On average, tree shade reduced mean and maximum air temperatures by 1.1 °C and 3.7 °C, respectively. Temperatures of standardised reference surfaces (black and white tiles and artificial grass) in tree shade were up to 45 °C lower compared to full-sun exposure, and were also lower in parks and nature strips compared to asphalt settings. The surface temperature of shaded natural grass was cooler compared to sunlit natural grass, although this difference did not vary between nature strip and park settings. The magnitude of air and surface temperature reductions due to tree shade was significantly, positively related to tree-level LAI and these relationships were stronger in asphalt and park contexts compared to nature strips. These findings can inform decisions made by urban managers and planners around the selection of tree characteristics to enhance cooling benefits in different contexts, as an important step towards more liveable and resilient cities. [ABSTRACT FROM AUTHOR]

• Urban tree inventories were used to assess growth and failure rates. • The highest growth rates were estimated in trees planted in gardens and for the exotics Celtis australis and Ulmus parvifolia. • During early establishment, vandalism and health decline were the main causes of tree failure. • Long-term monitoring recording tree size, health and management actions are necessary to assess growth and failure rates. The delivery of services and benefits provided by urban forests is threatened by tree limited growth, decline and mortality. Determining drivers of tree decline and mortality is challenging but essential in urban forestry planning to reduce environmental and socio-economic losses associated with tree failures. Urban tree inventories (UTI) are essential for managing and monitoring urban forests, which can help to identify successes (i.e., good tree growth/health) and failures (i.e., removals/dead trees). However, UTI are rarely implemented to assess urban tree growth and failure rates. Here, we used UTI from two Australian cities to demonstrate how these inventories can aid in (1) assessing species' relative growth rates and (2) identifying species failures and their determinant. We found UTI are useful to assess tree growth and failures. However, they require recording trees at the time of planting, long-term monitoring (e.g., recording tree size, health), and incorporating management actions (e.g., irrigation, pruning, removals) to inform species performance and improve urban planning and management. [ABSTRACT FROM AUTHOR]

Urban tree inventories are useful tools to assess the environmental and socio-economic services provided by urban forests. These inventories enable the evaluation of the climate change risk to urban forests, and governments rely on such inventories for urban planning and management. Here, we assessed the future climate risk of Australia and the state of urban tree inventories across 116 local government areas (LGAs), representing 21 % of the country's LGAs and encompassing 55 % of the national human population. We evaluated projected changes in temperature and precipitation by 2050 for each LGA and conducted a survey to obtain information on the extent and types of data available in existing urban tree inventories. Additionally, we compiled demographic, socio-economic, and geographical data for all LGAs to explore correlates with tree inventory status. Temperature increases in 2050 were predicted in all LGAs, with higher latitude and smaller LGAs identified to undergo greater increases in temperature compared to larger and lower latitude LGAs. Decreases in seasonal precipitation were predicted for 97 LGAs. Seventy-six (66 %) of surveyed LGAs had urban tree inventories, which most commonly included trees along streets and in parks. Sixty-one LGAs record information on tree mortality, while 31 LGAs dynamically update their inventories. The presence of an inventory and the area it covered were positively associated with human population density. More than 30 years ago, in 1988, John Gray wrote that "insufficient statistics were available in Australia to provide an accurate picture of the urban forest estate". Our research shows there has not been a significant advance in the adoption and use of urban forest inventories over the past three decades. Long-term, dynamically updated inventories are crucial for urban forest management to inform planting choices to support sustainable and resilient cities. • Urban tree inventories are useful tools to assess the environmental and socio-economic services provided by urban forests. • We used a survey to assess the state of urban tree inventories in Australian cities. • Of 116 local government areas (LGAs) in Australia, 76 (66 %) had urban tree inventories. • Species name, location and plating date are the most common attributes collected after tree establishment. • By 2050, temperature increases were predicted in all 116 LGAs and decreases in precipitation were predicted in 97 LGAs. [ABSTRACT FROM AUTHOR]

• Climate analogues and vulnerability metrics can be used to inform species selection. • Across 10 Canadian cities, 233 species (∼67 %) will be at high risk of increased temperatures by 2050. • Resilient species represent potential alternatives to replace species at high risk of climate change in Canadian cities. • Our approach is a potential tool to aid urban tree selection and integrate climate change into urban forest management. Urban forests provide ecosystem services to more than 4.2 billion people living in cities; however, the provision of these services is threatened by climate change. Cities will experience novel, warmer climates that will impact tree species survival. Here, we present an empirical approach combining the use of climate analogues and vulnerability metrics to guide urban tree species selection. Climate analogues can be used to identify where the current climate in a given location is similar to the projected future climate of another location. Using vulnerability metrics, tree species in both locations can then be compared and species at risk of future climate change can be identified and substituted with species known to be resilient to climatic changes in the other location. Using Canadian cities as a case study, we show how our approach can become a useful tool to inform species selection and facilitate urban forest decision-making in response to climate change. [ABSTRACT FROM AUTHOR]

Extreme climate conditions, including more frequent and prolonged heatwaves, are increasing in many regions throughout the world. Urban trees can aid in mitigating the adverse impacts of climate extremes; however, their capacity to do so is limited by species differences in ability to maintain function and retain leaves to provide shade under extreme temperatures. To assess tree vulnerability to heatwaves, we used a common garden experiment in Western Sydney, Australia, which included four widely-planted tree species; two native evergreen and two exotic deciduous species. Data were collected during 2019 and 2020, the two hottest summers on local record with maximum air temperatures reaching 45 °C. We monitored plant physiological status as stomatal conductance (g S) and midday leaf water potential (Ψ mid). We determined heat tolerance by measuring the leaf critical temperature (T crit) for photosynthesis and leaf turgor loss point (π tlp) as thresholds for loss of function and calculated the thermal safety margin. Plant performance was assessed by measuring tree growth and leaf damage after heatwaves. Species responded dynamically with g S decreasing as air temperature and vapor pressure deficit increased during heatwaves. Exotic species had higher g S , T crit and π tlp than native species. Leaf damage under heatwave conditions was overall lower in native species. Our results highlight the impact of heatwaves on urban trees and the value of physiological metrics to inform tree species selection to create more resilient urban environments. [ABSTRACT FROM AUTHOR]

• Urban trees presented functional adaptations in response to local climate. • Urban trees had different levels of trait plasticity along a climatic gradient. • Turgor loss point was the best surrogate for changes in precipitation and maximum temperature. • Leaf-level traits showed a greater plasticity across species and sites. In urban environments, long-term tree survival and performance requires physiological tolerance or phenotypic plasticity in plant functional traits. Knowledge of these traits can inform the likely persistence of urban forests under future, more severe climates. We assessed the plasticity of morphological and physiological traits of tree species planted along an urban climatic gradient in the Greater Sydney region during a severe, multi-year drought in eastern Australia. We selected four sites along a ∼55 km east-west transect, ranging from the cool/wet coast to the warm/dry inland. We assessed five tree species (four natives, one exotic) with different predicted climatic vulnerability based on climate-origins, estimating functional traits indicative of drought tolerance: carbon isotope composition (δ 13C), Huber value (HV), specific leaf area (SLA), wood density (WD), and leaf turgor loss point (π tlp). Broadly, trees planted in warm/dry sites had more negative π tlp , higher WD, δ 13C and HV, and lower SLA than cool/wet sites, indicating phenotypic plasticity to drought. The leaf-level traits π tlp , δ 13C and SLA were more strongly correlated with temperature and precipitation, compared to HV and WD. Species differed in the extent of their trait shifts along the transect, with greater plasticity evident in the exotic Celtis australis and the more temperate cool-climate Tristaniopsis laurina , compared to the more tropical, warm-climate Cupaniopsis anacardioides , which showed limited plasticity and lower drought tolerance. Our findings reveal adaptive capacity of urban trees to climate via plasticity in drought tolerance traits, which can direct species selection to improve urban forests resistance to climate change. [ABSTRACT FROM AUTHOR]