•Development of a database for urban woody species selection.•The database supports planning and planting processes of urban trees.•It considers especially the heterogenic urban site conditions for ...tree growth.•Taking into account the needs of citizen to urban trees.•The database includes almost 400 woody plants to support diverse plantings.
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.
Research Highlights: This paper presents a cross-city empirical study on micro-climatic thermal benefits of urban trees, using machine-learning analysis to identify the importance of several in situ ...measured tree physiognomy traits for cooling. Background and Objectives: Green infrastructure and trees in particular play a key role in mitigating the urban heat island (UHI) effect. A more detailed understanding of the cooling potential of urban trees and specific tree traits is necessary to support tree management decisions for cooling our progressively hot cities. The goal of this study was to identify the influence and importance of various tree traits and site conditions. Materials and Methods: Surface temperature, air temperature at 1.1 m and at tree crown height, as well as wet bulb globe-temperature of shaded and fully sun-exposed reference areas, were used to study the cooling effect of seven different urban tree species. For all 100 individuals, tree height, crown base, trunk circumference, crown volume, crown area, leaf area index (LAI) and leaf area density (LAD) were measured. Measurements were conducted in the cities of Dresden, Salzburg, Szeged, and Vienna as representatives for middle European cities in different climate zones. Results: Beside site conditions, tree species, height, height of crown base, as well as trunk circumference, have a great influence on the cooling effect for city dwellers. The trunk circumference is a very valuable indicator for estimating climate regulating ecosystem services and therefore a highly robust estimator for policy makers and tree management practitioners when planning and managing urban green areas for improving the availability and provision of ecosystem services.
•Species differ significantly in their ability to reduce thermal load.•LAD and Emax were most appropriate to explain reductions in air temperature.•One unit increase in LAD reduces surface ...temperature by 4.63K.•Tilia and Corylus exhibit the highest rates of Emax and LAD.•Both species are the best options to reduce air and surface temperatures.
Vegetation and trees in particular play a key role in mitigating thermal load in urban areas. The goals of this study were to analyse species-specific microclimatic effects and to identify the role of leaf-area-density, transpiration, and stomatal conductance for cooling effects at urban sites. Air temperature, relative humidity and surface temperature were used to study the effects of six tree species with similar age structure in a residential area with comparable site conditions. Transpiration, stomatal conductance and leaf-area density were measured during the summer months in 2013. Air temperatures and relative humidity were monitored for four trees per street in hourly intervals, and surface temperatures were recorded in the afternoon for three hot days on the shaded and unshaded asphalt surfaces beneath the trees.
Species differ significantly in their ability to reduce air and surface temperatures, as well as to increase relative humidity. Trees showing both a high leaf-area density and a high rate of transpiration are more effective in cooling the air temperatures. Differences in the surface temperatures of the tree shaded areas are more pronounced compared to the air temperatures. Thus, the surface temperatures of the full sun exposed areas are up to 15.2K warmer than that in the tree shaded areas. The results provide information to decrease thermal load in urban areas for future tree planting by choosing species with high cooling potential. The highest cooling potential was measured for Corylus colurna and Tilia cordata ‘Greenspire’ and the lowest for Ulmus × hollandica ‘Lobel’.
KEY MESSAGE : Distinct species-specific differences were found in the response to temperature, precipitation and the self-calibrated Palmer Drought Severity Index that are confirmed by pointer year ...analyzes and superposed epoch analyzes. Trees in urban environments are exposed to heat stress, low air humidity and soil drought. The increasing temperatures and the more frequent heat and drought events will intensify the stress level of urban trees. We applied a dendrochronological approach to evaluate the species-specific suitability under increasing risk of drought of five tree species at highly sealed urban sites in the city of Dresden (Germany). Climate-growth correlation analyses show that temperatures and water availability from April to July in the current year and in summer and autumn of the previous year are the main determining factors for radial growth. However, distinct species-specific differences were found in the response to temperature, precipitation and the self-calibrated Palmer Drought Severity Index. During the study period, the influence of temperature and drought on radial growth during summer months increases for Acer platanoides and Acer pseudoplatanus, whereas no changes occurred for Quercus petraea, Quercus rubra, and P. × hispanica. Pointer year analysis and superposed epoch analyses revealed a species-specific response to extreme climatic events. While for A. platanoides and A. pseudoplatanus a higher number of negative pointer years and significant growth declines in drought years were found, Q. petraea and Q. rubra showed more frequent positive pointer years but no significant growth reductions during drought. Based on these response patterns we classified the studied tree species according to their suitability and drought tolerance for urban sites.
Two hundred and fifty urban woody species are used in Central European parks and gardens. Based on reliable publications we attempt, for the first time, to extensively classify and assess them with ...regards to their usability after predicted climate changes. A new Climate-Species-Matrix has been developed for this purpose. In a two-dimensional assessment, four degrees of drought resistance and winter robustness are the decisive criteria. The woody species (divided into trees of more than 10
m in potential height and trees/shrubs of up to 10
m in height) were placed into 16 categories by decreasing tolerance, ranging from 1-1 (very suitable) to 4-4 (very limited usability). For many of these species, as well as many others that are not mentioned in this study, not all questions could be answered. Nonetheless, this categorization provides a sound basis for decisions in planning the use of woody species in cities. This planning process must also include additional criteria, dependent on individual requirements such as, soil parameters, shade resistance, aesthetics, etc. This paper is therefore meant to be a basis for discussion and supplementation for further research.
•Mortality of common beech can be reliably predicted from growth characteristics.•Trees that grew slower in relative basal area had a much higher mortality risk.•Predicted mortality correlated well ...with vitality assessment of branching pattern.•The findings demonstrate that crown decline and mortality are related at dry areas.
For many tree species, growth patterns derived from tree-ring time series have been shown to be good indicators of tree mortality. Although tree rings of common beech (Fagus sylvatica) have been widely used to answer complex questions of forest ecology, there are only few studies using growth characteristics, such as growth decline or growth variability, as informative predictors of tree mortality in old-growth beech forests. To do this, we used dendrochronological data of living and dead trees from a nature reserve in eastern Germany. Using a logistic regression model, we predicted tree mortality based on growth characteristics (basal area increment; variance, autocorrelation, mean sensitivity of ring widths; growth trends) over different time horizons. Beech mortality could reliably be predicted up to 20years in advance on the basis of relative basal area growth. Trees that grew slower in relative basal area than 0.95cm2/cmy on average over a 20-year-period had a much higher mortality risk than faster-growing trees. Other statistical characteristics of the dendrochronological time series, such as the variance or autocorrelation of ring widths, the mean sensitivity or growth trends, did not convey significant additional information and did not lead to better mortality predictions.
Severe droughts have the potential to reduce forest productivity and trigger tree mortality. Most trees face several drought events during their life and therefore resilience to dry conditions may be ...crucial to long-term survival. We assessed how growth resilience to severe droughts, including its components resistance and recovery, is related to the ability to survive future droughts by using a tree-ring database of surviving and now-dead trees from 118 sites (22 species, >3,500 trees). We found that, across the variety of regions and species sampled, trees that died during water shortages were less resilient to previous non-lethal droughts, relative to coexisting surviving trees of the same species. In angiosperms, drought-related mortality risk is associated with lower resistance (low capacity to reduce impact of the initial drought), while it is related to reduced recovery (low capacity to attain pre-drought growth rates) in gymnosperms. The different resilience strategies in these two taxonomic groups open new avenues to improve our understanding and prediction of drought-induced mortality.
Street trees planted at tree pits with impermeable pavements are exposed to a high level of both, atmospheric and edaphic stress. For many species tree physiology, optimal growth, and consequently ...long-term vitality may be hampered under these harsh conditions. Therefore, maintaining the vitality and promoting the ecosystem services provided by urban trees, for example aesthetic values and microclimatic benefits, it is important to establish trees with a high tolerance to stressful urban environments. Measurements of leaf gas exchange, leaf water potential, leaf surface temperature and chlorophyll-fluorescence were used for identification of specific response of Corylus corluna L.,
Ginkgo biloba
L.,
Liriodendron tulipifera
L., and
Tilia cordata
Mill. ‘Greenspire’. The summer months in 2013 with a period of heat and drought over eight weeks only interrupted by two rainy days were appropriate to access tree’s strategies to cope with low water availability. During the measurement period, the influence of high temperatures, high values of vapor pressure deficit (VPD) and low soil water availability on stomatal conductance, water-use efficiency (WUE) and leaf water potential (Ψmin, Ψmax ) was highest for Liriodendron followed by Ginkgo. These species showed high reductions in WUE in case of higher air temperatures and high values of VPD. Results indicate an avoidance strategy under increasing heat and VPD. In contrast, Corylus and Tilia followed a tolerance strategy indicated by decreasing values of Ψmin and lower reductions of WUE. In conclusion, wide species-specific variation in response to high temperatures and high VPD indicates that substantial potential exists in the selection for dry and hot urban places.
This paper presents a psychological perspective to the selection of trees for urban residential areas. Sixty tree species suitable for urban planting sites were rated by lay participants regarding ...preference. We then used outward tree features to predict the preference ratings. Twenty-five different plant characteristics served as possible predictors in a regression model for tree preference. We found that the distinction between conifers and deciduous trees, the maximum tree height, and the crown height-to-width ratio were valuable predictors for preference, explaining more than 70% of the variance. This adds support for evolutionary theories of landscape preference. The regression model presented in this paper can be applied to calculate a preference estimate for other tree species using their known physical data, which may facilitate tree selection tasks in green space planning. By specifying preference-relevant tree characteristics, our findings may also inform the process of selecting diverse species for sites where a homogenous overall appearance is a planning goal.
This study focuses on the climate and growth response of the sessile oak (Quercus petraea (Matt.) Liebl.) and the northern red oak (Quercus rubra L.) using dendrochronological methods. Tree-ring ...series of street trees in the city of Dresden, Germany and in a nature reserve close to the urban area were analysed, and the climate and growth response and moving correlation functions (CF) were computed. Moreover, the impact of 13 years of drought was examined by superposed epoch analysis (SEA). Our results show that differences emerge from peculiarities of the different site conditions, indicating that city oaks contain a higher level of noise in their ring width data due to human activities that degrade the strength of growth-climate associations. Importantly, climatic conditions during the previous summer and autumn and during the current spring season display significant correlations with annual growth. The stability of the climate–growth relationship was tested via moving correlation functions. A strong increase in the correlation with the temperature and precipitation in April was found for the trees of northern red oak in forests. Drought years induced significant reductions in radial growth for the northern red oak only. Nevertheless, the long-term impact of drought years must be considered as marginal because of the fast recovery of the radial growth after one to two years. In the future, the growth of the northern red oak may be restricted by an increased frequency of droughts and warmer and drier conditions in April.
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