Trees for tough urban sites

The main body of work in this thesis was to develop and test a working procedure for identification of new tree species and genotypes that holds the potential to diversify urban tree populations. This process has been set in context through a literature review which characterise species-specific information about the tolerance of trees to the environmental stresses in urban paved sites. With a Scandinavian focus, a review of literature was made in order to characterise species-specific information concerning site tolerance for urban paved environments as it is disseminated in scientific papers, dendrology literature, books addressing plant use in urban environments, plant nursery catalogues. The information was evaluated against the requirements of urban tree planners which should ideally be; contextual; local, referring to existing urban plantings, specify the urban site type(s) for which a given species can be recommended, and include the full range of tree species that are well adapted to the urban paved environment in a given climate region. In the analysis of the literature, abundant restrictions and misleading guidance were apparent. The results showed that existing information is piecemeal and that most is either too general (dendrology literature) or too specific or contradictory (scientific literature) to meet the requirements of urban tree planners, while books intended for plant use in cities do not sufficiently integrate the regional perspective. Moreover, contextual information local to the Scandinavian region is mainly provided for already much used species. With a focus on the northern parts of Central Europe and the adjoining milder parts of Scandinavia (CNE-region), a working procedure for the identification of potential tree species and genotypes for in inner-city environments was developed. The procedure was made through two case studies; in the Qinling Mountains, China, and in north-east Romania and neighbouring parts of the Republic of Moldavia. In total, 27 tree species were identified as tolerable for warm and periodically dry habitats. Of these tree species, only four are currently much used or used to some extent in northern Europe. Accordingly, the reaming 23 tree species identified hold potential to supplement and diversify the urban tree populations in the CNE-region

How green is an urban tree? The impact of species selection in reducing the carbon footprint of park trees in Swedish cities

Introduction: Planting trees in urban areas can mitigate some of the emissions generated in cities by carbon sequestration (annual uptake of CO2 through the process of photosynthesis) and carbon storage (amount of carbon stored in the tree's biomass throughout its lifespan). The aim of this study was to calculate the carbon footprint from nursery production to final establishment of different tree species grown for planting in urban parks in a northern European context.Material and methods: The analysis included a cradle-to-gate approach and investigated the amount of carbon the adult trees needed to sequester in order to compensate for initial carbon emissions and which temporal perspectives are of concern. Greenhouse gas emissions were estimated based on an inventory of consumption of fuels, energy, materials and other production inputs during cultivation, delivery, planting and establishment of three different tree species in three different locations in Sweden. The tree species considered in the analysis (Salix alba, Quercus rubra, Pinus sylvestris) were selected due to significant differences in their growth rates. Salix alba is a competitive strategist in resource-rich habitats, and is proficient at converting these resources into vigorous growth. Pinus sylvestris is a pronounced stress strategist with good ability to handle resource-limited habitats, and invests in traits accordingly, resulting in significantly slower development. Quercus rubra has its main distribution in cool and moderately resource-rich habitats, but has relatively high stress tolerance and can be considered intermediate between the other two species in terms of growth rate.Results and discussion: The results showed that within 16 years of planting, all species in all three cities, except Pinus sylvestris planted in Umeå, compensated for initial carbon emissions, i.e. showed net absorption of CO2 after emissions from cultivation, delivery, planting and establishment of the trees had been deducted. There was a clear link between the time by which compensation of initial carbon emissions was achieved and growth rate of the different species, with the fast-growing Salix alba showing the best results. The single largest source of emissions among all activities carried out during cultivation, delivery and planting of all species, regardless of the city in which they were planted, was fuel consumption during tree planting

Selection of Shrubs for Urban Environments-An Evaluation of Drought Tolerance of 120 Species and Cultivars

comprise a very large proportion of the plant material used in public as well as private green spaces. Yet, there is currently a lack of quantitative assess-ments of stress tolerance in a large proportion of available species and cultivars of shrubs, thus complicating any design process involving shrubs. The aim of this study was to evaluate drought tolerance of many common and less traditional shrubs in-tended for public planting. Through this compilation, a first contribution (dataset) to species selection to obtain expected ecosystem services of shrubs is offered. As water stress is a major constraint for landscape plants in urban environments and is likely to increase in many regions under future climate scenarios, the quantitative drought tolerance of a species or genotype must be a fundamental consideration for plant selection for urban environments. In this study, we used water potential at the turgor loss point (TP0) as a key trait for evaluating drought tolerance of different species of shrubs. TP0 is a highly instructive trait because it represents a quantifiable measure of physiological drought tolerance. More negative TP0 values represent greater drought tolerance by allowing the leaf to maintain physiological function over a greater range of leaf water potentials. TP0 was estimated for a wide range of shrubs, representing a total of 44 genera and 120 species and cultivars. The mean TP0 value for all 120 shrub species and cultivars was -2.76 MPa, with the overall species TP0 value ranging from -1.48 MPa to -4.23 MPa. Intraspecific variation (variation between cultivars) was evaluated using five cultivars of Spiraea japonica and one wild collected genotype. Within this species, there was a range of TP0 values of 1.66 MPa, with S. japonica 'Little Princess' having the highest estimated drought tolerance (TP0 = -2.78) and the wild-type S. japonica having the lowest (TP0 = -4.44 MPa)

Experimental evaluation of waterlogging and drought tolerance of essential Prunus species in central Europe

Fruit-bearing and flowering minority tree species, such as many species from the Prunus genus, are essential for multiple ecosystem services in the landscape. Although common, but never dominating, these minority species are often overlooked compared to commercial timber trees in relation to climate change. Induced stress on trees through climate change in central Europe will not only be caused by drought but also by extreme precipitation and pluvial flooding. This study experimentally address this by testing both waterlogging and drought tolerance in three key species of Prunus for central Europe that naturally span a wide variation of habitat conditions. The selected species Prunus mahaleb, Prunus avium and Prunus padus were subjected to both drought and waterlogging in a greenhouse experiment. Plant functionality in the form of midday leaf water potential, stomatal conductance and turgor loss point together with different aspects of biomass allocation and growth was tested. All included species lost their stomatal conductance and leaf water potential within a few days in the waterlogging treatment. Only P. padus had the capacity to recover with new leaves after the waterlogging ended, suggesting that avoidance strategies though leaf shedding can be a complementary mechanism to withstand waterlogging. P. padus kept its stomatal conductance and water potential for the longest time in the drought treatment followed by P. mahaleb and P.avium. This longevity in the drought treatment for P. padus could be explained by both tolerance strategies through lower turgor loss point, but also avoidance strategies with fast changes in growth and higher allocation of biomass to the roots. There is a clear risk that ecosystem service from Prunus species in the landscape can be negatively affected not only by drought but also by increased events of waterlogging. This highlights the need for including minority species and also other climate stressors in addition to drought in the planning and management of multifunctional landscapes

NORTH-EAST ROMANIA AS A FUTURE SOURCE OF TREES FOR URBAN PAVED ENVIRONMENTS IN NORTH-WEST EUROPE

Trees are an important feature of the urban environment. The problem today lies not in finding a wide range of well-adapted tree species for park environments, but in finding species suitable for urban paved sites. In terms of north-west Europe, it is unlikely that the limited native dendroflora will provide a large variety of tree species with high tolerance to the environmental stresses characterising urban paved sites in the region. However, other regions with a comparable climate but with a rich dendroflora can potentially provide new tree species and genera well-suited to the growing conditions at urban sites in north-west Europe. This paper examines the potential of a geographical area extending over north-east Romania and the Republic of Moldavia to supply suitable tree species for urban paved sites in Central and Northern Europe (CNE). The study involved comparing the temperature, precipitation, evapotranspiration and water runoff in the woodland area of Iasi, Romania, with those the current inner-city climate of Copenhagen, Denmark and those predicted for Copenhagen 2100. The latter included urban heat island effects and predicted global climate change. The results revealed similar pattern in summer water deficit and temperature between natural woodlands in Iasi and inner-city environment of Copenhagen today. On the other hand, there is a weak match between Iasi and the future Copenhagen. In order to match the future scenario of Copenhagen with the present situation in Iasi, a greater understanding in a early phase that the solution not only depends on suitable tree species, but also on technical solutions being developed in order to have trees in paved environments in the future. On the basis of precipitation and temperature data, natural woodlands in north-east Romania have the potential to be a source of suitable trees for urban paved environments in the CNE region, even for a future climate if other aspects in the planning of trees in paved sites are included

Stadsträd för framtiden : granar

I jakten på ovanliga och otraditionella träd för urbana miljöer handlar det många gånger om att återupptäcka gamla favoriter. En växtgrupp som är ovanlig i nyplanteringar idag är granar (Picea). Här lyfts några odlingsvärda arter fram, alla med kvaliteter som kan ge urbana platser och planteringar en unik identitet

Solitärbuskar : mångfald och användning

I många planteringar är det viktigt att få höjd och volym under årets alla delar. En växtgrupp som erbjuder generös blomning, spännande bladstruktur och fina säsongskvaliteter, inte minst höstfärger, är solitärbuskarna. De bidrar med sin storlek till en tydlig och uppskattad struktur och kan fungera både som blickfång och som bakgrund till andra växter. I detta Movium Fakta presenteras ett urval av solitärbuskar för olika typer av offentliga växtmiljöer och deras användning

Using stomatal conductance capacity during water stress as a tool for tree species selection for urban stormwater control systems

Improving our understanding of how different tree species function in urban stormwater management systems is important, as tree pits may provide a temporary reservoir for stormwater and as trees have the potential to actively reduce stormwater runoff by transpiration. While urban tree planting pits are increasingly used for shortterm water storage during stormwater runoff events, this storage can have negative effects on both tree vitality and water removal capacity, since stress from waterlogging result in stomatal closure. However, sensitivity to water stress varies by species. It is therefore important to determine which tree species can maintain long-term vitality and continued transpiration even under water stress, and thus are suitable for such locations. Here, we studied how nine different tree species, varying in expected tolerance to water stress, were affected by short-term and seasonal waterlogging, in a greenhouse experiment. The seedlings (Magnolia x loebneri, Tilia tomentosa, and Sorbus torminalis - low water logging tolerance; Cercidiphyllum japonicum, Rhamnus cathartica, and Fraxinus ornus - medium water logging tolerance; Quercus palustris, Acer saccharinum, and Fraxinus pennsylvanica - high water logging tolerance) were exposed to two days, five days and seasonal waterlogging. The treatments reflected best practice (optimal), suboptimal and total lack of tree pit drainage, using Swedish standards. Stomatal conductance and leaf water potential were determined regularly over a period of 71 days, and morphological adjustments were registered. Four of the species were affected already after two days of waterlogging, with reduced stomatal conductance either during the waterlogging or immediately after, and only the most waterlogging tolerant species were unaffected by the five-day treatment. However, all plants survived waterlogging for almost 30 days before the estimated permanent wilting was reached in some plants. We suggest that tree species selection for stormwater management systems should consider the species' capacity to maintain high stomatal conductance during waterlogging, as there were clear differences between species. The effectiveness of the selected species could have an important impact on the stormwater management capacity of cities, as well as on other aspects of ecosystem service delivery from urban trees

Accumulation of antimony and lead in leaves and needles of trees: The role of traffic emissions

Antimony (Sb) is a toxic metalloid, which has been increasingly used in the brake lining of ve-hicles, and increased concentrations have been found in soils near abundant traffic. However, since very few investigations of Sb accumulation in urban vegetation have been undertaken there exists a knowledge gap. We studied the concentrations of Sb in leaves and needles of trees in the Gothenburg City area, Sweden. In addition, lead (Pb), also associated with traffic, was investi-gated. Sb and Pb concentrations of Quercus palustris leaves at seven sites with contrasting traffic intensity varied substantially, correlated with the traffic-related PAH (polycyclic aromatic hy-drocarbon) air pollution at the sites and increased during the growing season. Sb but not Pb concentrations were significantly higher in needles of Picea abies and Pinus sylvestris near major roads compared to sites at larger distances. In Pinus nigra needles at two urban streets both Sb and Pb were higher compared to an urban nature park environment, emphasising the role of traffic emissions for these elements. A continued accumulation of Sb and Pb in three years old needles of Pinus nigra, two years old needles of Pinus sylvestris and eleven years old needles of Picea abies was observed. Our data suggest a pronounced link between traffic pollution and Sb accumulation in leaves and needles, where the particles carrying Sb seem not to be transported very far from the source. We also conclude that there exists a strong potential for Sb and Pb bioaccumulation over time in leaves and needles. Implications of these findings are that increased concentrations of toxic Sb and Pb are likely to prevail in environments with high traffic intensity and that Sb can enter the ecological food chain by accumulation in leaves and needles, which is important for the biogeochemical cycling