Henrik Sjöman

Magnolias as urban trees – a preliminary evaluation of drought tolerance in seven magnolia species

Abstract Tree selection must ensure that trees are capable of thriving in the environment in which they are placed. Inappropriate species or trees of poor quality will never develop any substantial capacity for delivering ecosystem services. The aim of this study is to evaluate seven species of Magnolia for their drought tolerance by estimating their water potential at leaf turgor loss to help provide quantitative data for their capacity to tolerate dry urban sites. According to the results, Magnolia virginiana is ranked as the most drought-tolerant, while Magnolia x loebneri “Leonard Messel” is the most sensitive to drought. However, in comparison with other plant groups previously studied, magnolias have to be treated as drought sensitive. Consequently, magnolias used in this study should be used in garden and park environments, as their potential for use along streets can be limited by their vulnerability to drought. The turgor loss point methodology used in the study provides an efficient alternative to decades of observation, especially when new genotypes or underutilised trees are being evaluated. It is now possible to show the group’s general sensitivity to drought as well as quantifying individual species sensitivity to drought.

Herbaceous Plants for Climate Adaptation and Intensely Developed Urban Sites In Northern Europe: A Case Study From the Eastern Romanian Steppe

Abstract In the increasingly compact city, services currently provided for in parks will in future be compressed into smaller green unit-structures, often associated with paved surfaces. Left-over spaces in urban environments, such as traffic roundabouts and strips along paths, roads and other corridors, will be important in the future city in order to deliver different eco-system services, especially stormwater management. It is therefore essential to start now to develop the knowledge and experience needed to create sustainable plantings for these sites. This paper presents the findings of a field survey in eastern Romania that sought to identify potential species for urban paved plantings in the Scandinavian region (northern Europe). The research approach is rooted in the hypothesis that studies of natural vegetation systems and habitats where plants are exposed to environmental conditions similar to those in inner-city environments can: 1) identify new or non-traditional species and genotypes adapted to urban environments; and 2) supply information and knowledge about their use potential concerning growth, flowering, life form, etc. In total, 117 different herbaceous species, all of which experience water stress regimes comparable to those in urban paved sites in Scandinavia. The initial information obtained from this field survey present a base of knowledge of which species that have a future potential for use in urban environment, which is of great importance in the following work within this project instead of testing species randomly without this knowledge of the species tolerance and performance in similar habitats.

Improving confidence in tree species selection for challenging urban sites: a role for leaf turgor loss

High species diversity is argued to be the most important requisite for a resilient urban forest. In spite of this, there are many cities in the northern hemisphere that have very limited species diversity within their tree population. Consequently, there is an immense risk to urban canopy cover, if these over-used species succumb to serious pests or pathogens. Recognition of this should motivate the use of less commonly used species. Analysis of plant traits, such as the leaf water potential at turgor loss (ΨP0), can provide useful insights into a species’ capacity to grow in warm and dry urban environments. Therefore, the aim of this study was to evaluate ΨP0 of 45 tree species, the majority of which are rare in urban environments. To help evaluate the potential for using ΨP0 data to support future decision-making, a survey of professionals engaged with establishing trees in urban environments was also used to assess the relationship between the measured ΨP0 and the perceived drought tolerance of selected species. This study demonstrates that ΨP0 gives strong evidence for a species’ capacity to tolerate dry growing conditions and is a trait that varies substantially across species. Furthermore, ΨP0 was shown to closely relate to the experience of professionals involved in establishing trees in urban environments, thus providing evidence of its practical significance. Use of plant traits, such as ΨP0, should, therefore, give those specifying trees confidence to recommend non-traditional species for challenging urban environments.