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

Abstract

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 (Ψ P0), 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 Ψ P0 of 45 tree species, the majority of which are rare in urban environments. To help evaluate the potential for using Ψ P0 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 Ψ P0 and the perceived drought tolerance of selected species. This study demonstrates that Ψ P0 gives strong evidence for a species' capacity to tolerate dry growing conditions and is a trait that varies substantially across species. Furthermore, Ψ P0 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 Ψ P0 , should, therefore, give those specifying trees confidence to recommend non-traditional species for challenging urban environments.

Designing vegetation barriers for urban air pollution abatement: a practical review for appropriate plant species selection

“…This observation supports the selection of anisohydric plants for enhanced stomatal uptake of pollutants, except where prolonged periods of soil water deficiency are projected to occasionally occur. Alternatively, and with a focus on continued ecosystem service provision under dry urban conditions, Sjöman et al 130 recommend the selection of species that employ drought tolerance mechanisms as opposed to water loss avoidance strategies. Sjöman et al 130 present leaf water potential at turgor loss as a reliable measure of a plant's ability to maintain physiological function during drought conditions.…”

“…Alternatively, and with a focus on continued ecosystem service provision under dry urban conditions, Sjöman et al 130 recommend the selection of species that employ drought tolerance mechanisms as opposed to water loss avoidance strategies. Sjöman et al 130 present leaf water potential at turgor loss as a reliable measure of a plant's ability to maintain physiological function during drought conditions. Speciesspecific datasets based on this measure were used where possible to inform the primary source for the drought tolerance factor in Table 4 41 .…”

“…Improving plant diversity in urban areas is imperative for increased urban ecosystem resilience to environmental hazards including and beyond air pollution 7,11,68 . Furthermore, several studies have demonstrated that diversity not only in species but in vegetation type and structure is important for air quality, carbon sequestration and the sustainable provision of diverse ecosystem services 128,130,148 . Discouragement of monoculture planting is another reason for which it was decided that the species in Tables 3 and 4 would not be ranked.…”

Variations in seasonal drought tolerance rankings

“…Spring drought tolerance is lower in both annual plants (Farooq et al 2012) and deciduous trees (Sjöman et al 2015(Sjöman et al , 2018a) when compared to summer tolerance. Sjöman et al (2015Sjöman et al ( , 2018a identifies, however, that Acer species which are most drought tolerant in spring are not necessarily the most tolerant in summer. It is, therefore, important to clarify if tolerance ranks are maintained throughout the season.…”

Tissue Culture Clonal Propagation of Hybrid White Oaks for the Urban Environment

“…The genus Quercus is a species-rich clade of long-lived trees that inhabit a wide variety of ecological conditions across their natural range and provide a rich genetic source for plant breeding material (Cavender-Bares, 2019). Oaks are generally known to be drought tolerant, making them ideal candidates for planting in typically low soil moisture conditions found in the urban environment (Abrams, 1990;Osuna et al, 2015;Sj€ oman et al, 2018). Oaks are commonly a major component of urban forests across eastern North American cities and are frequently requested by residents as a desirable street tree (Raupp et al, 2006).…”