Societal Impact Statement: Diversification of urban forests is essential to enhance their resilience to future biotic threats as well as those posed by a changing climate. Arboreta and botanic gardens host a wide range of plant material that can be evaluated to inform tree selection policy. This study demonstrates that plant functional traits, such as the water potential at leaf turgor loss, can be highly instructive when developing evidence‐based recommendations for urban environments. However, if botanic collections are to fulfil a critical role in understanding plant response to environment, they should not be managed solely as visitor attractions but must have scientific objectives at the forefront of management policy.Summary: Arboreta and botanic gardens host a multitude of species that can be utilized in research focused on improving diversity within urban forests. Higher tree species diversity will enhance the resilience of urban forests to abiotic and biotic threats and help deliver strategies that foster sustainable communities. Consequently, this study aims to demonstrate the value of botanic collections as a resource for research into tree species selection for more resilient urban landscapes. As water stress is a major constraint for trees in urban environments, understanding the drought tolerance of species is essential for urban tree selection. This study evaluates a key functional trait relating to drought tolerance. Using vapor pressure osmometry, the water potential at leaf turgor loss was evaluated for 96 species using plant material from seven botanic collections in North America and Europe. Leaf turgor loss contrasted widely in the temperate deciduous trees evaluated and, in summer, ranged from −1.7 MPa to −3.9 MPa. Significant differences in drought tolerance were also apparent across genera and closely related cultivars. Osmotic adjustment was shown to be a major physiological factor driving leaf turgor loss. A meta‐analysis also demonstrated that leaf turgor loss was closely related to a drought‐tolerance scale based on observations of tree performance under drought. Arboreta and botanic collections can play a vital role in the evaluation of plant material for urban environments, provided they are curated with scientific objectives at the forefront of management policy and are not managed purely as visitor attractions.

Poor soil health is a critical problem in many urban landscapes. Degraded soil restricts plant growth and microorganism activity, limiting the ability of urban landscapes to perform much needed ecosystem services. Incorporation of approximately 33% compost by volume into degraded soil has been proven to improve soil health and structure over time while avoiding the financial and environmental costs of importing soil mixes from elsewhere. However, additions of high volumes of compost could potentially increase the risk of nutrient loss through leaching and runoff. The objective of our study was to consider the effects of different compost amendments on soil health, plant health and susceptibility to nutrient leaching in order to identify ranges of acceptable compost characteristics that could be used for soil remediation in the urban landscape. A bioassay was conducted with Phaseolus vulgaris (Bush Bean) to measure the effect of nine composts from different feedstocks on various plant health parameters. Leachate was collected prior to planting to measure nutrient loss from each treatment. All compost amendments were found to improve soil health. Nutrient-rich, manure-based composts produced the greatest plant growth, but also leached high concentrations of nitrate and phosphorus. Some treatments provided sufficient nutrients for plant growth without excess nutrient loss. When incorporating as much as 33% compost by volume into a landscape bed, the optimal compost will generally have a C:N ratio of 10–20, P-content <1.0% and a soluble salt content between 1.0 and 3.5 mmhos/cm. These recommendations should ensure optimal plant and soil health and minimize nutrient leaching.

This study investigated the relationship of stem anatomy to differences in rooting ability between Quercus bicolor Wild. and Quercus macrocarpa Michx. cuttings. Quercus bicolor cuttings were found to have a significantly greater proportion of parenchymatous gaps in the sclerenchyma sheath over a 9-week period compared with Q. macrocarpa cuttings. In Q. macrocarpa , the percentage gap was generally low, coinciding with the low percentage rooting observed in this species. Percentage rooting correlated well (r ² = 0.75) with the percentage parenchymatous gap in the perivascular region of Q. bicolor cuttings. The problems with accepting this relationship as causal are stated in the discussion. Untreated cuttings showed normal stem organization: a dermal tissue system that included the initial stages of phellem formation, a cortex, and a ring of closely arranged vascular bundles in early stages of secondary growth. The locations of the five distinct lobes of the pith were coordinated with the locations of root primordia. Callus growth was first detected in the cortex (i.e., external to the fiber bundles), followed by proliferation within the phloem, opposite the lobes of the pith, 8 to 12 days after cuttings were treated with indole butyric acid (6000 mg·L ⁻¹ dissolved in 50% v/v ethanol in water). By 14 to 16 days, root primordia had developed within the proliferative tissue in the secondary phloem. In both species, root primordia penetrated parenchymatous gaps in the fiber sheath directly, the fiber bundles being displaced laterally as the roots increased in size.