Improving urban forest establishment, resilience and performance using trait-based tree selection

2015 | Dr. Andrew Hirons, Myerscough College, United Kingdom

Trees greatly enrich our urban environment through their provision of a wide range of ecosystem services. However, the contribution trees make is proportional to the health of the individual tree and urban forest as a whole. Impoverished growth environments, high mortality rates and poor species diversity act to diminish the ecosystem services provided by trees and make the urban forest vulnerable to a future climate scenarios. Professionals tasked with securing the future of our urban forests will be greatly aided by robust selection guidance on tree species and cultivars. Plant traits relating to the tolerance of water deficits will be particularly valuable since water deficits frequently perturb tree development in urban environments and lead to early tree mortality. For example, the leaf water potential at turgor loss (ΨP0) provides a robust measure of a plant’s ability to survive low water availability since a more negative ΨP0 allows the leaf to maintain physiological function for longer in drying soils. Using a novel approach, this project aims to develop quantifiable trait-based guidance for a wide range of species that can be used by arboriculturists, urban foresters, landscape architects and tree nurseries to help establish a resilient urban forest for the future. The Hyland R. Johns research grant has kindly supported this research so please look for the results that will be shared at ISA conferences and in Arboriculture and Urban Forestry.

Study Results

A fundamental task in establishing the urban forest is to select species that are suitable for the proposed planting site(s). Studies on the mortality of newly planted trees have consistently shown drought tolerance to be one of the most important traits conferring survivorship and establishment success. Like so many aspects of tree tolerance to environmental stress, drought tolerance can be informed by a number of different mechanisms. Significantly, adaptations to avoid drought such as deep rooting might work very well in natural landscapes, but trees that possess this characteristic may not be able to root deeply in urban environments because of the restrictions imposed by other infrastructure. Therefore, an ability to tolerate low tissue water status is drought tolerance trait that is highly relevant for urban sites. This research uses a novel method to evaluate the leaf turgor loss (wilting) point of species and has evaluated the drought tolerance of over 80 species from a wide range of temperate genera, including: Betula, Carpinus, Fraxinus, Ostrya, Quercus, and Tilia. The turgor loss point in temperate trees is approximated -3 MPa during summer but highly significant differences occur across species. Quantifiable information on drought tolerance will be very useful for professionals trying to identify suitable species for challenging urban environments where low water availability may be a problem. It will also have a role in persuading tree nurseries to grow currently underutilised species. Look out for species selection guidance that incorporates this work.

Year: 2015

Funding Duration: 3-5 years

Grant Program: Hyland R. Johns Grant

Grant Title: Improving urban forest establishment, resilience and performance using trait-based tree selection

Researcher: Dr. Andrew Hirons

Key words:

Peer Reviewed Publications from Grant:

General Audience/Trade Publications:

• Hirons, A. and H. Sjöman. (2018). Tree Species Selection for Green Infrastructure: A Guide for Specifiers.

Professional Presentations:

For more information on this project, contact the researcher via TREE Fund at treefund@treefund.org.