Tree Selection for Green Infrastructure

The Natural Environment Research Council (NERC) issued a call for funding in 2015 for a Green Infrastructure Innovation Project. This opportunity prompted a new collaboration between three academic partners (University Centre Myerscough, Lancaster University and the Swedish University of Agricultural Sciences) and an industrial partner, Trees and Design Action Group (TDAG).

Trees form a critical component of green infrastructure (GI) and provide a wide range of ecosystem services to urban dwellers. However, these valuable services are at risk of being compromised through limited species diversity, inappropriate species selection, impoverished growth environments, and high tree mortality rates. Provision of many of these ecosystem services relies on healthy trees and their value often scales with tree size, necessitating tree development to maturity and continued health: to perform well, trees must thrive, not simply survive.

Despite the centrality of appropriate species selection to the successful delivery of GI schemes, there remains scant guidance for the many actors involved in their establishment. The outcome of this deficit in guidance is that urban planners, landscape architects and local authority officers rely heavily on a narrow range of 'traditional' species.

Our belief was that guidance on tree species selection, underpinned by science and available to all communities tasked with delivering GI projects, would have the capacity to transform the long-term security of associated ecosystem services. Furthermore, by identifying a range of species that are suitable for different GI scenarios will give those specifying plantings the confidence to try new species, broaden the expectation of diverse plant material from nurseries and act to increase the resilience of vital GI schemes.

Therefore, the primary objective of this project was to develop a decision support tool and guidance for landscape (and allied) professionals to aid species selection of trees used in urban environments. TDAG members represent the widest possible range of stakeholders in this sector, including but not limited to, landscape architects, urban planners, local authorities, educators, private companies and those in the charitable sector.

NERC awarded funding to the project (NE/NO17773/1) that commenced in March 2016 and completed in June 2018. The application for the Landscape Institute Innovation Award has been prompted by feedback on Tree Species Selection for Green Infrastructure: A Guide for Specifiers (published by TDAG) during the first year of publication.

As researchers, Drs Hirons and Sjöman are passionate about integrating scientific evidence into practice. Therefore, the successful NERC application allowed them to translate some of their primary research and conduct further meta-analysis to systematically report evidence-based species profiles. TDAG provided an independent platform with a track record of delivering excellent guidance for those engaged with establishing trees in urban environments.

After about a year, a project evaluation took place by the funders, NERC. The following sub-set of testimonials came from their evaluation:

'Your Tree Species Guide is absolutely fantastic. An invaluable source of information. I design gardens and am often pulling my hair out trying to find specific information about particular a particular tree. … so your guide has been exactly what I needed!' (Landscape Architect/Garden Designer, UK)

'I have been using the guide as additional reference for developers and consultants when discussing the surface water management of sites particularly in relation to SuDS. We also refer to it on our Flood and Water Management website. I believe it to be a very useful resource and as a Landscape Architect find it very helpful as well as easy to use.' (Landscape Architect, UK)

'I am a chartered landscape architect and I have found your Tree Species Guide invaluable especially in challenging situations such as paved areas and above podiums.' (Landscape Architect, UK)

'I'd like to say how excellent the guide is. It's helped me decide on species for many of my projects this year. It is now my go-to source for species selection. It's easy to use and very clear.' (Manager of Tree Planting Charity)

'Together with the publication, the accompanying dataset is an essential data source for our participatory urban greening app (Wild Streets) - it forms the basis for all other data collected for our project.'

'Evidence-based approaches are critically lacking when specifying trees for urban forests. Given that the guide is based on ecological principles of adaptation, as well as cutting edge research on stress responses of tree species, the guide has given us confidence in the recommendations we are making to our stakeholders.' (Researcher, Canada)

'I and my colleagues have found the guide useful especially when dealing with some of the major developments within the city. You may like to know that we are providing a link to the tree selection guide in the Trees and Landscape section of a new design guide for planning and development in the city – this guide is set to replace a number of SDPs and SPGs.' (Principal Arboriculturist, UK Local Authority)

'The guide has been very useful and I refer to it regularly. It is particularly helpful with regard to drought and waterlogging tolerance and likely suitability for SuDS applications. I receive large numbers of consultations on landscaping schemes as part of developments and the guide has helped inform my decision making and response to consultation.' (Tree Officer, Wales)

'I’ve found the tree selector guide really helpful. The interesting thing about it is that it brings up a wider variety of species for particular environments than you might get if you only looked at what your preferential suppliers can provide – so it’s a learning tool too. … I’m pretty sure the guide will become a tool that no self-respecting tree professional can do without!' (Arboricultural Officer, England)

'We use the TDAG guide on almost a weekly basis to check selections of species and genera that are shown on landscape plans. Not only have we found it useful for checking selections, it also provides sufficient detail to challenge selections, where appropriate. I have forwarded the link to a number of landscape practices and am waiting for an improvement in plant selection!' (Planner, UK)

'Every group of students who have been shown this guide have verbally responded with amazement at the generous production of this guide, as well as its quality and usefulness. From my point of view, this is a top quality, generous and invaluable tool that can be used to help inspire people to plant trees that will stand the test of time. It can be tricky to inspire people to plant, but when the right tools become available that support confidence, provide clarity and a higher level of surety as well as making planning easier, then it takes it to the next level.' (Educator, UK)

These testimonies demonstrate the clear value of the Tree Species Selection for Green Infrastructure guidance (and associated data) to a wide range of landscape professionals both in the UK and internationally. The guide has also been referred to in the Garden Design Journal (July 2018) and The Telegraph (April 6th 2019). Around 10,000 unique visitors have visited the webpage associated with the project on the TDAG website and the recorded lecture supporting the dissemination has been viewed over 1000 times.

This project meets the criteria for judging as it combines original research on plant traits (for example, leaf turgor loss point and stem water potential at 50% hydraulic conductivity), a meta-analysis of plant literature, supporting commentary and effective graphic design to create a tool that can be readily used in day-to-day landscape practices. The project combines research with guidance and has already been shown to influence tree selection practices both nationally and internationally (e.g. Canada, Sweden and The Netherlands). It helps drive the use of science in the landscape and provides an evidence base to support tree selection decisions. The NERC evaluator of the project said this:

'It’s an absolutely first-class exemplar of effective, user-focussed translation of high-quality research in to effective, user-friendly resources with tangible impact, and one that should, in my view, be held out to the NERC research community as a gold-standard project.'