By Samantha Newton, Program Co-Manager, Which Plant Where
Which Plant Where is a web-based plant selection tool that helps users find the right plants for the right location. It is the world’s first plant database to use powerful climatic modelling for future climate scenarios to guide plant selection and it is an essential tool for urban green space managers in local government and residents to find the right plants that will survive and thrive both now and decades into the future.
The impact of climate change on urban forests
Our climate is changing. The planet is getting hotter and so are our cities; and seemingly small changes have big effects. Although the mean
Prof Michelle Leishman and Dr Alessandro Ossola monitoring plant growth and health.
average temperature has only changed by 1.4°C so far, this has already had a considerable impact on plants and animals around the world.
Current modelling indicates the mean annual temperature may increase by a further 3-4°C by the end of this century. Rainfall patterns are also changing, and this poses a challenge for our urban environments. How will our parklands and street trees cope? Trees provide a multitude of ecosystem services for our cities and their inhabitants, from mitigating extreme heat to supporting biodiversity and improved human health and wellbeing.
To ensure these services are maximised, cities require healthy, functioning and diverse urban forests. Increased temperatures and shifts in rainfall patterns due to climate change are putting pressure on our existing urban forest, and some species that have succeeded in the past may fail in the future. It is vital that we put resources towards maintaining and monitoring our urban forests to ensure they are resilient and can adapt to climate change.
The frequency of these extreme heat days is increasing as the average temperature increases, leading to more record heat days. We’ve already seen in recent years heatwaves with several days of temperatures over 40°C in Western Sydney for example, and the impact that has had in tree loss in the following weeks and months (Tabassum et al, 2021).
Tree mortality from these heat events has an environmental cost (microclimate and animal habitat) and an economic cost (tree replacement). The study conducted on the effects of the 2019/2020 heatwaves in Western Sydney (Tabassum et al, 2021) found that 10 per cent of the 5,500 trees surveyed had some damage to the canopy.
The cost of replacing these trees was estimated to be from $500K to over $1 million, depending on the size and species selected as replacements. Selecting the right species at the planning stage is a critical part to ensuring the best return on investment in urban forests. In short – we need to know which species will be resilient to climate change and will be able to survive and thrive under future climate scenarios. This is the question that Which Plant Where set out to answer.
Development of the which plant where database
To discover which plants will cope with a changing climate, we conducted a range of different research experiments over a five-year period.
Firstly, researchers used computer models to map the climate suitability throughout Australia of 2,500 species. Secondly, we established 12 living labs across Australia to test how a subset of species performed in local conditions. Thirdly, we exposed 113 different plant species to increased temperature and drying conditions to assess their environmental tolerances and to observe their stress responses.
Our primary goal was to assess the suitability of a whole range of plants that are commonly grown in urban environments and to look at how they may respond to climate change. Another aim was to identify plant species that are currently under-utilised but could be suitable to urban environments in a future climate.
The results of these experiments have been developed into an online plant selector tool that will enable climate plant selection for three future climate scenarios: 2030, 2050 and 2070. We want to ensure that our urban landscapes are liveable, resilient and healthy places for us to live and grow.
Sudden death of plants following summer heatwave.
How it works
Which Plant Where is the first tool of its kind. It not only recommends plants for a particular location, it also provides information on the future suitability of that plant in that location under future climate scenarios. This is important to guide investment in planting decisions, especially for street trees and parklands.
Users can search the Which Plant Where online database by plant name, postcode or suburb to find out more about which plants are suitable for their location. For each species there is information on habit and attributes, preferred growing conditions and tolerances.
A search by location will bring up a list of all plants in the database that are suitable for the climate of that location. There are several filters that can be used, relating to plant form and growing conditions. For example, users can search for groundcovers for a shady garden in Glebe, Sydney, or small street trees for Keilor, Melbourne.
Each species displays a summary of its suitability for the postcode of your green space location. The suitability of that species in your chosen location under the three time periods (2030, 2050, 2070) is colour-coded for ease of use. Subscribers also have access to detailed climate suitability maps for each species for the three time periods.
The palette tool is another unique feature. For growers, nurseries, landscape architects and urban greening professionals, creating a palette of suitable plants, and sharing this with colleagues and clients, is a simple way to validate and streamline your greening projects. Once you build your palette you can calculate values for planting diversity, biodiversity, carbon value and shade value.
Dr Muhammad Masood measuring photosynthesis on Hakea laurina.
The science behind the tool
The research that has contributed to the Which Plant Where project was divided into three modules, each investigating unique challenges and opportunities associated with creating and maintaining urban green spaces. Findings from all three modules have been instrumental for the development of the Which Plant Where interactive tool.
Module 1: species attributes and climatic tolerances
Module 1 focused on the creation of maps for each species in the tool to identify areas suitable for the species to grow in, under both current and future climates. These maps were created using state of the art modelling techniques which utilised species occurrence records and climatic data to extrapolate the most suitable growing regions for species under a variety of climate scenarios.
To complement the maps, a database of useful attributes such as tolerances, size, form and biodiversity benefits was created to help users select the most appropriate species for their urban green spaces.
Module 2: success and failures
Module 2 related success and failures of urban street tree plantings with local conditions such as climate as well as planting and management techniques to help improve the success of our urban forests. Measurements of plant performance across Local Government Areas with contrasting climates were made to assess plant species’ plasticity to growing conditions.
A series of urban plantings called ‘living labs’ of different complexities (e.g. single/few species vs mixed communities) were set up in different states across the country to understand biodiversity, shading and cooling co-benefits provided by urban green spaces. The outcome of these studies is a wide range of resources and best-practice guidelines on all aspects of urban greening that are available as part of the Which Plant Where online plant selector.
Module 3: heat and drought tolerant species
Module 3 subjected a sample of 113 species and cultivars to controlled heatwave and drought conditions in state-of-the-art glasshouses to help understand the abilities of different plant species to withstand extreme conditions. These study species were a mixture of well-known and commonly found horticultural species as well as opportunity species that may be well suited to extreme conditions.
Traits such as wilting point, leaf critical temperature, leaf thickness and leaf area were measured to help rate species by their heat and drought tolerance.
A critical resource
Which Plant Where was developed by Macquarie University, Western Sydney University and Hort Innovation to provide growers, government, landscape architects and urban greening professionals with integrated tools and resources to enable climate ready decision making and to develop resilient green spaces of the future.
Visitors to the site can search and view over 2,600 species with information on their climate suitability for particular locations, as well as their traits, environmental tolerance and growing requirements. Subscribers can also access climate modelling, mapping, co-benefits calculator and palette creator free.
This article is a contribution of the Which Plant Where project, funded by the Green Cities Fund, as part of the Hort Frontiers Strategic Partnership Initiative, with co-investment from Macquarie University, Western Sydney University, the New South Wales Department of Planning and Environment, and funds from the Australian Government.
Visitors to the Which Plant Where site can search and view over 2,600 species, with information on their climate suitability for particular locations as well as their traits, environmental tolerance and growing requirements. Subscribers can also access climate modelling, mapping, a co-benefits calculator and palette creator free! For more information, and to use Which Plant Where, visit www.whichplantwhere.com.au
