What plant, where? A talk by Professor Michelle Leishman

By Pip Gibian


Professor M Leishman

At the Parramatta and Hills February meeting, the speaker was Prof. Michelle Leishman from the School of Biological Sciences at Macquarie University. As well as being a botanist, Michelle has extensive knowledge of climate change, particularly its effects on plants and the urban environment. She started her talk by reiterating some of the irrefutable facts about climate change, illustrated with graphs. We know that the average temperature of our city is rising, and that average rainfall is falling, particularly in our far western suburbs. What can we do now to ensure our suburbs remain liveable despite these facts? It is now proven that on hot Summer days, leafy green suburbs remain cooler than those with little vegetation and open parklands. Aerial photos with heat-sensitive cameras clearly demonstrate this. To counteract climate change we need to increase areas of vegetation between our buildings and expand current green spaces. As housing blocks become smaller and houses larger, there is little space left for trees or any living plants.  Planning laws should change to reflect the need for increased green space in the future. Tests show that trees reduce temperatures more than green grass, by providing shade. As well as lowering summer temperatures, trees help combat pollution, reduce carbon dioxide in the atmosphere, provide habitat for birds and other animals and have beneficial physical and psychological effects on the human inhabitants. This latter fact was clearly demonstrated during COVID lockdowns. 

These factors lead to difficult decisions about what to plant to increase urban vegetation. Damage to old established trees has already been seen during heat waves, with leaf burn and even plant death. What we previously planted as street and park trees may no longer cope with increasing climate change. The need for evidence-based decisions has triggered the WHICH PLANT WHERE project. For about five years, Michelle has been heavily involved with a group of researchers, studying and testing a large number of native plant species, looking for resistance to high temperatures and low water availability. The results have lead to the development of the WHICH PLANT WHERE website, which is to be launched in March or April 2022. The team has incorporated test results with facts about the occurrence, natural habitat, rainfall and usual growing conditions in the wild of a very large number of native plants. The collated information is being used to recommend which species to plant in a certain area. Some further specifics were added, including a description, size and shape, whether the plant has poisonous fruit, or is likely to drop large limbs. 

In the WHICH PLANT WHERE website, you can enter a postcode and be given a large list of appropriate plants. Your search can be narrowed down by adding further requirements, eg asking for a shrub or tree of a specific size, and choosing whether it is for a home garden or a public park. The listed plants include further information and a photo. The results have been further divided into how hardy a species is likely to be under future conditions. This is done with a “traffic light” coding, green for good, orange for not as good and red for not likely to do well. This coding has three time zones, namely now, in a few years, and in many years. Some recommended species will be designated “green” now, but may in the long-term be in the “red” category, as climate change worsens. The website covers the whole of Australia, suburban and rural, including all postcodes. Of course, conditions can vary in a suburb and also in a home garden, so the website does have limitations. However, this will be the only reference available for information which considers the effects of climate change on the growth of a native plant.

You can read more about the WHICH PLANT WHERE project, and access the search once it launches at their website: whichplantwhere.com.au 

Story by Pip Gibian, member of Parramatta and Hills group of the Australian Plant Society.