Researchers from the Which Plant Where project at Western Sydney University are taking a deep look at how urban trees can adapt to drought conditions to help keep cities green in the face of a changing climate.
The study, conducted by the Hawkesbury Institute for Environment, studied five tree species within a 55 km stretch across the Greater Sydney area — Penrith, Parramatta, Inner West and Sydney — covering a climate gradient from cool, wet coastal zones to the drier, warmer inland.
“We need more specific knowledge on which species show potential to be adaptable across a range of locations and climates and which species might actually prove to be more vulnerable than expected,” lead researcher Dr. Manuel Esperon-Rodriguez said.
Nettle trees (Celtis australis), Tuckeroo (Cupaniopsis anarcardioides), Tallowwood (Eucalyptus microcorys), Watergum (Tristaniopsis laurina) and Brush box (Lophostemon confertus), also called Queensland Box, were the perfect subjects as commonplace urban trees with different origins and climate preferences.
Researchers measured leaf area, wood density, isotopic carbon and leaf turgor loss point to estimate each species’ plasticity, the ability to modify features and functions according to the climate.
The study found that cooler climate species actually showed better plasticity under warmer conditions than species originally from warmer climates with the exotic originating nettle tree as the most drought tolerant across all sites.
Leaf turgor loss point, the time it takes for a tree to wilt, turned out to be a key factor in estimating drought tolerance and plasticity as there is a significant correlation between the turgor loss point and annual rainfall and temperature across the Greater Sydney area’s climate gradient.
Dr Esperon-Rodriguez hopes that with turgor loss point as a good measuring stick, urban planners and landscapers will be able to better select long lasting trees that will both beautify urban spaces and thrive in future conditions.
“This type of research can be used to help green our towns and cities as a warming climate places greater demands on urban trees.”