A project undertaken at Western Sydney University, and supervised by Dr Manuel Esperon-Rodriguez.
Urban forests provide multiple environmental and socio-economic services to citizens. These include heat mitigation, biodiversity conservation and social integration. The delivery of these services, however, relies on healthy and thriving urban forests. Climate change threatens the health of urban forests and thus will impact the delivery of services. Further, urban trees face harsh environmental conditions (e.g., droughts and heatwaves) exacerbated by urban heat islands, which cause dieback and reduced tree vitality. Therefore, the long-term stability of urban forests depends on the identification of species that are resilient to climate change. For this, we need to understand how urban trees respond to environmental conditions by determining the climate sensitivity of urban tree growth and identifying vulnerable or resilient species to changes in climate.
Studies of the effect of climate change on urban trees are rare and, to date, research on climate sensitivity of urban tree growth has been conducted at the local level, limiting broad assessments of species’ responses to climate. This study evaluated urban tree growth and performance by reconstructing growth histories and developing realised climate sensitivity indices of urban trees in Australian cities distributed along temperature and precipitation climatic gradients.
Platanus acerifolia at various urban sites.
We selected a common set of 10 urban tree species -based on bioclimatic modelling of risk of climate failure- planted in seven Australian cities with contrasting climates: Adelaide (South Australia); Mandurah (Western Australia); Melbourne (Victoria)’ Mildura (Victoria); Parramatta (New South Wales, NSW)’ Penrith (NSW); and Sydney (NSW). We collected tree rings of street trees planted in these cities to determine spatial and temporal patterns of tree growth in relation to climate extremes. We found evidence of local adaptation of urban trees. For example, some species showed higher average annual growth in dry cities (e.g., Mildura) compared to wetter cities (e.g., Sydney). This was also observed when we analysed species’ recovery and resilience after drought events.
Our results suggest that temperature may play a more significant role at determining annual growth for some species compared to precipitation. This finding could be related to the use of irrigation in cities during periods of lower water availability or severe climate stress.
Our results can help guide species selection to maximise services delivered by urban trees under future climates and minimise environmental and socio-economic losses to governments and citizens.