The influence of climate and drought on urban tree growth in southeast Australia and the implications for future growth under climate change

The recent decline in the health of the City of Melbourne's deciduous tree species to a recent drought event has led to concerns about the vulnerability of the city's trees to future climate change. Understanding the response of tree growth to past climate is critical for determining the likely impacts of climate change on future growth and can provide insights into the suitability of current species to future climates. We used dendrochronogical approaches to determine the relationships between climate and tree radial growth for common deciduous tree species in Melbourne's urban forest. Chronologies were successfully developed for Quercus robur, Ulmus procera, Ulmus L. and Platanus acerifolia with all found to be sensitive to past climatic variability. All four species showed radial growth in a given year was negatively impacted by arid conditions in the previous autumn and arid conditions in the spring orearly summer of that year. Interspecific differences in climate – growth relationships, consistent with xylem anatomy trait differences (ring vs. diffuse porous), were observed. Successive years of drought had a significant negative influence on radial tree growth. Future climate change scenario testing suggested that a shift towards a warmer, drier climate would exacerbate declines in radial growth, and thereby health, highlighting that the studied species are vulnerable to climate change. From a planning perspective, a balance between (a) conserving these vulnerable tree species through proactive management; and, (b) planting more drought and heat tolerant species is likely the best approach towards adapting Melbourne's urban forest to climate change.