Urban forest responses to climate change: A case study in Canberra

Climate change is affecting tree growth and vitality, including potentially accelerating growth rate or exacerbating drought stress. Physiological and phenological changes of a tree may eventually disrupt the beneficial effects that it provides to the ecosystem (‘ecosystem services’). This research examined how the urban forest in Canberra has responded to climate change in the last 20 years. A road survey was conducted to document the growth of commonly planted trees across the city, which was then compared with a tree growth model (DISMUT) that reflected growth around the turn of the 20th century. The results suggest that urban trees have various mechanisms whereby they respond to climate change, and these mechanisms are partially based on tolerance to heat and drought, leaf phenology and age. In general, trees with high tolerance, evergreen leaves and young age grow faster and bigger than expected, while drought-intolerant, deciduous and older trees are more likely to exhibit restricted size. Water deficit is one of the main threats to tree vitality in Canberra. Species alleviate water deficit stress by forming dead branches or showing crown dieback. However, these symptoms undermine the ecosystem services that urban trees can provide. Urban forest management should be modified to adapt to the changes in trees, including accelerated growth and severe stress symptoms. DISMUT models can be updated to incorporate the systematic deviations in growth to improve predictions and scenario planning.