Intermediate, rather than Isohydric or Anisohydric, Species were More Resilient to an Extreme Heatwave in a Common Garden in Sydney

In a Sydney common garden after a three-day extreme heatwave with temperatures exceeding 40°C, seven tree and shrub species showed extensive crown dieback exceeding 40%.

• Why it matters: Urban forests face climate extremes, but it is unclear which species traits explain why some species fail while others persist, limiting resilient species selection.
• What they did: Over about five years, growth and survival were monitored for 48 urban tree and shrub species, and crown dieback was quantified after the heatwave; 15 functional traits were measured for 30 species.
• The result: Plant functional traits linked to heat and drought tolerance explained 20–30% of variation in crown dieback, while survival was not related to any single trait, making crown dieback a more sensitive early indicator of cumulative thermal stress.