Comment on: “Mapping the climate risk to urban forests at city scale” by Esperon-Rodriguez et al.

With the bulk of the global population now living in cities, creating a cool, green refuge through extensive urban forests is a priority. However, we are concerned that tree species currently growing in our cities may not tolerate future climates. Esperon-Rodriguez et al. (2024) recently presented an estimate of ‘climate risk’ for a given tree species in a given location using a climate safety margin, based on the difference between the current climate of that city and the realized climate niche of that tree species globally. We attempted to validate this method by relating safety margin estimates with hydraulic vulnerability, a key plant functional trait linked to tree species drought tolerance. However, we found no relationship and therefore caution against the use of climate-based, safety margin methods of assessing urban tree species suitability or climate risk without further context. To develop a robust method of validation, we suggest greater focus on establishing urban forest inventory and tree health data in future climate analogue cities.