Biogeographic status, climate-origin and functional traits predict heat tolerance of urban trees under climate warming

Source abstract

ABSTRACT Urbanization together with climate warming pose important threats to the survival and functioning of urban vegetation, particularly ornamental species that may fail to acclimate to new climates. We analyzed the heat tolerance of 17 urban trees in Córdoba (Spain), differing in biogeographic status(native vs. exotic), leaf habit (evergreen vs. deciduous), and bioclimatic origin (Mediterranean, (sub-)tropical, or temperate). At species level, we measured photosynthetic fluorescence at nine thermal intervals (25°C- 60°C) to obtain the critical thermal thresholds of PhotoSystem II (T crit , T 50 , and T 90 ) and linked it to climate-origin distance and leaf and wood traits. Native Mediterranean and temperate species showed the highest heat tolerance. Conversely, (sub-)tropical exotics were heat-sensitive—especially those with greater climatic displacement relative to the native range, exhibiting earlier PSII damage (T crit ) and sharper functional decline. Higher heat tolerance correlated positively with conservative structural traits, such as greater wood density, leaf mass per area and leaf thickness, all of which were highest in native Mediterranean species, whereas leaf habit (evergreen vs. deciduous) had no effect. Our study suggests that integrating biogeographic and bioclimatic origins with thermal thresholds can provide valuable information for urban tree selection and the development of more resilient green infrastructure under rising temperatures.