Analysis of Córdoba's urban trees identifies which species best tolerate heat

The orange tree emerges as one of the most heat-vulnerable trees, according to a University of Córdoba (UCO) study that analyzed 17 tree species found in Córdoba's urban environment

Global warming is transforming ecosystems around the world. Urban trees are also affected by these changes, especially in cities like Córdoba, where summers are growing longer and more intense. These trees also play a key role in regulating urban climate through shade and evapotranspiration. But do trees keep performing this function as temperatures rise?

Taking up this question, researchers Cristina C. Bastias and Sonia Vega, at the Department of Botany, Ecology and Plant Physiology, analyzed the heat tolerance of 17 tree species found on the streets of Córdoba to see how they respond to rising temperatures. Mediterranean hackberry, carob, olive, holm oak, cork oak, ash, poplar, elm, privet, jacaranda, and orange are among the species selected, both because they are some of the most widespread in the city and because they represent a range of biogeographic origins, climatic provenances, and characteristics: native or exotic; evergreen or deciduous; and Mediterranean, subtropical, or temperate in bioclimatic origin.

"We measured how the efficiency of the photosynthetic apparatus in the leaves of these 17 species declines, using chlorophyll fluorescence. This allowed us to identify the temperature thresholds at which the photosynthetic performance of these species begins to be impaired, which could compromise their ability to 'cool their surroundings,'" explained researcher Sonia Vega.

The results show that not all urban tree species respond in the same way to high temperatures. Overall, native species from Mediterranean and temperate climates showed greater heat tolerance than exotic species of subtropical origin. However, subtropical species like orange, chinaberry, catalpa, and tipu are commonly planted in Córdoba's parks and streets, often chosen on cultural or aesthetic grounds, among others. Although one might assume at first glance that species from warm climates would cope well with Córdoba's temperatures, it is worth remembering that their climate of origin features a combination of temperature, humidity, and water availability, the latter two being scarce in southern Spanish cities such as Córdoba. As a result, these species' functioning and their role in cooling the environment could be compromised. Native Mediterranean species such as holm oak and olive were by far the most heat-tolerant compared with the other species analyzed.

What are the most heat-adapted trees like?

Greater heat tolerance correlated with structural traits that conserve resources such as water, including higher wood density, leaf mass per area, and leaf thickness, all of which are characteristic of native Mediterranean species. Leaf habit (whether a tree is evergreen or deciduous), on the other hand, was not a determining factor in greater or lesser tolerance in this study.

These results provide the keys to selecting the tree species best suited to an urban environment with rising temperatures, as is the case in Córdoba. Incorporating these criteria into urban planning can help create more resilient green infrastructure capable of coping with the rise in temperatures associated with climate change.

Reference:

Vega-Rosete, Sonia & Bastias, Cristina C. (2026). "Biogeographic status, climate-origin and functional traits predict heat tolerance of urban trees under climate warming." Urban Forestry & Urban Greening. 126. 129728. 10.1016/j.ufug.2026.129728