Position within the climatic niche explains tree vulnerability to drought mortality

An international team led by Enric Batllori, a researcher at the l’Institut de Recerca de la Biodiversitat (IRBio) de la Universitat de Barcelona, has analyzed how the distance of tree populations to the edge of the climatic niche influences their vulnerability to extreme episodes of drought and heat. The results, recently published in the journal Global Ecology and Biogeography, provide a new perspective on global patterns of tree mortality and the implications of climate change for forest ecosystems. The magnitude of climate anomalies, the cumulative effects of drought, the physiological limits of species, and the geometry of the climatic niche emerge as key factors for understanding tree mortality on a global scale, which is affecting even drought-resistant species.

A global analysis of tree mortality

The research analyzes a global database of observations of tree mortality associated with hotter droughts, which includes 44 species of angiosperm and gymnosperm trees. This database has allowed us to examine mortality in relation to the climatic niche of each species, defined based on the climatic conditions associated with its global geographic distribution. The position within the niche of the sites affected by mortality has been compared with mortality patterns, assuming a randomly distributed mortality across the climatic niche. The study also incorporates data on hydraulic traits of the species to analyze how plant physiology is related to the position within the climatic niche and the intensity of climatic anomalies.

64.3% of mortality episodes occurred closer to the edge than to the center of the climatic niche. The analysis, however, also reveals that when historical climatic conditions are considered, both core and marginal populations in the niche suffered mortality.

In angiosperms, the intensity of climatic anomalies, that is, the difference between the historical climatic conditions of the populations and the conditions during the mortality episodes, correlates with the drought tolerance of the species. In gymnosperms, marginal populations are particularly vulnerable, and the influence of other factors such as the cumulative effects of drought or thermal stress would explain the mortality.

Ecological implications

This study highlights that the vulnerability of forests is widespread, affecting both core and marginal populations even in drought-tolerant species. These results have important implications for the adaptive management of forest ecosystems, as they indicate that no area is immune to the effects of climate change if extreme conditions persist or intensify.

The research was carried out in collaboration with researchers from the University of Florida, the University of Stirling, CREAF, the University of New Mexico and the Autonomous University of Barcelona. The project was funded by the Ministry of Science, Innovation and Universities (PID2020-115264RB-I0) and the Generalitat de Catalunya (AGAUR 2021 SGR 00849).

Article :
Enric Batllori et al. "Effects of Niche Marginality on Hotter-Drought Tree Mortality in Angiosperms and Gymnosperms" Global Ecology and Biogeography, 2025; 34:e70128 https://doi.org/10.1111/geb.70128