Vegetation patterning can both impede and trigger critical transitions from savanna to grassland

Environmental Research Letters, vol. 20, pp. 094052

Abstract

Abstract Tree-grass coexistence is a defining feature of savanna ecosystems, which play an important role in supporting biodiversity and human populations worldwide. While recent advances have clarified many of the underlying processes, how these mechanisms interact to shape ecosystem dynamics under environmental stress is not yet understood. Here, we present and analyse a minimalistic spatially extended model of tree-grass dynamics in dry savannas. We incorporate tree facilitation of grasses through shading and grass competing with trees for water, both varying with tree life stage. Our model shows that these mechanisms lead to grass-tree coexistence and bistability between savanna and grassland states. Moreover, the model predicts vegetation patterns consisting of trees and grasses, particularly under harsh environmental conditions, which can persist in situations where a non-spatial version of the model predicts ecosystem collapse from savanna to grassland instead (a phenomenon called ‘Turing-evades-tipping’). Additionally, we identify a novel ‘Turing-triggers-tipping’ mechanism, where unstable pattern formation drives tipping events that are overlooked when spatial dynamics are not included. These transient patterns act as early warning signals for ecosystem transitions, offering a critical window for intervention. Further theoretical and empirical research is needed to determine when spatial patterns prevent tipping or drive collapse.

Authors 5

1. Jelle van der Voort Aachen Mathematical Institute

   Leiden University

   Affiliation as printed

   Mathematical Institute, Leiden University, 2300 RA Leiden, The Netherlands

2. Mara Baudena

   Institute of Atmospheric Sciences and Climate · National Research Council

   Affiliation as printed

   National Biodiversity Future Center (NBFC), 90133 Palermo, Italy

   National Research Council, Institute of Atmospheric Sciences and Climate (CNR-ISAC), 10133 Torino, Italy

3. E. Meroni

   Ben-Gurion University of the Negev

   Affiliation as printed

   Physics Department, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel

   The Swiss Institute for Dryland Environmental and Energy Research, BIDR, Ben-Gurion University of the Negev, Midreshet Ben-Gurion 8499000, Israel

4. Max Rietkerk

   Utrecht University

   Affiliation as printed

   Copernicus Institute of Sustainable Development, Section Environmental Sciences, Utrecht University, Utrecht, The Netherlands

5. Arjen Doelman Aachen Mathematical Institute

   Leiden University

   Affiliation as printed

   Mathematical Institute, Leiden University, 2300 RA Leiden, The Netherlands