The Relationship Between Grazing Pressure and Environmental Factors Drives Vegetation Fragmentation Across Global Drylands

[Data Availability Statement] The data and the R codes used in this study are available on Figshare (https://figshare.com/s/4205db542a2816e48c46).

[Aim] To evaluate how grazing pressure, a key land-use factor, interacts with climatic, vegetation, and soil variables to shape the fragmentation of perennial vegetation across drylands globally.

[Location] 171 plots across 25 countries on six continents.

[Time Period] Field data: 2016–2019.

[Major Taxa Studied] Perennial grasses, shrubs, and woody plants.

[Methods] We conducted a standardised field survey across 171 45 m × 45 m plots to assess grazing pressure, vegetation, and soil properties. Vegetation fragmentation was quantified using three patch-based metrics derived from high-resolution satellite images. Linear mixed-effects models were used to relate fragmentation to climatic, vegetation, and soil variables. Predictor importance was assessed through multi-model inference and validated using a random forest approach.

[Results] Vegetation fragmentation increased with aridity, and this effect was 4.7 times stronger under high grazing pressure than under low pressure. The most influential interactions involved grazing pressure with soil amelioration (49.7% importance) and with vegetation cover (44.6%). Soil amelioration—measured as the enrichment of soil organic carbon beneath vegetation—reduced fragmentation, especially under high grazing pressure. In contrast, the ability of vegetation cover to sustain large patches diminished as grazing intensity increased. Soil amelioration was strongly linked to the proportion of facilitated plant species (p < 0.01), whereas soil organic carbon alone—beneath vegetation (p = 0.37) or in bare areas (p = 0.94)—was not significantly related.

[Main Conclusions] Grazing pressure and aridity interact to intensify vegetation fragmentation, potentially accelerating land degradation in drylands under future climate and land-use scenarios. Mitigating this fragmentation requires not only enhancing vegetation cover but also promoting plant–soil facilitation processes, especially under high grazing pressure. These findings underscore the critical role of plant-driven soil amelioration in maintaining ecosystem structure and resilience across global drylands.

We thank M. Dacal and J. M. Compañ for discussions about R codes, S. Soliveres for guiding the calculation of the percentage of facilitated species, S. Zhang for drawing the original icons used in the Figures 3 and 5, and all the members of BIODESERT network for the collection of field data. Y.Z. acknowledges support from the National Key Research and Development Program of China (2023YFF0806600), the National Natural Science Foundation of China (42307560), the Key Scientific Research Projects of Colleges and Universities in Henan Province (24A170014), the High-Level Foreign Expert Recruitment Program of Henan Province (HNGD2025025), the Key Projects of Science and Technology Research of Henan Province (232102320268), the International Science and Technology Collaboration Program of Henan Province (252102520050), and the Cultivation Programme for Young Backbone Teachers in Henan University of Technology (0008/21421292). F.T.M. acknowledges support by the European Research Council (BIODESERT project, Grant Agreement number 647038), by the King Abdullah University of Science and Technology (KAUST) and the KAUST Climate and Livability Initiative. M.B. acknowledges funding from a Ramón y Cajal fellowship from Spanish Ministry of Science (RYC2021-031797-I). H.S. is supported by a María Zambrano fellowship funded by the Ministry of Universities and European Union-Next Generation plan. E.V. is supported by the Spanish Ministry of Science, Innovation and Universities (PID2022-140398NA-I00 and CNS2024-154579).

Peer reviewed