The Role of Connectivity in Understanding Grassland-Shrubland Regime Shifts: Impacts of Aridity, Grazing and Wind Dynamics

Regime shifts from grassland to shrubland are a key feature of dryland degradation, yet the role of connectivity in understanding these transitions remains poorly quantified. Using a connectivity-based ecogeomorphic model with climate endmembers representing dry (Southwest Arizona) and wet (Northern New Mexico) conditions, we simulate vegetation change from 1895–2022. Under near-natural grazing (1 g/m²/year), grass biomass remained stable with negligible shrub presence. Moderate grazing (30%) initiated shrub emergence by 1930 in dry climates, while wetter systems largely retained grass (> 20 g/m²). High grazing (60%) drove abrupt, near-total grass loss, with shrub biomass exceeding 40 g/m² in dry and ~ 60 g/m² in wet climates. Connectivity metrics strongly predicted shrub expansion, with structural and functional connectivity of water and nitrogen correlating up to 0.96 with shrub biomass, providing early-warning signals 4–16 years before vegetation shifts. By identifying connectivity-based indicators, our study advances predictive understanding of grass-shrub regime shifts and supports proactive management under intensifying global change.