Climate-driven functional asynchrony accelerates shrub encroachment in the central plateau of México

Shrub encroachment is reshaping dryland ecosystems worldwide, yet its long-term functional implications remain insufficiently understood. This study examines the spatiotemporal dynamics and climate sensitivity of a semiarid ecotone in the Central Mexican Plateau from 1986 to 2020. Over the 34-year period, the landscape exhibited a directional structural shift, characterized by a net expansion of shrublands (+18.2%) and a severe contraction of native grasslands (declining more than 50%). Multi-decadal greening slopes did not differ significantly between persistent grasslands and shrublands. Climate sensitivity analysis revealed contrasting responses during the most recent decade (2010–2020): grasslands were negatively associated with temperature in the last decade, whereas shrublands exhibited a negative relationship in the first and the last decade (p < 0.05). While annual-scale analyses suggested a weakening of hydroclimatic control, cross-correlation revealed that interannual memory masks immediate climate sensitivity in shrublands at lag = 0 (precipitation and temperature). Under dry-warm climate extremes, grasslands displayed acute thermal vulnerability, whereas shrublands maintained functional resilience, likely by leveraging subsurface moisture storage in the unsaturated vadose zone. Together, these findings demonstrate an ongoing transition toward a woody-dominated alternative state driven by functional asynchrony and ecohydrological buffering, highlighting that evaluating dryland degradation requires integrating spatial persistence metrics with multi-scale functional analyses.