Arctic defaunation initiated a cascade of mammal–plant interaction shifts through dispersal dynamics

Amid accelerating defaunation, it remains unclear whether the loss of large mammals can trigger ecosystem collapse and through which functional pathways. Using sedimentary ancient metagenomics, we reveal the overlooked role of large mammal defaunation in driving the collapse of the glacial mammoth-steppe. Network analyses identified rewiring of mammal interactions during the late glacial triggering cascading effects. Crucially, megafaunal-mediated long-distance seed dispersal buffered vegetation turnover during periods of rapid climate warming but weakened with consecutive losses of vital dispersal interactions leading to the steppe–tundra’s transition to open woodland in the early Holocene. Trophic interactions could not prevent turnover and became more dominant afterwards with the more stable climate. We identified resilient interactions that may support recovery, demonstrating the potential of rewilding to restore Arctic ecosystems.