Which ecological change is least reversible?
Extinction is effectively irreversible because it eliminates the last living members of a species and therefore its unique evolutionary lineage and gene pool. Once no viable individuals or preserved reproductive material remain, ordinary ecological processes cannot recreate that species. Evolution might eventually produce organisms with similar traits, but not the same historical lineage. Succession can reverse or restart after disturbance, invasion can sometimes be controlled or eradicated, and evolutionary change may be altered by future selection or gene flow, though none is always easily r
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20