Inclusions and exclusions in treeline definitions

Abstract Körner and Hoch's (2023) definition of “treeline” to include only forest edges that are arctic or alpine, globally distributed and thermally limited is reconsidered for the alpine, with attention to the alpine treeline ecotone. They characterize the alpine treeline and the ecotone as a single phenomenon at a single fundamental niche limit, with all other montane forest edges at realized niche limits. The framework restricts treeline and the treeline ecotone to narrow but interesting ecophysiological questions but leaves other fundamentally limited edges, those in disequilibrium with a changed temperature regime, and the extensive zone of krummholz and tree‐species seedlings now often referred to as the treeline ecotone, without terminology. Recognizing other fundamental niche limited edges as treelines, if not alpine, and defining “alpine treeline” as a zone or line within the broader “alpine treeline ecotone”, are proposed to promote synergies in research in these related systems.