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Abstract

Definitions of what constitutes an ‘old-growth’ forest are manifold and often ambiguous. This chapter starts with a review of existing concepts and critically examines their usefulness in the context of ecosystem functioning and forest conservation. Using examples from all major forests biomes, the merits and limitations of structural, successional and biogeochemical definitions are discussed. Second, the plethora of related terms (primary, pristine, intact, virgin, etc.) is screened. A semantic meta-analysis based on entries in the Web of Science reveals that the usage of terminology in the literature depends strongly on the time period, discipline, and scientific community. Third, a model is presented that combines literature data on natural disturbance intervals and maximum longevities of pioneer trees to estimate the landscape fraction covered by old-growth forests (using the successional definition) without human impact. This fraction varies and is about 90%, 50% and 20% in tropical, temperate and boreal forest, respectively. Finally, detection and mapping methods of old-growth forests are discussed and a pragmatic approach to defining old-growth forest is advocated.