old-growth

The compound "old-growth" is a modern ecological term formed transparently from two native English elements. "Old" descends from the Proto-Germanic aldaz, carrying the core sense of "grown, adult, ancient," which perfectly describes the temporal aspect of these forests. "Growth" derives from the Proto-Germanic grōaną, meaning "to grow, to green," with the suffix -th forming abstract nouns of state or result, as in "strength" or "width." The compound's logic is entirely literal: it denotes plant life (growth) that has attained great age (old), specifically referring to ancient, ecologically mature forests characterized by large living trees, multi-layered canopies, and abundant decaying wood. This term emerged in the late 19th to early 20th century as forestry and conservation movements began to distinguish these pristine ecosystems from younger, managed woodlands.

Structure: old (aged) + growth (something that has grown) - old: From Old English eald, meaning "aged, ancient, mature." Its functional role is as an adjective modifying the noun. - growth: From the Old English verb growan (to grow) + the noun-forming suffix -th. Its functional role is as the head noun, referring to the result of the process of growing.