Primary, old-growth forests — structurally complex, carbon-dense, and irreplaceable on any human timescale once lost.
Old-growth (primary) forests are naturally regenerated stands, generally over a century old, that have experienced minimal human disturbance. They're defined structurally as much as by age: large living and dead trees, multilayered canopies of varied heights, and accumulated deadwood in different stages of decay — complexity that takes centuries to develop and cannot be recreated by planting.
An estimated 4.14 billion hectares of forest remain globally, covering 32% of the world's land area — but only about 34% of that is primary, old-growth forest.
Source: FAO Global Forest Resources Assessment, 2025This is the central reason old-growth loss is treated differently from forest loss in general: a clear-cut plantation forest can regrow in decades, but the ecological complexity of an old-growth stand — the deadwood, the fungal networks, the canopy structure — takes centuries to reform, if it reforms at all under current climate conditions. Replanting is not equivalent to restoration on any timescale that matters for the species depending on it now.
The remaining share of primary forest is unevenly distributed and shrinking. Because old-growth stands cannot be quickly replaced, their loss is effectively permanent within any relevant planning horizon — which is why tracking primary forest extent, rather than total tree cover, is the more meaningful long-term indicator.
Global estimates of remaining primary forest area are well supported by satellite and national inventory data, though definitions of "primary" and "old-growth" vary somewhat between countries and datasets, which affects cross-country comparisons. Carbon storage figures are strong at the stand level but harder to generalize globally due to regional differences in tree species, climate and soil.