old-growth forest

Old-growth European beech forest in Biogradska Gora National Park, Montenegro An old-growth forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Nations defines primary forests as naturally regenerated forests of native tree species where there are no clearly visible indications of human activity and the ecological processes are not significantly disturbed. One-third (34%) of the world's forests are primary forests. Old-growth features include diverse tree-related structures that provide diverse wildlife habitats that increases the biodiversity of the forested ecosystem. Virgin or first-growth forests are old-growth forests that have never been logged. The concept of diverse tree structure includes multi-layered canopies and canopy gaps, greatly varying tree heights and diameters, and diverse tree species and classes and sizes of woody debris. Cool temperate rainforest in Tasmania, Australia As of 2025, the world has 11.3 million square kilometers (4.4 million square miles) of primary forest remaining. Brazil, Canada, and Russia have 62% of the world's primary forest. The net area of primary forest has decreased by 1.1 million square kilometers (~424,000 square miles) since 1990, but the rate of loss more than halved in 2010–2020 compared with the previous decade.

Old-growth forests are valuable for economic reasons and for the ecosystem services they provide. This can be a point of contention when some in the logging industry desire to harvest valuable timber from the forests, destroying the forests in the process, to generate short-term profits, while environmentalists seek to preserve the forests in their pristine state for benefits such as water purification, flood control, weather stability, maintenance of biodiversity, and nutrient cycling. Moreover, old-growth forests are more efficient at sequestering carbon than newly planted forests and fast-growing timber plantations, thus preserving these forests is vital to climate change mitigation.