Old-growth forest

Combined, three countries (Brazil, Canada, and Russia) host more than half (61 percent) of the world's primary forest.

In British Columbia, Canada, old growth is defined as 120 to 140 years of age in the interior of the province where fire is a frequent and natural occurrence.

[10] In Australia, eucalypt trees rarely exceed 350 years of age due to frequent fire disturbance.

[12] In the boreal forest of Canada, catastrophic disturbances like wildfires minimize opportunities for major accumulations of dead and downed woody material and other structural legacies associated with old growth conditions.

[13] Typical characteristics of old-growth forest include the presence of older trees, minimal signs of human disturbance, mixed-age stands, presence of canopy openings due to tree falls, pit-and-mound topography, down wood in various stages of decay, standing snags (dead trees), multilayered canopies, intact soils, a healthy fungal ecosystem, and presence of indicator species.

A climax stand that is uniformly aged becomes senescent and degrades within a relatively short time to result in a new cycle of forest succession.

[19] Old-growth forests are unique, usually having multiple horizontal layers of vegetation representing a variety of tree species, age classes, and sizes, as well as "pit and mound" soil shape with well-established fungal nets.

In some ecosystems such as the temperate rain forest of the North American Pacific coast, fallen timber may become nurse logs, providing a substrate for seedling trees.

Some herbaceous plants in northern hardwood forests must have thick duff layers (which are part of the soil profile).

For example, an old boreal forest may contain some large aspen trees, which may die and be replaced by smaller balsam fir or black spruce.

However, in some forest ecosystems, this can lead to decisions regarding the preservation of unique stands or attributes that will disappear over the next few decades because of natural succession processes.

[4] Common cultural definitions and common denominators regarding what comprises old-growth forest, and the variables that define, constitute and embody old-growth forests include: Additionally, in mountainous, temperate landscapes (such as Western North America), and specifically in areas of high-quality soil and a moist, relatively mild climate, some old-growth trees have attained notable height and girth (DBH: diameter at breast height), accompanied by notable biodiversity in terms of the species supported.

The debate over old-growth definitions has been inextricably linked with a complex range of social perceptions about wilderness preservation, biodiversity, aesthetics, and spirituality, as well as economic or industrial values.

[13][26] In logging terms, old-growth stands are past the economic optimum for harvesting—usually between 80 and 150 years, depending on the species.

Old-growth forests were often given harvesting priority[clarification needed] because they had the most commercially valuable timber, they were considered to be at greater risk of deterioration through root rot or insect infestation, and they occupied land that could be used for more productive second-growth stands.

These services include making breathable air, making pure water, carbon storage, regeneration of nutrients, maintenance of soils, pest control by insectivorous bats and insects, micro- and macro-climate control, and the storage of a wide variety of genes.

[43][44] A 2019 study projected that old-growth forests in Southeast Asia, the majority of which are in Indonesia and Malaysia, are able to sequester carbon or be a net emitter of greenhouse gases based on deforestation scenarios over the subsequent decades.

As the effects of global warming grow more substantial, the ability of old-growth forests to sequester carbon is affected.

Climate change showed an impact on the mortality of some dominant tree species, as observed in the Korean pine.

According to the World Resources Institute, as of January 2009, only 21% of the original old-growth forests that once existed on Earth are remaining.

[50] The large trees in old-growth forests are economically valuable, and have been subject to aggressive logging throughout the world.

From certain forestry perspectives, fully maintaining an old-growth forest is seen as extremely economically unproductive, as timber can only be collected from falling trees, and also potentially damaging to nearby managed groves by creating environments conducive to root rot.

Ten thousand hectares of tall-eucalypt RFA old-growth forest have been lost since 1996, predominantly as a result of industrial logging operations.

[52] Recent logging attempts in the Upper Florentine Valley have sparked a series of protests and media attention over the arrests that have taken place in this area.

Additionally, Gunns Limited, the primary forestry contractor in Tasmania, has been under recent criticism by political and environmental groups over its practice of woodchipping timber harvested from old-growth forests.

[55] This coarse filter approach to biodiversity conservation recognizes ecological processes and provides for a dynamic distribution of old growth across the landscape.

A small proportion of old-growth forests also exist in South-West Australia and are protected by federal laws from logging, which has not occurred there for more than 20 years.

[57] In 2006, Greenpeace identified that the world's remaining intact forest landscapes are distributed among the continents as follows:[58] This article incorporates text from a free content work.