Old growth

Old growth
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Old_growth".

Old growth forest, also called primary forest, ancient forest, virgin forest, primeval forest, frontier forest or (in the UK) Ancient Woodland, is an area of forest that has attained great age and so exhibits unique biological features. Old growth forests typically contain large live trees, large dead trees (sometimes called "snags"), and large logs. Old growth forests usually have multiple vertical layers of vegetation representing a variety of tree species and age classes.

Redwoods in old growth forest in Muir Woods National Monument, Marin County, California.

Forest regenerated after severe disruptions, such as clear-cut or fire is often called second-growth or regeneration until a long enough time passes that the effects of the disturbance are no longer evident. Depending on the forest, this may take anywhere from a century to several millennia. Hardwood forests of the eastern United States can develop old-growth characteristics in one or two generations of trees, or 150-500 years.

Old growth forests may be home to rare species which depend on this now-rare habitat, making them ecologically significant. Biodiversity may be higher or lower in old growth forests than in second-growth forests depending on specific circumstances. Logging in old growth forests is a contentious issue in many parts of the world.

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1 Definitions
2 Characteristics
3 Importance
4 Logging
5 Locations of remaining intact forests
6 References
7 See also
8 External links

Definitions

Concepts of “old growth” vary widely and are not always easily applied or reconcilable with one another.

“Ancient Woodland” is a term used in the United Kingdom to refer specifically to woodland dating back to 1600 or before (in England and Wales), or 1750 (in Scotland). Before this, planting of new woodland was uncommon, so a wood present at these dates was likely to have developed naturally. By this definition Ancient Woodland may have had considerable artificial interference, the important characteristic being continuity of woodland on the land.

By contrast, in the US, “old growth” is often used to imply a forest has experienced little direct disruption during contemporary historical epochs and looks about as it would had Europeans not come to America. This criterion is difficult to apply, since it is often impossible to determine the history of human management (Euro-American or Native American). And, since landscapes are naturally dynamic, there can be no certainty what forests would look like now had pre-Columbian regimes been uninterrupted. While it is generally agreed that old forests defined as “old growth” have not been subject to logging, the role of natural disturbances in defining old growth is more ambiguous. Some definitions, for example, exclude recently burned forests, even where fire has been part of the natural dynamics for millennia; in other cases, such natural disturbance is incorporated in the old growth concept. However, it is often difficult to distinguish the ecological effects of natural disruption from human-caused disruption. Finally, even forests that have never experienced direct manipulation by Euro-Americans have been subjected to indirect effects in the form of invasive species, climate change, and regional modifications of ecological disturbance regimes (e.g., fire suppression).

Characteristics

Down wood decaying.

Many botanists specifically define old growth in terms of meeting several criteria, under which system forests with sufficient age and minimal disturbance are considered old growth. Typical characteristics of old-growth forest include 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), multi-layered canopies, intact soils, a healthy fungal ecosystem, and presence of indicator species.

Mixed age

The mixed age of the forest is an important criterion in ensuring that the forest is a relatively stable ecosystem in the long term. A climax stand that is uniformly-aged is a less stable ecosystem, because it becomes senescent and degrades within a relatively short time to result in a new cycle of forest succession.

Canopy openings

Openings in the forest canopy are essential in creating and maintaining mixed-age stands. Also, some herbaceous plants only become established in canopy openings but persist in a darker understory. Openings created by natural disturbance events such as wind, ice and mixed-severity fire retain much structural enrichment from dead trees, unlike openings created by logging.

Topography

The characteristic topography of old growth forest consists of pits and mounds. Mounds are caused by decaying fallen trees, and pits by the roots pulled out of the ground when trees fall due to natural causes. Pits expose humus-poor, mineral-rich soil and often collect moisture and fallen leaves soon form a thick organic layer and so able to nurture certain types of organisms, while mounds provide a place free of leaf inundation and saturation, where other types of organisms thrive.

Standing snags

Standing snags provide food sources and habitat for many types of organisms. In particular, several species of woodpecker must have standing snags available for feeding. The spotted owl is well-known for needing standing snags for nesting habitat.

Decaying ground layer

Down wood contributes carbon-rich organic matter directly to the soil, thus providing a substrate for mosses, fungi and for seedlings, and in creating microhabitats by creating relief on the forest floor. In some ecosystems, such as the temperate rain forest of the Pacific coast, down wood is significant for providing a seedling substrate, and is called nurse logs.

Soil

Intact soils harbor many life-forms that rely on them and usually have very well-defined soil profiles. Different organisms need certain well-defined soil profiles, while many trees need well-structured soils free of disturbance. Some herbaceous plants in northern hardwood forests need thick duff layers (which are part of the soil profile).

Fungal ecosystems are essential for efficient in-situ recycling of nutrients back into the entire ecosystem.

Importance

Old growth forests often contain rich communities of plants and animals that settle there thanks to the long period of pseudo-stability. These varied and sometimes species may depend on the unique environmental conditions created by these forests.

Old growth forest serves as a reservoir for species which cannot thrive or easily regenerate in younger forest, and so can be used as a baseline for research.

Old growth forests also store large amounts of carbon above and below the ground. They collectively represent a significant pool of climate gases such as greenhouse gases. Continued liquidation of these forests may increase the risk of global climate change.^[1]

Logging

The large trees in old growth forests are economically valuable, so these forests have been subjected to aggressive logging around the world. This has led to much controversy between logging companies and environmental groups. A great example of this was the controversy around Spotted Owls in the 1980s and 1990s.

In Australia, the regional forest agreement (RFA) attempted to prevent the clearfelling of defined "Old Growth Forests". This led to struggles over what constitutes "Old Growth". For example in Western Australia, the timber industry tried to limit the area of Old Growth in the karri forests of the Southern Forests Region; this led to the creation of the Western Australian Forests Alliance, the splitting of the Liberal Government of Western Australia and the election of the Gallop Labor Government. Old Growth Forests in this region have now been placed inside National Parks.

Locations of remaining intact forests

Main article: List of old growth forests

In 2006 Greenpeace identified that the world's remaining intact old growth forest area was distributed among the continents as follows:^[2]

35% in Latin America. The Amazon rainforest is mainly located in Brazil, which clears a larger area of forest annually than any other country in the world.^[3]
28% in North America. North America harvests 10,000 square kilometres of ancient forests every year. Many of the fragmented forests of southern Canada and the US lack adequate animal travel corridors and functioning ecosystems for large mammals.^[3]
19% in Northern Asia. Northern Asia is home to the second largest boreal forest in the world. The Siberian tiger once roamed across huge areas of Northern Asia but today can only be found in a small area of intact forest near the Sea of Japan. Only about 400 remain in the wild and 800 in zoos.^[3]
8% in Africa. Africa has lost most of its intact forest landscapes in the last 30 years. The timber industry is responsible for destroying huge areas of intact forest landscapes and continues to be the single largest threat to these areas.
7% in South Asia Pacific. The Paradise Forests of Asia Pacific are being destroyed faster than any other forest on Earth. Much of the large intact forest landscapes have already been cut down, 72% in Indonesia and 60% in Papua New Guinea.^[3]
Less than 3% in Europe. In Europe, more than 150 square kilometres of intact forest landscapes are cleared every year and the last areas of the region’s intact forest landscapes in European Russia are shrinking rapidly.^[3]