Old growth forest

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Old growth forest, sometimes called late seral forest, ancient forest, virgin forest, primary forest or ancient woodland is an area of forest that has attained great age and 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 a variety of different age classes.

Forest regenerated after severe disruptions, such as clear-cut or fire is often referred to as second-growth or regeneration until a long enough period has passed 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 are dependent 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.

Contents 1 Defining old growth 2 Characteristics of old growth forest 2.1 Mixed age 2.2 Canopy openings 2.3 Topography 2.4 Standing snags 2.5 Decaying ground layer 2.6 Soil 3 Importance of old growth forests 4 Logging in old growth forests 5 References 6 See also 7 External links

[edit] Defining old growth

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 at least 1600 in England and Wales, (or 1750 in Scotland). Before this, planting of new woodland was uncommon, so a wood present in 1600 was likely to have developed naturally. By contrast, in the U.S., old growth is often used to imply a forest has experienced little or no direct disruption by Euro-Americans and looks about as it would had Europeans not come to America. However, this criterion is difficult to apply, since it is often impossible to determine the history of human management (Euro-American or Native American). Further, 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 between the ecological effects of natural disruption and 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).

[edit] Characteristics of old growth forest

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.

[edit] 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 a uniformly-aged becomes senescent and degrades within a relatively short time-period to result in a new cycle of forest succession. Thus, it is a less stable ecosystem.

[edit] Canopy openings

Canopy openings are essential in creating and maintaining the mixed-age stands. In addition, some herbaceous plants only become established in canopy openings although they are able to persist thereafter in the darker understory. Canopy openings created by natural disturbance events such as wind, ice, and mixed-severity fire retain significant structural enrichment from dead trees, whereas canopy opening created by logging are structurally simplified and deprived of the legacy structures that normally occur in healthy old-growth forests.

[edit] Topography

Pit-and-mound topography is the characteristic lay of the land after trees that have fallen due to natural causes create pits where roots have pulled out and mounds where the root mass decays (with the soil clinging to the roots). These places provide, in the pit, fresh exposure of humus-poor, mineral-rich soil, often a place where moisture may collect and in which fallen leaves soon form a thick organic layer and so able to nurture certain types of organisms, while the mound provides a place free from leaf inundation and saturation where other types of organisms may thrive.

[edit] Standing snags

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

[edit] Decaying ground layer

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

[edit] Soil

Intact soils harbor many life-forms that rely on them. Intact soils generally have very well-defined horizons, or soil profiles. Different organisms may need certain well-defined soil horizons in order to live, while many trees need well-structured soils free of disturbance in order to thrive. Some herbaceous plants in northern hardwood forests must have 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.

[edit] Importance of old growth forests

Due to the lack of severe disturbance, old growth is often associated with rich communities of plants and animals that may be dependent upon the unique environmental conditions created by these forests. The age of the oldest trees indicates that disturbance events during the long period of development were of moderate intensity at most and did not kill all vegetation. This long period of pseudostability allows the old growth forest to become occupied over time by a wide variety of species, some of them rare.

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

Old growth forests also store large amounts of carbon, both above and below ground. These forests collectively represent a significant pool of climate gases. Continued liquidation of these forests may increase the risk of global climate change. However, because growth is roughly equal to decay within old growth forests, they do not sequester significant amounts of atmospheric carbon—this is in contrast with young forests ^[1] .

[edit] Logging in old growth forests

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.

[edit] References

1. ^ Trends in bole biomass accumulation, net primary production and tree mortality in Pseudotsuga menziesii forests of contrasting age S. A. Acker, C. B. Halpern, M. E. Harmon and C. T. Dyrness Tree Physiology 22:213–217

[edit] See also

• Ancient woodland

[edit] External links

• Primal Nature: Preservation and restoration of old-growth forests in the eastern United States
• Old growth locations in the eastern U.S.
• Old growth definitions from the Pacific northwest
• Wildlife and Vegetation of Unmanaged Douglas-Fir Forests
• Profiles of special species that live in Old growth forests
• "Of Spotted Owls, Old Growth, and New Policies: A History" (PDF)
• Gifford Pinchot Task Force
• Old-Growth Again Restoration Forestry
• NW Old Growth Campaign
• Umpqua Watersheds, Inc. information on western Oregon old-growth issues
• Oregon Natural Resources Council information on Pacific Northwest old-growth issues
• Forest Service
• Experimental forestry designed to convert tree plantations to old-growth
• Thinning To Enhance Biodiversity