Variable retention

Variable retention is a relatively new silvicultural system that retains forest structural elements for at least one rotation in order to preserve environmental values associated with structurally complex forests.^[1]

Some examples for environmental values are forest cover connectivity,

Variable retention is gradually becoming a popularly promoted tool for helping resolve the dilemma between demands for wood and demands to maintain habitat and ecology biodiversity and structural diversity in managed forests. What is at issue is how much a forest operation can log without adversely interfering with other ecological processes within the forest.

Variable retention minimizes the impact of logging operation by leaving biological legacies such as coarse woody debris (nurse logs and snags). Either few trees or many trees can be retained under the variable retention system, and trees can be retained in patches (aggregated retention) or left uniformly throughout a stand (dispersed retention); hence the name "variable retention."^[4] It is a technique for retaining trees as key structural elements of a harvested stand for at least until next harvest rotation in an effort to maintain species, habitat diversity and forest-related processes.^[5] A 2014 meta-analysis of retention forestry research found "support for wider use of retention forestry since it moderates negative harvesting impacts on biodiversity."^[6]

There are four key mechanisms through which variable retention is presumed to maintain biodiversity:

• By providing a constant supply of structural features that are at high risk to being lost due to modern forestry practices and that are known to be important to habitat availability, such as large trees, very young trees, snags, and coarse woody debris
• By providing adequate refuge for sensitive species that will colonize the surrounding managed forest environment as it develops suitable conditions
• By establishing habitat patches, Patch dynamics, that can serve as stepping stones for the dispersal of newly produced offspring, seeds, and spores
• By increasing the structural diversity of managed stands

Variable retention - Harvesting methods

The method of variable retention is a more deliberate process than

Ecologists regard the variable retention method of harvesting as being far less detrimental to the forest ecosystem than clearcutting. However, opponents claim that variable retention is much more laborious, tedious, time-consuming and expensive than clearcutting. A review of studies in British Columbia and in similar forest types indicates that while both aggregated and dispersed retention can contribute to biodiversity conservation there may be some negative consequences for timber production such as wind damage to retained trees and reduced growth rates of tree regeneration compared to clearcuts, concluding in favour of an adaptive management approach for balancing competing objectives of production of wood and biodiversity conservation.^[7]

Forestry organizations, such as the

Many logging companies have not maintained a total commitment to phasing out clearcutting and embracing variable retention harvesting, and even MacMillan Bloedel had occasionally fallen short of its commitment to phase out clearcutting. Although world markets are beginning to ask for certified wood obtained entirely through variable retention harvesting, it is not yet clear whether the general population of consumers will be willing to pay higher prices for such wood.^{[citation needed]}

See also

References

This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (June 2009) (Learn how and when to remove this template message)

• Mendocino Redwoo Company: Silviculture and Harvesting Methods
• Manomet Forest Conservation Program: Patch Retention Project
• Certified Sustainable Wood, Reforestation, Western Red Cedar Suppliers
• Maguire, Douglas A.; Halpern, Charles B.; Phillips, David L. (2007). "Changes in forest structure following variable-retention harvests in Douglas-fir dominated forests". Forest Ecology and Management. 242 (2–3): 708–726.
  doi:10.1016/j.foreco.2007.02.004
  .

External links

• Home page of Jerry F. Franklin - professor of ecosystem analysis, University of Washington
• TimberWest to Phase Out Clearcutting
• SpruceRoots Magazine: A Clearcut Case of Variable Retention
• Green Ridge State Forest Work Plan for 2008
• Mongabay.com: Variable Retention Glossary and Government Resources