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on November 30, 2013 at 9:00 AM, updated November 30, 2013 at 9:04 AM
By Jerry F. Franklin
and K. Norman Johnson
and K. Norman Johnson
Variable retention harvesting is prescribed in Sen. Ron Wyden's proposed legislation for harvesting in younger highly-productive Douglas fir and Western hemlock forests (the "moist forests") on the O&C lands of western Oregon. Understanding the forestry technique is critical to understanding the senator's plan.
Variable retention harvesting is modeled on patterns of natural disturbances, such as wildfire. In contrast to clear-cutting, where essentially all of the trees are removed, significant amounts (about 1/3 in the proposed legislation) of the pre-harvest forest are retained throughout the harvest area (see top photo). The retention would typically include unlogged forest patches up to several acres in size well distributed through the harvest area – "aggregated retention" -- as well as individual or small clusters of live and dead trees and down logs, distributed over logged portions of the harvest area -- "dispersed retention." Some of the aggregated retention will be along streams within the harvest area.
One important objective of variable retention harvesting is to "lifeboat" many of the forest-related plant and animal species, sustaining them within the harvest area until the new forest becomes established. For example, forest-dwelling small mammals and amphibians can be sustained by retaining heavily rotted logs that provide critical habitat for them.
Variable retention also provides for continuity in life-sustaining flows of energy into the soil from trees. In addition, the un-harvested forest patches or aggregates have special ecological value since they include undisturbed forest floors, a full range of tree sizes and mellow microclimates.
Variable retention harvesting is being widely applied globally as a versatile and effective silvicultural approach, particularly where management goals require integration of ecological, economic, and cultural objectives. It is currently being used on five continents in countries as diverse as Sweden, Canada, Australia, Argentina and Chile. It also is being used on a diversity of forest ownerships including federal, state, and local public lands, trust lands, and private forest lands. Hundreds of peer-reviewed publications document the scientific underpinnings and the ecological benefits of variable retention harvesting.
Of course, a key question is what stands would receive variable retention harvesting in Sen. Wyden's proposed legislation. Harvesting would occur only in moist forest stands designated for sustained yield management. All of these would be stands currently less than 120 years of age and most would be stands that originated after previous harvests (usually clear-cutting) 60-90 years ago. No old-growth forests or trees would be harvested.
As proposed for the Bureau of Land Management lands, variable retention harvesting has the additional major ecological benefit of providing the significant openings needed for development of the highly bio-diverse "early successional ecosystems." These are the ecosystems that initially develop on forest sites after a harvest or other major disturbance, such as wildfire. They are biologically rich communities of herbs, shrubs and trees that, in turn, support an immense variety of animal life because of the abundant and diverse sources of food – herbage, nectar, fruits, nuts, seeds and prey. (See bottom photo.)
Many of the species found in these early successional ecosystems are habitat specialists that require early successional habitats. These include many songbirds and butterflies. Also, as hunters know, they are favored and critical habitat for deer and elk, because there is food for them to eat. Research at Mount St. Helens – the biodiversity hotspot of the Cascade Range -- has been critical in helping us to understand the ecological importance of early successional ecosystems.
While private forest lands might be expected to provide for biologically rich early successional ecosystems, they generally do not. Production forestry on industrial lands -- the source of most private harvest in Western Oregon -- seeks to maximize economic returns with intensive practices, such as intensive site preparation, dense tree planting, and control of shrubs and herbs with herbicides. Encouraging shrub-dominated communities and gradual re-establishment of tree cover is not consistent with such goals.
In summary, variable retention harvesting proposed in Sen. Wyden's legislation is fundamentally different from clear-cutting and associated practices. Variable retention is grounded in principles derived from natural forest ecosystems. As proposed it will provide for both continuity in forest biota and creation of openings needed for early successional species and processes.
Jerry Franklin is a professor in the School of Environmental and Forest Sciences at the University of Washington; K. Norman Johnson is a professor in the Department of Forest Ecosystems and Society at Oregon State University. They each worked on development of the Northwest Forest Plan and on development of Sen. Ron Wyden's forest management plan unveiled this week.