Trust Lands HCP Silviculture
Click Here for Survey
Home > Science & Environment > Topics > Trust Lands HCP > Trust Lands HCP Silviculture
Trust Lands HCP Silviculture  

Diverse Forest scape in th Elbe Forest Douglas Fir Cone  Variable retention harvest on state trust lands

State Trust Lands Habitat Conservation Plan

Forest Stand Management and the trust lands HCP

Forest stand management (also known as silviculture) is the art and science of growing forest stands with characteristics that meet specific objectives. Broadly defined, it includes managing landscapes, stands and trees for wood products and for other ecosystem services, such as wildlife habitat, slope stability, and water quality. Modern forest management at Washington State DNR considers all major elements of the forest—a mix of tree species that is appropriate to the site; understory vegetation; wildlife, soils and structures such as snags and fallen logs. Various silvicultural prescriptions can accomplish multiple goals across the landscape and result in diverse forest ecosystems and structures, in concert with wood as the major commercial product. 

DNR manages forested state trust lands to provide revenue from forest products to benefit the state’s public schools and other trust beneficiaries. DNR carries out the Board of Natural Resources’ management direction. The Board interprets the trust mandate to support the beneficiaries, now and in the future. Board direction recognizes the need to balance current production with long-term productivity and environmental quality and includes long-term revenue production and soil productivity, habitat for wildlife, a supply of clean water; and natural spaces for people to enjoy.

The trust lands Habitat Conservation Plan was developed under Section 10 of the Endangered Species Act in cooperation with the US Fish and Wildlife and National Marine Fisheries Services. Its purpose is to provide lasting habitat protection for multiple species including northern spotted owl, marbled murrelet, and salmon. Wherever possible, the HCP guides DNR to maintain and create habitat elements and ecological processes that exist in un-managed forests. Silviculture is an important tool for achieving the HCP goals and is considered the main tool for integrating conservation and commodity production on forested state trust lands.

Planning a timber sale to meet multiple objectives
Animals, Habitat elements considered 
Creating habitat and thinning
Variable Retention Harvest

Planning a timber sale to meet multiple objectives
When a DNR timber sale is planned, the foresters in charge of the sale design consider32 HCP strategies and elements (such as the Wetland, owl and Northern Goshawk procedures) as needed for the specific site. They use a checklist to identify the animals and habitat elements that are present on the site, and ensure that these are addressed and protected in the timber sale design. On every proposed timber sale green trees, snags (subject to safety) and downed wood are left during harvest, as the building blocks for specific habitat. Areas such as wetlands and unstable slopes and rare habitats such as talus slopes are excluded from harvest. Harvest around riparian (streamside) forests is carefully managed, primarily by leaving riparian buffers, to protect water quality, provide habitat elements that support salmon, such as shade and large woody debris, and provide habitat for the many species that depend on riparian areas.

Animals, habitat elementsand HCP conservation strategies are considered for each timber sale
When a DNR foresters design a timber sale, they must consider animals, plants and habitat elements that occur in the landscape to honor commitments to the biodiversity on state trust lands made in the trust lands HCP. They design the timber sale to protect:

  • HCP Conservation strategies: Northern Spotted Owl, Marbled Murrelet, Multispecies conservation strategy for unlisted species (to avoid the need for future listings), and Riparian strategy (to address recovery of threatened or endangered Salmon species).
  • Other Federally and State-listed species:  Bald Eagle, Grey Wolf, Grizzly Bear, Oregon Silverspot Butterfly, Columbian White-tailed Deer, Lynx, Common Loon, Harlequin Duck, Northern Goshawk, California Wolverine, Pacific Fisher, Pileated Woodpecker, Vaux’s Swift, Bats, Western Pond Turtle, Purple Martin, Western Bluebird, Sandhill Crane.
  • Uncommon habitats: Talus, caves, cliffs, oak woodlands, balds, and mineral springs.
  • Habitat elements and areas of concern:  Riparian areas, wetlands, rain-on-snow areas, unstable slopes, large structurally unique trees, snags, and down logs.

Creating habitat and ‘thinning’ a stand
The trust lands Habitat Conservation Plan is intended to support and complement Federal efforts to ensure that sufficient habitat for native species is protected, or restored and perpetuated where it is lacking on the landscape. Specifically, an important goal is to create habitat for critical species that have been listed as ‘endangered’ under the Federal Endangered Species Act—such as northern spotted owls, marbled murrelets, and salmon.

Critical species” refers to species that are indicators for the health of their particular ecosystem. By focusing on the needs of critical species, we hope to secure sufficient habitat for all other species that require that habitat, known and unknown. By maintaining habitat for those species that are most sensitive to ecosystem disturbance, we hope also to maintain the habitat elements that are critical for ecosystems on a landscape basis.

Thinning of forest stands—where appropriate- is one of the most powerful tools we have to accelerate development of certain habitat elements.

As trees grow, competition gradually increases between individual trees for light, nutrients, and moisture. A naturally developing stand will ‘self thin’, as less successful trees are overtopped and shaded by their larger neighbors. Eventually, natural selection and disturbance events (like wind storms, fire or root disease outbreaks) will create habitat elements such as canopy openings, large snags and large fallen trees. The result is a complex multi-aged and multi-sized mosaic of high ecological and social quality and commercial value.

The purpose of thinning is to accelerate these otherwise slow natural processes to develop desired habitat conditions as efficiently and effectively as possible, mimicking the characteristics of unmanaged older forests. In developing habitats for the northern spotted owl, for instance, we wish to hasten habitat functionality as well as tree growth.

To meet habitat objectives, we introduce structural and species variability in forest stands as early as possible, and try to amplify them as the stand ages. For example, older trees are left from the previous harvest, and seedlings of shade tolerant and intolerant species are mixed when planting after harvest.
‘It’s not what you take, it’s what you leave’

Early thinning controls spacing and selects tree species that will comprise the future forest.  It also creates small openings, leaves small thickets, and enhances growth of the largest trees by lessening the competition for light, moisture and nutrients.

With commercial stand thinning we strive to keep trees and snags that have nesting cavities and large trees and fallen logs for prey species such as squirrels and voles. Food for prey species is also encouraged through management.. Thinning promotes the reestablishment or growth of a diverse  ground vegetation to support a wide variety of animal species including prey species for the Northern Spotted owl.. Roosts and perches are protected in the lower canopy branches where owls can successfully observe and pounce on their prey, particularly of suppressed trees and hardwoods where owls rest and sleep and observe these openings. Places to hide and thermal cover are provided by the dominant canopy and thickets. Later thinnings also can accelerate the development of a second canopy and increase the diversity of habitat niches.

Riparian forest restoration thinning is designed to restore older forest species and forest structure in streamside forests where historic timber harvest has created even-aged, often over-stocked forest stands. Canopy gaps and “skips”— areas that are left unmanaged—help to increase structural diversity and accelerate the development of habitat.  Accelerating the growth of large conifer trees is an important part of the HCP Riparian Forest Restoration Strategy. Over time, these trees will provide shade and nutrient-rich litter-fall for the stream while they are living, and contribute large woody debris to the stream channel when they die and fall over. Large diameter fallen logs in the stream create pools and cover which are important for salmon habitat.  Once the riparian forest stand is on a developmental trajectory to reach the older forest structural condition, there will be no further harvest next to the stream.

“Variable density stand thinning”, where canopy gaps, skips, and areas of greater and lesser tree density occur, allows structural diversity to develop within forest stands.

Variable Retention Harvest
DNR uses a Variable Retention Harvest (VRH) as a replacement for traditional clear-cutting to harvest trees and replant for the future. Variable retention harvest is an approach to harvesting based on the retention of structural elements or biological legacies (trees, snags, logs, etc.) from the harvested stand for integration into the new stand to achieve various ecological objectives. The following threshold targets apply on the Westside State Trust Lands:

  • Retention of at least 8 trees per acre of the largest size class of trees, and of these:
    • At least 2 per acre are suitable for wildlife
    • At least 3 per acre are snag recruits
    • At least 3 per acre are snags, provided that safety requirements are met
  • There are at least 2 down logs per acre of largest size class (at least 12 inches in diameter at the small end by at least 20-feet long).

The major ‘variables’ in the variable retention harvest system are tree types, densities, and spatial arrangement of retained structures.

 ‭(Hidden)‬ Files Filter

to specify items for consumption by a Data View. To change the list that this refers to, check the Miscellaneous group in the sidebar tool for the ListURL value and change the URL to point to a different list.

 ‭(Hidden)‬ Contacts Filter

to specify items for consumption by a Data View. To change the list that this refers to, check the Miscellaneous group in the sidebar tool for the ListURL value and change the URL to point to a different list.


Candace Johnson
Assistant Division Manager Silviculture/Regeneration


 Related Links

State Trust Lands Forest Management