Forest Restoration

The existing condition of forests in the Fort Clatsop Unit of the park in 2004, before forest restoration work began. The green area of forest was 25–30 years in age, while the dark blue areas were even younger.

In 2002, 963 acres of former timber lands were added to Lewis and Clark National Historical Park. These forests, however, looked very different from those encountered by the Corps of Discovery at the turn of the 19th century.

Decades of timber production had left behind crowded plantations of young western hemlock and Douglas fir trees. Gone were the old-growth giants and surrounding forest of mixed ages, sizes, and species. Gone, too, was the rich understory of ferns and shrubs, fallen logs, thick soils, and snags that a member of the Corps of Discovery described nearly 200 years earlier as “so thick it was almost impenetrable.” Just across the mouth of the Columbia River at Dismal Nitch, William Clark wrote in 1805 of finding spruce and fir trees of “an immense size and height, many of them seven and eight feet through and upwards of 200 feet high.”

An Impoverished Forest

Management for timber production removes vast quantities of biomass—living organisms—from the forest ecosystem. When felled trees are taken out of the forest, nutrients and organic matter cannot return to the ecosystem through decomposition. This biomass is essential for decomposers such as insects and fungi, which consume and transform it into nutrient-rich soils for future generations of trees. Industrial timber production also often removes understory shrubs, alders, and lichens, many of which serve as forest alchemists—transforming nitrogen in the air into a form vital for plant survival.

The shape of a forest matters too. Snags (standing dead trees) provide important wildlife habitat, while decomposing “nurse logs” serve as cradles for the next generation of plant life. And a varied forest structure opens what ecologists call successional pathways. When there is a patchwork of light, water, and nutrient availability throughout the forest, new trees can grow up to take the place of old ones without waiting for a catastrophic disturbance to open the floodgates.

 

In December 2007, a coastal gale brought hurricane-force winds that flattened thousands of trees throughout the park. Forests where all trees are the same age—like those managed for timber production—are especially susceptible to wind disturbance. In contrast, mixed-age and mixed-size forests are more resilient to these natural extreme wind events, which occur on average once every 20 years on the Oregon coast. Click to learn more about the Great Coastal Gale of 2007's impact on forests.

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Left: Some trees were left standing but girdled to create snag habitat, typical in an old-growth forest.
Center: Felled trees were lopped and scattered on the ground, speeding up decomposition and improving wildlife habitat.
Right: A simple wedge prism is used to check forest density post-treatment.

Lending a Helping Hand

Scientific research has shown that without active restoration, former timber plantations can remain in the same developmental stage for decades—or even longer. To restore the features of a mature, healthy forest on a shorter timescale, intervention is needed. Based on the park’s 1995 general management plan which set out the acquisition and restoration of these lands, the park released its forest restoration plan in 2011 and work began in 2012.

Using detailed surveys of tree height, diameter, density, and other measures, restoration prescriptions were developed for each stand throughout the project area. These prescriptions outlined specific actions—known as treatments—tailored to stand age and condition.

Many areas were treated with “variable density thinning,” a tested forest restoration technique where trees are thinned unevenly to mimic the structural complexity and spatial variation of a mature forest. Some areas receive no thinning at all, while others are cleared to simulate natural canopy openings. No large trees (greater than 20 inches in diameter) were cut in any of these treatments.

 

A map of the Fort Clatsop Unit shows where native trees were planted. Triangles indicate bigleaf maples planted in 2021, while areas with diagonal hatching were planted with Sitka spruce in 2019 and yellow-shaded areas were planted with both Sitka spruce and western redcedar in 2019–2020.

Thinning is not the only tool in the forest restoration toolbox. Some trees were girdled (a technique which kills a tree by cutting through the bark all the way around the trunk) to create snags. All felled trees were left on the forest floor to decompose, returning nutrients to the forest while creating additional wildlife habitat. To speed decomposition while limiting the spread of less desirable wood-rots, chainsaws and cutting equipment were lubricated with vegetable oil spiked with native fungal spores. Finally, park staff returned to treated stands in 2019–2021 to plant under-represented native species including western redcedar, Sitka spruce, and bigleaf maple.

To minimize disturbance to visitors and wildlife, forest restoration work was performed by small hand-crews, which treated about 10% of the total project area each year. For each age class of stands, around 20% of the area has been left untouched during the restoration process to serve as a refuge for wildlife, mosses, and fungi that may be disturbed by the treatments.

Progress Check

Is forest restoration working? The first phase of the project, which included thinning, snag creation, and new planting, began in 2012 and continued through 2022. Now, park science staff are measuring success of the treatments through ongoing forest monitoring and experimental seedling plots. While the current forest restoration plan is intended to guide work through 2031, lessons learned from monitoring will be used to help write the next chapter.

 

Some species, like the endangered marbled murrelet, have life histories that rely on old forests rich in large trees. These seabirds in the auk family nest primarily in old-growth forests, raising chicks on the flat tops of thick, mossy branches far above the forest floor.

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Rebuilding a Coastal Temperate Rainforest

Lewis and Clark National Historical Park lies within the Sitka spruce vegetation zone, a rare vegetation type typically extending no more than a mile inland from the Pacific coast. These forests are the wettest in North America—as the Corps of Discovery learned during their relentlessly rainy winter at Fort Clatsop. However, very little of this vegetation community remains in its pre-colonization state. 96% of the original coastal temperate forests in Oregon have been logged, while new development and ongoing timber harvest in Clatsop Country has resulted in a landscape where older forests with complex structures are increasingly scarce.

Park managers at Lewis and Clark hope to rebuild more than just this rare and valuable fragment of coastal temperate rainforest. When complete, this work “would allow a return to a forest landscape representative of that experienced by the Corps of Discovery” (from the park’s general management plan). What would it be like to wander between towering forest giants like those that greeted Lewis and Clark at the end of their long journey to the sea?

 

Frequently Asked Questions

 

Why is the park cutting down trees?

Forests that were planted for timber harvest are overcrowded and unhealthy. Because only a limited amount of water, light, and nutrients are available in a given area, removing some trees means that those that remain have access to more resources. This allows them to grow larger and stronger while making space for new growth, speeding up the return of a more natural forest structure. 

Exact prescriptions have been developed to implement the forest restoration plan. These prescriptions dictate variables like how many trees of which size and species should be thinned, the creation of snags (standing dead trees) to provide wildlife habitat, and which areas to leave untreated. 

Objectives for the forest restoration project are to restore the historic scenery, accelerate the return of structural and biological diversity, build soils, improve wildlife habitat, and build greater resilience in the face of climate change.

Won’t the former timberlands return to a natural condition by themselves?

A substantial body of scientific research suggests that intervention is needed to restore timber plantations to a mature forest structure. Without active restoration, tree farms can stay in the same developmental stage for decades or longer. When extremely dense forests compete for limited resources, trees are unable to grow larger. Meanwhile, young trees cannot establish themselves, leading to a holding pattern of trees of the same size and age as each other.

Why are some felled trees being left in the park? Does that increase fire risk?

Leaving felled logs on the forest floor to break down jumpstarts the return of understory plants by returning nutrients to the soil. These logs also provide wildlife habitat and can act as sponges to create moister zones in the woods. Far from being wasted, these logs are providing a valuable service enriching and feeding the next generation of forest life. 

Fire is very uncommon in temperate coastal rainforests. In Sitka spruce forests in western Washington, research indicates a natural fire return internal of over 1,100 years. For this reason, the park is able to allow felled trees to decompose in place, helping rebuild rich organic soils and serving as nurse logs for the next generation of trees. Park managers carefully monitor forests to determine if any future biomass removal may be needed.

What laws and policies authorize this project?

The National Park Service Organic Act of 1916, which established the NPS, states that the fundamental purpose of the National Park System “to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations.” 

Section 4.4.1 of the NPS Management Policies, the agency’s interpretation of the Organic Act, further addresses the biological resources within park boundaries, stating that the Service will “successfully maintain native plants and animals by preserving and restoring the natural abundances, diversities, dynamics, distributions, habitats, and behaviors of native plant and animal populations and communities and ecosystems in which they occur.” 

Sometimes, the NPS acquires lands that support the park’s purpose but may lack the ecological characteristics they had historically. In these cases, section 4.1.5 of the NPS Management Policies directs the Service to “reestablish natural functions and processes in parks unless otherwise directed by Congress. Impacts on natural systems resulting from human disturbances include the …disruption of natural processes. The Service will seek to return such disturbed areas to the natural conditions and processes characteristic of the ecological zone in which the damaged resources are situated.” 

The park’s 1995 General Management Plan recommended the acquisition and restoration of these lands. “The proposed boundary expansion would provide protection of the forested and agricultural landscape now surrounding the Fort area and, by practicing forest management on some of the land included, would allow a return to a forest landscape representative of that experienced by the Corps of Discovery.” In 2002, Congress passed the Fort Clatsop National Memorial Expansion Act which accomplished this boundary expansion.