Late Successional Mixed Conifer Forests

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Coast Range Ecoregion
Late Successional Mixed Conifer Forest within Oswald West State Park. Photo Credit: David Patte, USFWS

Late successional mixed conifer forests provide a multi-layered tree canopy, including large-diameter trees, shade-tolerant tree species in the understory, and a high volume of dead wood, such as snags and logs.

Ecoregions

Late successional mixed conifer forests are a Strategy Habitat in the Blue Mountains, Coast Range, East Cascades, Klamath Mountains, and West Cascades ecoregions.

Characteristics

Late successional mixed conifer forests are defined by plant species composition, overstory tree age and size, and the forest structure. They include characteristics such as a multi-layered tree canopy, shade-tolerant tree species growing in the understory, large-diameter trees, and a high volume of dead wood, such as snags and logs. Historically, fire was the major natural disturbance in all but the wettest climatic areas. Depending on local conditions, fires in western Oregon conifer forests were of moderate- to high-severity, with fire return intervals averaging 100 to more than 400 years. The historical fire regime created a complex mosaic of stand structures across the landscape.

Ecoregional Characteristics

Blue Mountains

A mixture of conifer species occupies many forest sites in the Blue Mountains. Mixed conifer forests can be divided in two subtypes based on temperature and moisture conditions. The warm mixed conifer type occupies the warmer and drier end of the spectrum. Douglas-fir and grand fir are the primary late successional tree species. Ponderosa pine and western larch may also be present. The cool mixed conifer type is indicated by the addition of more moisture-demanding and cold-tolerant species, such as subalpine fir and Engelmann spruce, at upper elevations or along streams where cold-drainage and deep frost eliminate some species. The understory in the Blue Mountains generally includes huckleberry, serviceberry, oceanspray, snowberry, wild ginger, goldthread, starflower, beadlilly, and oak fern.

Coast Range

Although there are several forest types in the Coast Range ecoregion, two types predominate: Sitka spruce and Douglas-fir. Sitka spruce forests occur within a narrow fog- and salt-influenced strip along the coast and extending up some valleys. Soils tend to be deep, acidic, and well-drained. Sitka spruce dominates the overstory, but western hemlock, western redcedar, Douglas-fir, big leaf maple, and red alder may be present. The lush understory has salmonberry, vine maple, salal, evergreen huckleberry, sword fern, deer fern, and a high diversity of mosses and lichens. Due to high precipitation, fires are rare and the primary disturbances include small-scale windthrow and storm surges. Inland, Douglas-fir forests dominate. Characteristic species are similar to those in the West Cascades Douglas-fir forests, described previously.

East Cascades

Mixed conifer forests span the eastern slopes of the Cascade Mountains. This habitat contains a wide variety of tree species and dominance patterns. Douglas-fir, grand fir, and western hemlock are the most common forest tree species and co-dominate most overstories. Several other conifers may also be present, including western red cedar, western white pine, western larch, ponderosa pine, and lodgepole pine. Undergrowth vegetation in the East Cascades includes vine maple, Oregon grape, huckleberry, oxalis, boxleaf, thimbleberry, and twinflower. Many sites once dominated by Douglas-fir and ponderosa pine (and formerly maintained by wildfire) may now be dominated by grand fir (a fire sensitive, shade-tolerant species).

Klamath Mountains

Mixed conifer forests in the Klamath Mountains ecoregion are characterized by conifers but have high tree diversity. Douglas-fir is usually dominant. Depending on site characteristics, other canopy trees include white fir, sugar pine, ponderosa pine, and incense cedar. Port-Orford cedar occurs on moist sites, such as riparian areas. Jeffrey pine and knobcone pine occur on serpentine soils. Broadleaf trees, such as tanoak, canyon live oak, golden chinquapin, and Pacific madrone, may occur in the subcanopy. Understories are mostly dominated by shrubs but can be dominated by forbs, graminoids, or may be relatively open.

West Cascades

Coniferous forests dominate the landscape of the West Cascades ecoregion. Late Successional Conifer Forests are older forests (hundreds of years old), generally occurring below 3,500 feet, but sometimes occurring up to 4,000 feet. Douglas-fir trees occur up to 5,000 feet but do not dominate the forests at higher elevations. Western hemlock is almost always co-dominant and usually dominates the understory. Other common trees include grand fir and western redcedar in the northern portion of the ecoregion, or incense cedar, sugar pine, white fir, and western redcedar in the southern portion of the ecoregion. The understory has shrub and forb species, such as vine maple, salal, sword fern, Cascade Oregon grape, western rhododendron, huckleberries, twinflower, deerfoot, vanillaleaf, and oxalis. In the absence of disturbance, Douglas-fir forests eventually will convert to western hemlock.

Conservation Overview

Oregon’s forests have long contributed to local economies through timber harvest. However, both timber harvests and a number of large fires have replaced much of late successional forests with younger forests in western Oregon. For the Coast Range, West Cascades, and Klamath Mountains ecoregions, loss of late successional forests since 1850 is estimated to be near 90 percent.

Federal lands contain substantial acreages of mature and late successional forests, but many of these forests occur in a patchwork with the much younger forests that are managed with shorter rotations to generate timber products. The younger forests still maintain their capacity to become older forests, and they can often support many species. However, late successional forests support a wide array of species, many of which require large patches of older or mature forests to survive and may be sensitive to changes in the forest seral stage.

The NWFP and National Fire Plan are both large, comprehensive natural resource planning efforts that include federal forests in western Oregon. The NWFP identifies conservation priorities for species affected by loss and fragmentation of large patches of late successional forests, assessing over 1,000 species. The federal plan is expected to provide at least 50 percent probability that populations of most species would stabilize with either good or only moderately limited distributions on public lands. For the majority of species, the probability of stable, well-distributed populations is estimated at 75 percent (USDA/USDI 1994). The adaptive management component of the NWFP has not been fully implemented. Adaptive management approaches could be used to experimentally deal with risk of uncharacteristically severe wildfires, restore wildlife habitat features, and accelerate the development of characteristics such as multi-layered canopies.

Late Successional Reserves established under the NWFP were intended to ensure enough high quality habitat to sustain identified species. However, many of the federal lands that are designated as Late Successional Reserves do not include forests at the late successional stage, while others are relatively small “checkerboards” of forests embedded in a matrix of private industrial timber lands, particularly in the Coast Range and Klamath Mountains. There is potential for the amount of late successional forests to increase over time, under current state and federal policies.

Many of the Late Successional Reserves are in Fire Regime Condition Class II or Condition Class III, where the risk of loss of key ecosystem components is moderate or high (see Disruption of Disturbance Regimes). This risk is particularly acute in the Klamath Mountains, where recent large-scale severe wildfires have impacted wildlife habitat. In addition, all planning efforts are limited by understanding of landscape management and by ecological data availability. The outcome of these decisions, and the ultimate long-term impacts of these plans, is unknown.

The National Fire Plan is attempting to address historical fire suppression and the impacts of recent catastrophic and uncharacteristic wildfires, recommending a variety of active management techniques for forests to increase fire safety and evaluation of their effects on fire behavior and the effectiveness of suppression. Results of implementing the National Fire Plan and its effects on both public safety and forest habitats are continually being evaluated.

In the Coast Range, three-quarters of the ecoregion is in state and private ownership. The Oregon Department of Forestry manages 550,000 acres in the Coast Range ecoregion, primarily in the Clatsop, Tillamook, and Elliott State Forests. The Northwest and Southwest State Forest Management Plans provide management direction for all Board of Forestry Land and Common School Forest Lands. The plans include management strategies for 16 resources, including fish and wildlife, timber, recreation, and water resources. The plans describe long-term desired future conditions, which include older forest structure. Most private forest lands are currently managed intensively for timber values using relatively short rotations, which will limit future development of late successional habitats in many areas.

Late successional conifer forests are particularly important for wildlife, mosses, and lichens. Depending on the ecoregion, Strategy Species associated with late successional conifer forests include ringtail, fisher,  Pacific marten, red tree vole, Marbled Murrelet, Northern Spotted Owl, Oregon slender salamander, and many others.

Limiting Factors and Recommended Approaches

Limiting Factor: Loss of Structural Habitat Elements

Where historical stands were perpetuated for 200 to more than 1,000 years, commercial forestlands are now commonly harvested every 60 years or less, which limits the maintenance and future recruitment of large-diameter trees. In addition, the amount of large-diameter snags and logs has been reduced over time through wildfire and timber harvest.

Recommended Approach

Develop programs, incentives, and market-based approaches to encourage longer rotations and strategically located large-diameter tree tracts. Where feasible, maintain structural elements, such as large-diameter tall trees, snags, and logs. Create snags from green trees or high-cut stumps where maintaining snags is not feasible or where snag management goals are not being met. Maintain forest stand structures on private industrial forest lands, and provide technical assistance to landowners to leave large downed wood, green trees, or snags in the upland portion of harvested forests, as well as along riparian areas, to provide benefits for a diversity of wildlife.

Limiting Factor: Impacts of Vegetation Spraying in Early Seral Stage Forest Stands

Within the past two decades, biologists have become increasingly concerned with intensive vegetation management in early seral forest stands and associated impacts on wildlife, from birds to big game.

Recommended Approach

Continue efforts to understand the impacts of vegetation management in early seral stage forest stands by advocating for scientific research on the issue. Provide outreach and technical assistance to help landowners understand the potential for impacts and alternate management techniques. More information on the importance of forest openings can be found in Specialized and Local Habitats.

Limiting Factor: Loss of Late Successional Stand Size and Connectivity

Late successional forest stands have been greatly reduced in size and connectivity, particularly at lower elevations. This can impact species that are highly adapted to late successional conditions and/or species that have limited ability to move over long distances to find new suitable areas. It also allows edge species to compete with ones adapted to extensive interior forest habitat.

Recommended Approach

Maintain existing plans to protect and develop habitat that has been identified as important to species of conservation concern. Use active management to accelerate development of late successional structural characteristics in key areas to expand existing late successional patches into larger areas; these will provide greater blocks of habitat for species with large area requirements or those that require interior forest habitat and are vulnerable to “edge effects”. Continue to carefully plan forest practices to maintain connectivity (KCI: Barriers to Animal Movement), particularly when species vulnerable to fragmentation are present. Seek opportunities to coordinate management of public and private lands (e.g., All-Lands Approach) whenever possible to address conservation needs. Use voluntary conservation tools, such as financial incentives and forest certification to achieve conservation goals on private lands. Carefully-implemented land exchanges in the Bureau of Land Management checkerboard areas offer potential to improve connectivity and habitat values. Recognize that a diversity of forest types and ages should be considered to support wildlife habitat connectivity and ecosystem services at a landscape scale. Historically, late successional coniferous forests throughout Oregon were an element of a shifting mosaic of forest types and ages across the landscape.

Resources for more information