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.
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.
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.
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).
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.
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.
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.
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.
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.
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.