West Cascades

West Cascades Ecoregion
Photo Credit: USFS

Description

The West Cascades ecoregion extends from just east of the Cascade Mountains’ summit to the foothills of the Willamette, Umpqua, and Rogue Valleys, and spans nearly the entire length of the state of Oregon, from the Columbia River to within five miles of the California border. The topography and soils of the West Cascades ecoregion have been shaped dramatically by its volcanic past. The West Cascades ecoregion has two geologically distinct areas: the younger volcanic crest (approximately 8 million years old) and the “old Cascades” to the west of the crest (at least 30 million years old). The volcanic crest includes the highest peaks in Oregon: Mt. Hood, Mt. Jefferson, and North, Middle, and South Sisters, all more than 10,000 feet. The “old Cascades” are characterized by long, steep ridges and wide, glaciated valleys.

This ecoregion is almost entirely forested by conifers, although the dominant tree species vary by elevation, site characteristics, and stand history. Douglas-fir is the most common tree below 4,000 feet, often with western hemlock as a co-dominant species. At higher elevations, dominant tree species include Pacific silver fir, mountain hemlock, or subalpine fir. Other common conifers include western redcedar, grand fir, and noble fir. Above approximately 7,000 feet, the conditions are too severe for tree growth, and alpine parklands and dwarf shrubs predominate, including some wetlands and barren expanses of rock and ice. In the southern areas, ponderosa pine, sugar pine, and incense cedar often are found with Douglas-fir at the lower elevations.

The climate and resulting fire regimes vary with latitude and elevation. The northern portion of the ecoregion is typified by less frequent but more severe fires, whereas the southern portion is typically drier with moderately frequent, mixed-severity, lightning-caused fires. Across the entire region, fire frequency and severity are increasing due to changing climate. At lower elevations, winter conditions are often mild with high rainfall. In contrast, above 4,000 feet, winters are typified by lower temperatures and much of the precipitation occurs as snowfall.

The West Cascades ecoregion is sparsely populated, with towns including Cascade Locks, Butte Falls, Detroit, Gates, Idanha, McKenzie Bridge, Blue River, Oakridge, Westfir, and part of Sandy and Sweet Home (the remainder of which lie in the Willamette Valley ecoregion). Local economies were once entirely dependent on timber harvest but have been greatly affected as market conditions (long-term and broad-scale changes in the forest products marketplace) and shifts in public forest management priorities have shaped Oregon’s timber industry. Many towns are increasingly promoting recreational opportunities, including hiking, camping, fishing, hunting, birding, mountain biking, and skiing.

Characteristics

Important Industries

Forest products, recreation (hiking, biking, wildlife viewing, hunting, fishing, snow sports)

Major Agricultural Products

Fruits, mint, cattle

Important Nature-based Recreational Areas

Mt. Hood, Willamette, Umpqua, and Rogue River-Siskiyou National Forests, Waldo Lake, Odell Lake, Detroit and Hills Creek Reservoirs, Crater Lake National Park, Three Sisters, Sky Lakes, and Mount Jefferson Wilderness Areas, Willamette Hatchery

Elevation

98 feet (along the western border of the ecoregion) to 11,240 feet (Cascade peaks)

Important Rivers

Clackamas (Oak Grove Fork), McKenzie, Rogue, Umpqua, Breitenbush, Middle Santiam, North and Middle Fork of the Willamette

Conservation Issues and Priorities

As with Oregon’s other forested ecoregions, habitats have been impacted by interrelated changes in ecological processes due to fire suppression, selective harvest practices, and unsustainable grazing. These changes have increased vulnerability of forests to insects, disease, and uncharacteristically severe wildfire. In addition, changing climate conditions are also putting this ecoregion at risk, with increased drought prevalence and warming temperatures affecting water availability and contributing to more frequent and severe wildfires. Recreational pressure is also a growing concern, with a variety of impacts resulting from activities like mountain biking, skiing, and off-road vehicle use and associated demands for new trails and facilities.

Key Conservation Issues of particular concern in the West Cascades ecoregion include Disruption of Disturbance Regimes, Water Quality and Quantity, Invasive Species, and Barriers to Animal Movement.

Climate

The West Cascades ecoregion is characterized by steep ridges and river valleys to the west and a high plateau to the east. The region has a mild to severe mid-latitude climate with dry, warm summers and mild or cool, very wet winters. The climate varies by latitude and elevation, especially near the volcanoes within this ecoregion.

Warming is projected in all seasons across the Cascades ecoregion, with the largest increases projected for summer. Summer average temperature is projected to increase by as much as 7°F for the 2040-2069 period and as much as 11°F for the 2070-2099 period (Figure 1). Late summer precipitation is projected to decrease by as much as 19% by the 2070-2099 period, and cool season precipitation is projected to increase by 6% (Figure 2). Less precipitation will fall as snow in Cascades in the future, leading to even wetter winters and drier summers. Confidence in cool season projections, however, is low after 2010-2039. Growing degree days are projected to more than double by the 2070-2099 period for this ecoregion under a high emissions scenario (SSP585). Frost days are projected to decrease from 171 per year until there are fewer than 100 per year, on average, under the high emissions scenario (SSP585).

 

Figure 1. Model median historical (1950-2010) and future projections of summer maximum temperature change for three periods (2010-2039, 2040-2069, 2070-2099) under a high emission scenario (SSP585) for the West Cascades. Future projections show increasing temperatures, with slightly less warming in the southwest (Raymond and Fusco, 2024).
Figure 2. Model median historical (1950-2010) total late summer precipitation and projected percent change for three future periods (2010-2039, 2040-2069, 2070-2099) under a high emission scenario (SSP585) for the West Cascades. Future projections for a high (SSP585) scenario show decreasing late summer precipitation across the region with a greater decrease in the north (Raymond and Fusco, 2024).

Limiting Factors and Recommended Approaches

Limiting Factor: Altered Fire Regimes

CMP Direct Threats 7.1, 11.3, 11.4

Many forests in the West Cascades ecoregion are at risk of losing one or more ecosystem components to wildfire. Fire suppression and certain forest practices have resulted in young, dense, mixed-species stands of trees that are at increased risk of forest-destroying crown fires, disease, and damage by insects. Under changing climate conditions these risks are expected to increase, with warming temperatures and more frequent drought contributing to shorter fire return intervals and more severe fires. Efforts to reduce risks of uncharacteristically severe fires can help to restore habitat but require careful planning to provide sufficient habitat features that are important to wildlife (e.g., snags, downed logs, hiding cover).

Recommended Approach

Use an integrated approach to wildfire issues that considers historical conditions, wildlife conservation, natural fire intervals, and silvicultural techniques. Consider the broader landscape context, including habitat connectivity, cumulative impacts, fish and wildlife species presence, and mapped or modeled suitable habitat when engaging in forest management and wildfire risk mitigation activities. Reintroduce fire where feasible; prioritize sites and applications. Maintain important wildlife habitat features, such as snags and logs, to sustain wildlife species that are dependent on dead wood. Maintain early-, mid-, and late-seral habitats to support a diversity of species. Monitor these efforts and use adaptive management techniques to ensure efforts are meeting habitat restoration and wildfire prevention objectives with minimal impacts on wildlife. Work with homeowners and resort operators to reduce vulnerability of properties to wildfire while maintaining habitat quality. Highlight successful, environmentally sensitive fuel management programs. In the case of post-wildfire recovery, maintain high snag densities and replant with site-adapted native tree, shrub, grass, and forb species. Promote revegetation with native species that are expected to be climate resilient. Prevent colonization of invasive vegetation, such as scotch broom. Manage reforestation after wildfire to create species and structural diversity, based on local management goals.

Limiting Factor: Water

CMP Direct Threats 7.2, 114

Water Quantity is a limiting factor for fish, wildlife, and livestock. Changing climate conditions are leading to rising temperatures and altered patterns of precipitation, which affect water availability across different times of year, and drought conditions are occurring more frequently. In high elevation areas, loss of snowpack due to warming climate conditions is affecting habitat for many species along the Cascade crest and is leading to reduced stream flow rates and peak flow rates that are occurring earlier in the year. In streams, seasonal low flows can limit habitat suitability, survival, and reproduction for many fish and wildlife species.

Water quality can also limit species and habitats. Runoff from agricultural areas and herbicides applied to forest lands can contaminate waterways. Warming temperatures, combined with higher nutrient levels due to agricultural runoff, are increasing the prevalence of toxic cyanobacterial blooms.

Recommended Approach

Provide incentives and information about water usage and sharing during low flow conditions (e.g., late summer). Promote water management actions that enable climate resilience and adaptation. Invest in watershed-scale projects for cold water and flow protection. Identify and protect cold water rearing and refugia habitat for aquatic species. Increase awareness and manage timing of applications of potential aquatic contaminants. Improve compliance with water quality standards and pesticide use labels administered by the DEQ and EPA. Work on implementing Senate Bill 1010 (Oregon Department of Agriculture) and DEQ Total Maximum Daily Load water quality plans.

Limiting Factor: Habitat Fragmentation

CMP Direct Threats 1, 2.1, 2.3, 3.3, 8.1

Increasing traffic volumes, road density, recreational pressure, and urban and rural development are contributing to habitat loss and fragmentation, and create significant barriers to animal movements. Hydropower systems, including high-head flood control and hydropower dams, also have significant impacts to species movement in this ecoregion. Levees, hydropower canals, and hardened stream banks reduce available habitat for fish and aquatic species and can entrap and kill wildlife. Altered hydrology from these systems, including impacts to temperatures and timing of water availability, can affect fish passage.

Recommended Approach

Work with community leaders and local governments to encourage planned, efficient growth. Support existing land use regulations to preserve forestland, farmland, rangeland, open spaces, recreation areas, wildlife refuges, and natural habitats. Work with community leaders and agency partners to protect wildlife movement corridors and to fund and implement site-appropriate habitat enhancement and restoration efforts to facilitate wildlife movement. Continue working with Oregon Watershed Enhancement Board, Oregon Department of Transportation, Oregon Department of Forestry, USFS, BLM, counties, local municipalities, irrigation districts, and other partners to inventory, prioritize, and provide fish passage at artificial obstructions, leveraging current work done by ODFW’s Fish Passage Task Force to expand implementation of fish passage priorities. Minimize entrapment risk in hydropower canals by providing crossing structures and escape devices at regular intervals. Provide incentives (e.g., financial assistance, conservation easements) and information about the benefits of maintaining wildlife habitat. Broad-scale conservation strategies will need to focus on restoring and maintaining more natural ecosystem processes and functions within areas that are managed primarily for other values. This may include an emphasis on more “conservation-friendly” management techniques for existing land uses, and restoration of some key ecosystem components such as riparian function.

Limiting Factor: Invasive Species

CMP Direct Threat 8.1

Invasive plants and animals disrupt and degrade native communities, diminish populations of at-risk native species, and threaten the economic productivity of resource lands. Invasive plants, particularly noxious weeds, have increased substantially. In many cases, the spread of invasives is facilitated by wildfire, as many invasive species can quickly colonize disturbed areas. In this ecoregion, Scotch broom is of particular concern. Scotch broom spreads aggressively to form monocultures, displacing native, beneficial plants and forage grasses, with seeds that can remain viable for decades, making it very difficult to eradicate. Himalayan blackberry is also widespread, with significant local impacts to meadows, riparian areas, and grasslands.

While not as disruptive as invasive vegetation, invasive animals have caused problems for native wildlife species in this ecoregion. A variety of sport fish, introduced to many high elevation lakes, compete with native amphibians for limited resources and prey on native species and/or their eggs or young. Barred Owl, expanding westward from their native range in the eastern US, compete directly with the native, threatened Northern Spotted Owl for food and habitat.

Recommended Approach

Emphasize prevention, risk assessment, early detection, and quick control to prevent new invasive species from becoming fully established. Prioritize efforts to focus on key invasive species in high priority areas, particularly where Key Habitats and Species of Greatest Conservation Need occur. Where needed, use multiple site-appropriate tools (e.g., mechanical, chemical, and biological) to control the most damaging invasive species. During post-fire recovery efforts, use techniques that prevent establishment of or quickly eradicate invasive vegetation. Ensure native species are used during restoration and revegetation efforts and promote native species that are expected to be climate resilient.

Limiting Factor: Recreational Activity

CMP Direct Threats 1.3, 4.1, 5.1, 5.2, 5.4, 6.1

Increasing demands for year-round recreational activity can disturb wildlife. Population growth has contributed to increased pressure on natural areas from recreationists, including those engaging in hiking, biking, camping, fishing, hunting, foraging, rafting, backcountry skiing, boating, paddleboarding, and off-road vehicle use. Expanded road and trail systems developed to help accommodate higher numbers of visitors are increasing habitat fragmentation and risks of behavioral impacts to wildlife. Recreational pressure can lead to an increase in wildlife stress response and behavioral changes that ultimately impact reproductive rates and population abundance. Human recreation can contribute to destruction of sensitive vegetation, harassment of wildlife from off-leash pets, spread of invasive species, and contamination of areas with refuse. Many species will avoid areas near trails, campgrounds, and access roads when humans are present.

Recommended Approach

Plan new recreational trail systems carefully and with consideration for native wildlife and their habitats. For example, limit use and access to certain areas to minimize disturbance to wildlife, avoiding areas more sensitive to damage such as wetlands. Take advantage of abandoned or closed roads, rail lines, or previously impacted areas for conversion into trails. Work with land management agencies such as the USFS to designate areas as high value recreation and low habitat impact areas. Institute road and/or area closures to protect species during sensitive times of year and decommission roads when possible. In high use areas, establish permitted entry systems to decrease recreational pressure. Engage in outreach and education to increase public awareness of recreation impacts to fish and wildlife species; develop messaging to communicate the need for “responsible recreation”.

Species of Greatest Conservation Need

Conservation Opportunity Areas