East Cascades Oak and Ponderosa Pine Forest

This narrowly restricted ecological system appears at or near lower treeline in foothills of the eastern Cascades in Washington and Oregon within 65 km (40 miles) of the Columbia River Gorge. It also appears in the adjacent Columbia Plateau ecoregion. Elevations range from 460 to 1920 m. Most occurrences of this system are dominated by a mix of Quercus garryana and Pinus ponderosa or Pseudotsuga menziesii. Isolated, taller Pinus ponderosa or Pseudotsuga menziesii over Quercus garryana trees characterize parts of this system. Clonal Quercus garryana can create dense patches across a grassy landscape or can dominate open woodlands or savannas. The understory may include dense stands of shrubs or, more often, be dominated by grasses, sedges or forbs. Shrub-steppe shrubs may be prominent in some stands and create a distinct tree / shrub / sparse grassland habitat, including Purshia tridentata, Artemisia tridentata, Artemisia nova, and Chrysothamnus viscidiflorus. Understories are generally dominated by herbaceous species, especially graminoids. Mesic sites have an open to closed sodgrass understory dominated by Calamagrostis rubescens, Carex geyeri, Carex rossii, Carex inops, or Elymus glaucus. Drier savanna and woodland understories typically contain bunchgrass steppe species such as Festuca idahoensis or Pseudoroegneria spicata. Common exotic grasses that often appear in high abundance are Bromus tectorum and Poa bulbosa. These woodlands occur at the lower treeline/ecotone between Artemisia spp. or Purshia tridentata steppe or shrubland and Pinus ponderosa and/or Pseudotsuga menziesii forests or woodlands. In the Columbia River Gorge, this system appears as small to large patches in transitional areas in the Little White Salmon and White Salmon river drainages in Washington and Hood River, Rock Creek, Moiser Creek, Mill Creek, Threemile Creek, Fifteen Mile Creek, and White River drainages in Oregon. Quercus garryana can create dense patches often associated with grassland or shrubland balds within a closed Pseudotsuga menziesii forest landscape. Commonly the understory is shrubby and composed of Ceanothus integerrimus, Holodiscus discolor, Symphoricarpos albus, and Toxicodendron diversilobum. Fire plays an important role in creating vegetation structure and composition in this habitat. Decades of fire suppression have led to invasion by Pinus ponderosa along lower treeline and by Pseudotsuga menziesii in the gorge and other oak patches on xeric sites in the east Cascade foothills. In the past, most of the habitat experienced frequent low-severity fires that maintained woodland or savanna conditions. The mean fire-return interval is 20 years, although variable. Soil drought plays a role, maintaining an open tree canopy in part of this dry woodland habitat.

Most occurrences of this system are dominated by a mix of Quercus garryana and Pinus ponderosa or Pseudotsuga menziesii. Isolated, taller Pinus ponderosa or Pseudotsuga menziesii over Quercus garryana trees characterize parts of this system. Clonal Quercus garryana can create dense patches across a grassy landscape or can dominate open woodlands or savannas. The understory may include dense stands of shrubs or, more often, be dominated by grasses, sedges or forbs. Shrub-steppe shrubs may be prominent in some stands and create a distinct tree / shrub / sparse grassland habitat, including Purshia tridentata, Artemisia tridentata, Artemisia nova, and Chrysothamnus viscidiflorus. Understories are generally dominated by herbaceous species, especially graminoids. Mesic sites have an open to closed sodgrass understory dominated by Calamagrostis rubescens, Carex geyeri, Carex rossii, Carex inops, or Elymus glaucus. Drier savanna and woodland understories typically contain bunchgrass steppe species such as Festuca idahoensis or Pseudoroegneria spicata. Common exotic grasses that often appear in high abundance are Bromus tectorum and Poa bulbosa.

This narrowly restricted ecological system appears at or near lower treeline in foothills of the eastern Cascades in Washington and Oregon within 65 km (40 miles) of the Columbia River Gorge. It also appears in the adjacent Columbia Plateau ecoregion. Elevations range from 460 to 1920 m. In the Columbia River Gorge, this system appears as small to large patches in transitional areas in the Little White Salmon and White Salmon river drainages in Washington and Hood River, Rock Creek, Moiser Creek, Mill Creek, Threemile Creek, Fifteen Mile Creek, and White River drainages in Oregon. Quercus garryana can create dense patches often associated with grassland or shrubland balds within a closed Pseudotsuga menziesii forest landscape.

Fire plays an important role in creating vegetation structure and composition in this habitat. Decades of fire suppression have led to invasion by Pinus ponderosa along lower treeline and by Pseudotsuga menziesii in the gorge and other oak patches on xeric sites in the east Cascade foothills. Most of the habitat experienced frequent low-severity fires that maintained woodland or savanna conditions. The mean fire-return interval is 20 years, although variable. LANDFIRE VDDT models: #R OAP1 Oregon White Oak-Ponderosa Pine model describes general successional pathways treating drier pine succession separate from more mesic Douglas-fir pathways.

LANDFIRE developed a state-and-transition vegetation dynamics VDDT model for this system which has five classes in total (LANDFIRE 2007a, BpS 0710600). These are summarized as:

A) Early Development 1 All Structures (tree-dominated - 10% of type in this stage): Shrub cover is 0-40%. The early stage is the initial post-disturbance community dominated by white oak sprouts from coppice origin. Bunchgrasses and associated forbs dominate understory with bare ground and rock/gravel abundant in interspaces. Native herbivory may maintain oak sprouts in "shrub" form for extended period. Early stage includes oak sprouts or seedling/saplings growth to 4-6 inches dbh. Occasional sites with ponderosa pine or Douglas-fir will have diameters up to 8 inches. Succeeds to class C (mid/open) after about 50 years. Herbivory and surface fires maintain the stand in class A. About a tenth of this area is wet enough to succeed to class B.

B) Mid Development 1 Closed (tree-dominated - 5% of type in this stage): Tree cover is 41-80%. The mid-seral, closed stage occurs at the more mesic end of the environmental gradient and supports a dense canopy of oak and ponderosa pine and/or Douglas-fir. Oak diameter ranges from 6-12 inches dbh with crown closure approaching 70%. Ponderosa pine and Douglas-fir may be 8-20 inches dbh. Sod-forming grasses and shade-tolerant shrubs will be prominent on the majority of sites. Species from more arid sites may be remnants of earlier, more open post-fire communities. Lasts up to 150 years in this class. Replacement fire about every few hundred years; mixed fire opens the stand (to class C).

C) Mid Development 1 Open (tree-dominated - 10% of type in this stage): Tree cover is 10-40%. The mid-seral, open stage occurs on arid slopes and benches and represents that portion of the environmental gradient where fire-tolerant communities develop as oak woodlands. Usually the dry site conditions limit tree density and canopy closure is relatively low (between 10-30%). Conifers may occur sporadically at low coverage. Oak diameter ranges from 6-10 inches dbh. Bunchgrasses and shade-intolerant shrubs, notably antelope bitterbrush, will be prominent on the majority of sites. Replacement fire is infrequent; surface fire maintains it in class C. Moist sites can fill in to late/closed conditions (class E).

D) Late Development 1 Open (tree-dominated - 65% of type in this stage): Tree cover is 10-40%. The late-seral, open stage is characterized by large, principally multi-stemmed (now, although historically wider spaced, giant-trunked trees were more common), white oaks in open stands with bunchgrass, forb, and shrub understories. These woodlands support crown closure between 10-30%. Diameters range from 10-18 inches dbh with ages over 350 years for those individuals surviving fires. Mature, large conifers may occur sporadically at low coverage. Bunchgrasses (Pascopyrum smithii and Festuca idahoensis) and shade-intolerant shrubs, notably antelope bitterbrush, will be prominent on the majority of sites. Surface fires maintain it in class D. Replacement fire resets to class A.

E) Late Development 1 Closed (tree-dominated - 10% of type in this stage): Tree cover is 41-80%. This stage has mature overstory ponderosa pine and/or Douglas-fir as emergents over a lower canopy layer of white oak. The conifers have survived a few burn cycles and may show fire scars; dbhs are 21+ inches. Oregon white oak may reach its largest diameters in eastside ecosystems in these river and stream terraces attaining a dbh of 18-20 inches. Canopy closure is high (60-80%) with a dense understory dominated by sod-forming grasses and shrubs. Mixed fire opens the stand.

Historical fire frequency is between 5-30 years in this type. Fire intensities were probably low in open stands but increased in severity as woodland vegetation transitioned to a denser, closed-canopy type along water courses. Canopy is fire-tolerant and therefore fire severity is low. The natural fire regime was a type I regime in the upland. In the more mesic river terraces and draws, fire frequency probably decreased with a fire interval of 50-60 years. With dense vegetation and the occurrence of fuel ladders, fire severity would become mixed. The fire regime may reflect a type III in this more mesic habitat (LANDFIRE 2007a, BpS 0710600).

Insects and disease may impact individual trees (either ponderosa pine or white oak) locally. Armillaria root rot, western pine beetle, western oak looper, western tent caterpillar, and the pine engraver have the greatest potential for damage (LANDFIRE 2007a, BpS 0710600).

Nutrient cycling, specifically carbon cycling, is an important ecological process within many ecological systems. However, biological decomposition in ponderosa pine forests is more limited than biological production, resulting in accumulation of organic materials, especially in the absence of fire (Harvey 1994, Graham and Jain 2005).

Conversion of this type has commonly come from agriculture and rural and urban development including past homesteading (WNHP 2011). Ongoing threats since European settlement include fire suppression, timber and fuelwood harvest, improper livestock grazing, and introduced species (WNHP 2011). Road building and development increase fragmentation (WNHP 2011).

This system is characterized by frequent (5-30 year fire-return interval) low-intensity ground fires that maintain the open savanna structure that is characteristic of most of this system (LANDFIRE 2007a fire regime I). Direct fire suppression and removal of fine fuels by improper grazing has increased fire-return intervals resulting in higher density of understory shrubs and canopy trees and increased fire severity. Logging and grazing have created scrub-like stands of oak that are more susceptible to stand-replacement fires (WNHP 2011). Improper grazing can result in loss of herbaceous cover or the replacement of native bunchgrasses with non-native species such as Bromus tectorum, Poa bulbosa, or Cynosurus echinatus. In summary, composition, abundance, and structure of native species in this system are significantly threatened by fire suppression, grazing, homesteading and development, and logging (WNHP 2011).

This narrowly restricted ecological system appears at or near lower treeline in foothills of the eastern Cascades in Washington and Oregon within 65 km (40 miles) of the Columbia River Gorge. It also appears in the adjacent Columbia Plateau ecoregion. Disjunct occurrences in Klamath and Siskiyou counties, Oregon, have more sagebrush and bitterbrush in the understory, along with other shrubs.