Pacific Northwest Lowland Mixed Hardwood-Conifer Forest

EVT 9170North Pacific Lowland Mixed Hardwood-Conifer Forest
CES204.073GNRTreeConifer-hardwood
Summary
This lowland mixed hardwood - conifer forest system occurs throughout the Pacific Northwest. It occurs on valley terraces, margins, and slopes at low elevations in the mountains of the Pacific Northwest Coast and interior valleys west of the high Cascade Range. These forests are composed of large conifers, including Pseudotsuga menziesii, Thuja plicata, Abies grandis, Tsuga heterophylla, and/or Picea sitchensis, with deciduous hardwood trees present and usually codominant. Major dominant broadleaf species are Acer macrophyllum, Quercus garryana, Alnus rubra, Frangula purshiana, and Cornus nuttallii. Conifers tend to increase with succession in the absence of major disturbance although the hardwoods, particularly Acer macrophyllum, persist in the overstory. The understory is characterized by deciduous shrubs such as Acer circinatum, Corylus cornuta, Oemleria cerasiformis, Rubus ursinus, Symphoricarpos albus, and Toxicodendron diversilobum, but evergreen shrubs, including Gaultheria shallon and Mahonia nervosa and forbs, such as Polystichum munitum and Oxalis oregana, can be dominant.
Source: NatureServe Explorer
Vegetation
These forests are composed of large conifers, including Pseudotsuga menziesii, Thuja plicata, Abies grandis, Tsuga heterophylla, and/or Picea sitchensis, with deciduous hardwood trees present and usually codominant. Major dominant broadleaf species are Acer macrophyllum, Quercus garryana, Alnus rubra, Frangula purshiana, and Cornus nuttallii. Conifers tend to increase with succession in the absence of major disturbance although the hardwoods, particularly Acer macrophyllum, persist in the overstory. The understory is characterized by deciduous shrubs such as Acer circinatum, Corylus cornuta, Oemleria cerasiformis, Rubus ursinus, Symphoricarpos albus, and Toxicodendron diversilobum, but evergreen shrubs, including Gaultheria shallon and Mahonia nervosa and forbs, such as Polystichum munitum and Oxalis oregana, can be dominant.
Source: NatureServe Explorer
Environment
In some places, hardwoods are truly only found in early-seral conditions. This is more true the farther north you get, so in Washington, there are a few places where hardwoods persist, outside of the dry Douglas fir - madrone forests around the Willamette Valley, Puget Trough and the western Oregon Interior Valleys. In the Coast Ranges and Cascades, there are hardwoods (mostly alder and bigleaf maple) found in most of the valley toeslopes. They also occur in areas with exposed talus, exposed rocks, and in dry places, and often with Oregon white oak and Oregon ash. This mix of deciduous hardwoods and conifers is a climax forest in many areas, while in others it is successional, with the conifers completely overtaking the hardwoods after 200 years or so without disturbance.
Source: NatureServe Explorer
Distribution
This system occurs throughout the Pacific Northwest elevationally below the Silver Fir Zone.
Source: NatureServe Explorer
Ecologically Associated Plant Species

Plant species that characterize this ecosystem type, organized by vegetation stratum. These are species ecologically associated with the ecosystem, not confirmed present in any specific area.

Tree canopy

Abies grandis, Acer macrophyllum, Cornus nuttallii, Picea sitchensis, Pseudotsuga menziesii, Quercus garryana, Thuja plicata, Tsuga heterophylla

Shrub/sapling (tall & short)

Acer circinatum, Alnus rubra, Corylus cornuta, Frangula purshiana, Oemleria cerasiformis

Short shrub/sapling

Berberis nervosa, Gaultheria shallon, Rubus ursinus, Symphoricarpos albus

Herb (field)

Agrostis howellii, Cardamine pattersonii, Erigeron howellii, Erythronium elegans, Lathyrus holochlorus, Lilium occidentale, Oxalis oregana, Polystichum munitum, Sidalcea hirtipes, Sidalcea nelsoniana, Sullivantia oregana, Toxicodendron diversilobum

Nonvascular

Otidea smithii, Phaeocollybia dissiliens, Phaeocollybia gregaria, Ramaria rainierensis, Rhizopogon exiguus, Rubroboletus pulcherrimus
Source: NatureServe Ecological System assessment
Ecologically Associated Animals (19)

Animal species ecologically associated with this ecosystem type based on NatureServe assessment. These are species whose habitat requirements overlap with this ecosystem, not confirmed present in any specific roadless area.

Mammals (5)

Common NameScientific NameG-Rank
Townsend's ChipmunkNeotamias townsendiiG5
Columbian White-tailed DeerOdocoileus virginianus leucurusG5T3Q
North American DeermousePeromyscus maniculatusG5
Trowbridge's ShrewSorex trowbridgiiG5
Douglas' SquirrelTamiasciurus douglasiiG5

Reptiles (2)

Common NameScientific NameG-Rank
Northern Alligator LizardElgaria coeruleaG5
Northwestern GartersnakeThamnophis ordinoidesG5

Amphibians (3)

Common NameScientific NameG-Rank
Oregon Slender SalamanderBatrachoseps wrightiG3
EnsatinaEnsatina eschscholtziiG5
Oregon Spotted FrogRana pretiosaG2

Insects (2)

Common NameScientific NameG-Rank
Spurred Bizarre CaddisflyLepidostoma astaneaG2
Blind Carabid BeetlePterostichus rothiG2?

Molluscs (5)

Common NameScientific NameG-Rank
Keeled Jumping-slugHemphillia burringtoniG3
Tillamook WesternslugHesperarion mariaeG3
Pacific SidebandMonadenia fidelis flavaG4G5T1T2
Broadwhorl Tightcoil SnailPristiloma johnsoniG3
Scaly ChaparralTrilobopsis loricataG2G3

Other (2)

Common NameScientific NameG-Rank
Salamander SlugGliabates oregoniusGHQ
Umpqua SidebandMonadenia fidelis ssp. 2G4G5T1
Source: NatureServe Ecological System assessment
At-Risk Species Associated with this Ecosystem (27)

Species with conservation concern that are ecologically associated with this ecosystem type. G-Rank indicates global conservation status: G1 (critically imperiled) through G5 (secure). ESA status indicates U.S. Endangered Species Act listing.

Common NameScientific NameG-RankESA Status
Howell's BentgrassAgrostis howelliiG2--
Oregon Slender SalamanderBatrachoseps wrightiG3--
Saddle Mountain BittercressCardamine pattersoniiG2--
Howell's FleabaneErigeron howelliiG2--
Coast Range FawnlilyErythronium elegansG2--
Salamander SlugGliabates oregoniusGHQ--
Keeled Jumping-slugHemphillia burringtoniG3--
Tillamook WesternslugHesperarion mariaeG3--
Thinleaf PeavineLathyrus holochlorusG2?--
Spurred Bizarre CaddisflyLepidostoma astaneaG2--
Western LilyLilium occidentaleG1G2Endangered
Pacific SidebandMonadenia fidelis flavaG4G5T1T2--
Umpqua SidebandMonadenia fidelis ssp. 2G4G5T1--
Columbian White-tailed DeerOdocoileus virginianus leucurusG5T3Q--
a fungusOtidea smithiiG3--
a fungusPhaeocollybia dissiliensG2G3--
a fungusPhaeocollybia gregariaG2--
Broadwhorl Tightcoil SnailPristiloma johnsoniG3--
Blind Carabid BeetlePterostichus rothiG2?--
a fungusRamaria rainierensisG2--
Oregon Spotted FrogRana pretiosaG2Threatened
a fungusRhizopogon exiguusG2G3--
Red-pored BoleteRubroboletus pulcherrimusG3--
Bristly-stem SidalceaSidalcea hirtipesG2--
Nelson's SidalceaSidalcea nelsonianaG2G3Delisted
Oregon SullivantiaSullivantia oreganaG2--
Scaly ChaparralTrilobopsis loricataG2G3--
Source: NatureServe Ecological System assessment
Component Associations (13)

Plant community associations that occur within this ecological system. Associations are the finest level of the U.S. National Vegetation Classification (USNVC) and describe specific, repeating assemblages of plant species. Each association represents a distinct community type that may be found where this ecosystem occurs.

NameG-Rank
Abies grandis - Acer macrophyllum / Symphoricarpos albus ForestG3 NatureServe
Acer macrophyllum / Acer circinatum ForestG4 NatureServe
Acer macrophyllum - Pseudotsuga menziesii / Acer circinatum / Polystichum munitum ForestG4 NatureServe
Acer macrophyllum - Pseudotsuga menziesii / Corylus cornuta / Hydrophyllum tenuipes ForestG3 NatureServe
Acer macrophyllum / Rubus spectabilis Riparian ForestG4 NatureServe
Acer macrophyllum / (Rubus ursinus - Toxicodendron diversilobum) Riparian ForestG3 NatureServe
Acer macrophyllum / Symphoricarpos albus / Urtica dioica ssp. gracilis Riparian ForestG3 NatureServe
Alnus rubra / Acer circinatum / Claytonia sibirica Riparian ForestG4 NatureServe
Alnus rubra / Elymus glaucus Riparian ForestG4 NatureServe
Alnus rubra / Oxalis (oregana, trilliifolia) Riparian ForestG4 NatureServe
Alnus rubra / Rubus parviflorus Riparian ForestG4 NatureServe
Quercus garryana - (Fraxinus latifolia) / Symphoricarpos albus Riparian ForestG2 NatureServe
Tsuga heterophylla - (Pseudotsuga menziesii) / Oplopanax horridus / Polystichum munitum ForestG4 NatureServe
State Conservation Ranks (2)

Subnational conservation status ranks (S-ranks) assigned by Natural Heritage Programs in each state where this ecosystem occurs. S1 indicates critically imperiled at the state level, S2 imperiled, S3 vulnerable, S4 apparently secure, and S5 secure. An ecosystem may be globally secure but imperiled in specific states at the edge of its range.

StateS-Rank
ORSNR
WASNR
Roadless Areas (12)

Inventoried Roadless Areas where this ecosystem is present, identified from LANDFIRE 2024 Existing Vegetation Type spatial analysis. Coverage indicates the proportion of each area occupied by this ecosystem type.

Oregon (3)

AreaForestCoverageHectares
Smith UmpquaSiuslaw National Forest1.5%46.98
EagleMt. Hood National Forest1.1%72
LarchMt. Hood National Forest0.7%38.79

Washington (9)

AreaForestCoverageHectares
Glacier Peak MMt Baker-Snoqualmie National Forest3.5%16.65
Higgins MountainMt Baker-Snoqualmie National Forest2.8%151.83
Mt. Baker SouthMt Baker-Snoqualmie National Forest2.2%59.58
Mt. Baker Noisy - DiobsudMt Baker-Snoqualmie National Forest1.3%293.4
Glacier Peak HMt Baker-Snoqualmie National Forest1.3%52.74
Glacier Peak LMt Baker-Snoqualmie National Forest1.3%72.18
Glacier Peak JMt Baker-Snoqualmie National Forest1.3%134.73
Boulder RiverMt Baker-Snoqualmie National Forest0.7%88.29
Glacier Peak KMt Baker-Snoqualmie National Forest0.5%98.37
Methodology and Data Sources

Ecosystem classification: Ecosystems are classified using the LANDFIRE 2024 Existing Vegetation Type (EVT) layer, mapped to NatureServe Terrestrial Ecological Systems via a curated crosswalk. Each EVT is linked to the USNVC (U.S. National Vegetation Classification) hierarchy through pixel-level co-occurrence analysis of LANDFIRE EVT and NatureServe IVC Group rasters across all roadless areas.

Vegetation coverage: Coverage percentages and hectares are derived from zonal statistics of the LANDFIRE 2024 EVT raster intersected with roadless area boundaries.

Ecosystem narratives and community species: Sourced from the NatureServe Explorer API, representing professional ecological assessments of vegetation composition, environmental setting, dynamics, threats, and characteristic species assemblages.

IVC hierarchy: The International Vegetation Classification hierarchy is sourced from the USNVC v3.0 Catalog, providing the full classification from Biome through Association levels.

Component associations: Plant community associations listed as components of each NatureServe Ecological System. Association data from the NatureServe Explorer API.

State ranks: Conservation status ranks assigned by NatureServe member programs in each state where the ecosystem occurs.