Willamette Valley oak savanna ecoregion

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Willamette Valley oak savanna

RESOLVE 403

The Willamette Valley oak savanna — the fertile lowland between Oregon's Coast Range and Cascades, historically a fire-managed mosaic of Oregon white oak savanna, prairie, and gallery forest along the Willamette and its tributaries. Less than 3% of the original oak savanna remains; most was converted to agriculture in the 19th-20th centuries. Surviving fragments concentrate in protected reserves and Oregon's wine-country foothills.

Marker placed inside the RESOLVE 2017 polygon at 44.9°N, 123.0°W.

Climate snapshot for this ecoregion

°C

°F

USDA zone range (now)

8a-8b

USDA

What seed packets and nursery tags reference. Coldest-day survival semantics.

Plotwright projection (2041–2070)

10a-10b

Plotwright

Where CHELSA models say the typical winter month is heading.

Average warming this ecoregion is on track for: +3.1°F by mid-century. SSP3-7.0 (current trajectory) · CHELSA v2.1 bio06 sampled across 10 of 10 points within this ecoregion's bounding box.

• Loss of indigenous-managed fire has driven Douglas fir encroachment across most surviving oak savanna; the climate envelope itself is not the limiting factor for Oregon white oak.

• Summer-drought intensification is on-trajectory for the oak-prairie palette, which is selected for it; lengthening dry seasons stress the conifer encroachers more than the savanna natives.

• Garden-relevant: Willamette Valley natives (Oregon white oak, camas, native Iris tenax, blue-eyed grass) carry forward strongly under projected warming — a model palette for the warm-dry-summer / wet-mild-winter PNW lowlands.

At a glance

States / provinces

Oregon

Dominant biome

Temperate Grasslands, Savannas & Shrublands

Realm

Nearctic

Approximate area

5,733 sq mi

Elevation range

100 – 1,500 ft

Climate type

Warm-summer Mediterranean (Köppen Csb)

Conservation tier

Nature Imperiled (Dinerstein NNH 4)

About the temperate grasslands, savannas & shrublands biome

Temperate prairies, steppes, and pampas of grasses and forbs with few trees, under continental climates of hot summers and cold winters. Their deep, fertile soils have made them among the most extensively converted biomes for agriculture.

National refinement sub-regions

Within this RESOLVE ecoregion, national agencies recognise finer-grained sub-regions. Plotwright assigns each sub-region polygon to its containing RESOLVE polygon by centroid.

EPA Level III (US-only) — 1 sub-region

3 · Willamette Valley

Source: USGS / EPA via Omernik (1987).

What's native here

Catalog plants whose Lady Bird Johnson Wildflower Center native-distribution range overlaps the 1-state/province roster for this ecoregion. Distinct from the “suited” section below — these are plants that belong here, not just plants that will grow here.

Grain caveat: native here means “native to at least one state / province this ecoregion crosses,” not necessarily native to this ecoregion's specific habitat. A plant tied to wet meadows that crosses Ontario will surface for any Ontario-spanning ecoregion. Finer per-ecoregion native-status data is a future arc.

Catalog plants suited to this ecoregion

Computed from each plant's stated USDA zone range against this ecoregion's USDA Plant Hardiness Zone Map 2023 (1991-2020 climatology) via ArcGIS FeatureServer published current zone range, with the CHELSA mid-century warming delta applied for the projection. Plants whose stated range falls outside both the current and projected zone end up dropped; the rest land in one of the three buckets below.

Climate-resilient picks · 164

These plants fit this ecoregion today AND remain in range under the mid-century SSP3-7.0 projection. Lead with these for a planting that holds up as the climate shifts.

Black tupelo (black gum)

Calendula (pot marigold)

Carolina allspice (sweetshrub)

Fragrant plantain lily

Maypop (purple passionflower)

Summersweet (sweet pepperbush)

Tulip tree (yellow poplar)

Currently suited · 85

These plants fit the ecoregion as it is today, but the mid-century projection moves them outside their stated zone range — plan for them to struggle by 2070.

Allegheny blackberry

American basswood

American plum

American red raspberry

Canadian serviceberry

Northern maidenhair fern

Short-toothed mountain mint

Newly possible by 2070 · 8

These plants don't fit the current zone range yet, but the mid-century projection brings them into reach. Long-horizon picks for the climate-adaptation wedge.

Wildlife your native plants here support

What this surface IS — and isn't

Inferred from the relationships catalog plants native to this region have with wildlife. We don't carry direct wildlife-range data per ecoregion — this lists what your native plant palette here can support, not a verified checklist of what occurs here. Cross-check the range note on each wildlife's detail page before treating a row as a presence claim.

Only plants with structured native-distribution data contribute here. Old World cultivars and most vegetables are excluded by design — this view shows “what your native palette supports,” not “what your whole garden does.” It will grow as more plants gain native-range data.

Larval hosts · 14

Plants that caterpillars and other larvae feed on while growing.

Butterfly

Spring azure

Celastrina ladon

4 native plants here: Blue elderberry, Blueblossom, Chokecherry + 1 more

Butterfly

Eastern tiger swallowtail

Papilio glaucus

3 native plants here: Quaking aspen, Scarlet bee balm, Virginia bluebells

Moth

Hummingbird clearwing moth

Hemaris thysbe

3 native plants here: Chokecherry, Scarlet bee balm, Wild bergamot

Butterfly

Pearl crescent

Phyciodes tharos

3 native plants here: New England aster, Smooth blue aster, Canada goldenrod

Moth

Polyphemus moth

Antheraea polyphemus

3 native plants here: Chokecherry, Oregon white oak, Quaking aspen

Moth

Hawkmoths

Sphingidae (family-level entry)

2 native plants here: Chokecherry, Wild bergamot

Moth

Io moth

Automeris io

2 native plants here: American red raspberry, Quaking aspen

Butterfly

Red-spotted purple

Limenitis arthemis astyanax

2 native plants here: Chokecherry, Quaking aspen

Butterfly · Specialist support

Skipper butterflies

Hesperiidae (family-level entry)

2 native plants here: Side-oats grama, Common yarrow

Moth

Cecropia moth

Hyalophora cecropia

1 native plant here: Chokecherry

Moth

Imperial moth

Eacles imperialis

1 native plant here: Vine maple

Butterfly

Mourning cloak

Nymphalis antiopa

1 native plant here: Quaking aspen

Butterfly

Silvery checkerspot

Chlosyne nycteis

1 native plant here: Cutleaf coneflower

Butterfly

Viceroy

Limenitis archippus

1 native plant here: Quaking aspen

Pollinators · 4

Wildlife that moves pollen between flowers as it forages.

Bee · Specialist support

Common eastern bumblebee

Bombus impatiens

18 native plants here: American red raspberry, Canada goldenrod, Common sunflower + 15 more

Bee

European honeybee

Apis mellifera

9 native plants here: Common sunflower, Blueblossom, Canada goldenrod + 6 more

Bird

Ruby-throated hummingbird

Archilochus colubris

5 native plants here: Scarlet bee balm, California fuchsia, Golden currant + 2 more

Bee

Mason bees

Osmia spp.

2 native plants here: Chokecherry, Golden currant

Nectar foragers · 9

Wildlife drawing nectar from the plant.

Bee

Sweat bees

Lasioglossum spp.

5 native plants here: California fuchsia, California poppy, Common yarrow + 2 more

Bee

American bumblebee

Bombus pensylvanicus

4 native plants here: Canada goldenrod, New England aster, Wild bergamot + 1 more

Fly

Hover flies (flower flies)

Syrphidae

4 native plants here: Canada goldenrod, Common yarrow, New England aster + 1 more

Bee

Rusty-patched bumble bee

Bombus affinis

4 native plants here: New England aster, Scarlet bee balm, Smooth blue aster + 1 more

Bee

Stem-nesting native bees

multiple genera (Ceratina, Hylaeus, Osmia, etc.)

4 native plants here: Common camas, Blueblossom, Canada goldenrod + 1 more

Butterfly

Common buckeye

Junonia coenia

3 native plants here: Canada goldenrod, New England aster, Smooth blue aster

Butterfly

Monarch butterfly

Danaus plexippus

3 native plants here: Canada goldenrod, New England aster, Smooth blue aster

Other

Green lacewings

Chrysopidae

1 native plant here: Common yarrow

Butterfly

Painted lady

Vanessa cardui

1 native plant here: New England aster

Pollen foragers · 3

Wildlife collecting pollen for food or provisioning.

Bee

Long-horned bees

Melissodes spp.

6 native plants here: Canada goldenrod, Common sunflower, Cutleaf coneflower + 3 more

Bee

Mining bees

Andrena spp.

3 native plants here: Chokecherry, Golden currant, Prairie smoke

Bee

Leafcutter bees

Megachile spp.

2 native plants here: Scarlet bee balm, Wild bergamot

Fruit foragers · 6

Wildlife eating the plant’s fruit.

Bird

Eastern songbirds (multi-species)

multiple species (Passeriformes)

16 native plants here: American red raspberry, Bearberry (kinnikinnick), Blue elderberry + 13 more

Bird

Downy woodpecker

Dryobates pubescens

5 native plants here: Blue elderberry, Golden currant, Chokecherry + 2 more

Bird

American robin

Turdus migratorius

4 native plants here: Blue elderberry, Chokecherry, Golden currant + 1 more

Bird

Cedar waxwing

Bombycilla cedrorum

3 native plants here: Chokecherry, Eastern red cedar, Pacific dogwood

Bird

Eastern bluebird

Sialia sialis

2 native plants here: Blue elderberry, Chokecherry

Bird

Baltimore oriole

Icterus galbula

1 native plant here: Chokecherry

Seed foragers · 3

Wildlife eating the plant’s seed.

Mammal

White-tailed deer

Odocoileus virginianus

5 native plants here: Oregon white oak, Blue elderberry, Chokecherry + 2 more

Bird · Specialist support

American goldfinch

Spinus tristis

4 native plants here: Common sunflower, Cutleaf coneflower, New England aster + 1 more

Mammal

Eastern gray squirrel

Sciurus carolinensis

1 native plant here: Oregon white oak

Shelter · 4

Wildlife nesting in or sheltered by the plant.

Bird

Black-capped chickadee

Poecile atricapillus

3 native plants here: Chokecherry, Oregon white oak, Quaking aspen

Beetle

Common eastern firefly

Photinus pyralis

2 native plants here: Oregon white oak, Quaking aspen

Beetle

Lady beetles

Coccinellidae

2 native plants here: Canada goldenrod, Chokecherry

Bird

Eastern phoebe

Sayornis phoebe

1 native plant here: Red-osier dogwood

Collections for this ecoregion

Curated multi-plant collections whose members all fit this ecoregion's zone range — no won't-grow members smuggled in. Overall fit class shown per collection is the weakest link across its members.

Currently suited · 2 plants

Bright shade foundation

A part-shade starting point with shrub structure and low foliage contrast.

Annabelle hydrangea

Coral bells

Currently suited · 8 plants

Climate-resilient natives for warming zones (eastern NA)

A pollinator-supporting palette of eastern NA natives whose USDA zone range and broad continental distribution score high on the climate-resilience composite. Every plant tolerates 6-7 USDA zones and is native across 15+ US states + multiple Canadian provinces. Holds up under the SSP3-7.0 mid-century projection without the gardener trading wildlife value for resilience.

Switchgrass

Little bluestem

Common milkweed

Black-eyed Susan

Wild bergamot

Sweet Joe-Pye weed

Cutleaf coneflower

New England aster

Currently suited · 6 plants

Mediterranean drought-tolerant edible

A low-water edible palette of culinary herbs + a hardy grape for hot dry sunny sites. Mediterranean-origin plants thrive on neglect; their primary failure mode is overwatering, not underwatering.

English lavender

Rosemary

Garden sage

Oregano

Common thyme

Fox grape

Currently suited · 9 plants

Native pollinator border (eastern US)

A continuous-bloom native pollinator strip for eastern North America. Covers spring through frost with host + nectar plants spanning monarchs, native bees, hummingbirds, and specialist Lepidoptera. Little bluestem provides the matrix grass + Hesperiidae host.