Vernal pools are one of nature’s most fascinating seasonal wetlands. These temporary bodies of water form in natural depressions, filling with rainwater in the fall and winter and gradually drying up in late spring or early summer.
Unlike ponds or lakes, vernal pools have no permanent connection to streams or rivers, meaning they experience cycles of flooding and drying that create unique ecosystems adapted to these conditions.
These seasonal wetlands are incredibly valuable for biodiversity, water filtration, and ecosystem stability, making them a crucial feature in wild and managed landscapes.
How Vernal Pools Work
Vernal pools function as temporary wetlands, storing rainwater in the wet months and slowly releasing it into the soil and atmosphere as temperatures rise.
Because they lack a continuous water source, vernal pools do not support
fish populations, which allows amphibians and invertebrates to thrive without the threat of predation.
Their unique hydrology creates a cycle that supports various plant and animal species, many of which have explicitly adapted to vernal pool environments. The drying phase is as crucial as the wet phase, as it enables certain plant species to germinate and mature while allowing animals to migrate to more permanent water sources.
Vernal Pools and Oregon Native Wildlife
The absence of fish in vernal pools makes them ideal breeding grounds for amphibians, insects, and other small aquatic creatures. In Oregon, these seasonal
wetlands provide essential habitat for a variety of native species:
Pacific tree frog (Pseudacris regilla) – A common and adaptable species, these frogs use vernal pools for breeding and lay eggs in the shallow waters.
Northwestern salamander (Ambystoma gracile) – A key vernal pool species, they rely on these wetlands for reproduction and larval development.
Long-toed salamander (Ambystoma macrodactylum) – This species breeds almost exclusively in fish-free water bodies like vernal pools.
Fairy shrimp (Branchinecta spp.) – These small crustaceans are specially adapted to the temporary waters of vernal pools, completing their life cycle before the pools dry up.
Western pond turtle (Actinemys marmorata) – While not solely dependent on vernal pools, these turtles use them as seasonal foraging grounds.
Mallards (Anas platyrhynchos) & wood ducks (Aix sponsa) – Many waterfowl species use vernal pools as seasonal feeding and resting spots during migration.
Dragonflies and damselflies – These insects rely on vernal pools for breeding, laying their eggs in the still water.
Oregon Native Plants Found in Vernal Pools
Vernal pools support diverse native plants that thrive in fluctuating water levels. These plants help with soil stabilization, water filtration, and providing food and shelter for wildlife. Here are some key species found in and around Oregon’s vernal pools:
Native Grasses:
Slough sedge (Carex obnupta) – A moisture-loving grass that thrives at vernal pool edges.
Tufted hairgrass (Deschampsia cespitosa) – A resilient grass that can tolerate both wet and dry conditions.
Western mannagrass (Glyceria occidentalis) – Important for erosion control in wetland areas.
Meadow barley (Hordeum brachyantherum) – Provides habitat for small insects and amphibians.
American sloughgrass (Beckmannia syzigachne) – Thrives in seasonally wet environments.
Native Flowers:
Showy milkweed (Asclepias speciosa) – A vital nectar source for pollinators, especially monarch butterflies.
Douglas' sagewort / Mugwort (Artemisia douglasiana) – A fragrant plant with silvery foliage, often found in moist meadows and riparian areas.
Common monkeyflower (Erythranthe guttata) – A bright yellow, moisture-loving wildflower that thrives in wet meadows and stream banks.
American yellowrocket (Barbarea orthoceras) – A resilient mustard-family plant with clusters of small yellow flowers, often growing in damp areas.
Common camas (Camassia quamash) – A striking blue-flowered plant that flourishes in vernal pool meadows and wet prairies.
Leichtlin’s camas (Camassia leichtlinii) – Similar to common camas but with larger flowers, providing an important food source for pollinators.
Winecup clarkia (Clarkia purpurea ssp. quadrivulnera) – A vibrant pink to purple wildflower that brightens open meadows.
Fragrant popcornflower (Plagiobothrys figuratus) – A delicate, white-flowered species that thrives in wet meadows and along waterways.
Native Trees:
Oregon ash (Fraxinus latifolia) – Common in riparian and wetland areas, providing shade and erosion control.
Pacific willow (Salix lucida) – Grows along the edges of seasonal wetlands, stabilizing soil.
Red alder (Alnus rubra) – Helps fix nitrogen in the soil and supports a range of wildlife.
Sitka spruce (Picea sitchensis) – Found in wetter coastal areas near seasonal wetlands.
Black cottonwood (Populus trichocarpa) – Thrives along riparian corridors and vernal pool peripheries.
Native Fruits:
Salmonberry (Rubus spectabilis) – Provides food for birds and mammals in riparian areas.
Thimbleberry (Rubus parviflorus) – A dense shrub that supports pollinators and wildlife.
Red elderberry (Sambucus racemosa) – Berries provide a critical food source for birds.
Pacific crabapple (Malus fusca) – Produces small, tart fruits eaten by various wildlife species.
Black hawthorn (Crataegus douglasii) – A valuable food source and nesting habitat for birds.
Vernal Pools and Water Filtration
Beyond their role in supporting biodiversity, vernal pools are essential in filtering and purifying water. As rainwater collects in these pools, it percolates through layers of organic matter and sediment, naturally removing pollutants, excess nutrients, and debris. The process helps recharge groundwater, preventing excess runoff and soil erosion. Native wetland plants play a crucial role in this filtration system, trapping sediments and breaking down contaminants before they reach more extensive waterways.
How to Create or Restore a Vernal Pool
Restoring or creating a vernal pool on your property can dramatically improve habitat diversity and water management. Here’s how the process typically works:
Site Selection: Choose a low-lying, full-sun area that naturally collects rainwater, or dig a shallow depression in the lowest area of your yard.
Gently shape the slope of the sides of the pool down to a depth of 1 ft.
Soil Preparation: Clay-rich soils retain water best, but your vernal pool will become more functional as the plants develop, regardless of the soil.
cover the vernal pool with 3-6 inches of wood chips. You can get a chip drop here: getchipdrop.com
cover the wood chips with 1-2 inches of super-rich soil and seed or plant into your pool.
Planting Native Species: Introduce moisture-loving grasses, sedges, wildflowers, and shrubs that can handle both wet and dry conditions. Here are links to some suppliers that have great PNW Native Seed mixes.
Heritage Seed: You must order large quantities; it would be great if you're working on a bigger project. Here's a link to their pricelist with the vernal pool mix on it: Heritage Seeds Price List
PT Lawn: You'll have to order some of the rest of the grasses and flowers separately; this is a bare-bones vernal pool mix. PT Lawn Vernal Pool Mix
Northwest Meadowscapes has a lot of the native flowers you're looking for You can order directly from them here: Northwest Meadowscapes
Avoiding Drainage Systems: Keeping the area free of artificial drainage will allow it to function naturally.
Monitoring and Maintenance: Over time, native plants will spread, and wildlife will begin using the pool. Minimal intervention is needed beyond removing invasive species.
Oregon’s native wet meadows, vernal pools, and riparian habitats are among the most endangered ecosystems in the state. Due to urban expansion, agriculture, and invasive species, these critical landscapes have been drastically reduced, with some habitats now covering only a fraction of their historic range. Wet meadows and vernal pools, which once supported a diverse array of native plants and wildlife, are particularly vulnerable because they rely on seasonal water cycles often disrupted by development and drainage.
This loss threatens rare plant species like camas and monkeyflower and impacts pollinators, birds, and amphibians that depend on these ecosystems. By restoring and incorporating these habitats into urban spaces, we can help reverse some of this damage while bringing our communities a wealth of ecological benefits.
Integrating native wetland plants into urban landscapes creates beautiful, low-maintenance environments that support biodiversity, improve water management, and enhance resilience to climate change. These plants thrive in rain gardens, bioswales, and naturalized yards, filtering pollutants from stormwater while providing food and shelter for pollinators and wildlife.
Beyond their ecological value, these habitats bring vibrant seasonal color, interesting textures, and a connection to Oregon’s natural heritage, making cities more dynamic and livable. By embracing these endangered ecosystems in our urban spaces, we can create pockets of thriving biodiversity, reconnect people with the land, and contribute to preserving Oregon’s unique and irreplaceable native landscapes.
Don't know where to start? Contact Urban Rewilding, and we can help.
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