Every time a migratory bird or passing butterfly lands on a plant that you've carefully cultivated, it's a gentle reminder that our gardens don't exist in a vacuum. These garden critters are picking up the trail that millions of years of evolution tell them to follow, even in the complicated mosaic of our modern world. Though many of us imagine nature as a place that’s “out there,” the truth is that every inch of this planet belongs to a larger ecosystem and that our lives (human or otherwise) are interconnected. At a time when our entire planet is experiencing rapid climatic changes and record-breaking declines in insect and bird populations, it can be all too easy to focus on the harm that humans do to our environment. Who's better positioned than gardeners to ask, "What if our power could go the other way? What good can we do for nature?"
Our lawns and backyards add up to millions of acres across the United States and the way that we manage that land has real impacts on the web of life. That means that sustainable practices have the potential to greatly benefit the environment. Luckily, we don't have to work alone — gardening is all about finding powerful allies in nature.
An Oregon white oak at Eagle Creek. Photo by Cathy McQueeny / Tualatin Soil and Water Conservation District
What is a Keystone Plant?
In ecology, a 'keystone species' is an organism with a larger-than-life influence on its ecosystem. Like the keystone at the center of an ancient archway, a keystone species is a load-bearing pillar of its environment. It's often quality over quantity with these organisms — even when they're not always common, they play an outsized role in supporting the wider network of life. Their absence loosens the glue that holds a healthy ecosystem together, while their presence strengthens its resilience.
In the Willamette Valley, we can find a textbook example in the Oregon white oak (Quercus garryana). A few hundred years ago, these long-lived oaks anchored over 600,000 acres of savannah habitat. This is not a strictly "natural" landscape in the first place — indigenous cultural burning kept shrubs and other trees from encroaching, creating a fertile savannah that attracted deer and other mammals to forage in grasslands below the oaks. While over 90% of that land has now been converted into communities, farmlands, and dense forests, each one of the surviving (or replanted) trees play a huge role in supporting our region's wildlife. They are refuges of shade, habitat, and nourishment in these dry grassland ecosystems, supporting more than 200 species of caterpillars and numerous other insects. Their twisted canopies offer ample space for birds to nest and feast on insect life, while the robust root systems stabilize soil and allow thriving communities of insects and microbes to decompose fallen leaves into rich soil. Catkins offer pollen in the spring and acorns provide dense nutrients for foraging animals in the fall.
Though most modern gardeners don't have the space for a sprawling Oregon white oak (if you do, plant one!), our region is filled with other ecological MVPs in all shapes and sizes. A healthy ecosystem thrives on diversity, but the reality is that space is often limited and keystone plants earn their titles by punching well above weight in terms of the wildlife they support.
Our keystone plant list for the Portland area features some of our region's best players — you'll see why!
An evergreen huckleberry at Cornell Farm.
Portland's Keystone Native Plants
Goldenrod
Solidago sp.
Upright flourishes of nutrient-rich golden blooms from mid-summer to fall attract a huge diversity of over 100 pollinator species and even more that use it as a host plant.
Native Sunflowers
Helianthus sp.
Upright flourishes of nutrient-rich golden blooms from mid-summer to fall attract a huge diversity of over 100 pollinator species and even more that use it as a host plant.
Native Aster
Symphyotrichum sp.
Attractive purple daisy-like perennial flower. Tops OSU Garden Ecology Lab's Native Plant Picks for Bees with visits from 74 different species of native bee.
Native Fleabane/Daisies
Erigeron sp.
Small clumping daisies. Act as host plants to at least 14 caterpillar species and supports numerous pollen specialist bees.
Oregon Grape
Mahonia nervosa & aquifolium
Attractive shrubs of with leathery, scalloped evergreen leaves. Profuse yellow flowers attract diverse pollinators and edible berries support birds.
Red and Evergreen Huckleberries
Vaccinium ovatum & parvifolium
Flowering, fruiting shrubs in the blueberry family that support over a hundred species of butterflies and moths.
Bitter Cherry or Chokecherry
Prunus emarginata or virginiana
From fragrant springtime flowers for bees to summer fruit for birds such as the Cedar waxwing, these are multi-tasking wildlife magnets. They host insects and bird nests.
Scouler's Willow
Salix scouleriana
Fast-growing deciduous tree that supports over 250 species of caterpillars (including the Western tiger swallowtail, dreamy duskywing, and mourning cloak butterfly), as well as other wildlife. Needs consistent moisture but is more drought-tolerant than most native willows.
Oregon White Oak
Quercus garryana
Long-lived, drought-tolerant deciduous tree with a sprawling crown. One of the most important wildlife plants in the Willamette Valley. Hosts gray hairstreak and Propertius duskywing caterpillars.
Be the Keystone
This is an incomplete list and a healthy ecosystem has a diverse array of different plants, but these are great plants to get started on building high-impact habitat that invites nature to share your garden. Ultimately, the species that has the most influence on your garden is you, the gardener. What are you going to plant?
For More Information
National Wildlife Federation's Keystone Plants by Ecoregion: https://www.nwf.org/keystoneplants
OSU's Plant Picks for Bees: https://extension.oregonstate.edu/catalog/em-9363-native-plant-picks-bees
Portland Plant List: https://www.portland.gov/bps/planning/environ-planning/portland-plant-list
Tualatin Soil and Water Conservation District: https://conservationdistrict.org/2020/do-you-have-oregon-white-oak-trees-on-your-property-2020-2.html
The Nature of Oaks: The Rich Ecology of Our Most Essential Native Trees by Douglas W. Tallamy
Thank you for this wonderful reminder and great list of keystones
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