A keystone species is a plant, animal, fungi, or microbe that plays an outsize role in its ecosystem. If it is threatened or disappears, the whole food web and ecosystem is at risk of collapsing. Keystone species even literally shape the landscape itself. Read on to find out which plants are keystone species and how to incorporate them into your garden, yard, or local park.
What is a keystone species?
While every species plays a role in its ecosystem, some are particularly important to their local food webs. Maybe they feed many other species, or their roots anchor the landscape, or they keep predators from running amok.
In all cases, if these species disappear, the ecosystem suffers a serious blow. We call these keystone species.
Animals, plants and bugs—all can be keystone species
Keystone species can come in all forms.
For example, beavers are a keystone species. Western ecologists have come to realize that by building their dams, beavers shaped the entire continental U.S. Their dams create pools and marshes that host native species from birds to fish to amphibians, and in turn, those species clean the water and reduce erosion and flooding.
A famous keystone story: wolves
One of the most famous examples of a keystone species is the wolf in Yellowstone National Park. For millennia, wolves kept deer populations in check, which in turn kept the ecosystem in balance.
When humans hunted wolves to extinction, the elk population ballooned and they ate voraciously—reducing grasses, flowers, shrubs, and trees that other animals like birds, bees, and butterflies relied on.
Fewer plants meant more erosion. Even the lakes and river temperatures rose as fewer trees shaded them. Since wolves were reintroduced to Yellowstone, we’ve seen major beneficial changes to the ecosystems.
Bees are keystone species, too. Without bees to do their pollinating magic, many flowers and trees can’t reproduce at all.
What are keystone plants?
In many cases, plants are the foundations of entire food webs. Trees shelter and feed wildlife from bears all the way down to fungi; grasses and flowering plants feed animals all the way up the food chain. Roots also anchor the landscape, enrich soil, and affect the flow of water. Plants play incredibly important roles in ecosystems!
What do keystone plant species do?
Feed wildlife.
Plants form the basis of food webs. Flowers feed butterflies, bees, and hummingbirds. Grass seeds feed birds through the winter. Tree leaves nourish the caterpillars of butterflies and moths and grazing animals like moose and elk, and their nuts feed many species.
Provide shelter.
Trees are homes for birds and many other animals; along rivers and lakes, they also keep water cool for fish and aquatic species. Many bees, butterflies, and insects make their homes in tree bark, on flowering plants, or even inside hollow grasses.
Anchor the landscape.
Grasses and plants with long taproots dig deep into the ground, preventing erosion and aerating the soil for other plants. Trees stabilize hillsides and riverbanks, and enrich the soil with leaves and dropped sticks and bark.
Some native plants are more supportive than others
All native species are important, but some plants punch above their weight in terms of supporting ecosystems. For example, University of Delaware Professor Doug Tallamy found that just 14% of native plant species were supporting 90% of butterfly and moth species.
What does this mean for you, a human concerned about the environment?
It’s great news. Plants are often the easiest things in a landscape for humans to influence. You can’t make endangered native bees reproduce, but you can plant flowers that nourish and shelter them. You can’t bring back a lake that was drained to build your town, but you can plant species that used to grow there in a local park with a pond and give homes back to native wildlife.
So if you can plant one or more of these species, you can know that you’re giving the maximum boost you can to your local environment and wildlife.
Keystone trees
These native trees are gorgeous, generous keystone cornerstones.
Oaks
If you can plant an oak tree, you are planting a keystone species in your region no matter where you are.
There are many kinds of oaks, so look up the kinds native to your area here. They range from the gloriously gnarly live oaks of coastal California and the South, to the graceful laurel oaks of the southern Atlantic coast, to the shrubby, sturdy gambel oaks of the Mountain West. These species support literally hundreds of different native pollinators and caterpillars.
An ode to the oak
If you had to pick one tree that would bring the maximum boost to native wildlife, no matter where you live in the U.S., it would be an oak. Oak leaves are incredibly important as a food source for young butterfly and moth caterpillars, which in turn feed birds. Their acorns feed everything from bears to flying foxes to beavers; birds nest in their branches; their roots stabilize the soil and nourish beneficial fungi; and their open canopies allow woodland plants to grow beneath them. (Why did oaks become so crucial? Learn more here.)
By the way, if you feel like you have no room for an oak tree? Professor Doug Tallamy notes that they start supporting the food web right away. That means that if you plant an oak and 25 years later it gets too big for that space, it still contributed to the ecosystem for 25 years.
Willows
In many parts of the U.S., willows are also keystone plant species. There are tons of types of willows, not just the classic weeping willow—in fact, the majority of varieties of willows are small or even shrub-sized.
Willows tend to like to grow on riverbanks and other wet areas, so the usual rule of thumb is that if your soil tends toward wet, plant a willow; if it tends to be dry, plant an oak.
Other keystone trees
Other trees that turn up frequently in keystone lists are cottonwoods, crabapples, and cherry trees.
You can find the specific trees that are keystone species in your region here, or explore our native plant profiles:
Keystone shrubs
Native blueberry bushes are keystone species in many parts of the U.S., including the Eastern U.S. and Pacific Northwest. Many species of willow are categorized as bushes and appear here, too. For example, if you live in the desert, the coyote willow is a keystone species for you, supporting 240 different kinds of caterpillars.
Find the specific shrubs that are keystone species in your region here, or explore these plant profiles:
Keystone flowers
In almost every state, goldenrod is a hugely important food source for native species. So are sunflowers and asters — check the list to find your specific native varieties. In many regions, Black-eyed Susans also top the lists.
Keystone flowers include:
How were keystone species discovered?
Ecologist Robert Paine is credited with introducing the concept of keystone species.
In the 1960s, Paine was studying the tidal pools of the Washington state coastline. These tidal pools were normally extremely diverse, but he found that when he removed starfish from an area, within a year the number of species in that area dropped by half. The starfish, which are actually predators, had been keeping mussels from overgrowing the area. Left unchecked, these mussels rapidly spread and forced out other species.
Since then, other scientists have confirmed and fleshed out these ideas.
Do I have to plant keystone species?
Yes, please!
If you have the right room and conditions for them, definitely consider planting keystone species. You can find which ones are keystone species for your region here. But don’t worry too much about it—any native species is hands-down better than none!
We hope this helped answer a few questions about keystone species and what roles plants play in our landscapes. Native trees, shrubs, and flowers are the often-unsung but essential heroes that keep the amazing, intricate ecosystems of North America flourishing.
If you can plant any of these species—or convince your local authorities to plant them in your parks—you know you’re giving your local wildlife the maximum possible boost. And if you want to learn more about native plants and ecosystems, check out What is a host plant? and Native plants for butterflies. Happy planting!
Recommended Reading:
Keystone Plant Guides – Homegrown National Park
Sources
- Denchak, Melissa. Natural Resources Defense Council: Keystone Species 101.
- Wagner, Stephen C. Nature Education Knowledge Table: Keystone Species.
- Skonberg, Kelsey. Pacific Horticulture: Your Keystone Plant Matrix with Garden Futurist Doug Tallamy
- Narango, Tallamy, and Shropshire. Few keystone plant genera support the majority of Lepidoptera species. Nature Communications, Nov. 13, 2020.
- National Wildlife Federation, Commission for Environmental Cooperation. Keystone plants by ecoregion.
- Fralish, James. “The Keystone Role Of Oak And Hickory In the Central Hardwood Forest.” U.S. Department of Agriculture, Forest Service, Southern Research Station.
- Hipp, Manos, and Cavendar-Bares. “How Oak Trees Evolved to Rule the Forests of the Northern Hemisphere.” Scientific American, Aug. 1, 2020.
- Tallamy, Doug. “The Chickadee’s Guide to Gardening.” The New York Times, March 11, 2015.
- Estes et al. “A keystone ecologist: Robert Treat Paine, 1933–2016.” Ecological Society of America, Sept. 13, 2016.
- Shedd Aquarium, Keystone Native Plants – They’re for the birds (and bees!)
