What do starfish on the Pacific Northwest Coast, and Oak trees, Goldenrod, and Blueberries in New England, as well as beavers, wolves, and Sagebrush have in common with Roman stone arches?
These plants and animals are all considered keystone species. Just as the wedge-shaped keystone at the top of a Roman stone arch holds the entire structure together – and it all comes tumbling down if that one central stone is removed – certain native plants and animals play a similar outsized role in supporting the interconnected web of life in any given region.
The term “keystone” was first applied to biological systems by ecologist Robert Paine in 1969, who studied predator-prey relationships in tidepools on the rocky coast of Washington State. He removed starfish from a previously biodiverse tidepool, leaving a nearby pool unchanged as a control. As a result, barnacles (starfish prey) proliferated, then came a population explosion of mussels. Without the starfish predator there to keep mussels and barnacles in check, diversity was cut in half within a year. Algae, sea anemones, limpets and other organisms in this previously balanced little ecosystem were crowded out or moved away. His conclusion – that not all species are equal, some are much more important for the health of the ecosystem – was revolutionary at the time. These days, protecting keystone species to maintain the biodiversity of the whole system has become a guiding principle in conservation.
We’re increasingly aware that we can employ keystone species in our yards too, although we don’t suggest introducing wolves or beavers! If you want to support wildlife in general, or focus on birds or butterflies, you need to supply the plants that feed bugs (and avoid killing bugs with toxic chemicals). Plants that are essential to many creatures are recognized as keystone plants. Insects and other “bugs” are fundamental parts of complex food webs. Many beneficial insects have a diet of other insects, which means they’re predators on duty doing pest control in your garden if you welcome them. Others are herbivores that eat plants. Oh oh! Won’t they ruin the garden? No, they won’t do much damage, because birds and animals eat them, keeping the system in balance. Birds are the starfish of your garden.
Essential pollinators, too rely on keystone plants. Many native bees specialize on the pollen of particular plants, ensuring the ongoing survival of the plant species – not to mention the fruits, vegetables and berries that sustain us humans. Asters, Willows, Sunflowers, Hollies, Hibiscus, Goldenrods, among others, are keystone species that support bee specialists that depend on their pollen, generalists that feed on many species, along with numerous caterpillars that turn into butterflies, moths or bird food.
Entomologist Dr. Douglas Tallamy has popularized the concept of keystone plants, based on his research, to help gardeners choose the most important and productive native plants. These are the select few plants (or plant families) that provide food for the most insects and also for specialist insects that can feed on no other plants. His research has found that insects are a fundamental part of the diet for 96% of North American terrestrial birds. Baby birds consume an enormous quantity of insects, especially caterpillars, which Tallamy describes as “a lot of protein in a soft wrapper.” Turns out that the bugs are keystone species too.
Symbiotic relationships between plants, insects and animals have evolved together over eons, which is why native plants are so important. Plants have evolved toxic or distasteful chemical compounds to deter insects and other herbivores from eating them. Native insects have developed ways to circumvent or metabolize these chemicals, leading them to specialize on specific plants or plant families. Monarch butterflies are the poster children of specialists. Detecting milkweed’s chemical signature, Monarch butterflies lay eggs on the leaves so their larvae (caterpillars) hatch on the only plant they can eat. 90% of our native insects are specialists that can only eat particular plants. Since, as Tallamy has concluded, only 14% of native plants support 90% of moth and butterfly species (Lepidoptera), it would be helpful for us to know which plants to include in our gardens if we want to protect and enjoy butterflies – or birds.
Dr. Tallamy and The University of Delaware, where he teaches, along with The National Wildlife Federation, and the U.S. Forest Service, in an ongoing collaboration, have developed a useful website that identifies keystone plants in every part of the United States. On the grand scale, the site includes downloadable charts listing the top keystone plants with their associated insects for each Level 1 Ecoregion, along with lists of the top 30 keystone plants for butterfly and moth caterpillars and for pollen specialist bees.
All gardening is local and the interactive part of the website gets down to the local level, providing information based on zip code. If you click on the Native Plant Finder and enter your zip code, you can search through galleries of the most valuable native plants for your local area, with photos of plants and some of the insects they support.
Ecoregion maps beautifully show the geology of the continent, with state lines indicated (faintly), and roads not at all, so different from the maps we usually employ to understand where we are and where we might be going. Developed by the Environmental Protection Agency (EPA), these maps delineate areas in various colors, with numbers keyed to a list of regions where ecosystems are generally similar. Level 1 divides the continent into 12 large regions such as Great Plains, Marine West Coast Forests and Eastern Temperate Forests (where we are). Level 2 breaks down the Regions into more detailed areas and Level 3 divides the map into 182 smaller areas that reflect more discrete habitats as defined by landforms, elevation, past glacial activity, water bodies and more.
The website for Tallamy’s own initiative, Homegrown National Park, provides clear information and instructions on how to go about making beautiful yards and gardens that function as wildlife habitats and provide ecosystem services such as building soil, sequestering carbon and protecting watersheds. Regional listings are sorted by keystone trees and shrubs and keystone flowering plants, noting that these work as container plants and are suitable for any size garden. Trees, being large and relatively long-lived, are tremendously important. In just about every region, from New England to Texas, throughout the Midwest and into California and interior Alaska, local species of Oaks, Maples, Willows and Prunus species (Cherries and Plums) were among the top keystone plants.
Source: homegrownnationalpark.org
We were pleased to see how many of the flowering perennial plants we already grow are listed among keystone species across the nation, and endeavor to introduce even more. The species may vary from region to region, but members of the Goldenrod (Solidago) and Aster (Eurybia, Symphyotrichum, Euthamia) genus are widespread and valuable keystone plants, along with diverse Coreopsis, Rudbeckia, Helenium, Viola and even Vaccinium (Blueberry) species.
Other useful resources:
The Audubon Society provides information on the best native plants for birds when you enter your email address and zipcode
The Xerces Society for Invertebrate Conservation provides recommended pollinator plant lists for 21 distinctive regions of the continent.
We are happy to see a growing awareness that our gardens, indeed our entire yards, can be more than a collection of pretty plants that please us (although they should certainly do that too!). Understanding that you don’t get butterflies unless you feed caterpillars and you don’t get birds if you kill all insects certainly changes the way we gardeners have traditionally operated. Our yards are habitats that can nurture local wildlife and help reverse the ill effects of habitat fragmentation and loss due to development, invasive plants and other factors. With recent findings that a third of all birds are species of concern and documented declines in insect populations, we are compelled to create landscapes that sustain both wildlife and people, right where we live.
Keystone plants support habitat health and create beauty wherever they grow. Whether your garden is on a large country plot or a small suburban lot, whether it’s part of a foundation planting, the corner of a patio or a few pots on a balcony high in the air, adding keystone plants to create new pollinator habitat or enhance what is already there will draw in, nourish and protect birds and insects. Your yard will become a lot more like a tide pool with starfish – more dynamic, complex, self-sustaining and interesting.
