Plant a keystone species

Why it matters

Most gardeners know that native plants support more wildlife than non-native plants. What fewer realize is how extreme the difference is, and how concentrated ecological support is in a small number of plants.

Research by University of Delaware entomologist Dr. Doug Tallamy and colleagues, published in Nature Communications in 2020, found that 90 percent of the caterpillar species in any US region rely on just 14 percent of native plant species for food. Five percent of plant species support 75 percent of all native caterpillars. These are the keystone plants.

Caterpillars are the reason this matters so much. Ninety-six percent of terrestrial bird species feed their nestlings almost exclusively on caterpillars and soft-bodied insects. No caterpillars means no baby birds. North America has lost roughly 3 billion birds since 1970. The collapse of insect food webs is one of the drivers of this loss.

A single native oak tree supports over 500 species of caterpillars. A goldenrod supports 110 species and 12 specialist bee species that can only reproduce on goldenrod pollen. A non-native ornamental typically supports fewer than five.

What to plant

The keystone genera that show up across most US regions are:

• Oaks (Quercus): support over 500 caterpillar species nationally, more than any other genus. Every ecoregion has native oak species. Even a small oak in a suburban garden supports a disproportionate amount of local wildlife.
• Willows (Salix): support over 450 caterpillar species. Shrubby native willows work well in smaller gardens and moist spots.
• Wild cherries and plums (Prunus): support over 440 caterpillar species. Several species are small enough for most gardens and produce fruit that birds eat directly.
• Goldenrod (Solidago): the top herbaceous keystone plant. Supports 110 caterpillar species in the East and is the host for 12 specialist bee species. Blooms late in the season when little else is flowering.
• Asters (Symphyotrichum): support around 100 caterpillar species and dozens of specialist pollinators. Easy to grow, bloom into autumn.
• Birches (Betula): support over 400 caterpillar species. Native birches are fast-growing and work well in northern gardens.

To find the specific keystone species for your region, use the National Wildlife Federation's native plant finder at nwf.org/NativePlantFinder.

How to do it

1. 1Identify keystone plant species in your area: use the National Wildlife Federation's native plant finder at nwf.org/NativePlantFinder. Enter your zip code and it will show you native species in your area along with the number of butterfly and moth species supported by each plant.
2. 2Choose one tree, shrub, flower, or grass: if you have space, a keystone tree is the highest-impact choice. If space is limited, a shrubby keystone like goldenrod, native willow, or native cherry works in a smaller footprint.
3. 3Source a local ecotype: buy from a reputable native nursery and ask whether the plant is a locally propagated ecotype. Plants grown from local seed are better adapted to your climate and more ecologically valuable than the same species grown from distant seed stock.
4. 4Plant correctly: dig a hole as deep as the root ball and two to three times as wide. Set the plant so the root flare is at or just above soil level. Water thoroughly and mulch around the base, keeping mulch away from the trunk.
5. 5Resist the urge to tidy: leave leaf litter under keystone trees and shrubs. Over 90 percent of native moth and butterfly species overwinter in leaf litter or hollow stems as eggs, pupae, or adults. Clearing leaves removes the very insects the plant was meant to support.

Sources: Tallamy & Shropshire (2009), Conservation Biology; Narango, Tallamy & Marra (2017), Biological Conservation; Rosenberg et al. (2019), Science; NWF Native Plant Finder.