Confessions of a Landscape Designer: Keystone Native Plants and Why They Matter

When we select exotic ornamental plants solely for their appearance, we often choose species that have no deep ecological value in our local landscapes. Many of these ornamentals are “alien” to our ecosystems. They arrive from distant places and have not coevolved with the insects, birds, and soil life of this region. Insects often cannot digest their leaves or use their flowers for food, leaving wildlife with few resources in what appears to be a pretty garden. Research shows that landscapes dominated by non-native species can function like ecological dead zones because they fail to support the food webs that sustain life. Native wildlife needs habitat and nourishment that only the plants they evolved with can provide.

Entomologist Dr. Doug Tallamy, author of Bringing Nature Home and The Nature of Oaks, has pioneered our understanding of how plants support ecosystems. His research reveals that a relatively small group of native plants plays an outsized role in sustaining life because they act as keystone native plants. These are the foundation species that produce the majority of the food needed by insects and the birds that eat them. In North America, just a small percentage of native plants support the vast majority of caterpillar species, which are essential food for fledgling birds.

Tallamy’s work quantifies this in a way that makes the concept impossible to ignore. Only about 14 percent of native plant genera account for roughly 90 percent of the butterfly and moth species that rely on plants as hosts. These insects, in turn, form the core of terrestrial food webs. Without keystone native plants, food webs collapse because the energy captured by plants cannot efficiently reach higher trophic levels such as birds and mammals.

The science highlights a stark contrast between native and alien ornamental plantings. Many exotic ornamentals were selected precisely because they are resistant to insect feeding. Gardeners enjoy plants that stay “perfect.” But those same chemical defenses that deter serious leaf damage also mean that native insects cannot process them as food. In one well-known comparison between a native oak and an alien Bradford pear, researchers found orders of magnitude more caterpillars on the oak than on the pear. This difference matters because insects are the base of nearly all terrestrial food webs and because over 96 percent of land birds feed their young insects during nesting season.

For gardeners who want to make a real difference, the first step is understanding that not all native plants are equal in ecological value. Keystone native plants are the powerhouses of biodiversity. They host insects that no alien ornamental can support. As we begin to replace sterile, exotic ornamentals with keystone native plants, our landscapes become part of a functioning ecosystem again.

This series will explore what keystone native plants are, the science behind their value, and how gardeners can use them to rebuild habitat in their own yards, in community gardens, and across neighborhoods.

Why do you think gardeners have historically valued ornamentals over ecologically meaningful plants, and what might change as we learn more about keystone native plants?

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