Native plants are the foundations of our ecosystems, critical to all that we love about our region.

They’re intimately woven into a network of relationships — between plants and insects, insects and birds, forests and fish, and much more — playing key roles in food webs of complex interdependency. They’re at the heart of our region’s biodiversity, supporting processes critical to healthy ecosystems and to our own health and well-being.

But these ecosystems and the biodiversity they support are in trouble.

Because of cumulative habitat loss, the spread of invasive species, climate change and other factors, both the numbers and diversity of insects, songbirds, amphibians, mammals and more are experiencing alarming declines here in the Northwest and around the world.

It doesn’t have to be this way. We can help reverse these trends by promoting native plants in landscapes large and small. And to rise to this challenge, we must not only fully appreciate the foundational role that native plants play in our ecosystems and how they can help heal damaged habitats, but also understand what a genuine native plant is. We need to understand that introduced species and cultivars are not the ecological equivalents of native plants.

Some in the gardening community have suggested that a definition of a native plant is a social construct, not a scientific one, and that gardeners can define for themselves what is native based on a loose set of criteria, including aesthetics and personal preference. But such interpretations ignore a growing body of scientific evidence regarding the co-evolved relationships of native plants with other organisms in our ecosystems and how that co-evolution has created the distinctive biological communities we see in the Pacific Northwest today.

Gardeners can, of course, select whatever plants they want in their home gardens or landscapes. But there is ample evidence that those of us who care about biodiversity and ecosystem health — indeed, the health of the planet — should favor bona fide native species as much as possible in our home landscapes.

The species that were present in the Pacific Northwest before the arrival of Europeans evolved and developed complex, often highly specialized ecological relationships with the rest of the organisms in their ecosystems.

Understood from this perspective, a species’ “nativeness” is a vital factor in ecological relationships that can make the difference between life and death, successful reproduction or the winking out of local populations. They are not interchangeable with species that have not formed these relationships.

Mounting scientific evidence indicates that native plants provide a far more complete set of vital services to our ecosystems than non-native plants. This is partly because they provide critical pollinator resources to insects, which in turn pollinate our gardens and fruit trees, feed our wild birds, recycle nutrients and more.

But native plants do more than that: They also are hosts for insects in their larval stages, essentially helping to birth our insects. Though not common here, Monarch butterflies, as many people know, would perish without the milkweed host plants their caterpillars require. The same is true for most of our local species of butterflies, moths, beetles and other herbivorous insects — without the specific native plants they require for their eggs and feeding larvae, their populations will decline and disappear.

And our native insects are critical. As the great entomologist E.O. Wilson said, they’re “the little things that run the world” — vital processors and conveyors of energy in complex food webs, the strands of which we barely fathom but which are fundamental to the health of our ecosystems and our own survival.

Because of insects’ irreplaceable roles in these food webs, the presence or absence of appropriate, co-evolved native host plants and their impacts on insect populations ramify throughout the rest of the ecosystems, most notably affecting populations of songbirds and small mammals.

While the plights of salmon and orcas are well known to most Northwesterners, far fewer of us are aware that insects are exhibiting large-scale population declines. Leading entomologists consider habitat loss and alteration, including the increasing dominance of non-native plant species in our landscapes, among the factors contributing to these declines.

In response, the Xerces Society for Invertebrate Conservation and respected wildlife conservation organizations recommend increasing native plant species in our gardens and managed landscapes as a key strategy for supporting these populations.

Non-native plants have not been around long enough to have formed the kinds of specialized relationships that native plants have developed with their ecosystem neighbors over thousands of years. This can be true even for cultivars derived from native species, sometimes referred to as “nativars.” Selective breeding for traits that are attractive to people can result in unintended genetic changes that make nativars unattractive, unpalatable, indigestible or otherwise inappropriate hosts for native insects and their larvae.

If specialized insects can’t find the host plants and other resources they need, they’ll disappear from those portions of the landscape. If songbirds can’t find the large numbers of caterpillars and other insects they must have to feed their nestlings, that next generation will fail and local populations will wink out. And when similar problems are occurring across large areas, the chances of population replenishment from nearby habitats become less and less likely.

There is no call to remove all non-native plants from our gardens and managed landscapes (unless the species are invasive in natural areas). However, our neighborhoods and urban parks are typically already so dominated by non-native plants and cultivars that it is vital for new plantings to be bona fide, wild type natives.

No matter how we perceive our gardens and home landscapes, they’re not static displays — they’re part of the surrounding ecosystem. As stewards of our ecosystems, we have compelling reasons to select wild type native plants for our gardens and landscapes as much as for our natural areas. Indeed, we have an opportunity to make our home landscapes allies in the effort to support complex food webs, biodiversity and ecological resilience in the decades ahead.

As Kristin Currin and Andrew Merritt write in The Pacific Northwest Native Plant Primer: “To cultivate a landscape that adds to the local ecology rather than diminishes it, native plants are the way to grow the future.”

Jim Evans is an island restoration ecologist and educator who serves on the board of the Vashon Bird Alliance. A version of this article appeared in the spring 2024 issue of Douglasia, the Journal of the Washington Native Plant Society.

A bumblebee visits the flower of a black twinberry, a native plant. (Jim Evans photo)

A woodland skipper nectars on pearly everlasting, a native plant. (Jim Evans photo)