Native Groundcovers and Trees: The perfect pairing!

Photo: Native groundcovers, Margaret Fisher

Plant NoVA Natives

Native groundcovers are becoming increasingly popular, for good reason: even if they have minimal time for gardening, people want to use native plants to support our local birds and butterflies. To avoid invasive non-native groundcovers such as English Ivy, Vinca, Yellow Archangel, and Japanese Pachysandra, they turn to native plants for the same landscaping benefits without the damage to our trees and the rest of the environment.

Equally popular among time-pressed residents are native trees, which are similarly easy to install and which have benefits that far exceed those of any other plants. Not only does the great mass of tree leaves and roots provide food and homes for birds, soak up stormwater, and cool the air, the insects that evolved with native plants are adapted to the chemical make-up of those plants and are able to co-exist peacefully with them. An American Beech tree, for example, is the host plant to 126 species of lepidoptera (butterflies and moths), Hickory to 200 species, Black Cherry around 450 species, and native oaks over 500 species. (The numbers for non-native trees are in the single digits or even zero.)

Over 30 species of locally native plants make excellent groundcovers, with options available for any growing condition. Several are evergreen, and many have the bonus of a month or two of colorful flowers. Some form a tight mat on the ground, while others such as ferns and White Wood Aster provide a taller look. Native sedges provide even more options. Some sedges make a beautiful substitute for the invasive Liriope, some look more like a grass that never needs mowing, and still others sport spiky seed heads that add a touch of quirkiness to the garden. Our local conventional garden centers are starting to carry some of these plants, and many more can be found at native plant garden centers.

Encircling native trees with native groundcovers makes eminent sense. Turf grass does poorly under trees because of the limited light. Trees do not appreciate lawn chemicals, not to mention the risk of injury from lawnmowers and string trimmers. A harmful but common practice, especially in commercial areas, is to pile layer after layer of mulch in a “mulch volcano” around trees and spray it with herbicides to prevent grass and weed growth. Not only does this poison the soil, but mulch that is touching the trunk will rot the bark, and compacted mulch prevents rainwater from reaching the roots. Arborist wood chips, which allow the water to run through, are an improvement over shredded bark mulch if applied properly and can protect the tree as it gets established. But in the long run, why not use nature’s alternative to a toxic mulch bed, which is to allow the fallen leaves to remain in place and add a “green mulch” made up of native plants? The trees and the soil will thank you for it.

Learning about Native Plant Communities

Photo: New York Ironweed, Matt Bright

Audubon at Home Ambassadors held their annual Potluck Ambassadors’ Brunch at the Fairfax County Government Center on March 19—a welcome gathering, their first in two years. Thirty-two Ambassadors attended, and enjoyed a presentation on “Earth Sangha’s Native Plant Compendium, Plant Communities and Native Plant Selection” given by Matt Bright, Conservation Manager for Earth Sangha.

Plant communities are assemblages of plant species that grow in a particular habitat and interact with each other, wildlife, and the environment around them. Knowing the features of the landscape and the dominant vegetation allows us to predict what other plant species “belong” there, and provides a basis for making plant selections. Plant communities are a natural extension of “right plant, right place.”

New York Ironweed, Matt Bright

A plant community is simply the native plants that tend to grow together in any given habitat.  So, for example, different plant communities are found on a steep dry slope, or in the floodplain near a stream, or in an open area. Often the assemblage of plants present is governed by topography.  

Conserving and restoring plant communities allows us to protect plants and wildlife in ways that mirror natural environments. Restoring common, dominant native plants that are the ecosystem drivers can create ecological uplift—the drivers will create the conditions that bring along rarer, passenger species that need those conditions to thrive and reproduce. 

Plant communities can also help guide choices not only about what to plant, but how much.  For example, a floodplain forest often has a dense herbaceous layer, while a mesic to dry forest understory is often sparse, with large areas of leaf litter. The density that occurs in nature may not match gardening conventions, such as planting a single specimen surrounded by 18” of mulch. Planting for succession will create a multilayered understory, with varying age classes of mature canopy trees and young saplings. 

Plant communities can provide far greater benefit over the complete life cycle of wildlife species than focusing narrowly on a single species. For example, many people have learned that milkweeds are essential for Monarch caterpillars. While they are necessary, Milkweeds are not sufficient. They are actually relatively poor insect hosts: Goldenrods are much more important late-season nectar sources for migrating Monarch butterflies, and as hosts for specialist bees. A diversity of species within a plant community supports a greater diversity of wildlife.

Matt Bright stressed that ecological value is in the details. An example is leaf litter, which provides essential habitat to many species. He cited results from a recent study that shows large declines—by a shocking two-thirds—in lepidoptera populations when leaf litter is removed. This confirms Audubon Ambassadors’ advice to their clients to “leave the leaves!”

Reconnecting areas has tremendous ecological value. Matt cited results from an 18-year experiment showing that creating even narrow corridors between areas of habitat resulted in fewer extinctions, faster recolonization by native plants, and 14% greater biodiversity in connected sites than in isolated ones.

Matt provided good, practical (and work-saving) advice for prospective native gardeners and restorationists:

• Focus on dominant species that will create conditions to create ecological uplift. For a first round of planting, he suggests sticking to common, generalist species, which have more “right places” and are more frequently the right plant that will establish more quickly. Generalist plants often support specialist wildlife.

• Leave healthy areas of intact habitat alone. Remove invasives, and before replanting wait to see what regenerates from the seed bank. Volunteer plants are free, and can guide you towards what to plant in the future.

Although plant communities may seem daunting, Matt argued they are actually less work than picking and choosing plants individually. He provided several sources of guidance:

• Earth Sangha Native Plant Compendium: You will learn a lot about native plant communities from this text-heavy website, which provides useful advice on high-value generalist canopy trees, understory trees and shrubs, and plants for wet and dry meadows.

• Plant NOVA Natives Natural Plant Communities made easy is perhaps the most comprehensible site, which offers practical advice and will help you understand the concept of plant communities.

• Natural Ecological Communities of Northern Virginia, by Glenn Tobin—this site is more oriented to the quantitative user. Tobin has begun developing a scheme to help identify plant communities.

• Department of Conservation and Recreation, Natural Heritage Program—this site provides descriptions of each of the natural communities of Virginia, as well as its key plant species. Very data rich. Definitive and technical.

• Nature Serve Explorer—this site uses different common names for the communities than the DCR site.