Native Alternatives to Invasive PlantsThe indispensable guide for everyone who loves dazzling gardens and cares about the health of North America's remaining wild landscapes. In this handbook, plant professionals and home gardeners alike will discover hundreds of spectacular native plants for every region, specially chosen as alternatives to the invasive species that are degrading and destroying the continent's natural habitats. SPECIAL FORMAT: 240 pages
- Preventing Plant Invasions, by Janet Marinelli
- The Role of Roadside Managers, by Bonnie Harper-Lore
- Invasive Plants: Questions and Answers
- Native Plants: Questions and Answers
- Plant Provinces of North America
- Encyclopedia of Native Alternatives to Invasive Plants
- C. Colston Burrell
Sample entry: Native Alternatives to Ailanthus altissima
Sample entry: Native Alternatives to Berberis thunbergii
Sample entry: Native Alternatives to Lonicera japonica
- Herbaceous Plants
Sample entry: Native Alternatives to Ranunculus ficaria
Sample entry: Native Alternatives to Cortaderia selloana
- For More Information
- List of Invasive Garden Plants
- Index of Invasive Plants
Preventing Plant Invasions
By Janet Marinelli
As the old saying goes, an ounce of prevention is worth a pound of cure. This is especially true of the struggle to control invasive species. In the New York metropolitan area, where I live, roadsides have been overtaken by solid stands of purple loosestrife, and forest understories are thick with Japanese barberry. Biologists consider invasive species such as these to be one of the two greatest threats to native plants and animals, second only to the outright loss of habitat to suburban sprawl, agriculture, and industrial development. Land managers fight a daily battle to remove invasives from important natural areas.
The conventional wisdom, at least in horticultural circles, used to be that most invasive plants were introduced accidentally—in agricultural seed stocks, say, or even on the bottom of some unsuspecting tourist's shoes. But during the course of researching Brooklyn Botanic Garden's influential 1996 handbook Invasive Plants: Weeds of the Global Garden, my colleagues and I were dismayed to discover that about half of the worst invasive plants currently degrading natural habitats from coast to coast were brought here intentionally, for horticultural use.
Allegheny serviceberry, right, native to the eastern states, is a beautiful alternative to the invasive callery pear, left. The lovely white flowers are followed by purple-black berries that are relished by birds. (Photos: Jerry Pavia, David Cavagnaro)
While the vast majority of species planted on highway rights-of-way, in public landscapes, and in home gardens are not invasive, a small percentage have adapted too well and escaped cultivation. These plants have become established, or naturalized, in the wild. Not every naturalized plant is a threat to native ecosystems, however. The BBG handbook Native Alternatives to Invasive Plants is concerned with those nonnative plants that not only establish viable populations in but also alter the structure and/or functioning of those ecosystems.
Many invasive plants are still being sold as garden specimens or for wildlife plantings and erosion control, despite their documented ability to degrade natural areas. And although no system is in place to effectively screen them for potential invasiveness, new plants from around the world are constantly being introduced to satisfy the preoccupation with the new and exotic that has characterized horticulture for at least the past hundred years. The more we learn about invasive plants, the more we realize how difficult they are to control, much less eradicate. The most prudent course of action clearly is to avoid planting these species in the first place.
Since BBG's original handbook on invasive plants was published, we have received numerous requests for a companion volume featuring ecologically safe alternatives. The Encyclopedia of Native Alternatives to Invasive Plants, at the heart of this book, recommends a variety of beautiful, regionally native species that fill the same needs as the worst nonnative invasive plants commonly used in horticulture. If you select these species, it is highly unlikely that you will be unleashing North America's next invasive menace. Regional natives aren't the only ecologically responsible choices; nonnatives that have been planted in gardens for decades without demonstrating any signs of invasiveness are good candidates for landscaping as well. But by selecting regional natives you will be preserving the natural character of your area. You will also be preserving the complex interrelationships between the native plants and the butterflies, birds, and myriad other creatures with which they have coevolved.
The Role of Roadside Managers
By Bonnie Harper-Lore
Highway corridors crisscross North America, connecting neighboring parkland, farmland, and your land. Totaling over 12 million acres in the U.S. alone, the rights-of-way that border the highway pavement are highly disturbed landscapes, beginning with the original construction and continuing with upgrades, mowing, spraying, snowplowing, grading, and the placement of signs and utility lines. The plants likely to establish on disturbed lands are invasive. And so highway agencies across the country are often blamed for increasing the spread of invasive plants.
Native wildflowers planted along the Taconic State Parkway in New York delight travelers and provide food and shelter for wildlife.
State departments of transportation (DOTs) do bear some of the responsibility, because they became a conduit for invasives by often relying on plants perceived as problem solvers. During construction, the quick establishment of groundcover to stabilize slopes and ditches is a critical concern. Revegetation not only controls erosion but also minimizes runoff and sedimentation of nearby waters. When highway departments began revegetation they adopted an agricultural approach, routinely using mixes of legumes and grasses. What we did not know then was that many of these easy-to-grow and quick-establishing problem solvers would soon become invasive. During the past few decades, transportation policy and lessons learned from the 1970s energy crunch have encouraged an ecological approach to vegetation management, including the planting of native species along roadsides.
While it has become clear that invasive plants should no longer be used, finding alternate problem solvers has not been easy. Native Alternatives to Invasive Plants is designed to provide DOTs, as well as other land managers, designers, and gardeners, with a range of regionally native alternatives.
Invasive Plants: Questions and Answers
What is an invasive species?
The U.S. government defines an invasive species as one "that is not native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health."
The multiflora rose is lovely looking, but its rampant spread has made it an outlaw in several states.
How do plants become invasive?
Simple physics dictates that two plants cannot occupy the same spot, so when a nonnative plant settles into a new ecosystem, it displaces a native. Invasive plants may grow faster, taller, or wider and shade out native species. Many stay green later into the season or leaf out earlier, giving them an advantage over natives. Nonnative plants can change the vertical and horizontal structure of ecosystems, alter hydrology, and disrupt nutrient cycles—all with devastating effects on native plants and animals.
How much damage do invasive species cause?
According to a paper by Cornell ecologist David Pimentel and others, invasive species cause major environmental damage amounting to almost $120 billion per year. About 42 percent of the species on the U.S. List of Endangered and Threatened Species are at risk primarily because of nonnative invasives. (See Ecological Economics, Volume 52, Issue 3, 1 February 2005, pages 273–288.)
Is it possible to predict whether a plant will be invasive?
A foolproof system for predicting invasiveness has proven elusive, but a few traits should raise red flags. For example, nonnative species bearing fleshy fruits dispersed by birds are at the top of the suspect list. Declining to plant—or recommend—such species can help prevent plant invasion. However, the most prudent prevention measure is to choose a regionally native species.
Native Plants: Questions and Answers
What is a native plant?
The federal Plant Conservation Alliance defines a native plant species as one that occurs naturally in a particular region, ecosystem, and/or habitat without direct or indirect human intervention. A plant endemic to Europe and introduced to North America is not native to this continent. Likewise, a plant native to one region of North America is not native to another region unless it originated there without help from us.
Purple loosestrife, of Eurasian origin, is displacing native wetland plants across much of North America.
Ecologically speaking, political boundaries such as national or state lines have no bearing on plant distribution. Plant ecologists have divided North America into 15 plant provinces (see Plant Provinces in North America map below). The species in these distinct vegetation regions are determined by such regional factors as high and low temperatures in summer and winter, total annual precipitation, timing and nature of precipitation, elevation, and soil type.
What is local provenance, and why is it important?
Provenance refers to the specific place from which a plant or seed originated. Plants of local provenance—those whose native origin is close to where they will be planted—are apt to be better adapted, and therefore perform better, than plants of more distant origin because temperature, precipitation, and other factors vary within each plant province.
Growing plants that are not of local provenance can also affect the gene pool of a native species. The genetic makeup, or genotype, of a plant may vary from place to place. When a nonlocal genotype is planted, it can mix with the local plants and alter the local gene pool in a way that decreases the plant's ability to survive in the area.
Fireweed is a long-blooming native named for its tendency to colonize burned and disturbed sites.
Can a cultivar of a native plant be considered native?
Technically, a cultivar is a plant that has been selected for cultivation because of a particular attribute or group of attributes—a particular flower color, say. To ensure that these characteristics are retained, cultivars typically are propagated by cloning via rooted cuttings. A cultivar produced by cloning a wild plant may be described as native, but it is not necessarily of local provenance. So, whenever possible, avoid selecting cultivars of native species, unless they have been propagated from local plant stock. What's more, look for local genotypes produced from seed rather than by cloning, because they maintain the maximum genetic diversity.
Can native plants be invasive?
Yes, but they rarely are. Some species display invasive growth tendencies in their native regions in response to disturbances caused by us—for example, native grapevines may grow vigorously after timber cutting creates an opening in the forest canopy, flooding once shaded areas with sunlight. However, this aggressive growth spurt usually slows down as trees and other plants fill the gap in the canopy. The vast majority of the most severe and persistent invasives are not native to the region.
Plant Provinces of North America
North America's natural vegetation is divided into plant provinces, or regional vegetation types.
Key to Map:
Adapted from North American Terrestrial Vegetation, edited by Michael G. Barbour and William Dwight Billings (New York: Cambridge University Press, 1988).