Invasive Plants: Weeds of the Global Garden

Hundreds of horticultural plants have jumped the garden gate, threatening native species. This ground-breaking book tells you which plant invaders are problems in your area and how to control them. It ought to be in every library, and on every gardener's bookshelf!

  • Introduction: Redefining the Weed, by Janet Marinelli
  • Plant Invaders: How Non-native Species
  • Invade & Degrade Natural Areas, by John M. Randal
  • Tools & Techniques: Chemical-free Weed Controls, by Beth Hanson
  • To Spray or Not to Spray, by Henry W. Art
  • Encyclopedia of Invasive Plants
    • Trees
    • Shrubs
    • Annuals & Perennials
    • Grasses
    • Vines
    • Aquatic Plants
  • For More Information
  • Contributors

1. Redefining the Weed

by Janet Marinelli

Used to be, gardens were tiny enclaves in a vast wilderness. Beleaguered gardeners struggled daily against the forces of nature, not the least of which were weeds—hence the traditional definition of a weed as any plant from outside the garden that ends up inside the garden where it isn't wanted. But, boy, have the tables turned. Today, around the globe, shrunken fragments of once-awesome wilderness are hemmed in by human-dominated land. Now it is our activities, including our gardens, that threaten natural areas and the creatures they harbor. Hundreds of species that we've carried from their native ranges to new areas, including prized horticultural plants, have overrun native vegetation. These have become the true weeds of the modern world.

People have been rearranging the planet's flora for centuries. Many of the exotic plants we've introduced by intention or accident have been beneficial to us and ecologically benign. But a small percentage have run rampant. Gaining a foothold first in areas disturbed by human activities, they moved into natural areas where they've not only driven out indigenous species but in the worst cases radically altered the ecosystems they've invaded.

In 1993, after an extensive review of exotic species, the Congressional Office of Technology Assessment (OTA) concluded that pest plants and animals have an effect not only on natural areas but also on agriculture, industry and human health. In its report, Harmful Non-Indigenous Species in the United States, the agency noted that from 1906 to 1991, just 79 problem plants and animals caused documented losses of $97 billion, and that a worst-case scenario for a mere 15 potentially high-impact species could cause another $134 billion in future economic losses.

Thousands of non-indigenous plant species are known to persist outside of cultivation in the United States. How many of these are plant invaders? In the course of researching this book, we tallied the species on the two most comprehensive national natural areas weed lists ever compiled: one of plants being reported as problems on Nature Conservancy preserves nationwide, and another compiled by the National Association of Exotic Pest Plant Councils, an umbrella organization of state groups concerned about the ecological impact of invasive non-native species. After submitting the combined list to various state weed authorities for their additions and subtractions, we arrived at a total of just over 300 plants invading wildlands in the 49 continental states and Canadian provinces. (We didn't have room for the plant invaders of Hawaii, which could easily fill an entire volume.) According to our calculations, about half of the 300 continental plant invaders were brought here to beautify our gardens. A much tinier fraction of native plants are showing signs of invasiveness, but there is considerable disagreement over why and what kind of threat they pose; this, too, is a subject for another volume.

The problem is surprisingly widespread. Hawaii, California and Florida appear to be the hardest hit, but few—if any—regions of the U.S. and southern Canada are without non-native pests. According to The Flora of North America, the most comprehensive reference on this continent's plants, one-fifth to one-third of all species growing north of Mexico have come from other continents.

This ground-breaking handbook focuses on 80 of the invasive plants used horticulturally. These include the most serious invasives, such as purple loosestrife, which are so widespread that they'd be found on any "most wanted list" of plant invaders. Others, such as baby's breath, are problems in a geographically limited area-in this case, Great Lakes dune systems-but threaten unique habitats or rare plants. A few, like dame's rocket, right now appear to be only slightly invasive but are on weed experts' "to watch" lists because it often takes decades for a plant to begin spreading out of control—and once invasives are well established they are extremely difficult to manage.

In the chapter that follows, co-editor John Randall, who regularly criss-crosses the country to study invasives for The Nature Conservancy, explains how problem plants damage natural areas and why some introduced species become pests while others don't. Next is a section on the tools and techniques to control invasive plants, from hand-pulling to prescribed burning to, as a last resort, chemical herbicides.

The core of the book is an encyclopedia of invasive species used horticulturally, which was written by many of North America's leading weed experts and natural areas managers from 20 states and the District of Columbia. The encyclopedia is organized by plant type: trees, shrubs, annuals and perennials, grasses, vines and aquatic plants. To find out which ones are problems in your area, look in the index and in individual encyclopedia entries under the section "Where has it spread?" Each plant write-up will not only help you identify invasives and understand their ecological impacts but also tell you which to avoid planting and how to control plants already on your property that threaten nearby natural areas.

Scientists don't yet know whether some invasives represent permanent threats to the Earth's biodiversity, or whether they will become less dominant over the long haul as the plant communities they've invaded change and mature. In any event, the most prudent course of action is to avoid planting these species—because when it comes to invasive plants, as land managers have learned the hard way, an ounce of prevention is worth a pound of cure.

Marc Albert

works with the habitat restoration programs of the Golden Gate National Recreation Area and received his MA in integrative biology from the University of California, Berkeley.

Edward R. Alverson

is Willamette Valley stewardship ecologist for The Nature Conservancy, and is responsible for managing and restoring a number of natural areas in the Valley. He is based in Eugene, Oregon.

Susan Antenen

is director of science and stewardship for The Nature Conservancy on Long Island, New York. She previously directed the Forest Restoration Project at Wave Hill in the Bronx, New York.

Steven L. Apfelbaum

is a research ecologist with Applied Ecological Services, Inc. and Taylor Creek Restoration Nurseries, in Brodhead, Wisconsin, firms involved in hundreds of ecological restoration projects throughout the U.S. and Canada.

Henry W. Art

is the Samuel Fessenden Clarke Professor of Biology and director of the science division at Williams College in Williamstown, Massachusetts.

Gary Bell

is southern California area ecologist for The Nature Conservancy in Temecula, California. He has a PhD in ecology from Carleton University in Ottawa, Canada.

Bernd Blossey

is director of the Biological Control of Non-indigenous Plant Species Program at New York State College of Agriculture and Life Sciences at Cornell University in Ithaca, New York.

D. Daniel Boone

is a graduate student in the Appalachian Environment Lab at the University of Maryland. Previously, he worked as a forest ecologist with The Wilderness Society and as the botanist and coordinator of the Maryland Natural Heritage Program.

Carla Bossard

is an associate professor of plant ecology at St. Mary's College of California in Moraga and received her PhD in ecology in 1990 from the University of California, Davis. She has written widely about Scotch broom and its establishment in native habitats.

David Boyd

is a resource ecologist at the California Department of Parks and Recreation in San Rafael. He has managed several large eucalyptus removal projects.

Laurie Deiter

is integrated pest management coordinator for the City of Boulder Open Space Department where she coordinates the IPM program on 28,000 acres of range, forest and agricultural lands. She was named Weed Manager of the Year in 1993 by the Colorado Weed Management Association.

Joseph M. Di Tomaso

is assistant non-crop weed specialist in ecology, in the vegetable crops department at the University of California, Davis, where he received his PhD in botany/weed science in 1986.

Glenn D. Dreyer

is director of the Connecticut College Arboretum and an adjunct associate professor of botany at Connecticut College.

John E. Ebinger

is emeritus professor of botany at Eastern Illinois University in Charleston where he has taught for the past 33 years. He received his PhD from Yale University, and for the last three decades has studied the vascular flora and the structure and composition of the forest communities of Illinois.

James A. Eidson

is North Texas land steward for The Nature Conservancy of Texas where he manages five prairie preserves, two suffering from invasion by tall fescue. He has an MS from Texas A&M University where he focused on prairie restoration and control of exotic and invasive species on wildlands.

William Glass

is a district heritage biologist with the Illinois Department of Natural Resources, Division of Natural Heritage. He manages state-owned natural areas, including prairie, savannahs, forest and wetlands, and endangered and threatened species habitats in six counties.

Roger L. Hammer

is a naturalist and resource management supervisor for Metropolitan Dade Parks Department's Natural Areas Management Division and past director of Castellow Hammock Nature Center in South Dade, Florida. He is also chairman of the Native Plant Workshop and author of many articles on the flora of southern Florida.

Beth Hanson

is the former managing editor of BBG's 21st-Century Gardening Series.

Patricia Dalton Haragan

is associate curator of the Davies Herbarium at the University of Louisville in Kentucky. For the past 15 years, her research has focused on the weed flora of Kentucky and other parts of the U.S. She is the author of several books including Weeds of Kentucky and Adjacent States: A Field Guide.

Bonnie Harper-Lore

is a landscape architect and roadside vegetation coordinator for the Federal Highway Administration where she serves as a technical resource to all 50 state highway agencies. She is a founding member of FICMNEW (Federal Interagency Committee for the Management of Noxious and Exotic Weeds).

Kim D. Herman

is stewardship and natural areas coordinator for the natural heritage program of the Michigan Department of Natural Resources in Lansing.

John Hunter

is assistant professor of biological sciences at the State University of New York College at Brockport. He has a PhD in plant biology from the University of California, Davis, and his research focus is the ecology of trees in forests and woodlands.

Kristine Johnson

is resource management specialist at Great Smoky Mountains National Park in Tennessee, and serves on the board of directors of the Tennessee Exotic Pest Plant Council.

Elizabeth Johnson

is an ecological consultant. During her eight years with The Nature Conservancy in New Jersey as director of science and stewardship, she managed 17 preserves, each with its own set of invasive weeds. She has an MS from Rutgers University.

Greg Jubinsky

is an environmental program manager with the Florida Department of Environmental Protection. He coordinates statewide use of biological control agents (grass carp and insects) for management of invasive plants and establishes screening methods to prohibit new introductions of invasives.

Mike Kelly

is president of the San Diego conservation group, The Friends of Los Penasquitos Canyon Preserve. He is also a member of several citizen advisory groups for parks and secretary of the California Exotic Pest Plant Council. He has a BS from San Diego State University.

Jill Kennay

is the natural resources manager at the Natural Land Institute in Rockford, Illinois. She has a degree in ecology from the University of Illinois.

Jo Kitz

manages the Cold Creek Preserve in the Santa Monica Mountains for Mountains Restoration Trust. She is past-president of the Los Angeles/Santa Monica chapter of the California Native Plant Society.

Norma Kline

is a conservation biologist, presently working with the Pennsylvania Department of Conservation and Natural Resources.

Carol Lippincott,

botanist, and

Sandra McDonald,

weed scientist, are both completing doctoral dissertation research at the University of Florida on the biology, spread, and ecology of cogongrass.

James O. Luken

is an associate professor in the Department of Biological Sciences at Northern Kentucky University. His research focuses on the physiological and population ecology of invasive woody plants.

Janet Marinelli

is director of publishing at the Brooklyn Botanic Garden. She is the editor of several previous BBG handbooks, including Going Native: Biodiversity in Our Own Backyards and The Environmental Gardener. She is the author of The Naturally Elegant Home and Your Natural Home, both published by Little, Brown and Company, and is currently writing a book on the future of gardening in an age of extinction.

Bill McClain

has been involved in natural areas management and research for more than 25 years. His primary interests are prairie and forest communities and exotic species control. As a field biologist, he was responsible for the stewardship of several sites where smooth buckthorn was a management problem.

Victoria Nuzzo

is a natural areas biologist with Native Landscapes in Rockford, Illinois. She specializes in protection, management, and monitoring of natural areas with an emphasis on the spread and control of invasive species.

John M. Randall

is invasive weed specialist at The Nature Conservancy, where he provides leadership, technical support and advice on weed control to Nature Conservancy preserves nationwide. He is a founding member, past president and current board member of the California Exotic Pest Plant Council, and a board member of the National Association of Exotic Pest Plant Councils. He holds a PhD in ecology from the University of California, Davis.

Sarah Reichard

is a post-doctoral research fellow in the Department of Zoology at the University of Washington in Seattle. Her research aims to prevent new invasions rather than control existing ones.

Peter Rice

is a researcher in the biological sciences division of the University of Montana, in Missoula, where he focuses on introduced species, "a biotic form of pollution."

Amy Samuels

is a graduate student in the Department of Environmental Forestry and Biology at State University of New York College of Environmental Science and Forestry in Syracuse, New York.

John E. Schwegman

is native plant conservation manager for the Illinois Department of Natural Resources. He received an MA in botany from Southern Illinois University at Carbondale.

Leslie A. Seiger

has a PhD in ecology from George Washington University, where she wrote her dissertation on the ecology and control of knotweed. She is now studying invasives as a post-doctorate fellow at San Diego State University.

Jake Sigg

is chair of the Invasive Exotics Committee for the California Native Plant Society and is president of its Yerba Buena Chapter. He is retired from Golden Gate Park and Strybing Arboretum and Botanical Gardens, where he supervised the gardening staff and was de facto curator of collections.

Guy Sternberg,

an arborist and landscape architect, is a statewide director of the Illinois Native Plant Society. He runs a research arboretum, Starhill Forest, and has contributed pieces to several of the Taylor's Guides garden encyclopedia series, and was co-author and photographer of Landscaping with Native Trees.

Carolyn M. Thurman

is assistant director of science and stewardship for the Pennsylvania Chapter of The Nature Conservancy. Her focus is on site conservation planning and biological monitoring in a management context.

Sara L. Webb

is an associate professor of biology and director of the Environmental Studies Program at Drew University in Madison, New Jersey. Her research interests include the Norway maple invasion, windstorm disturbance to forests and consequences of forest fragmentation for biodiversity.

Sandra Vardaman Wells

is a restoration biologist with the Natural Areas Management Section of the Metropolitan Dade Parks Department where she develops and implements resource management plans for publicly owned natural resource sites in Dade County, Florida.

William Wiesenborn

is a biologist with the Bureau of Reclamation in Boulder City, Nevada and is interested in biological diversity and water resource planning.

Brian Winter and Gordon Yalch

both work in The Nature Conservancy's Minnesota Western Preserves Office; Winter as director of science and stewardship of the Northern Tallgrass Prairie, and Yalch as preserve management assistant.

Steve Young

is a botanist for the New York Natural Heritage Program, where he inventories and studies the state's rare plants. From 1985 to 1990 he was the botanist at the Mercer Arboretum and Botanic Gardens in Houston.

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