Unnatural Landscapes: Tracking Invasive Species

By Ceiridwen Terrill


  Book cover
Book cover
Book cover

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please click on the live link to order from University of Arizona Press or from Amazon

To go to the author's bio page click here Ceiridwen Terrill










This page links readers to more information about invasive species and organizations working to eradicate or control them in the United States and abroad.




Non-native or exotic species are plants and animals that have been introduced by humans or human activity in locations outside their natural range. In North America , plants and animals are considered exotic if they were introduced after European settlement (i.e., after the mid-1500s).  Exotic species may become invasive, threatening the health of native species and sometimes whole ecosystems.  But not all exotic species become invasive.  The response of a plant or animal to a new environment determines whether or not it is invasive.


Common traits of invasive species include: fast growth, high reproductive rates, and high dispersal ability.


The problem:  Established populations of invasive species compete with native species for limited natural resources:  nutrients, water, sunlight, and space.  The U.S. Fish and Wildlife Service notes that invasive species cost the United States approximately $34.7 billion each year.


But we have to remember: everything is native somewhere.  Invasive species are not “evil.”  They’re just doing what they’re supposed to do:  survive and thrive, but unfortunately they can really cream native plants and animals.


Extinctions have always occurred.  Plants and animals have always moved from one place to another.  The problem is the accelerated rate of extinctions and of movements of exotic species around the world.  Acceleration began around 1500 and has continued exponentially since that time. 


Let me make it absolutely clear:  the idea behind restoration is NOT to return to a pre-1500s (pre-Columbian) environment, to a mythic pristine, virgin wilderness untainted by human activities.  For example, where I live in Portland, Oregon English ivy and Himalayan blackberry are local examples of invasive species that can be controlled but may never be eradicated.  English ivy is beautiful in England, but here it has this very nasty habit of choking trees to death.  English Ivy attaches itself by rootlets and weighs down branches, often causing them to break. It prevents photosynthetic processes by blocking sunlight.


The goal of restoration is to tip the scales back in favor of native species, to make invaders a smaller component within a healthy, mostly native community.

The issue of invasive species has largely remained within scientific circles and the goal of this book is to move the conversation outward, into the public consciousness.


There are things that regular folks, nonscientists can do to minimize exotic species introductions.


A list of things you can do to be part of the solution is at the bottom of this page!


Selection of Invasive Species

Photos are by the author.

(Common names are used here.)



Russian Thistle


Russian Thistle: The celebrated "tumbling tumbleweed" of Hollywood Westerns


Tumbling Tumbleweed



Black Rat Anacapa Island, California


Black Rat


Crystalline ice plantCrystalline Ice Plant


Crystalline ice plant Water blisters visible on plant




Nesting Western Gull Surrounded by Crystalline Ice Plant


Hottentot fig


Hottentot Fig


Hanging out with Phil Pister




invasive morning glory






English Ivy


ivy 2



ivy forest


Forest Smothered in English Ivy






Some preventative measures to help stop the spread of invasive species


Boot brushes Boot brush for scraping off seeds



Campers on Santa Cruz Island Camping equipment


Wash Camping Gear Thoroughly


Crowd of visitors to S.C. Island


Educational Programs About Invasive Species


harmful speciesharmful species


Department of Fish and Game Office


Information Campaigns by County, State, and Federal Agencies


Island Packers


Information Campaigns by Private Concessionaires


Some things regular folks can do: 

  1. In landscaping prefer native plants over exotic ones.  Native plants attract birds and butterflies and will lower the risk of birds ingesting exotic seeds and spreading them.
  2. Buy birdseed for your feeders that has been cracked or cooked so that it doesn’t germinate and spread.
  3. Shake out your camping gear so you don’t carry around any seed hitchhikers, hose your car tires and hiking boots (mud can carry around exotic seeds).  Pick the seeds out of your shoelaces.
  4. A lot of folks don’t want to hear this but leash your dogs in wild areas.  Dogs can carry around seeds in their fur and between their toes.  They also break down the soil around stream banks.  Invasive plants love disturbed soils.
  5. If you’re a horse person and you trail ride, buy weed-free feed.  If your feed store doesn’t carry it, keep asking until they do.
  6. Don’t own exotic pets.  But if you do, don’t let them go!  They may escape and become invasive (snakes, for example). 
    1. SNAKES:  Alligators in the Florida Everglades are threatened by invading snakes like the popular pet snake, the Burmese python, one of the world's largest snakes. These pythons can grow to be more than 20 feet (6 meters) long in their natural habitat in Southeast Asia.
    2. FISH:  Never dump aquariums into streams.  Unfortunately, sometimes people think they’re doing their pet fish a favor by setting them “free.”  Actually, most fish die when exposed to nonnative conditions, so you’re not doing them any favors, but some of the more hearty fish may survive to become invasive.  Examples: angelfish, swordtail, glow-light tetra, hatchet fish and tire track eel
    3. AQUATIC PLANTS:  Aquarium plants can also take over a native stream system.  Example:  well known and common aquarium plant:  Hydrilla (Hydrilla verticillata), also known as water thyme, is a well-known aquarium plant native to parts of Asia and Africa.
  1. If you’re a boater, empty your bilge water, hose your boat down and allow it to dry completely before entering a new waterway, so you don’t take any hitchhiking snails or mussels or plant species with you.
  2. There are organizations in your area that host volunteer days for citizens to help control invasive plants.
  3. If you’re really gung-ho, you can do what I do which is to make medicines and use invasive plants in cooking.  Take Himalayan blackberry for example:  eat the delicious fruit, make jam, and then rip them out.
  4. I use blackberry leaves for tea (if they haven’t been sprayed with herbicides) and the roots and stems for gastrointestinal problems.


Selection of Native Species Photographs for your pleasure:


Red Mangrove


Native Red Mangrove Tree on Isla Coronado (Isla Smith), Bahía de los Angeles


native buckwheat


Island Buckwheat, Channel Islands, California




Dudleya, Channel Islands, California




Indian Paintbrush


lemonade berry


Lemonade Berry, Channel Islands, California


native sage




tree sunflower


Tree Sunflower


anise swallowtail caterpillar


Anise Swallowtail Caterpillar making due with invasive sweet fennel. Fennel excretes an allelopathc substance (chemical) that retards or prohibits the growth of native plants.


swallowtail 2



Hanging out with Phil Pister


Finding Pupfish with Phil Pister