Invasive Plants

Invasive plants, otherwise known as 'noxious weeds,' are invading the Rogue River-Siskiyou National Forest in ever increasing numbers. Please help us eliminate noxious weeds by helping to prevent the spread of these plants and by learning to recognize and destroy them!

Aliens Stole my Habitat!

by Terry Rich -Bureau of Land Management; Photos courtesy of "Weeds of the West, 5th Edition"

Unwanted and Uninvited Invaders Wreak Havoc With the Natives

Leafy SpurgeIf you regularly read the Weekly World News, as I suspect most readers of Bird Conservation do, you know that aliens have been mucking around here on earth for a long time, perpetuating all sorts of awful things on us and on our animals. But while too many Americans have been puzzling over designs in wheat fields and fuzzy pictures of pie plates, the real aliens have been stealing our native vegetation at rates of hundreds of thousands of acres per year.

Plants growing where we don't want them are often called "exotics." But exotic plants are anything but "fascinating," "romantic" and "wondrous" and are better labeled "aliens," "invaders" or "weeds." In Hawai'i, banana poka, a luxuriant vine with showy flowers, drapes the native vegetation with a green tapestry that makes stunning photos. But this South American weed is strangling koa forests and driving three endemics, the Hawai'i Creeper, Hawai'i Akepa and the 'Akiapola'au, closer to extinction.

Along the river bottoms of western North Dakota, early summer brings a golden glow that simmers in the sunset, weaving the green prairie uplands to the woody draws. But leafy spurge is steadily choking out the grasses and forbs that evolved in the domain of Common Yellowthroats, Yellow-breasted Chats and Song Sparrows. The bottoms fill with an alien that native plants can't beat and native animals can't use. In moist areas in the prairie uplands, Baird's Sparrow and Bobolinks, two declining neotropical migrants, find habitat similarly rendered unusable.

Mature Annual BluegrassFrom Minnesota to Massachusetts unsuspecting tourists marvel at the spectacular purple flowers ringing wet meadows and woodland ponds. Where Red-winged Blackbirds, Marsh Wrens, Sedge Wrens, and rails once thrived, the native emergent vegetation gives way to the deadly beautiful flower, purple loosestrife that pushes out sedges, rushes and cattails. On the east Coast, Phragmites is impacting similar ecosystems.

Even the plant that Americans love above all others, the one we spend billions of dollars and millions of Saturday afternoons on, the one we lavish with fertilizer and water, is an enemy in the wild. Kentucky bluegrass Image (Mature) 42K, abetted by livestock (alien mammal) grazing, forms a nearly impenetrable sod in moist places. Native grasses, forbs and shrubs required by many neotropical migrants are kept out of the ecosystem.

A Creepy Invasion

Alien plants are among the most destructive phenomena currently affecting bird populations. The problems are several. Alien plants often creep into the landscape over a period of time so that casual observers don't realize what is happening. Aliens often can be destroyed when they cover a few square meters. But once they have had a chance to disperse, then we sadly may understand Aldo Leopold's comment on cheatgrass , "One woke up one fine spring to find the range dominated by a new weed."

Although the effects of alien takeovers on native bird populations have not been widely studied, the general pattern is similar, whether talking about grasses, forbs, vines or trees. Once established, they have a relentless ability to totally dominate the land surface, crowding out most native plants and producing a monoculture of themselves. Without their natural competitors, predators, diseases and parasites, these monocultures can persist, apparently indefinitely.

Mature CheatgrassIn the western U.S., one of these aliens, the cheatgrass that Leopold noted, is steadily expanding its domination of what used to be called shrubsteppe. These vast historical landscapes of sagebrush, perennial bunchgrasses and flowers have been home to the sagebrush obligates -- Sage Sparrow, Sage Thrasher, Sage Grouse and Brewer's Sparrow. Brewer's Sparrow may have been the most abundant bird in the Intermountain West. But today it is one of the most consistently declining species tracked by the Breeding Bird Survey. The Sage Grouse, on a 40-year decline in Oregon and Idaho, is being discussed for listing as endangered.

Other species which use shrubsteppe habitat to some degree also will suffer -- Northern Harrier, Short-eared Owl, Mourning Dove, Gray Flycatcher, Rock Wren, Loggerhead Shrike, Vesper Sparrow, Lark Sparrow, Black-throated Sparrow, Green-tailed Towhee and Spotted Towhee. Even the Horned Lark and Western Meadowlark, which are the only shrubsteppe species persisting in cheatgrass habitats, are more abundant in the native vegetation types.

Cheatgrass is a doubly nasty alien because it is a fire-adapted species. It burns readily and comes back the following year with a vengeance from seed. In the mean time, native species, which are not fire adapted, get burned out. As a site burns again and again, cheat eventually dominates the landscape.

Conversion also fragments the remaining shrubsteppe so that patches of good native vegetation may be separated by large seas of the desiccated monoculture. This further harms area-sensitive species such as the Sage Grouse and the Sage Sparrow and produces impossible barriers for other sagebrush species like the pygmy rabbit and sagebrush vole.

What Can We do?

Research on biological controls for many of these invasive species shows promise. Weevils, mites, moths and fungi are being sought in the countries of origin, tested and released. Certainly there is some hope in the long run that alien plants can be "controlled." This doesn't mean we'll be able to restore historical vegetation across the landscape but rather that the species can be slowed from spreading further and perhaps knocked back in some areas.

Another simple, but probably overlooked strategy is to become a vigilant observer and help detect the appearance of an new alien invader in your area. County "weed boards" have been in this business for a long time, watching for the appearance of a patch of some "noxious weed" so they can hit it quickly with chemicals, mechanical means, or other tools. Learn about the aliens that are a threat in your area from these people. Finally, in the case of shrubsteppe, we need to identify those areas not susceptible to cheatgrass invasion -- shrubsteppe with precipitation exceeding 16 inches -- and then seek their long-term protection.

I recently returned from my first trip to the Big Island of Hawai'i. In eight days of traveling and birding, I saw no native bird species below 500 m and every plant I asked about in the lowlands was from some other country. This was a frightening and sobering experience. We think something so extreme cannot happen here. But this is an ongoing process -- the aliens we've got keep spreading and new ones keep coming. And that's a lot scarier than the half-alligator half-human on the loose in Miami.

-Terry Rich

(Terry Rich is the Nongame Bird Program Manager for BLM and chairs both the Western Working Group and the Management Steering Committee for Partners in Flight.)

Bird Conservation - Summer Nesting 1997 Pages 12-13