Nature in Trouble: Aliens in National Parks

Why Worry About Non-native Species?
Postmodern deconstructionism is the fashionable, backside-of-existentialist philosophy that every object and condition is of equal value, nothing much matters, and it's futile to rebel. As if it isn't hard enough to understand what is best for ourselves and our world, this perspective has seriously diminished our culture's ability to decide and act on what is important. The introduction of non-native species (nns) has been one of the most devastating human impacts on this planet's ecology, third only behind outright extinction and habitat destruction. A laissez faire attitude towards this phenomenon has dire consequences for us, for our children, and for our planet. But to understand the damage done by these often accidental introductions takes a little explanation.
Here are a few examples of alien invasions in the U.S. Kudzu, Melaluca, Brazilian pepper, Russian olive, purple loosestrife, spotted knapweed and other plant species have taken over many of this nation's great ecosystems, dumbing down their complexity, turning these elegant assemblages into simpler, non-interactive systems that support fewer species. Tamarisk and cheatgrass increase fire frequency in many habitats where fire has not played an evolutionary role, simplifying those ecosystems. The introduction of elm, maple and chestnut blights destroy our nation's most prominent deciduous tree populations, and non-native insects like gypsy moth and maple borer further harm our native forests.
Have you ever been stung by fire ants in the Southeast, or thought about what to do if (when) your trip is attacked by Africanized bees? Whirling disease, Asian tapeworm and other disease organisms are threatening trout and native fish populations. Avian malaria and brown tree snakes are literally eliminating the native bird fauna of Hawaii and the South Pacific. Most people see only non-native house sparrows, starlings and pigeons in their urban environments, not native birds. The aids virus alone seems like a big enough problem, not mention threats posed by that new Nile virus in the Northeast. These are just a few examples, and 10.5% of Grand Canyon's plant species are nns, a proportion equivalent to that in the United Kingdom.
As with all invasions, conquest affects both the vanquished and the conqueror. nns gradually become “naturalized”, or incorporated into the ecosystem, but that process occurs over evolutionary time—tens of thousands to millions of years. If we were dealing with the natural establishment of a rare foreign species, North American ecosystems could handle and gradually incorporate the immigrants. However, the sudden arrival of thousands of nns during the past century is swamping the ecological adjustment capacity of our ecosystems, which are being launched off on unknown courses.
Making matters worse, aliens tend to show up in the most biologically diverse habitats (springs, wetlands and river bank habitats here in the West), settings where their impacts are most likely to be most serious. Making matters even worse, a study in Dresden, Germany (where long-term records of nns arrival are kept) reported that the mean time between the introduction and eruption of alien plant populations was 267 years. Therefore, we can't even guess at the ecological implications of new species arrivals in our life times. It's simply best not to bring in new species, and to eliminate those we can, wherever possible, before we lose our native ecosystems.
Therefore, nns invasions are ecologically bad because: 1) they disrupt the stability of ecological communities, particularly by 2) altering natural disturbance regimes and increasing the rate of ecological change beyond that tolerable by most species; 3) they degrade fish and wildlife habitat quality; 4) nns destroy economically important populations; 5) they degrade aesthetic values and recreational experience (e.g., the invasion of camelthorn and Russian olive along Southwestern rivers; 6) nns alter landforms (stream channels, etc.); 7) nns include the transmission of new disease organisms with devasting population consequences; 8) they can strongly affect public health; 9) nns damages are extremely costly (several billion dollars/yr in the U.S. at present), and 10) control measures require considerable, time-consuming follow-up monitoring, if control is possible at all.
A Success Story in Grand Canyon
Most, if not all, U.S. national parks are vigorously pursuing control of nns because the nps mandate is to manage for native assemblages, where possible. However, parks often require landscaping and nps staff are not all botanists. The National Park Service at Page planted ravenna-grass, a large and invasive ornamental bunch grass, believing it to be a non-dispersing species like pampas-grass. Fortunately, Tina Ayers (nau botanist) and I detected the rapid population explosion just as it was beginning, and with the help of two dozen volunteers we removed 10,000 plants from the river corridor in Grand Canyon in 1994–1996. This species is now rare to non-existent in Grand Canyon, and the few that spring up quickly fall to the shovels of the vigilant nps vegetation crew.

Tamarisk in Grand Canyon
As a nns, tamarisk or saltcedar (Tamarix ramosissima/pentandra) is a conundrum in Grand Canyon. It is a Eurasian shrubby phreatophyte that dominated the riparian zone of southwestern rivers during the 20th Century. It is a good colonizer, but a lousy competitor. It supports only a few herbiovorous invertebrate species, but many pollinator species, and now provides much altered habitat and food resources for the river's bird fauna. The U.S. Fish and Wildlife Service (fws) has declared Mile 46 to Mile 72 of the river corridor as critical habitat for the endangered southwestern willow flycatcher, a species that nests preferentially in tamarisk.
Tamarisk produces millions of small, short-lived, wind- and water-dispersed seeds each year. As is abundantly apparent this year, and well documented in the literature, tamarisk colonizes moist fine-grained riverbanks on the heels of floods. The Adaptive Management Work Group's “$50 million experiment” this year is shaping up to be the only massive germination event for tamarisk in the river corridor in the past 25 years, so be sure to thank them for reinitiating the invasion process there. More importantly, over the past 70 years, tamarisk has been actively invading the Canyon's many tributaries, streams that are now unique systems in having not been grazed, mined, or otherwise much affected by human activities. Such systems are essentially gone in the West, and are at risk in Grand Canyon.
A Tamarisk Control Program in Grand Canyon
The Grand Canyon Wildlands Council (Kelly Burke, Kim Crumbo and myself) and the National Park Service (Norm Henderson, John Spence, Frank Hays, Lori Makarick and others) have funded a tamarisk control program in Grand Canyon. This project is supported through the Arizona Water Protection Fund, and cost shared with the nps and gcwc. We plan to stall the invasion of tamarisk in more than 60 tributaries, killing tamarisk by applying Garlon® to freshly cut stems. When you actually count them, there are generally not many tamarisk in the in-park tributaries (in contrast, the Paria, lcr, and Kanab, Havasu and Diamond creeks are loaded). We expect that our teams of well-trained group of volunteers can handle a tributary a day or so. By removing tamarisk from the tributaries, we can set back the invasion process there by 50 years or so, while the fws gets their Act together and starts managing for ecosystems, rather than single species.
We also plan to replace the tamarisk stand at Lees Ferry with native cottonwoods, willows and other native species. This site was photographed in pre-dam time, and prior to the arrival of tamarisk in the 1920s–1930s, the area just downstream from the launch ramp was dominated by those native trees. We will mechanically remove tamarisk, and plant a beaver-proof stand of native trees and shrubs, monitoring plant growth over the next couple of years and changes in the bird community. This part of the program is overseen by Fred Phillips (Phillips Consulting), who has successfully transformed more than a mile of the lower Colorado River shoreline near Parker from tamarisk hell into a delightful native cottonwood and willow stand. Cottonwoods and willows are culturally valuable to tribes such as the Hopi and the Navajo. Roots, branches, and logs are used in baskets, kachinas, and structures. In addition, restoration provides an opportunity for education, especially for volunteers who may not otherwise learn about the nns problem. From this cultural perspective, having interfered with natural processes, we have a responsibility to care for nature in an active way. Restoration is one way to do that. This project is an important pilot study, in that it provides the opportunity to evaluate what it will take to transform tamarisk stands downstream into native vegetation, once the fws and amwg figures out their ecosystem mangement responsibilities.
What's Right?
As the victims of post-modernism, we are accustomed to fatalistically accepting whatever happens. The obstacles to change are daunting, the issues are confusing, and the politics are abysmally confounding. But we do have a choice in this matter, and sacrificing our natural heritage to a bunch of aliens is the wrong path. The fight against aliens requires creativity, hard work, a good sense of rebelliousness, as well as a little information. The battles can, and should, be waged in our backyards, as well as on regional, national and global scales. Non-native species that don't spread are not the problem, and many ornamental species do not pose any ecological threat. But those that can reproduce from seed or rhizomally should be actively removed and eliminated, from our yards, our neighborhoods, our roadways, our parks and from our regions, it at all possible. Tending to your own environment can make a difference. Join your native plant society (every state has one), and let your local nursery house know they should not be distributing species that can go wild. I think each of us should take on the task of thwarting the spread of at least one alien species. Make a difference in this war. We welcome your comments on this tamarisk management plan, and hope you will consider the issue of non-native species introductions more seriously.

Larry Stevens
Grand Canyon Wildlands Council Science Advisor