Throughout my adventures in Nature, I’ve heard the words “invasive species” used extensively by environmentally conscious individuals and organizations as well as those government agencies who oversee public lands. The context in which “invasive species” is used is typically with a connotation of being bad — something that needs to be destroyed. Being the “suspicious scientist” type, I’ve given some thought and done some research on the subject of invasive species which I would like to share with you. My purpose in writing this blog is both to present my views and to solicit your views. Whether you agree or disagree with me, I’d like to hear from you.
First, let’s define “invasive species”. The one that strikes me comes from the Yukon Territories Canadian Government :
“An invasive species is defined as an organism (plant, animal, fungus, or bacterium) that is not native and has negative effects on our economy, our environment, or our health. Not all introduced species are invasive. Invasive plants and animals are the second greatest threat to biodiversity after habitat loss. In other North American jurisdictions many invasive plants are responsible for habitat damage, loss of subsistence resources, and economic loss.”
From where I sit, this definition offers a concise description of the current usage of the term “invasive species”. But for me, there are some incongruities in the current idea of invasive species that need clarification and consideration:
This is an interesting paradox. We are defining invasive species as
those factors that negatively affect the human race and not necessarily the environment. There is no population control of our own invasiveness. Yet, we try to control the invasiveness of other species.
Invasive species are a normal part of evolutionary processes
Invasive species are essential to the process of evolution. Many times, evolution takes place when a species moves on to new territory and adapts to a new environment. Darwin’s finches in the Galapagos Islands are a famous example. Almost everything on earth is an invasive species.
Therefore, we must be careful when we employ a negative connotation to the words “invasive species”. As I will point out later in this blog, there are some invasive species that do a great job in controlling other invasive species.
Invasive species are not as widespread as some would have us believe
Researchers at the Center for Limnology at the University of Wisconsin–Madison found that invasive species follow a “nearly universal pattern in ecology — that invasive species are rare in most locations and abundant in a few.” The study’s lead author, Gretchen Hansen, notes that “high abundance is the exception, not the rule.” The study suggests that invasive species management should focus on those exceptions where the invaders do in fact spread like wild fire. The study goes on to suggest that managers try to identify invasive species “hot spots” where they are prolific and then spend conservation funds where it will have the greatest impact.
The claimed negative effects of certain invasive species are sometimes without scientific basis
Recently, I spend two days at the Fish and Wildlife Service bird sanctuary at Bosque del Apache near Socorro, New Mexico. It was a wonderful time watching and photographing thousands of migrating birds. The preserve offered a really great tour of the facility which was conducted by very capable volunteer docents. Part of the tour addressed the issue of the invasion of salt cedar into this human engineered wetland. Information was offered on the many bad things about Tamarisk. I have a tendency to check out the science behind the information from tour guides that they have acquired during their training by their handlers. But, the tour guide was so convincing that I believed the information that was offered about the negative aspects of Tamarisk as an invasive species. I believed their information until I found this web site and video.
The web site offers a very holistic perspective on the Tamarisk issue that has caused me, once again, to affirm that mother Nature has much better ways of coping with her ecosystems than does mankind. Indeed, the Tamarisk is a beneficial plant in certain environments. The web site states:
“States in the Southwest spend millions of dollars each year on pesticides and herbivorous beetles to control salt cedar. Now, however, studies suggest that salt cedar uses up no more water than native species and that the spread of salt cedar is largely due to changes in hydrology caused by building dams and irrigation canals. This video explores both sides of the debate over salt cedar and examines whether the battle against it is a misguided use of public funds.“
Removal of invasive species can sometimes be more harmful than the species that we wish to eradicate
I find myself deeply disturbed about the means by which some organizations attempt to eradicate an invasive species. To me it seems that the bad consequences of poor eradication methods is far greater than the effect of the invasive species.
The classic example is described by Rachel Carson when the US Government desired to kill off sagebrush. Sagebrush was then considered “invasive” by farmers and ranchers who wanted more grazing land. Carson writes:
As noted in my blog post on Rachel Carson’s legacy, Carson described how the U.S.Forest Service used chemical weed killers to kill sagebrush and substitute grasslands for cattle ranchers who leased government land. In her own words, she described this folly by our government:
“The earth’s vegetation is part of a web of life in which there are intimate and essential relations between plants and the earth, between plants and other plants, between plants and mammals…. It was no accident that the great plains of the West became the land of the sage. The bitter upland plains, the purple wastes of sage, the wild, swift antelope, and the grouse are then a natural system in perfect balance. ..One of the most tragic examples of our unthinking bludgeoning of the landscape is to be seen in the sagebrush lands of the West, where a vast campaign is on to destroy the sage (using weed killer) and substitute grasslands.…it is clear that the whole closely knit fabric has been ripped apart. The antelope and the grouse will disappear along with the sage. The deer will suffer too… The spraying also eliminates a great many plants that were not its intended target. The sage was killed as intended. But, so was the green life-giving ribbon of willows… Moose had lived in these willow thickets, for willow is to the moose what sage is to the antelope. Beaver had lived there too, feeding on the willows, felling them and making a strong dam across the tiny stream. Through the labor of the beavers, a lake backed up. Trout in the lake thrived so prodigiously that many grew to five pounds. Waterfowl were attracted to the lake, also. But with the ‘improvement’ instituted by the Forest Service, the willows went the way of the sagebrush, killed by the same impartial spray. The moose were gone and so was the beaver. Their principal dam had gone out for want of attention by its skilled architects, and the lake drained away. None of the large trout were left. The living world was shattered.”
Due to human insensitivity and an ignorance regarding the interconnectivity in Nature, government funds have been used to “manage” our environment and sometimes create ecological disasters. What is not understood by many of Nature’s stewards is that it is impossible to manage Nature.
There are some recent examples of questionable means of killing off invasive species. Despite the lessons taught by the Rachel Carson story, the US Department of Agriculture has chosen to fight off a Buffelgrass invasion by employing the aerial spraying of Roundup – a common weed killer. Much like the folks in Rachel Carson’s day, these people seem to be sure that their aerial spraying will stop the invasion of Buffelgrass without harming anything else. There is no doubt that Buffelgrass is an species that meets the definition of invasive species because it was introduced by mankind through cattle ranching and grazing operations (yes- the same people who now want to kill wolves and get rid of the sage brush ). But, the proposed cure is worse than the effect of the invasive species.
Here is a great video on the anthropomorphic perspective of the invasive Buffelgrass.
In another example, the US Fish and Wildlife Service at their Bosque del Apache nature preserve used chemical weed killers to killing off the Tamarisk (Salt Cedar) that lined the edges of their artificially created wetlands for birds. Earlier, the US Park Service, in cooperation with others, established a Tamarisk eradication program along the banks of the Colorado River. They also used herbicides.
However, Nature seems to have offered a control of its own. The Tamarisk Leaf Beetle has appeared. It can selectively kill Tamarisk and is apparently doing so along the Colorado River. I was recently told that the Tamarisk Leaf Beetle is now starting to appear at Bosque del Apache.
I find the story of the Tamarisk Leaf Beetle most interesting because the beetle is an invasive species. As it turns out, this invasive insect is considered beneficial to man because it is killing out an invasive specie that mankind wants to eradicate – the Tamarisk.
The lesson, as I see it, is that passive restoration using certain kinds of invasive species is a real and a viable approach to resolving certain ecological issues that mankind wants to control. In other words, let Nature take her own course.
I’d love to hear from you on the subject of invasive species.
Worth Your Extra Attention
Thanks for reading this blog post.
One of my loyal readers, Garry Rogers, just published a wonderful post entitled Outdoor Recreation Aids Invasive Plants . His perspective in this article is a must read for everyone interested in this subject.
Garry has written other interesting posts on the subject:
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My name is Bill Graham. As a Marine Biologist who has worked in the US and Mexico for 30 years, I am a student of Nature, a teacher, a researcher, and a nature photographer. Through my work, I have acquired an ever growing passion for how everything in Nature is connected. Today, I travel extensively contemplating about, writing about, and photographing Nature’s connections. I also work with conservation projects in the USA and Mexico and mentor talented youth.