What are successful invaders?
There are certain members of the plant and animal world that I call successful invaders. Some are admired; others are reviled. A few are both liked and despised at the same time.
Where I live, the Western juniper, Juniperus occidentalis, fits into that last category. It is a native species but due to fire suppression and habitat destruction, it has spread like -excuse the reference- wildfire. Juniper has taken advantage of the situation and has significantly expanded its range. I have heard a lot about how much water it can suck out of the landscape – supposedly 30 gallons a day. Its root system taps downwards and outwards to effectively use the available water. Many people don’t like them for that reason and because at times they have a not-so-pleasant scent. I’ll always remember listening to a person that lives in the wealthy part of town saying that she eliminated all 18 junipers on her property as soon as she moved in. Eighteen trees.
However, juniper also has its good side. As it ages it epitomizes the image many people associate with the Wild West. I love to photograph them. The form of the tree generally changes from a pyramid-like shape to a twisted, sprawling irregular one. It can be covered by purplish berries (that are really cones) and these are used in gin production. Wildlife loves it for cover, nesting, and food. Its wood is bi-colored and long lasting.
Some animals do what they can to fit in so that you won’t notice they are invaders. I have a pair of European starlings, Sturnus vulgaris, that nested on my property last spring. I don’t know many people that are fond of starlings. They are referred to as being ugly, dirty birds that many think should be destroyed. However, if you look at their breeding plumage closely it’s actually quite beautiful and iridescent. Anyway, back to my story…the pair on my property produced a brood of young and taught them how to sing and call. The weird thing is that they sound like the much more well-liked Western meadowlark – not starlings. There aren’t any meadowlarks close by but they do live many miles away to the east.
Some plants moved here from far away and have settled in throughout North America. The common mullein, Verbascum thapsus, is one of those successful invader plants. It is a member of the snapdragon family and bears long stalks of yellow flowers and produces a lot of seeds. Mullein can grow 5-10 feet high (!) Its large leaves have a thick whitish covering of soft “hair”. It is native to Europe and was introduced here in the mid-1700’s for use as a fish poison. Where I live it is considered a noxious weed whose presence should be controlled and monitored by landowners. It will grow in almost any open area and will push native plants out.
This plant has some interesting uses. As previously mentioned, it was used as a fish poison. It stuns the fish so that they float to the surface where they can be easily caught. A dye was made from the flowers and was used on hair and on cloth. It also has medicinal uses and has been used to treat chest colds, bronchitis, and asthma. Mullein was also used to treat bruises, rash, tumors, and other maladies. I learned in a high school plant ecology class that its soft leaves can be used as toilet paper in an emergency.
Mullein is easy to pull but I decided to leave a few in my yard. Why? The songbirds, which I do not feed, LOVE them.
There are other successful invaders that have become so successful that they have become a threat to the environment. Consider the white-tailed deer. White-tailed deer, Odocoileus virginianus, have steadily moved westwards, northwards, and to the south in North and South America. There are more than there have ever been – even though hunters use much more sophisticated technology to hunt them. However, there are fewer people hunting them and their natural predators have been eliminated in parts of their range.
About 100 years ago, small scale agriculture pushed the deer off much of their range east of the Rockies. White-tailed deer were also overhunted in North America in the late 1800’s. Their population dropped precipitously from 24-33 million, down to only 350,000.
Rebounding with a vengeance
During the Industrial Age, farms were abandoned leaving behind a patchwork of habitats that was ideal for deer. Wildlife conservation adapted practices that created green space for populations to become established. Preserves for regulated hunting were set up. As a result, the population rebounded with a vengeance! The current population is estimated to be over 30 million and they are much more densely packed than in the distant past. That density has caused numerous problems.
I read an interesting article about white-tailed deer on Staten Island in New York City. The population on the 60-square mile island has increased from 24 to 793 in just six years. That’s a 3,304% increase! The deer cause traffic accidents, eat gardens, and pass on tick-borne illnesses but the far greater problem is that they are destroying habitat. The community can cull the animals with sharpshooters, have hunters take them, apply contraceptive vaccines, or use surgical sterilization. None of these options has been popular with the public so nothing is currently being done. When an animal is given the Disney treatment, in this case as the main star in the Bambi movie, it can become much more difficult to control.
Successful invader Velcro
Successful invaders have taken advantage of various situations. Consequently, they are firmly established in their new range. They velcroed themselves into their new homes and peeling them away will be a difficult, if not impossible, task.
Heffernan, T. (2012, October 24). The Deer Paradox. Retrieved November 3, 2015, from http://www.theatlantic.com/magazine/archive/2012/11/the-deer-paradox/309104/
O’Connor, B. (2015, January 14). Deer are invading New York City, and we don’t know how to stop them. Retrieved November 3, 2015, from http://www.theverge.com/2015/1/14/7537391/new-york-city-deer-problem
The Herb Companion staff. (2009, August/September). Herb to know: Mullein (Verbascum thapsus). Retrieved November 3, 2015, from http://www.motherearthliving.com/plant-profile/herb-to-know-mullein-verbascum-thapsus.aspx