U of M News Wire
February 7, 2008
Fossil fuels and nitrogen fertilizers may be slowly reducing the number of plant species globally, U of M study says
By Deane Morrison
U of M News Wire
The number of plant species worldwide may be dwindling from the effects of chronic low levels of nitrogen on terrestrial ecosystems, according to a University of Minnesota study.
The study, conducted by David Tilman, Regents Professor of Ecology, and former university graduate student Christopher Clark, was published in the Feb. 7 issue of Nature. Research was carried out at Cedar Creek Ecosystem Science Reserve, a field station operated by the university's College of Biological Sciences.
Loss of biodiversity from high levels of atmospheric nitrogen has been reported in parts of Europe and the United States, but this is the first long-term study of the impact of much lower levels of nitrogen deposition over much of the developed world.
"Even at low levels, comparable to nitrogen deposition over many industrialized nations, we lost about one plant species in six at our test site [17 percent over 23 years]," Clark said. Rare species were more vulnerable to loss than common species.
But Clarke and Tilman also discovered some good news -- that the loss of species can be reversed. Thirteen years after addition of nitrogen was stopped, species numbers had recovered.
"Many ecosystems worldwide may be losing plant species because of nitrogen deposition from fossil fuel combustion and agricultural fertilizers," said Tilman. "But with a rapid, coordinated national and international effort, we can likely stem or reverse these losses of biodiversity."
Over the past 60 years, fossil fuel combustion and agricultural fertilizers have doubled the amount of nitrogen inputs to terrestrial ecosystems worldwide. The level could double again as nations in Asia and South America industrialize.
Nitrogen is an essential nutrient for plant growth, but too much causes a few species to flourish at the expense of their competitors. Within an ecosystem, species have different roles that contribute to the productivity and stability of the community. When some species are missing, the functioning of the ecosystem as a whole is impaired.
The study was performed in three prairie-like grassland ecosystems at Cedar Creek Ecosystem Science Reserve. All of the plots were treated with varying levels of nitrogen addition from 1982 to 1991. Treatments to half of the plots in one of the fields were stopped after 1991, but nitrogen addition has been continued in all other plots.
The study was funded by the National Science Foundation.
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Growing Concerns
A parenting question-and-answer column with Dr. Martha Erickson of the University of Minnesota
Question: My wife and daughter always have been very close, but over the past few months our daughter (now 14) has become rude and irritable toward her mother. It seems like my wife can’t say or do anything right. I don’t want to interfere, but the bickering is driving me nuts. Should I intervene? And, if so, how?
Answer: You probably know it’s not unusual for both boys and girls in their early teens to become moody and to challenge their parents. And girls often find words to be powerful tools in that challenge. A major developmental task for a teenager is to establish herself as a separate individual, with opinions and feelings all her own. Sometimes that is a painful process, both for the teen and for the parents who see their cheerful, cooperative child disappearing right before their eyes. Because mothers often have been the primary caregiver, they often take the brunt of the criticism. Especially when mothers and daughters have been very close, the daughter may feel a need to push extra hard for a period of time to make that shift toward greater independence.
This does not, however, mean that your home life needs to be ruined. Nor does it mean that there should be no limits set on your daughter’s behavior. It is important that you and your wife draw together at this time, working in unison as you guide your daughter through this passage in her life and yours.
I suggest you sit down and talk honestly with your wife about how you feel about the conflict between her and your daughter. Then decide together how you will deal with your daughter’s behavior -- and, specifically, which behaviors are acceptable and which ones are not. It is hard to tell a person not to be irritable; however, as parents, you can and should communicate clear expectations to your daughter about treating family members with respect. For example, you can tell your daughter you understand that she feels irritable, but tell her clearly that it is not okay for her to make personal attacks, to swear, or name-call. Then, together with your wife, immediately impose a consequence such as a loss of a privilege if your daughter crosses that line.
You use the term “bickering” in describing the conflict between your wife and daughter, which sounds like your wife is rising to -- and perhaps escalating -- your daughter’s challenging behavior. If that is the case, I also suggest you talk with your wife about how you can support her in remaining clear, calm and parental with your daughter. When under attack, it is easy to sink to the child’s level and begin a counter-attack. But it is much more effective to say quietly, “I can see you’re upset. We’ll talk about this when you’ve calmed down.” With you taking a strong parental stand with her, your wife should find it easier to avoid entering into the fray.
One last word of caution: if irritability seems to have become a way of life for your daughter -- that is, if she remains extremely irritable over time and across varied situations -- it could be a sign of depression or other emotional problems. Be especially alert to any changes in your daughter’s friendships, diminished interest in activities she normally enjoys, or a slip in school performance. If you see those signs, seek professional help from a mental health professional through your health care provider or your daughter’s school.
Dr. Erickson is a senior fellow and director of the Harris Programs in the Center for Early Childhood Education at the University of Minnesota.
Want to hear more parenting advice?
Dr. Erickson and her daughter can be heard every Sunday, from 2 - 4 pm, on “Good Enough Moms,” on FM107.1 radio in the Twin Cities or via Webcast at www.FM1071.com
