Integrated Topic Two

Topic Two – “Tales That Tree Rings Tell”

In this lesson we want to look at a research article that was done on the size of tree rings. As we look at the article we want to focus on selecting the main points the writer is making. Then we will write a short essay.

Main Ideas

Think of the main idea as the point the writer is trying to make in a paragraph. Other information in the paragraph is made up of supporting ideas such as examples, facts, causes, or reasons. The main idea (Topic sentence) is usually at the beginning of the paragraph in the first or second sentence. But sometimes it can be in the middle or at the end.

Read at the paragraph below.  As you read, ask : What point is the writer trying to make?

 “For more than 100 years, tree rings have served as a reliable way to estimate past climate conditions because in warmer years, which usually mean better growing conditions, tree rings tend to be wider. But herbivores that nibble away at trees also have an effect on tree ring size — a phenomenon that was known but never measured. Now, researchers from Norway and Scotland report the significant effect of grazing sheep on tree ring size over a nine-year period. “

Herbivores=animals like sheep that eat plants

Writer’s Point: Researchers report the significant effect of grazing sheep on tree rings size over a nine-year period.

Writing Task

Topic Question: Using the research describe by the writer, explain how herbivores have an effect on tree ring growth.

Read and understand the topic questions above. Then as you read the article below, outline the main and supporting ideas on a piece of paper.

Herbivores’ Nibbles Affect Climate Tales That Tree Rings Tell
By SINDYA N. BHANOO
Published: July 29, 2011
For more than 100 years, tree rings have served as a reliable way to estimate past climate conditions because in warmer years, which usually mean better growing conditions, tree rings tend to be wider. But herbivores that nibble away at trees also have an effect on tree ring size — a phenomenon that was known but never measured. Now, researchers from Norway and Scotland report the significant effect of grazing sheep on tree ring size over a nine-year period.
The researchers, whose findings are published in the current issue of the journal Functional Ecology, created nine fenced-off areas in the mountains of southern Norway. Some contained no sheep, some had about 10 sheep per square mile and some had about 30 sheep per square mile. Although sheep prefer to eat grass and herbs, in the mountains this is sometimes not enough, and they turn to shrubs and small trees for nourishment.
After nine years, the researchers sampled cross sections of more than 200 birch trees in the enclosed areas and measured the trees’ ring widths. “What we found is that the number of sheep had a very large impact,” said James Speed, an ecologist at the Museum of Natural History and Archaeology in Trondheim, Norway, and the study’s first author. “This shows how important the number of herbivores is.”
In areas where there were no sheep, the radial growth in the tree rings was double that areas with few sheep. And it was three times the growth seen in areas with the most sheep. There was also, however, a clear pattern corresponding to climate. Finding ways to factor in the effect of herbivores might help researchers make more accurate climate estimations, Dr. Speed said. One way to estimate past herbivore populations might be to study the fossilized remains of fungi that live on dung, he said. Retrieved July 31, 2011, from http://www.nytimes.com