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树的年轮与周边的食草动物有关?

所属:生活杂谈 来源:New York Times 阅读:5524 次 评论:1 条 [我要评论]  [+我要收藏]

小编摘要:树的年轮疏密许多年以来都是人们评估过去气候条件的依据。但最近实验发现,周边食草动物的多少也会对年轮的疏密产生重要的影响。

导读:100多年以来,人们都利用树木年轮的疏密判断过去的气候条件,气候越好,年轮越疏。但是最近挪威和苏格兰研究者通过实验发现食草动物对年轮疏密也有重要影响:树周边食草动物越多,年轮越疏,并存在对应数量关系。这一发现将有助于科学家更加准确地评估以前的气候条件。



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.

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2011-08-03 16:32 编辑:claudiaenglish
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