TPO#23 cedar tree

The reading claims that scientists have advanced several hypotheses to explain the decline of populations of the yellow cedar trees, a species of tree that is common in northwestern North America, and provides three hypthesis of support. However, the professor states that the explanations in the reading are unconvincing and he refutes each of the author's hypotheses.

Frist, the article avers that one hypothesis is that yellow cedar decline may be caused by insect parasites, specifically the cedar bark beetle. In contrast, the lecturer opposes this point by stating that the problem in this hypothesis is that the healthy trees is more resistance to the insects. In fact, he says that barks and leaves of the tree produce chemical materials that protect the trees from the insects, so beetle attacks the trees which already died and not the live one. This explains that insects are not responsible for declining.

Second, the passage asserts that the second hypothesis attributes the decline to brown bears because they claw at the cedar in order to eat the tree bark. On the other hand, the professor counters this point by saying that although some trees are be affected by bears, but it is not the cause of declining the population. Actually, he mentions that there is trees population cross the island coast of North America and there are no bears in this Island, so the decreasing in the trees population is with or without the bears. He argues that brown bears are not responsible for decreasing.

Third, the article posits that the third hypothesis states that gradual changes of climate may be to blame. Conversely, the professor casts doubt on this point by explaining that the reading forgot to the fact that tree dies in low elevation and in high elevation, so the tree should be die only in high elevation because the low temperatures instead of low elevation. In fact, the tree dies in low elevation also so the the low temperatures don't kill the tree.