tpo23. Summarize the point in the lecture which disapproves those of reading.

The reading claims that scientists have advanced several hypotheses to explain the declining the population of the yellow cedar, a species of tree that is common in northwest North America. It provides three hypotheses. In contrast, the professor states that we still don't know what killing the trees and none of the hypothesis is convincing and he refutes each of the author's hypotheses.

First, the article avers that the cedar bark beetle attacks cedar trees and the beetle larvae eat the wood. However, the speaker opposes this point by saying that the problem with this explanation is that the healthy trees are resistant to the beetle. He mentions that the barks leaves of the tree are saturated with powerful chemicals that are poison to the beetle so the beetle unlikely is the responsible of the declining. In fact, the beetle may attack the damage or sick trees but not the healthy one.

Second, the passage posits that the beers aggressive feeding habits may critically weaken enough trees to be responsible for decline. On the other hand, the speaker counters this point by stating that the yellow cedar trees have been declining in North America and the coast Island and there are no bears on Island. Actually, he argues that since the declining with or without the bears, so the bears are not responsible for the declining.

Third, the article asserts that gradual changes of climate may be to blame because the root is damaged from freezing. Conversely, the professor casts doubt on this point by explaining that a lot of trees are declining in lower elevation which it is warm there, so freezin damage would expect to see trees dying in lower elevation also. He states that instead, trees die in warm climate also and this is not what killing the tree. This appears a contradiction to the information made in the passage.