TPO 23 q1

In this set of materials, the reading passage propose three hypotheses to explain the decline of yellow cedar trees population. While, in the listening, the professor casts doubt on what is presented in the text and rejects each of the author's ideas.

First of all, it is clearly stated in the text that attack of a special insect, the cedar bark beetle, may cause this decline in population of them. The professor believes the this claim is problematic, he says the this trees produce a kind of chemical substance which has poison for the insects and kill them, so they can resist the attacks by this defense mechanism. Also, she states that the other trees which do not have any mechanism to kill insect can survive which shows that the insects is not the reason.

In addition, the professors disagrees with this idea of the reading that the brown bear which fed from Cedars cause damage to them. He points out that the bears cannot be considered as the main reason for decline in population because they are living only in some areas. However, the number of trees were shrink in all areas whether with bears or without them. Therefore, another factor should kill the cedars rather than bears.

Finally, in the text it is mentioned that the climate change, especially late winter and freezing, has bad effect on the root system of cedars and undermines the health of trees; however, the professor provides some evidences to oppose this view. He explains that the number of trees are decreased in all areas including warm and cold regions. In the warm areas the root of trees are not frozen at any time while the trees were destroyed, so the cold weather in winter cannot be the factor for damages.