The reading passage claims that an especial species of tree called yellow cedar are declining drastically in the northwestern United States for a century because of some hypotheses alleged by scientists.

The reading passage claims that an especial species of tree called yellow cedar are declining drastically in the northwestern United States for a century because of some hypotheses alleged by scientists. However, the lecturer finds all the ideas dubious and presents some evidence to refute them all. First, the author contends that beetles are the main reasons of diminish of cedar population that attack this tree and eat the wood. Conversely, the lecturer brings up the idea that healthy trees are much more resistant to insect infestation owing to the fact that cedar trees contain an especial substance that poisons to insects. So, it is less likely that beetles be the main reason of cedar's decline. Furthermore, the author holds the view that decrease of brown bears might the other reason of this decline because they use to eat tree bark with a high concentration of sugar. In contrast, the professor underlines the fact that bears damage some trees in mainland and island. In fact, there are some trees on the island that are damaged as well without the presence of brown bears. Finally, as set forth by the author climate change may play a significant role in declining of cedar trees owing to the fact that temperature will affect root systems of yellow cedar. On the contrary, the speaker dismisses this issue due to the fact that majorities of trees are dying in low elevation. In fact, there are more trees in cold weather at high elevation.