TPO23#1

The reading passage provides three hypotheses to explain the main causes for the decline of the population of the yellow cedar trees. However, the professor states that we still do not know the main reasons for their decline and none of the explanations is adequate.

To begin with, the article contends that the invasion of the cedar bark beetle is responsible for the decline in the yellow cedar population. On the other hand, the professor explains that healthy yellow cedar trees are resistant to these beetles. He points out that all healthy barks and leaves contain powerful chemicals that are poisonous to insects and causes their death. He says that probably beetles attacked the yellow cedar trees after they already damaged and sick. Thus, the insects are not the fundamental cause responsible for the decline in the population of the yellow cedar.

Secondly, the author implies that the presence of brown bears and their aggressive feeding behavior may be responsible to the population decline since bears feed on the tree bark which has sugar content. The professor, in contrast, explains that brown bears may be responsible to the decline of some trees only and not the overall decline. He mentions that there are also decline in the population of the trees across the northwestern coast of the North America, in mainland and the Island, although there are no bears in the Island. The fact that there is a cedar's decline with or without the presence of the brown bear indicates that brown bears are not the main cause for the decline.

Finally, the reading posits that the climate change may count as a reason for the decline of the trees since it causes damage to the rooting system. The professor opposes this point by stating that there are more damaged trees at low elevation in warmer climate rather than in high elevation at cold climate. According to the reading, we must expect that the damage of the cedar trees will be more in the cold and not in the warm weather. In fact, the high elevation may cause the cedar roots to be more sensitive to cold but not responsible for their damage.