23.1 tpo

The reading passage claims that the number of yellow cedars, a kind of tree which is widespread in North America is been decreasing for a couple of decades now. However, the lecturer finds all the ideas implausible and presents some evidence to refute them all.

First, the author argues that a kind of insect named beetle is one of the main reasons of this phenomenon. Conversely, the lecturer brings up the idea that healthy trees of yellow cedar are resistant to beetles' attack since some parts of the trees which are attacked by beetles are saturated with a kind of chemical which is lethal for beetles. If the insect attacks the tree, the insect is damaged itself because of the existence of that chemical.

Furthermore, the reading passage asserts that another reason is of this evidence is that these trees are a part of brown bears' diet. In contrast, the professor underlines the fact that although bears damage the trees, they are not the main cause of this declining in population of these trees. He claims that the declining in population of trees has happened in some areas where no bear has ever lived there. For instance, no bear lives off the coast and on the islands where the yellow cedar trees have died. He believes that this evidence reveals the fact that bears are not responsible.

Finally, the reading holds the view that climate change is another reason of happening. On the contrary, the speaker dismisses this issue due to the fact that if changes of climate were responsible, many other trees of other kinds should have died too. He also claims that climate change may make the trees more sensitive but it is not the reason of their death