problems related to decline tree

The passage asserts that population of yellow cedar is declining in North America and provides three reasons of support. The professor casts doubt on this point by saying that mentioned reasons provided by passage are not adequate and rebunks all of them. First, the article states that insect parasites specially beetles attack cedar bark and will damage them. The lecturer, on the contrary, rebuts this view by explaining that cedar trees are much resistant than other types of tree species, since they produce chemical which is poisonous for parasites. He also avers that beetles attack sick trees, so they are not foundamental cause for declining of cedar. Second, beers feed from cedar' bark which is contained sugar, since beers weaken cedar tree, according to the article. The lecturer debunks this point by arguing that beers are not main cause for decreasing in cedar population, sicne they never effect all population cross the North America. He also states that in some parts of mentioned region, population of cedar is declining, even though there are no beer overthere. Third, the reading claims that changing in climate has effected root system of cedar trees. The professor repudiates this view and says that the passage has forgotten a tip about changing clamate in lower elevation which wethear is cold, although cedar tree are sensitive in higher elevation. So this passage's claim is not convincing.