The reading passage and lecture discusses the same topic but present it from different perspectives. The article states that populations of yellow cedar have been steadily declining for more than a century and provides three reasons for support. In the lecture, Professor says that unfortunately we donot know what is killing the yellow cedar and none of the information is adequate. He opposed each of the author’s reasons.
To begin with, reading avers thatdecline in yellow cedar population may be because of the insect parasites, cedar bark beetle. However, this argument is strongly rebutted in the lecture by saying that healthy cedar plants are resistant to cedar bark beetle than other insects. Bark and seeds are usually saturated with sugars. Sugars are usually poisonous to insects. Therefore, yellow cedar plants are resistant to insects. Insects might have caused the damage for disease plants but not for healthy plants. Therefore, they may not be cause for decline of yellow cedra trees.
Second, article pushes forth the idea that decline in tree population may be because of brown bears which claw at the cedars in order to eat the tree bark. However, this point is challenged by the lecturer. He posits that although bears may have caused the damage to trees declining may have seen in along coast of north-west America where bears population is less or present. Thus, bears may not have contributed to decline in cedar tree population.
Third, reading passage states that changes in the climate may have caused the decline in cedar population. The professor counters this point by asserting that cedar trees living in lower elevations are warm and those living in higher elevations are facing the freezing temperatures. Though trees living in the higher elevations are surviving and those in lower elevations are dying. The climate variations may not be the cause for decline in cedar tree population
Hi Rakeshchanda, I think you did a pretty good job with this one. Your format is good and you did a good job of summarizing the main ideas of the reading. Still, you had some errors in your facts and your second body paragraph was very difficult to understand. I think based on these errors, I could probably only rate this essay a 3 out of 5.
Here are the reading and lecture:
Populations of the yellow cedar, a species of tree that is common in northwestern North America, have been steadily declining for more than a century now, since about 1880. Scientists have advanced several hypotheses to explain this decline.
One hypothesis is that the yellow cedar decline may be caused by insect parasites, specifically the cedar bark beetle. This beetle is known to attack cedar trees; the beetle larvae eat the wood. There have been recorded instances of sustained beetle attacks overwhelming and killing yellow cedars, so this insect is a good candidate for the cause of the tree’s decline.
A second hypothesis attributes the decline to brown bears. Bears sometimes claw at the cedars in order to eat the tree bark, which has a high sugar content. In fact, the cedar bark can contain as much sugar as the wild berries that are a staple of the bears’ diet. Although the bears’ clawing is unlikely to destroy trees by itself, their aggressive feeding habits may critically weaken enough trees to be responsible for the decline.
The third hypothesis states that gradual changes of climate may be to blame. Over the last hundred years, the patterns of seasonal as well as day-to-day temperatures have changed in northwestern North America. These changes have affected the root systems of the yellow cedar trees: the fine surface roots now start growing in the late winter rather than in the early spring. The change in the timing of root growth may have significant consequences. Growing roots are sensitive and are therefore likely to suffer damage from partial freezing on cold winter nights. This frozen root damage may be capable of undermining the health of the whole tree, eventually killing it.
Listening part:
Unfortunately，we still do not know what is killing the yellow cedar. None of the explanations discussed in the reading is adequate.
First, the cedar bark beetle. Well, the problem with this explanation is these healthy yellow cedars are generally much more resistant to insect infection than other tree species. For example, the bark and leaves of the yellow cedars are concentrated with powerful chemicals that are poisonous to insects. So, healthy cedars are unlikely to suffer from the insect damage. So, how can we explain those dead cedars that were infected with beetles? In those cases, the beetles attacked trees that were already damaged or sick and what probably dead any way. So, the beetles are not the fundamental cause responsible for the decline of the yellow cedars.
Second, although bears damage some trees, they are not the cause of the over all population decline. Yellow cedars population has been declining all across the northwestern coast of North America, both on the mainland and on the islands just off the coast. There are no bears on the islands, yet the islands cedars are still in decline. Since the decline occurs with and without bears, the bears can not be responsible.
And finally, the theory about root suffering from frozen damage. Well, the reading passage forgot to take one fact into account. Many more trees are dying in the lower elevations where it is warmer than in the higher elevations where it is cold. If freezing damage were responsible for the decline, we would expect to see more trees die in the cold weather of the high elevations. Instead, more trees die in the relative warm of the low elevations. So, although the climate change may have made the cedar roots more sensitive then they used to be, this is not what killed them.