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.
The reading states that yellow cedar in northwestern North America, which is type of trees has been started to be declined and author provides three hypotheses in the reading to this declination. However, the professor in the lecture refuses the hypotheses and says unfortunately up to now no precise reasons have been found.
First of all, the professor in the lecture posits that this type of tree produce a kind of chemical substances, which is poisonous to insects. Therefore, when this poison is existed on the wood of the yellow cedar, the beetle cannot be responsible for declining, because the beetle by attacking the tree would also be damaged. Although, the reading claims that attacking the cedar bark, beetle can be the reason of deteriorating of tree.
Secondly, according to the professor, even though cedar bark like the wild berries contains sugar, and berries of their sugar are in the bears’ diet, but cedar bark cannot be declined because bears eat them. He adds that yellow cedar growing in island and in island no bears live, thus disappearing of this tree in all places, regardless of existing bears corroborate that bears cannot be responsible for this declination. On the contrary, the reading confirms that sugar in the bark of these trees incites bears to eat these trees.
Finally, the professor goes on to refute the last claim in the article by explaining that the number of yellow cedars is declined in lower elevation is more than those of high elevation. Furthermore the lecture challenges that freezing of root can be responsible of this declination due to being warm in low elevation. While, the reading ascertains that climate changing disturbed the pattern of seasons, and thus affects on time of the growing of this tree and because growing of roots has been changed to winter can be reason that tree cannot grow.
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this type of tree produce a kind of chemical ...
this type of tree produces a kind of chemical ...
Attribute Value Ideal
Score: 25 in 30
Category: Very Good Excellent
No. of Grammatical Errors: 1 2
No. of Spelling Errors: 0 2
No. of Sentences: 11 12
No. of Words: 311 250
No. of Characters: 1506 1200
No. of Different Words: 144 150
Fourth Root of Number of Words: 4.199 4.2
Average Word Length: 4.842 4.6
Word Length SD: 2.553 2.4
No. of Words greater than 5 chars: 106 80
No. of Words greater than 6 chars: 80 60
No. of Words greater than 7 chars: 46 40
No. of Words greater than 8 chars: 33 20
Use of Passive Voice (%): 0 0
Avg. Sentence Length: 28.273 21.0
Sentence Length SD: 7.149 7.5
Use of Discourse Markers (%): 0.818 0.12
Sentence-Text Coherence: 0.399 0.35
Sentence-Para Coherence: 0.645 0.50
Sentence-Sentence Coherence: 0.142 0.07
Number of Paragraphs: 4 4