tpo23writing听写

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Unfortunately, we still don't know what’s 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 the healthy yellow cedars are much more resistant to insect infestation than other tree species. For example, the bark and leaves of the yellow cedar are saturated with powerful chemicals that are poisonous to the inserts. So healthy cedars are unlikely to suffer from insect damage. So, how can we explain those dead cedars that were infested with beetles. In those cases, the beetles are attack trees that were already damaged and sick. And would probably die anyway. So, the beetles are not the fundamental cause responsible for the decline of yellow cedars.  Second, although bears damage some trees. They are not the cause of the overall 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 island cedars are still in decline. Since the decline occurs with and without bears, the bears cannot be responsible. Finally, the theory about the roots suffering from the frost damage. Well, the reading passage forgets to take one fact into account. Many more trees are dying at lower alleviations where it is warm than at higher alleviations where it is cold. If freezing damage were responsible for the decline, we would expect to see more trees dying in the cold weather of higher alleviation. Instead, more trees are dying at the relative warm of lower alleviation. So, although the climate change may have made the cedar roots more sensitive than it used to be, this isn't what’s killing them.