TPO-23 - Integrated Writing Task 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 expla

The reading states that the populations of yellow cedar in northwestern North America have been decreasing for the past century, and brings some reasons to support this claim. However the speaker says that the cause is still unknown and each reason of the passage is not adequate.

First, the article writes that insect parasites like cedar bark beetle are responsible for the decline of yellow cedar trees because they attack and eat the wood of the tree, but the lecturer says that healthy yellow cedar trees are very resistance to this beetle and they have saturated chemical that defend the wood. the speaker thinks that this beetle attack those treeS which are damaged and already old.

Second, the passage claims that brown bears claw at the cedar tree to eat the tree bark which has high sugar content, and the tree has been weakened because of their aggressive feeding habits. Though the speaker says that sometimes bears damage tree but not many times, and there are regions that there are not any bears there, but the population of the tree is declining, so they are not related together.

Third, the passage writes that gradual changes of climate over the last hundred years is blamed, because the temperatures have changed and the root system of the yellow cedar grows in late winter rather than in early spring. However, the lecturer refuses this reason because he thinks that this tree is available in both high elevation areas which are cold, and in low elevation areas which are warmer, and more trees are dying in the lower elevation areas rather than high elevation regions.