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

Both the reading passage and the listening discuss the decline of the yellow cedar population. The author provides three hypotheses that might have caused this. However, the lecture contradicts the author and provides an explanation against each of these hypotheses.

First of all, the author mentions that cedar bark beetle larvae feed on yellow cedar tree wood and that could be one possible explanation behind the decreased population of yellow cedar trees. In contrast, the lecturer states that healthy beetles are resistant to the yellow cedar tree. The tree bark and leaf are poisonous to the beetle's health thus they found evidence of dead beetles inside the tree. It could not be the fundamental reason for this declination.

Second of all, the text contends that bears destroyed the trees by eating tree bark which contains sugar. However, the lecture rebuts that bears might have damaged some trees on the mainland but there are no bears on the islands. The decline of yellow cedar trees happened both on the mainland and the island. So bears could not be responsible for reducing the population on the island.

Finally, the author states that frozen weather damaged the root of the tree which eventually lead to killing the tree in upper alleviation. On other hand, the professor claims that tree population decreased where there is lower alleviation and the weather is warm.