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

The article and lecture are about the steady decline in the population of yellow cedar tree species, common in northwestern North America. The article states three hypothesis which can be accounted for as reasons for this decline whereas the speaker refutes these hypothesis by telling that the reasons are inadequate to explain the decline.

First, the reading posits that insect parasites, cedar bark beetle are responsible for yellow cedar decline. The beetle larvae eat the wood, thereby killing the yellow cedars. The lecture dismisses this explanation as many cedar trees are known to be resistant to beetles because their bark and leaves are saturated with chemicals toxic for beetle.

Second, brown bears have discussed as possible reason. They claw at cedars to eat the tree bark which has sugar content as high as wild berries. Their aggressive behaviour weakens the tree and gradually kills it. This point has been contradicted in the lecture as cedars have seen a decline on the island off the coast also where there are no brown bears.

Third, gradual climate change has been accounted for as one of the reason for reducing cedar trees. The seasonal and day to day temperature affects these trees and roots are harmed considerably from frost. The speaker rejects this and explains that many more cedar trees die at lower elevation rather than at higher elevation where frost damage occurs.