The narrator says, "[the tree] loomed in my memory as a huge lone spike dominating the riverbank, forbidding as an artillery piece." what literary device is the narrator/author using in this passage

The literary device that is used in this extract is SIMILIE.

Explanation:

A similie is a comparison that becomes explicit by the use of the words "like" or "as". In this case, the tree (the memory of the tree) is compared to a spike and to an artillery piece, and the comparison is evident because of the use of the word "as".

"[The tree] loomed in my memory as a huge lone spike dominating the riverbank, forbidding as an artillery piece."