Amur or Chinese cork tree
檗 refers specifically to the Amur cork tree, a type of tree valued for its cork-like bark. The meaning is a single botanical entity without broader abstract extensions.
檗 combines 木 (tree) with 辟, which likely contributes a phonetic element. The character was created to name a specific tree, the Amur cork tree.
The bottom 木 tells you it's a tree, and the top 辟 looks like a complex, layered structure—like the thick, corky bark of the Amur cork tree.
For ハク, imagine peeling back the cork bark of the tree: the sound of the bark snapping off is a crisp 'hack!' — hack cues ハク.