This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
樴 combines 木 (tree/wood) with 戠, which likely contributes a phonetic element. The exact historical development is uncertain.
The left side is 木 (tree), and the right side 戠 is a complex shape. Without a clear meaning, picture a wooden marker or post, as the tree radical suggests something made of wood.
For ショク, imagine a wooden post used as a shock absorber: shock -> ショク, and the wood 木 absorbs the impact.