numerary adjunct for trees
棵 centers on counting trees: it is a numerary adjunct (classifier) used specifically for trees. Its meaning is narrow and functional, not a broad concept.
棵 combines 木 (tree) with 果, which likely contributes the sound. The character was created as a classifier for trees, with 木 providing the semantic category.
The left side is a tree 木, and the right side 果 looks like fruit on a tree. Picture counting trees by their fruit: one 棵, two 棵, three 棵.
For カン, imagine counting cans hanging from the trees: can -> カン, and each tree gets one can as a counter.