。
To a tree, branches are the equivalent of human arms and legs.
Literal
Tree [for-にとっては] branches [topic-は] human [possessive-の] limbs [to-に] are-equivalent.
~にとって ('for, to, from the viewpoint of') is the compound particle for marking whose perspective a claim applies from. Here 木にとっては adds the contrastive は, emphasising 'from the tree's point of view (as opposed to some other).' 相当する ('to correspond to, to be equivalent to') takes に to mark the thing being equated with.