@Gokufighther could be poison, shield, spiritual damage(we did saw a monster that could possesses people), it can be a strength down debuff, speed down debuff, defense down debuff, intelligence down debuff, magic down debuff, it can be a strength up buff, speed up buff, defense up buff, intelligence up buff, magic up buff, it can also be abnormal status resistance, abnormal status resistance down.
It can be a million different things that would not show anything when hitting a tree, if its healing, i will call it bad writing. Calling it just a simple plot point does not makes justice for this absurd, if its healing.