Kodama of the Center Tree's power and toughness are each equal to the number of Spirits you control.
Kodama of the Center Tree has soulshift X, where X is the number of Spirits you control. (When this creature dies, you may return target Spirit card with converted mana cost X or less from your graveyard to your hand.)
Soulshift is a leaves the battlefield trigger, so the gamestate is referenced immediately before the Soulshift trigger to determine the value of X. Soulshift X includes Kodama of the Center Tree. So, X is always at least 1.
Kodama of the Center Tree can return itself to its owner’s hand if you control five or more Spirits when it is put into a graveyard from the battlefield.