Artificial Forest

At the start of your turn remove a tapper from Artificial Forest. Then, if there are no tappers on Artificial Forest untap it.
{t} Add {g} to your mana pool: Put a tapper on Artificial Forest
{t} Add {g}{g} to your mana pool: Put two tappers on Artificial Forest
{t} Add {g}{g}{g} to your mana pool: Put three tappers on Artificial Forest