Key Interactions-
Veteran Explorer + Primal Growth
Treefolk Harbinger + Forest or Lignify or Dungrove Elder or Woodfall Primus Silhana Ledgewalker + Blanchwood Armor

Fangorn Forest is another mono-green beat-down-style deck like any other--except this one has a fetish for forests. This is one of the only decks you will ever play that wants to top-deck lands as often as it does other spells, as everything in the deck gets stronger based on the number of forests in play. The Hexproof-touting Treebeard-wannabe known as Dungrove Elder serves as your main beat-stick while Silhana Ledgewalker carries Blanchwood Armor and Primal Bellow to victory without fear of removal.

If your opponent allows you to get to the magic number of seven lands while he's busy navigating through all of your forests, you can drop the wolf-laden bomb Howl of the Night Pack on him and unleash a can of furry vengeance that even Liam Neeson couldn't deal with. And with this deck, getting to seven forests isn't even hard. The crazy Veteran Explorer + Primal Growth interaction gets you four forests for four mana. Throw in a multitude of other land-searching cards, and you'll be sprouting tress so fast even Johnny Appleseed would be proud.

Treefolk Harbinger serves to make sure that you either have a Treebeard to threaten people with, or enough forests to make him an actual threat. He can also tutor for Lignify to answer a problem creature. If your walnuts are big enough--and lord knows you will have enough trees to grow them on--then you can also find and hard-cast the miser Woodfall Primus for some serious cool points.