First of all Druidic Defender Campaigns are prime.
You have acess to Wall of Thorns so that means you have 5ths right? Start Awakening some stuff. It's gonna bite your XP but if you can Awaken yourself 3-6 fury allies or trees that'll help a lot. The hump is the will save required for the spell, but druids have high wis and good will so it shouldn't be that hard. And if you have iron will hurrah to that.
Have any ranks in Craft(trapmaking)? If not, have a shovel? Make yourself some tiger traps around yon forest. Weave a cover out of twigs and stuff. If you're worried about animals getting stuck in it, theres 2 solutions. The first is, don't worry about it. You'll be able to check the holes often, set any broken bones, heal them and send the animal on its way. The second is a bit more complicated. Make a check to go find yourself "marked" leaves and such. Use these in the construction of the hole. Other animals will know its another animals territory and stay away. That'll help a little at least. If you're down with blowing off some 2nd level spells slots, you can cast Speak with Animals, and alert the creatures of the forest of #1 the invaders and the danger the present #2 the traps you've placed and some signs to look for the make sure they don't get trapped in them. When you get 6th's
Have you Communed with Nature yet?
How large is this force of Undead? If you have some summoning feats, you can summon a lot of decently powerful allies. Example: You could use your 5th level slot to summon 1d4+1 Lions or Dire Wolves. If you filled all your slots with Summons, you could basically summon, then run away. And by run away I mean use Wild Shape to escape no problem.