That's okay, because Trebs aren't going to be very useful against wood elves anyway. Sure, if they hit they'll smash a unit. But if the scatter at all, they'll miss the unit entirely because wood elves tend to run quite small units.
You're going to be facing a nasty amount of shooting, some of it being S4 at short range. He's also going to have lots of small units that can dodge around your big units all day long. The exception will be dryads, treekin, and treemen which are his heavy hitters.
I'd reccomend LOTS of archers with braziers. It doesn't matter so much against dryads, but bigger forest spirits take double damage from flaming attacks. Likewise, a medium size unit of knights with the flaming banner will also make short work of tree spirits.
Magic weapons are also needed - the forest spirits have a 5+ ward that can be bypassed with a magic weapon... or Grail Vows.
You might also condsider using a unit with the Ranger Standard, to go in and get his units that are hiding in the trees. Likewise, the Twilight Banner will allow you to get though a forest and get set up for a charge the turn after.
By and large, you're going to want a decent number of smaller units instead of a small number of large ones. Give him too many threats to be able to avoid them all, and prevent him from ganging up too much force onto any one of your own units.