WotC Hates Goblinoids IV: Is This Joke Still Funny?
Every goblinoid I've rated so far could be fixed by removing all LA, then slapping on a minus sign if there were RHD left. The forestkith goblin is no different in that regard.
As far as ability adjustments go, +2 dexterity and -2 intelligence are moderate at best, and Small-size means a lot of the classes that'd benefit from such adjustments aren't really practical. Similarly, weapon familiarity with nets is kind of disappointing when they don't work against stuff bigger than a human. Discordant Frenzy is another useless ability, because it requires at least three forestkith goblins attacking together. Last of the non-useful abilities is Light Sensitivity, AKA: "the 5 GP drawback".
That said, forestkith goblins aren't without their merits. Their climb speed actually bypasses a number of common low-level obstacles, their natural bite is nifty, +1 natural armor is better than nothing, and they have a very unique and interesting ability in Tree Shape.
Said ability allows the goblin to turn into a plant for 12 hours once per day. The downside is that unlike the spell of the same name, it can't be ended prematurely, unless the sun sets or the plant takes damage. Even so, one should be able to get some use out of this ability.
The forestkith goblin suffers from a number of problems, but ultimately has enough interesting abilities to stave off -0 LA. At the same time, it's hardly worth the +1 LA currently assigned to it. With that in mind, I'll assign +0 here.