If the treelings can adapt to other social environments, then you should include a more unusual and specific reason as to why this is. So far, what I see, based on physiology, is a race with a tough bark-like skin, and sturdy structure. There is nothing indicating to me that this race should be charismatic. Everything scream STR and CON to me, a penalty to DEX, and probably a mental stat to round it out. Natural Armor and Powerful Build are tough to balance out. Overall, I think a race should have just slightly more advantages than disadvantages, so I'd try to balance out Powerful Build first; The skill penalties are a start, and make sense. I might also include something in the way of the opposite of light sensitivity, so that they can't spend too much time indoors, and such. Natural Armor could just be that slight advantage, in my opinion.