Our daughter is not quite 18 months old. She has started to gnaw and chew on a bed made of wood. She does not eat the wood but spits it out. We have put several different condiments on the spot she chews on.
She could be getting in her molar teeth (the back ones). These can be particularly painful and may feel better when she gnaws on the hard wood. You can purchase wooden teething rings if that's the case. You could also have a few teething toys laying around in her crib, giving her an option on what she chews on.
Second Option
There is another condition, called Pica, that involves the inappropriate eating of non-nutritous foods. My sister suffered from the most common form of Pica in all 5 of her pregnancies: she absolutely HAD to chew ice. Her body craved something that contributed nothing to her overall nutritional needs.
Check for Lead
Either way, I would be 100% SURE there is no lead paint on the wood that she's chewing. Lead can cause permanent brain damage in young children (why so many recalls of toys are due to using lead-paint.) To be on the safe side, I would have your pediatrician do a simple blood test and check her lead levels.
If it continues to be a problem, perhaps you should consider having her sleep in a play yard instead, until the habit seems to be broken. You could also try smearing a little teething medication (like baby Orajel) on the wood to discourage her eating it. It tastes terrible but won't harm her.
Of course, if this continues and you're still worried, call your doctor. He can give you other ideas, or, at the very least, set your mind at ease.