Why does wood accumulate energy?

Normally, binding energy is negative -- once it is removed while objects approah each other, the objects will not be able to fly apart without additional energy. Yet, tree burns, which means that once you supply some fire, the molecules get out of their potential holes and drop into a lower hole. Why the plants are devised so that they construct themself by elevating the atoms into "vulcanic craters"? Is it because environment molecules are in lowest energy states and constructing any new configurations menas to raise the energy?