The two main mechanisms of action of damage to recalcitrant seeds are desiccation effect on the intracellular structures and the effect of metabolic damage from the formation of toxic chemicals such as free radicals.[5] An example of the first type of damage would be found in some recalcitrant nontropical hardwood seeds, specifically the acorns of recalcitrant oaks, which can be stored in a nonfrozen state for up to two years provided that precautions be taken against drying. These seeds showed deterioration of cell membrane lipids and proteins after as few as 3–4 days of drying.[6] Other seeds such as those of the sweet chestnut (Castanea sativa) show oxidative damage resulting from uncontrolled metabolism occurring during the drying process.[7]