As time passes, some trees develop bald or barkless places on their trunks as a result of harsh weather conditions. The bald part usually begins at the place where the roots emerge from the ground, and grows increasingly thinner as it continues up the trunk. Intense sunlight will bleach these parts, forming a very characteristic part of the tree. With Bonsai the bark is removed with a sharp knife and the barkless spot is treated with calcium sulfate in order to speed up the bleaching process. Click here for an image of all Bonsai styles.