Fallen leaves. Yellow and red fallen Prunus leaves lie scattered on grass. Deciduous trees shed their leaves in autumn to prevent excessive water loss and to avoid frost damage. The change in colour is due to breakdown of the green pigment chlorophyll, which absorbs energy from sunlight (photosynthes- is) in healthy leaves. The genus Prunus contains around 400 species, including many orchard fruits such as plum, peach, apricot, cherry and almond.