Deciduous means "falling off at maturity" or "tending to fall off" (deriving from the Latin word lang: decidere, to fall off) and is typically used in reference to trees or shrubs that lose their leaves seasonally and to the shedding of other plant structures such as petals after flowering or fruit when ripe. In a more specific sense deciduous means the dropping of a part that is no longer needed, or falling away after its purpose is finished. In plants it is the result of natural processes; in other fields the word has a similar meaning, including deciduous antlers in deer or deciduous teeth, also known as baby teeth, in some mammals, including human children.

Botany

In botany and horticulture, deciduous plants, including trees, shrubs and herbaceous perennials, are those that lose all of their leaves for part of the year. This process is called abscission. In some cases leaf loss coincides with winter - namely in temperate or polar climates. While in other areas of the world, plants lose their leaves during the dry season or during other seasonal variations in rainfall, including tropical, subtropical and arid regions of the world.

The converse of deciduous is evergreen, where green foliage is persistent year round. Plants that are intermediate may be called semi-deciduous, and lose old foliage as new growth begins, others are semi-evergreen and lose their leaves before the next growing season but retain some during winter or during dry periods. Some trees, including a few species of oak have desiccated leaves that remain on the tree through winter; these dry persistent leaves are called marcescent leaves and are dropped in the spring as new growth begins.

Many deciduous plants flower during the period when they are leafless as this increases the effectiveness of pollination. The absence of leaves improves wind transmission of pollen for wind-pollinated plants, and increases the visibility of the flowers to insects in insect-pollinated plants. This strategy is not without risks, as the flowers can be damaged by frost or, in dry season regions, result in water stress on the plant. Nevertheless, there is much less branch and trunk breakage from glaze ice storms when leafless, and plants can reduce water loss due to the reduction in availability of liquid water during the cold winter days.

Leaf drop or abscission involves complex physiological signals and changes within plants. The process of photosynthesis steadily degrades the supply of chlorophylls in foliage; plants normally replenish chlorophylls during the summer months. When days grow short and nights are cool, or when plants are drought stressed, deciduous trees decrease chlorophyll pigment production allowing other pigments present in the leaf to become apparent, resulting in fall color. These other pigments include carotenoids that are yellow, brown, and orange. Anthocyanin pigments produce reds and purple colors, though they are not always present in the leaves but are produced in the foliage in late summer when sugars are trapped in the leaves after the process of abscission begins. Parts of the world that have showy displays of bright fall colors are limited to locations where days become short and nights are cool. In other parts of the world the leaves of deciduous trees simply fall off without turning the bright colors produced from the accumulation of anthocyanin pigments.