Biennial bearing bearing is a term used in pomology

Pomology

Pomology is a branch of botany that studies and cultivates pome fruit, particularly from the genera Malus, Prunus and Pyrus belonging to the Rosaceae. The term is sometimes applied more broadly, to the cultivation of any type of fruit...

 to refer to trees that have an irregular crop load from year to year. In the "on" year too much fruit is set, leading to small fruit size. Excess weight in the main branches can be too much for their mechanical resistance, causing them to break. Another major consequence is that flower induction

Flower induction

Physiological process in the plant by which the shoot apical meristem becomes competent to develop flowers. Biochemical changes at the apex, particularly those caused by cytokinins, accompany this process...

 will be lower, and the subsequent year will be "off" year (too little fruit).

The behavior could be due to plant hormones, particularly gibberellins produced in excess in the "on" years in the embryo

Embryo

An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

s of the young fruit. It could also be caused by depletion of carbohydrate

Carbohydrate

A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...

 reserves in the tree.

Biennial bearing is more common in certain fruit crops like apple

Apple

The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...

, pear

Pear

The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....

, apricot

Apricot

The apricot, Prunus armeniaca, is a species of Prunus, classified with the plum in the subgenus Prunus. The native range is somewhat uncertain due to its extensive prehistoric cultivation.- Description :...

 and avocado

Avocado

The avocado is a tree native to Central Mexico, classified in the flowering plant family Lauraceae along with cinnamon, camphor and bay laurel...

, and almost non-existing in grapes.

Horticultural management

This disorder can be reduced by winter pruning

Pruning

Pruning is a horticultural practice involving the selective removal of parts of a plant, such as branches, buds, or roots. Reasons to prune plants include deadwood removal, shaping , improving or maintaining health, reducing risk from falling branches, preparing nursery specimens for...

, and thinning

Thinning

Thinning is a term used in agricultural sciences to mean the removal of some plants, or parts of plants, to make room for the growth of others.- Forestry :...

 of flowers and young fruit

Fruit

In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...

.