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Cladoptosis is a natural process in which shrubs and trees lose their branches. By contrast with an accident or damage to the tree in which a branch is wrenched off, leaving an ugly wound behind, cladoptosis is a controlled branch loss which is initiated by the tree. This process is quite normal in many trees, although excessive cladoptosis can be a sign that trees are distressed, so it is something for gardeners to watch out for.
In the cladoptosis process, the tree identifies a branch which it wants to lose and it begins the process of abscission, growing a layer of specialized tissue where the tree meets the branch which cuts off the vascular supply to the branch. Eventually, the branch dies and falls off, leaving a neat abscission scar behind. The same process is used in trees which lose their leaves.
There are several theories about why trees engage in cladoptosis. Some people theorize that it is done for the same reason that trees lose their leaves: to conserve energy. Cladoptosis is especially common during periods of drought and resource stress, making this theory quite plausible. Unlike deciduous shedding, it can be carried out year-round, making it an excellent adaptive tool for trees which might be struggling to survive in a changing climate.
This process may also be a form of self-pruning. Humans prune trees to shape them, but they also prune them to encourage a healthy pattern of growth, and trees may do the same thing. By shedding branches in a controlled fashion, trees can develop strong trunks and crowns, and reduce the risk of branch loss in winter storms and harsh conditions. Cladoptosis also allows a tree to shed branches in dense areas, allowing light to reach every area of the tree.
Some botanists have theorized that cladoptosis may also be an adaptation to discourage climbing plants. Much as animals shudder to shake off insects, trees may drop branches to dislodge climbing plants like lianas and ivy which can slowly choke trees to death. In the tropics, where climbing plants are especially widespread, cladoptosis is also a very common occurrence, lending some credence to this theory.
Because cladoptosis is natural, it can be difficult to identify when a tree is stressed, and when it is merely shedding branches for health reasons. Gardeners may want to keep an eye on the shedding patterns of the trees in their gardens, taking note if a tree sheds more branches than it normally does and investigating to determine the cause. A tree might not be getting enough nutrients or water, or it might be stressed by climbing vines or animals.