Bark pockets are patches or inclusions of bark partially or fully embedded in the wood of a tree. They can also be used as biomonitors. Bark pockets are considered a nuisance in the lumber industry because they are considered a defect, and lower the grade of the wood.^[1] Bark pockets can also weaken tree forks, and can result in damage to the junction under stress.^[2]

Bark pockets can be formed by inosculation, formation of a tree fork, encapsulation of a branch, joining together of an uneven trunk, or encapsulation of another object.^[3][4] During inosculation, the bark trapped between the two joining trunk becomes surrounded with wood once the trunks fuse. The resulting bark pocket formed during inosculation or in a tree fork is referred to as included bark.^{[citation needed]}

When a branch is encapsulated, the outer bark on the branch may remain inside the wood of the tree, as the trunk widens and grows around the branch.^{[citation needed]}

Bark pockets can be used as an indicator of air pollutants during which the time they formed.^[3]

They can be used to monitor heavy metals such as lead and copper, as dust or other matter deposited on the bark at the time of formation is still present.^[5][6]

One study analysed the amount of polycyclic aromatic hydrocarbons (PAHs) present in bark pockets as a historical record of air quality, possible due to the interaction between PAHs and lipids in the bark.^[7]