Included bark
Risks
Included bark may result in a union that is weaker than expected .
Where two stems ( or a branch and a stem ) meet in an acute , V- shaped union , there may be included bark . This occurs when both stems increase in diameter during normal growth . Each year , both stems grow slightly thicker and put on new bark , preventing a strong union of timber from being formed between the two stems . This can indicate a weakened union and is a common cause of failure .
The failed union in the image shows where two stems have grown adjacent and competing for many years ( co-dominant stems ).
Unions with included bark will be more prone to failure when either stem is subject to lateral load that ‘ opens ’ the union .
Control measures
Conduct load and pull tests to simulate working loads on the structure .
Load unions in compression if possible .
Brace stems together .
Insect damage
Risks
Insect damage can remove the bark and cambium , exposing the timber to decay and compromising the ability of the tree to put on new growth in response .
Many species of insect feed on , or make their nests in , trees .
Insects such as ants , termites and borers can compromise tree structure . Look for entry holes , abnormal swellings , wood debris and ( in the case of termites ) lines of termites going up and down the tree .
Some types of insect – in particular borers and termites – can also do enough direct damage to the tree during their tunnelling to cause structural failure .
In some circumstances , insect damage may significantly compromise tree strength .
Control measures
Investigate extent of damage ; check for presence of decay .
Conduct load and pull tests to simulate working loads on the compromised structure .
Avoid loading the compromised structure if possible .
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