The bark of a tree is dead tissue, placed there to insulate the tree to some extent and protect it from damage…squirrels and bears climbing, lawnmowers running into, etc. As the tree grows and expands the bark naturally has to give and separate a bit. On rough-barked species we generally don’t see those cracks but on smooth- or thin-barked trees they may occasionally show up. Sometimes, as on a birch tree, we declare that the curling bark is attractive and we enjoy it.
On young or smooth-barked trees we occasionally see “frost cracks” caused on a winter day when the sun warms one side of the tree. The bark expands a bit, but then the sun goes down and cold air shrinks the bark; voila, a crack appears on the south, warmest side. Or more often two appear, one on the east, another on the west…points where the difference between warm and cold is greatest. (Rapid growth, as from a wonderfully moist growing season such as we had in 2013 can lead to similar cracks.)
Good for the tree? No! Should you be distressed? No. Trees have been getting frost- or growth-cracked for eons and somehow survived.
Sometimes on rough-barked trees, the outer layer will pull away from the main stem as it grows. Should this perturb you? Not necessarily.
Diseases and insects, though, can cause bark to loosen and sometimes fall away, so in this case investigation is in order. Get a little concerned. Take a good look at the inner surface. If you see tiny drilled holes or winding grooves, those may be insects that are tunneling into the tree. Not good.
When should you worry?
Perhaps you see soft, dark, perhaps oozy and foul-smelling areas. These indicate a bacterial rot sometimes called Slime Flux. Or you may encounter the light-colored, stringy or fluffy material that indicate a fungal disease.
Begin to be apprehensive..
Back off and take a good look at that tree. Are there areas of bare branches overhead? This is the portion of the tree fed by the sap that used to pass through that diseased or insect-infested area. Dead branches can be a hazard.
Now begin to worry! Get an Arborist to look at that tree. The tree’s condition, the cause of the problem, options for treating the disease or dealing with the insect, the tree’s location, the possible damage that would result from falling branches or the whole tree, the effect on the landscape by removing it, all need to be weighed to help you decide if it’s time for real distress.