Question
How often do you recommend to remove or shorten and lighten long horizontal branches and thin the terminal foliage to reduce the branch weight or cut back long branches to an upright branch closer to the trunk on liquidambar trees to reduce the potential for summer limb failure.  

Answer
Tree limbs that drop in summer without any apparent cause is not uncommon.We call it Summer limb failure. There are some species of trees that are known for such failure. For example, liquidambars commonly drop fairly large limbs. Usually they are limbs of around 4 inches to a foot in diameter. These limbs are large enough to cause significant damage if your car is parked under neath them. Other commonly grown trees that have summer limb drop include: eucalyptus, oak, ash, ornamental pears, sycamore,silver maple and poplar. Interestingly, summer limb failure has been studied through out the world and some of the data has been reported through a program called the California Tree Failure Report Program. In California the most reported month of summer limb failure is July and usually the failures are reported between noon and 4:00 pm insituations with little or no wind. Failures that are reported as occurring at night are more often associated with higher wind speeds. What causes summer limb failure? There has been a lot of conjecture and some research on the topic but there isn抰 a clear consensus as to what really causes the problem. It is felt that high water flow in conjunction with high water demand by the plant causes water stress in the branch because of an apparent inability to keep up with the transpirational demand of the foliage. That is to say that water loss through the foliage is occurring faster than the plant can take it up through the roots. There is also a thought that there may be a reversible accumulation of ethylene in the wood because of stress, which causes the cellular 揷ement?to dissolve and cause limb weakening. In any case, whatever the cause there are few things you can do to help reduce the impact of summer limb failure and avoid serious damage to your property.First, since most of the failures are reported as occurring on long horizontal limbs, the most important task is to remove or shorten and lighten long horizontal branches.Thin the terminal foliage to reduce the branch weight or cut back long branches to an upright branch closer to the trunk.