Answer: Based on your description I am not certain what is wrong with your plant. The peak of the home heating season usually means a warmer and drier atmosphere (especially up near the ceiling) and a number of insect probelms will appear. The prime insects to check for would be spider mites, scales, mealybugs, aphids and thrips. Spider mites would be my first guess, especially if you are seeing any fine webbing along the undersides of the leaves. These would be treated with insecticidal soap; increasing the surrounding humidity level would also help although it would be hard to do with such a large plant. Scales will also appear with a vengeance at this time of year; they look like little discs and in the soft stage can be scraped off with your fingernail. These can also be treated with insecticidal soap when in the soft crawler stage. Be sure to follow the label instructions carefully, treat both the top and bottom sides of the leaves and all aover the stems, branches and trunk. Repeat as directed, too, to catch later maturing pests.
If you find absolutely no sign of insects, there is also a possibility although less likely that it is suffering from dieback (Phomopsis), which simply causes leaves to wilt, die, and fall off. Then smaller and eventually larger branches begin to die off. The best you can do in that case is to maintain even soil moisture and prune off the affected branches. Luckily, this plant is quite amenable to pruning.
Certainly remove and destroy any dried foliage as soon as it happens and trim away any truly dead wood. This plant can regrow from wood that is bare but not dead, so be careful not to prune away too much. Good luck with your tree!
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