Answer: Lots of conditions will cause leaves to drop from a kumquat tree. It could be a reaction to heat stress, too much or too little water, or, if the leaves are on the inner most parts of the branches, leaf drop can be a normal shedding of older leaves. As long as your tree is putting out new growth and looks otherwise healthy, a few shedding leaves shouldn't cause too much alarm.
I'm not so positive about your olive tree. Generally when only half of a tree's canopy is affected, it points to a problem with the roots. Root rot can cause these symptoms and it's just a matter of time before the entire tree is affected. If you've dug down to inspect the roots and everything seems fine, do a careful inspection of the trunk and branches of the affected part of the tree. You may find insect or disease problems. Best wishes with your landscape!
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