Tree decline tends to begin months or years before obvious symptoms of dieback appear, so it's hard to tell from the photos what the original cause(s) may have been. Drought stress, root damage or girdling roots, soil salt buildup, secondary issues like wood-boring insects or wood decay fungi, and other factors can all play a role. (Our page What Causes Trees and Shrubs To Die? provides more information.)

We recommend you have the tree evaluated by a certified arborist or licensed tree expert. Although all have advanced training, some have more diagnostic experience than others, so you can inquire before hiring if they have familiarity with causes of maple decline. Dead and dying branches will need to be pruned off before they fall due to wood decay, since they cannot recover. Arborists cannot cure every condition or reverse decline, but they may be able to narrow-down a diagnosis as well as look for sources of tree stress that might be able to be alleviated (or avoided for a future replacement tree).

Miri