Maple decline can occur due to a variety of factors. Maples grown in urban areas often experience stresses that they would not in a forest setting, and those stresses can set them up for problems. Air pollution, salt, restriction of roots, and competition with turf for nutrients and water are a few examples. The vertical crack you are describing on the stem/trunk could be a result of sunscald or frost crack. These cracks are particularly common on the south or southwest side of trees as this side is exposed to the sun in winter. The cracks occur when we have a warm winter day, where the sun shining on the stem of the tree can cause the cambial tissue to expand. Then, when there is a rapid drop in temperature, the bark contracts quicker than the cambial layer, causing the tree to crack. To sum it up, there are a collection of assaults that could have occurred to your tree. Keep in mind that most trees don't die overnight. However, once the decline occurs it is hard to reverse. It sounds like your tree is beyond help. I suggest removing the tree or, if the tree is particularly valuable to you, consulting a professional arborist.

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