Vertical cracks on tree trunks are generally one of two things; frost cracks or sunscald. Both show up primarily on the southern or western exposures of the trunk. Frost cracks are common in areas with extreme temperature fluctuations; the sun warms up the trunk during the day and then freezing temperatures at night can cause the sun-warmed cells to burst. Sunscald is a lot like sunburn; it can damage thin-barked trees any time of the year. Because of the injury, your maple will benefit from a little extra TLC this year. Mulch it with 3-4 inches of organic mulch like shredded wood. Keep the mulch a few inches away from the trunk and extend the mulch ring at least two feet from the trunk. Although water is expensive, make sure your tree gets watered well at least once a month if you have a prolonged dry spell in your area. Set a trickling garden hose on it for an hour or drill a 1/8-inch hole near the bottom of a 5-gallon bucket, set the bucket at the base of your tree, and fill it with water. You can buy 5-gallon Tree Gators which trickle water, too.