Your trees are not unusual or unhealthy. Smooth and light-barked trees i.e. Ash, Mulberry and Cirtus, are especially susceptible to cracking due to rapid growth, freezing or sunburn. The bark is not elastic enough to prevent splitting. When cracks occur, they create callous tissue, a hard and very strong substance that forms around the wounds. The cracks look bad but they don't often cause long-term health problems. Although ugly, they create a durable bark with character. If cracks are severe, they can be invaded by insects such as flat-headed borers. To protect from sunburn, the trunks and main stems of young trees can be wrapped with shade cloth or burlap, or painted with a specialty tree product created right here in Arizona called Go-Natural Paint.