Complex sentence: A wound to the bark, caused by pruning, insects, poor branch angles and natural cracks and splits, causes sap to ooze from the wound, fill with bacteria, darken and stain the bark, eventually taking on a foamy appearance and unpleasant odor.
Split into simpler sentences: A wound to the bark, caused by pruning, insects, poor branch angles or natural cracks and splits, causes sap to ooze from the wound. Bacteria may infect this sap causing it to darken and stain the bark, eventually taking on a foamy appearance and unpleasant odor.