Larger and fuller crowns means more leaves. More leaves means more sugar-producing photosynthesis.
More sugar means more syrup.
This low density will grow the large full-crowned trees needed for optimal syrup production. Roadside trees are excellent for tapping because the road openings encourage large and full crowns. Once March and April temperatures reach 40 degrees Fahrenheit, enzymes change the starch to sugar. The sugar flows up and down the tree trunk, where we can tap it. Heating during the day and cooling at night pumps the sap up and down the trunk of the tree.