- The author tapped 65 black walnut trees ranging from 7-35 inches in diameter, placing taps on trees 8 inches or larger based on their diameter. - He found that trees closer to water sources produced more sap early in the season, while sap production increased for all trees later in the season with more sun. - Black walnut syrup has a higher sugar content than maple syrup but yields less sap per tap. The author's research found tapping the main root or branch of the tree produced more sap.