Growth Rates of Sugar Maple Trees Tapped for Maple Syrup Production Using High-Yield Sap Collection Practices

The amount of sap that can be extracted annually from trees for maple syrup production using current equipment and practices is more than double the typical yields achievable when current maple industry tapping guidelines were developed. The growth rates of trees tapped with these "high-yield" practices at 18 sites in Vermont were measured and evaluated to determine whether they were sufficient for the replenishment of conductive wood to remain at sustainable levels when current tapping guidelines are followed. The basal area increments of healthy codominant or dominant trees across the sites ranged from 1.8 (+/- 0.2) in.(2)/year in 10-in. diameter trees, to 3.5 (+/- 0.3) in.(2)/year in 18-in. diameter trees. The estimated minimum growth rates required ranged from 1.4 in.(2)/year in 10-in. trees to 2.6 in.(2)/year in 18-in. trees. These results suggest that the growth rates of many trees tapped with high-yield sap collection practices are sufficient for this activity to remain sustainable when current tapping guidelines are followed. However, an average of 35% of sampled trees had growth rates below the estimated minimums. This indicates that tapping practices must be modified for some trees to ensure that adequate replenishment of conductive wood is maintained and that growth rates must be measured to be certain sustainable tapping practices are implemented.