The article by Abby Van Den Berg et al (Maple News November 2013) provides valuable research support for understanding the key variables behind tapping guidelines. Prior to 2005 there was no research supporting any of the guidelines in use. However, maple producers need to pay careful attention to the caveats mentioned in the article. The use of the conservative guidelines promoted in that article should be restricted to the best trees in the best growing conditions. This research implies that the older conventional guidelines should not be used. Because there are many trees that are growing in less than the best conditions, these results also support my proposal that most producers should use even more conservative tapping guidelines than the “conservative guidelines.” My 2005 Maple Digest article was based on the same analysis used by Van Den Berg et al but took into account the growth rates of all maple trees being tapped in common growing conditions. The resulting guidelines are repeated here:

• No tree should have more than one tap unless it has a high growth rate or is very large. For producers with vacuum, this should not be a problem since one taphole is sufficient to remove much of the available sap in the tree. Those with buckets or gravity-based tubing will collect less sap, but this guideline should still be used.

• Taphole depth should be closer to 1 inch and not more than 2 inches, especially in smaller, slower growing trees. Again, knowing the growth rate of your trees will help you determine the appropriate hole depth for your sugarbush.

• Expand the tapping area vertically by 12-15 inches above or below old tap holes. This increases the likelihood of finding new wood and allows more time for wood growth over old holes.

• Use a tapping pattern that allows you to know what parts of the tree were tapped for as much as 20 years previously. We tap in a consistent direction with a paint spot below the hole to be able to quickly spot the direction. The new hole is 1-2 inches laterally from the previous hole and about 8-12 inches higher or lower to give us good possibilities to get into wood not stained (blocked) by earlier tapping.

Measuring the growth rate of individual trees is not easy, but there are some general guidelines. Here is what I have found from my research.

• Larger trees with good canopy exposure (dominant or co-dominant) usually are growing faster than smaller diameter trees. Often small trees have growth rates suppressed by canopy dominants.

• Trees with taphole closure in one or two growing seasons are growing faster than trees where holes remain open for longer than two seasons.

December 2013