Old Growth Maple Trees
While hiking in the Northeast Kingdom of Vermont last weekend, I came across a handful of old growth maple trees that were nearly five feet in diameter. Talk about standing out in the crowd! Since maples can live to 400 years old, I have no doubt that these trees were thriving when Vermont became the 14th state in 1791. They may have lost some branches and the centers are rotting out, but they are strong and standing tall.
Note the five foot long walking stick for scale!
Old growth trees are not common here in Vermont. By the late 1800’s, Vermont was mostly denuded of trees to clear the land for sheep and to provide lumber, charcoal for the iron industry, firewood, and pulp for paper. Only about 20% of our trees were left uncut and those were up in the high elevations. The sheep were eventually replaced by cows. The forests have come back and they now make up about 80% of our landscape. Finding old growth trees in relatively good health is rare and I feel privileged that I found these majestic maples and was able to sit in their presence.
I wondered if these big trees had ever been tapped for making maple syrup. There are signs of past sugaring throughout the woods in this general area but nothing near the trees that I could see. Based on the roughly 20 million sap buckets that were hung on maples in 1860, I tend to think these beautiful trees have been tapped at some point in their long history. These trees got me thinking about the lessons I have learned about tapping maple trees.
How Many Taps per Maple Tree?
The Current Use and Organic guidelines allow for increasing numbers of taps based on the diameter of the tree. According to the guidelines, trees 9” or 10" to 15” can have one tap, trees 15” to 21” can have two taps, and trees over 21” diameter can have three taps. As recently as the 1970s, up to four taps were allowed. I’ve personally never put more than two taps per tree. I didn’t want to seem greedy. I was horrified to once see seven or eight buckets hanging on one tree.
Historically, I put in either one or two taps depending on the size of the tree. I also tapped trees down to the minimum diameter. It just seemed like I should since the tubing was running right past and I didn’t want to miss out on the sap. However, years ago I attended a class put on by Wade Bosley from UVM’s Proctor Maple Research Center, and I realized that my tapping process had room for improvement. My top two take-aways from Wade’s lecture: only put one tap per tree if you are using vacuum and only tap trees that are at least 12” in diameter.
Why Only One Tap per Maple Tree?
The reasoning behind Wade’s advice was that with vacuum the sap gets pulled from quite a bit of the tree circumference. When there are multiple taps on the same tree, each tap tries to pull sap from overlapping areas on the tree. You might get more sap from two taps, but you won’t get double the amount. It’s a little different for buckets, since the volume of sap removed is only about half of what it is with vacuum. Bucket taps won’t compete with each other and you would likely get twice as much sap with two buckets.
My sugaring lines are all 3/16” tubing and I have plenty of vertical drop to give myself natural vacuum. I listened to Wade, but I like to prove things to myself, so I decided to change two of my sap lines to have all one-tap trees and another two lines to have all two-tap trees. The total number of taps per line was the same for all four lines. All lines feed directly into a collection tank so I was able to monitor the flow from each line. Based on the sap run data over three days, the lines with only one tap per tree were 15% more productive. This was a small experiment much less rigorous than UVM’s, but the result made me a believer. One tap per tree.
Even more important to me than the productivity is the tree health. One tap vs. two taps means half the number of holes in a tree. That just has to be better for the maple tree in the long run. There is also half as much brown wood which greatly increases the odds of good productivity in future years.
Why Not Tap the Small Maple Trees?
Not tapping trees that were 10” or 11” in diameter was tough for me. Those trees seemed to be in their prime and ready to pump out sap, so I was hesitant to bypass them. However, Wade showed data indicating that sap yield increases with the size of the tree. In general, bigger trees have bigger crowns so that makes sense. Of course I had to prove it to myself. I measured the circumference of 200 trees, found the average tree size per line feeding into the collection tank and then measured the flow from the 20 lines on three different days.
The normalized data clearly show that bigger trees produced more sap. Armed with this knowledge, I now pass right by the smaller trees that aren’t 12” in diameter yet; I know their time will come.
It’s All About the Trees
Maple syrup is entirely dependent on the maple trees. I hope that the trees in my sugarbush will be tapped for decades and maybe even centuries more. I want to leave them healthy for future generations. To that end, I’m only putting one tap hole in each tree. I’m also not tapping the little trees – or the really big trees. A maple tree like I visited recently with a diameter of 55” is off the charts. And once they’re that old, I think they deserve a break. They’ve earned it.