Illustration by Adelaide Tyrol
Our sugarhouse is within walking distance of an elementary
school, so we've given tapping demonstrations to hundreds of school
kids over the years. At the part where someone drills a hole in the
tree and it sort of bleeds, the next question is invariably: "Does
tapping hurt the tree?"
The stock answer is no, as long as you don't overdo it: use the
smaller "health" spouts, follow conservative tapping guidelines,
give the tree a year off if it looks stressed. As proof that
sugaring is sustainable, we point to some of the trees in our
sugarbush that have been tapped for close to a hundred years and
are better off for it. Better off because we thin out the trees
around them, giving the chosen trees extra light, water, and
nutrients. Their increased vigor, when compared to the maples in
unmanaged sections of the forest, is plain to see.
But the sugarmaking being practiced today in many commercial
bushes - including our own - is not the same sugarmaking that was
practiced even 10 years ago. New technologies, like high-yield
vacuum pumps and spouts that keep tapholes open longer, have vastly
increased the amount of sap we're collecting from each taphole.
Generally speaking, we're taking about twice as much sap per tree
each spring as my grandfather took - some guys are taking three
times as much.
So can a modern sugarmaker take too much sap from a tree? The
short answer is probably still no. To come up with a longer, more
satisfying answer, we'd first need to figure out how much sap is
available to a tree at any given time, and this question gets
tricky because there's the water part of sap and the sugar
It's reasonably safe to assume that water is relatively easy for
a tree to come by. Twenty inches of snow converts to about 54,000
gallons of water per acre, so even if you're taking 20 gallons of
water from a tree over the course of a sugaring season, it's a drop
in the bucket compared to the moisture that's available. The
problem is that nobody knows for sure where the groundwater in the
sap you're collecting came from. Was it melting snow? Or Hurricane
Irene in August 2011?
The sugar part of sap is no easier to account for, and we don't
know its history either.
We do know that the soluble sugars in maple sap are part of a
tree's nonstructural carbohydrate reserves (otherwise known as tree
food.) Picture these reserves like a bank account that the tree
adds to when it's photosynthesizing and draws upon in the spring to
open its leaves and grow its early twigs, in the fall to establish
cold hardiness, and in the winter to keep living cells alive.
And we can measure these reserves.
Conventional wisdom holds that a traditional sugarmaker does not
take a harmful amount of the reserves. According to a report
published in 1903 by the venerable UVM maple researcher Dr. C.H.
Jones, only about four to nine percent of an eight- to
ten-inch-diameter tree's total carbohydrate reserves are removed;
almost no one taps trees that small, and presumably the
carbohydrate loss is significantly less in bigger trees. To make
the allometric model that estimate was based on, someone had to dig
up a whole tree and record the live weight and dry weight of every
piece - from the root hairs to the branch tips. Considering the
amount of time, money, and logistics this entailed, you can
understand why no one has created a model using a 30-inch diameter
This isn't to say that maple researchers aren't reexamining the
can-you-take-too-much-sap question from other angles. In 2010, Mark
Isselhardt, a researcher at the Proctor Maple Research Center in
Underhill Center, Vt., measured the carbohydrate reserves of trees
under high vacuum before, during, and after the season. One
intriguing finding was that trees under high vacuum had slightly
higher levels of carbohydrates in early summer, meaning that
perhaps the trees mobilized reserves to accommodate for the
additional loss, and perhaps this diversion of resources came at
the expense of radial growth, which in the fall of 2011 was
slightly less than the gravity-only and the non-tapped control
trees. But Isselhardt cautions against taking anything from the
study as gospel truth. "It's tempting to jump to conclusions, but
the sample size was small and the data lack statistical power. At
best we can only say that the results add to the mystery."
And so, for now, we're still at "no." People tend to see
scientists as sages who have all the answers - I'm as guilty as
anyone in this regard - but the truth is that they're much better
at asking questions than answering them. This can be frustrating,
but it's also kind of cool. There's still so much we don't know
about sugaring, about nature in general. So many puzzles wait to be
Dave Mance III is the editor of Northern
Woodlands. The illustration for this column was drawn by Adelaide
Tyrol. The Outside Story is assigned and edited by Northern
Woodlands magazine and sponsored by the Wellborn Ecology Fund of
New Hampshire Charitable Foundation: firstname.lastname@example.org