The Comparison Tree Method
The Comparison Tree
Method (also referred to as the Five-Tree Tester Method) is used to
identify trees with higher than average sap content. Follow the steps
below to use the Comparison Method to identify high sap sugar trees.
The Cornell Sugar Maple Research Program is actively looking for trees
with high sap sugar concentrations.
1) Select as
many trees as possible to test for sugar content.
The larger the number of trees that can be tested per location, the
higher the potential for identifying candidate trees. We have found
that out of 100 trees, we might be able to identify two candidate trees.
2) Keep as many
factors constant as possible.
Factors such as slope, aspect, contour, and microsite are possible sources
of variation and should be kept constant.
3) Keep tapholes
Drill tapholes at the same relative location (height and compass orientation)
on all trees. If you are going to test immediately after drilling, drill
all tapholes within a one or two hour time period. Drill tapholes as
close to the beginning of the spring sap flow as possible. If trees
are tapped too late, early sap flows may be missed; if they are tapped
too early, the taphole may "dry out" before the season ends.
If the tree is tapped when it is frozen, it may be seriously damaged
because the bark is more likely to split when the spout, or spile, is
4) Sample all
trees within the same time period.
Sampling and testing of all trees should occur within a relatively short
time period (one hour if possible). This way you control for changes
in sap content that may be caused by weather or different times during
the sap season.
5) Sample during
the spring sap season.
Early to mid-season is when sap sugar concentration is likely to be
at its maximal level. Sampling during this period offers the best opportunity
for detecting differences in sap sugar concentration between trees.
Because maple sap may flow in late fall when weather conditions are
right, some producers have attempted fall sap collection. However, tapholes
drilled in the fall produce only about half as much sap as in the spring.
Also, sugar concentrations from fall tapping are about two-thirds below
that expected from a spring tapping. Fall tapping for sugar production
is therefore not recommended.
6) Test healthy
To be selected for the Sugar Maple Tree Improvement Program, a tree
must be of good form and free of defects, evidence of harmful insects
and disease, and other factors that could influence sap sugar concentration.
7) Test trees
that are capable of flower and seed production.
Trees selected for the Sugar Maple Tree Improvement Program should be
capable of flower and seed production. This way twigs taken from the
tree and cloned will produce individuals capable of immediate seed production.
Sugar maples acquire flowering and seed production potential at about
30 years of age, which generally coincides with the minimum commercial
tapping diameter. Although sap sugar concentration can be measured on
small diameter, immature trees, only trees that meet minimum commercial
tapping diameter (10 inches diameter at breast height) should be tested
as potential candidates for the Sugar Maple Tree Improvement Program.
8) Tap trees
with crowns close to the ground.
Candidate trees should have well-developed crowns within 30 feet of
the ground. This allows the use of pole pruners for cutting twigs from
the tree crown. These twigs are used to clone the trees by rooting of
cuttings or grafting.
the sap content of the tree using a hydrometer or refractometer.
Follow the instructions on the hydrometer
and refractometer sections
of the web page.
10) If you identify
a tree with higher than normal sugar content, test neighboring trees.
When a tree is suspected of having sap with above average sugar content,
test the sap content of the five nearest trees. Record the results on
the Sugar Maple Testing Form. Make sure to mark
the tree with higher sap content and the neighboring trees with plastic
flagging or in some other way. If possible, measure the selected tree
and candidate tree several times during the sap season. The sap sugar
content of the candidate tree must be at least 30% sweeter than the
average of five surrounding trees (standards) and must exceed the sweetest
standard tree by a minimum of 0.5 percent.
11) If you have
a tree you think qualifies for the Sugar Maple Tree Improvement Program,
contact your Cooperative Extension agent or the Cornell Uihlein Maple
Extension agents in many counties are familiar with the Sugar Maple
Tree Improvement Program and should be able to help you to determine
if you have a candidate tree. If your county Extension agent is unfamiliar
with the Sugar Maple Tree Improvement Program, have him or her contact
the Cornell Uihlein Maple Program in the
Cornell Department of Natural Resources.