Essays - by Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321;;

A Summary of Maple Sap Data Collected in the St. Johnís Sugar Bush - Spring 2000


Stephen Saupe
Biology Department
College of St. Benedict/St. John's University
Collegeville, MN  56321

     The purpose of this experiment was to the physiology of maple sap flow in the St. John's sugar bush.  Specifically, we were interested in answering the following questions:  (1) Does the sugar concentration of maple sap produced by a tree change during the course of the season? (2) Does the sap of individual trees vary in sugar concentration? (3) Do all tapped trees produce sap on the same days? (4) Does a correlation exist between tree diameter and sap sugar concentration?
Methods and Materials:
     Sugar maple (Acer saccharum) trees in the St. John's sugar bush (Collegeville, MN; Stearns County)were tapped on March 7 or March 10, 2000 using a brace and bit (9/16th inch).  An aluminum spile was inserted in the the hole and the sap was collected in a plastic pail covered with a tin lid or in a plastic sap sack.  Twelve different trees were monitored during the course of the season.  Of these, 8 had only a single tap and 4 had multiple taps.  Sugar concentration in the sap was measured with an Atago hand held refractometer.

     Appendix 1 provides a copy of the raw data from this experiment.

Sugar Concentration.  Sugar concentration in the sap of the trees studied ranged from 1.5 Ė 6.0%.  The mean concentration of all trees on all days was 3.0% with a std dev of 0.5%.  During the course of the season, the average [sugar] in the trees sampled varied considerably (Fig 1), however, there was a slight trend toward increasing concentrations increasing for the first few days followed by a slow decline.  Similarly, the concentration of sugar in the sap of a given tree also varied significantly over the season (Fig 2).  There was a positive correlation (r = 0.55) between tree diameter and the average concentration of sucrose in sap over the course of the season (Fig 4).  

Sap Flow.  The number of trees that were producing sap on any given day during the season varied from none to all of the them.  On average, 67% of the study trees produced sap on a sample day (Fig 3).  In trees that had multiple taps, on just 61% of the days were all the taps in the same tree running (Table 1).

Table 1. Table 2.


Figure 3 Figure 4


Table 1.  Percent of taps that were running

Tree #

% of days during season in which all taps were running









     Many thanks to my Plant Physiology (BIOL327) class for helping to collect data.


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