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Is the climate changing in eastern Ontario?
With the release of this discussion paper, the Forest Science Committee hopes to further stimulate dialogue among EOMF members and partners about their experiences and observations with respect to how the climate may be changing in eastern Ontario – with a view to further exploring what the changes may mean in terms of adaptation and management actions on the ground.

pdfIs_the_Climate_Changing_in_Eastern_Ontario_Discussion_Paper_Final.pdf

Is sugar maple the only sweet maple?

By Dr. J. Peter Hall

tinrooftappingSugar maple, a rather iconic species in Canada is found throughout eastern Canada to about 49 degrees north. There are 60-70 species of maple throughout the northern hemisphere with ten species in Canada. In eastern Ontario we have Sugar maple, Red Maple, Silver Maple, Black Maple, Mountain maple, and Striped maple. In addition exotic maples are common particularly Norway Maple and Manitoba maple.

Sugar maple grows best on fertile, well-drained loamy soils, of most soil types and forms pure stands or grows in association with other hardwood species such as yellow birch, beech and cherry, basswood, red spruce and hemlock. Sugar maple is shade tolerant and reproduces vigorously on areas disturbed by cutting or storm damaged. It is one of our more common species here in eastern Ontario

As the early European settlers observed, the making of syrup and sugar from the sap of sugar maple was a well-established practice of First Nations peoples, a tradition rapidly acquired by themselves and continued to this day. The principle of making syrup is unchanged from the earliest times; sap is collected from trees, and then reduced by boiling until a thick golden-golden brown syrup is obtained. Many technological advances have been made at all stages, but the principle is the same. Canada now produces 80-85% of the world’s maple syrup.

In selecting trees for sap production; dominant/co-dominant, large bushy crowns, free of insect or disease symptoms are used. Seedling trees preferred but stems from vegetative origin are frequently used in stands with a history of cutting. Larger trees should be tapped, the minimum diameter is usually recommended to be at least ten inches in diameter with more taps on larger trees [Table 1] A well-managed sugarbush would contain 175 to 225 tapholes per hectare, or 70 to 90/acre.

Table 1. Number of recommended taps per tree diameter.

Diameter
(cm)
Diameter
(inches)
No. taps
<25 <10 0
25 - 36 10 - 14 1
37 - 48 15 - 19 2
49 - 61 20 - 24 3
>62 >25 4

Trees are also selected for sweetness; some trees are ‘sweeter’ than others and this characteristic will persist over time although it is not known if this is a heritable trait. The sugar content of maple sap is approximately 2.5% so it takes roughly 40 litres/gallons of sap to make one litre/gallon of syrup which is 87.2% sugar. Trees are often selected on the basis of sap production since the rate of sap flow varies from tree to tree and seems to be consistent over time; both sweetness and flow rate appear to decline over the season and the amount of impurities increases. Thus the ‘early runs’ are often preferred. Incidentally, roadside and open-grown trees often have higher sweetness than trees in stands. Tapping and syrup production have also been carried out during the autumn but this is seldom done.

It is often recommended that stands of pure sugar maple are to be preferred for tapping, but whether this is based on efficiency of production or has a biological basis is not really known. Some ecological principles would suggest that a mixture of other tolerant hardwoods [and/or softwoods] helps create a stand more resilient to stress, a condition which may prove healthier in the long term.

Sugar maple preferred over other maples, but other maples have been tapped for syrup production, notably red, silver, Norway and Manitoba maples. Some people have thought that using other species for production would increase overall syrup production and might take some of the pressure off current sugarbushes. This idea was tested by the then Ontario Department of Lands and Forests [now OMNR] in the 1960’s to determine sugar concentration and compare the taste of syrup produced from other different species.

Table 2 shows the average sugar concentration over two years of fifty or more trees of five common maple species. All species had a 2% or more concentration of sugar, well within the range of commercial maple sap production. The tree to tree range was wide; sugar maple had the highest concentration in one year, Norway and Manitoba maples in the other. Some of the variation reflects site differences and street trees vs. woodlot trees.

Table 2. Average sugar concentration and range in five maple species over two years.

Species Yr. 1 Avg. Yr. 1 Range Yr. 2 Avg. Yr. 2 Range
Norway 3.3 1.9 - 5.3 2.9 1.8 - 4.9
Manitoba 3.3 2.2 - 4.8 2.1 1.0 - 6.3
Sugar 2.6 1.4 - 4.2 3.9 2.1 - 8.0
Red 2.4 1.2 - 4.4 - -
Silver 2.1 1.1 - 3.6 2.1 1.5 - 3.6

A similar comparison was done of trees on the same site [Table 3.] showed sugar maple to be the sweetest. Silver maple had the lowest sugar concentration in both years, but Norway maple was comparable to sugar maple. Ranges of sugar concentration were wide with Manitoba maple having the widest range. The sap from trees in thinned/unthinned areas varied with the highest concentration in trees in the heaviest thinned areas where the dominant crown classes occurred. Suppressed trees all had similar concentrations reflecting the usual management decision to tap the dominant and co-dominant trees.

Table 3. Comparison of sugar content of four maple species on the same site.

Species No.Trees Avg. % sugar Range % sugar
Sugar 48 3.3 2.3 - 5.1
Silver 30 1.7 1.1 - 2.6
Norway 49 3.0 1.9 - 5.5
Manitoba 50 2.1 1.0 - 6.3

A test was made of the quality of the syrup manufactures from the five species of maple plus a commercially made artificial syrup, by about fifty judges in three separate tests. Results showed that the two most popular were the syrup from Norway maple and the artificially flavoured syrup, and silver maple was rated overall to be lower than all others even though some judges rated it highest of all. However, it is possible to manufacture “agreeably tasting syrups” from all species of maple. So if you have plenty of maples, it seems that syrup can be produced from them.

Further Reading

Anon., 1967. Sap and Syrup of Five Maple Species, Ontario Dept. Lands & Forests, Research report #69, 62p.

Drummond’s Sugar Bush, CR21, Leeds-Grenville brochure 3p.

Coons, C.F., 1989. Sugar Bush Management for Maple Syrup Producers, Ministry of Natural Resources, Ontario. Queens Printer for Ontario, 48p.

Farrar, J.L., 1995. Trees in Canada, Fitzhenry & Whiteside, 502p.

D. Lachance et al, 1995. Health of Sugar Maple in Canada. Canadian Forest Service, Ottawa, Information Report S-T-X-10, 27p.