There are approximately 150 species of maple trees located within the Northern Hemisphere, with 10 of them native to North America (NRCAN-2015). One of the most commonly grown species of maple is the Sugar Maple (Acer saccharum). Sugar maple is a keystone species, meaning it is a significant ecological element of Northern hardwood forests, like those we can find in the Saint-Lawrence lowlands. As its leaf is represented on our Canadian flag, it is widely exploited due to its maple syrup production as well as its wood quality (Houston, 1999). Its wood is described as hard and durable material which is suitable for manufacturing furnitures, paneling and flooring (Tirmenstein, 1991). However, a decline in sugar maple growth has been observed since the early 1970’s due to its heavy industrialization (Bishop et al., 2015).
Sugar maple trees can live up to approximately 200 years and grow up to 35 m high and measure up to 90 cm in diameter (NRCAN-2015). Sugar maples have simple leaves (single), in opposite arrangement on the twigs. They are usually five-lobed but leaves with three or four lobes are also possible. Leaves are of a dark yellowish-green colour on the adaxial surface and a lighter green on the abaxial surface of the leaf. They are generally smooth on both surfaces. The margins in between the lobes are shallow and smooth, which distinguishes them from the leaves of the similar-looking red maple (Acer rubrum), which has much more serrated and sharp lobe margins. Additionally, lobes on the sugar maple have a “U-shaped” connection whereas the lobes on the red maple have a “V-shaped” connection (Luzadis,Gossett-1996). The sap of the sugar maple is transparent as opposed to the white sap of the invasive Norway maple, thus making it easier to differentiate the two. Trunks are straight and often branch-free for two-thirds or more of their height. The crown is narrow, round-topped, and the roots go deep and spread wide. The tree produce paired samara fruits with wings 30–35 mm in length (NRCAN-2015).
Figure 1: On the left we see a comparison between a Norway maple leaf (left) and a sugar maple leaf (right). The discolouration of the sugar maple is due to fall conditions. The norway maple stays dark green throughout fall since it is not native to Canada and hence it is not adapted to seasonal changes. On the right is sugar maple bark.
The bark on young trees is smooth and dark grey. As it grows, it develops long, vertical, firm, irregular ridges curling outward along one side, somewhat scaly and can turn into a dark brown color.
Sugar maples are typically found in temperate regions and are a climax species (Fleming, 1995) exclusive to the Northern American Continent, facing temperatures that range from -40°C to 37°C (Luzadis & Gossett, 1996). Sugar maples can be found in elevations ranging between 914 m and 1676 m in warmer regions (Luzadis & Gossett, 1996). Acer Saccharum grows in a wide variety of plant communities throughout Eastern North America; amongst mixed and or pure tree stands where they most commonly flourish alongside white ash, black cherry, basswood, ironwood, beech, white pine, red oak and yellow birch (Fleming, 1995).
Sugar maples require moist soils with good drainage; they do not thrive in shallow waters and dry soils. Acer Saccharum needs a soil that allows for deep root growth and can be found on either acidic (pH 3.7) and or neutral (pH 7.3) soils; the prefered pH is between 5.5 to 7.3. The Sugar Maple participates in nutrient recharge of the soil by shedding its leaves periodically which furthermore decays into organic matter (Luzadis & Gossett, 1996).
Figure 4: Panoramic view of a pure sugar maple stand.
“How does the density and basal area coverage of overstorey sugar maple trees affect the growth and abundance of understorey trees?”
The study is taking place at the Morgan Arboretum, which is located near the Macdonald Campus situated in the St. Lawrence Lowlands. The arboretum contains 245 hectares of forested land inhabited by wildlife including plants, insects, rodents, amphibians and large mammals (Morgan Arboretum, 2014).
Understorey and overstorey vegetative surveys focusing on sugar maples, but also including other trees species, are being conducted. We set up four plots measuring 50m by 50m within the arboretum, two of which are within a pure sugar maple tree stand while two others are in a mixedwood stand near the yellow trail indicated in Figure 4. Four square plots measuring 10 m x 10m were randomly placed within the 50m x 50m plots.
Figure 3: A 50m by 50m plot which contains four randomly placed 10m by 10m plots and three circular subplots randomly set up within the 10m x 10m plot to measure understorey tree species.
Within the 10m x 10m plots, we counted and measured all of the overstorey trees with a diameter breast height (DBH) of 10 cm and higher. Using the data collected, the relative dominance, the relative density and the basal area of sugar maples will be calculated.
Three circular subplots with a radius of 2 m were randomly placed within the smaller 10m x 10m square plots. The studied species of trees with a DBH of less than 10 cm within the subplots were recorded and placed in three categories. Class A consists of trees with a height below 0.5 m, class B includes trees between 0.5 and 1.5, Class C includes understorey above 1.5 m. The data from the understorey survey will be used to calculate the frequency and the relative density of the sugar maple tree species.
Figure 4: Location of the 50m by 50m plots within the Morgan Arboretum.
Here is a video that summarizes the methods.
According to our observations and data collection so far, we noticed that in the mixedwood tree stands, the plots tend to be more densely populated with understorey sugar maple trees, other woody plants and shrubs. Meanwhile, in the pure sugar maple stands, the trees tend to be more evenly distributed with little to no understorey trees. We hypothesized that intraspecific competition seems stronger in pure sugar maple stands than in mixed tree stands. Overstorey trees seem to outcompete understorey trees by taking a significant amount of basal area to develop. This hypothesis is in accordance with recent studies which have found that sugar maple trees are under higher competitive pressures in pure stands over mixed tree stands (Martin-Ducup et al. 2016). Similarly, another study suggests that competition is more fierce among conspecifics and that radial growth of sugar maples is affected by the distance between conspecifics (Henrick et al., 2009). When the distance between two sugar maples was smaller, the competitive pressures were higher thus supporting our idea that sugar maple growth is favored when conspecifics are at an optimal distance from each other which allows for more basal area to be covered.
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Hartmann, H., Beaudel, M., Mazerille, M.J., Messier, C. “Sugar maple (Acer saccharum Marsh.) growth is influenced by close conspecifics and skid trail proximity following selection harvest.” Forest Ecology and Management. Vol. 258.5. 20 August 2009, pp. 823-831. Web. October 25, 2016.
Houston, David R. “History of Sugar Maple Decline.” Sugar Maple Ecology and Health: Proceedings of an International Symposium, 1999. pp. 19-26. Web. October 27, 2016. <http://www.treesearch.fs.fed.us/pubs/13134 >.
Luzadis, V.A. and Gossett, E.R. . “Sugar Maple.” Forest Trees of the Northeast. Cooperative Extension Bulletin 235. Cornell Media Services. 1996. pp. 157-166. Web. October 2, 2016. <http://dx.doi.org.proxy3.library.mcgill.ca/10.1016/j.foreco.2009.05.028>.
Martin-Ducup, Olivier, Robert Schneider & Richard A. Fournier. “Response of sugar maple (Acer saccharum, Marsh.) tree crown structure to competition in pure versus mixed stands.” Forest Ecology and Management, vol. 374, August 15, 2016, pp. 20-32. Web. PDF. October 27, 2016 <http://ac.els-cdn.com/S0378112716302213/1-s2.0-S0378112716302213-main.pdf?_tid=079b45de-9c78-11e6-9855-00000aacb362&acdnat=1477595182_c74bd4060a8506606669a0027f828da0>.
Morgan Arboretum. “Welcome to the Arboretum”. October 30, 2014. Web. October 25, 2016. <http://morganarboretum.org/>.
Natural Resource Canada. Sugar Maple Factsheet, 2015. Web. October 28, 2016.<https://tidcf.nrcan.gc.ca/en/trees/factsheet/86>.
Sir Sanford Fleming College. “Sugar Maple.” Sir Sanford Fleming College, 1995. Web. September 28, 2016. <http://www.lrconline.com/Extension_Notes_English/pdf/sgr_mpl.pdf>.
Tirmenstein, D.A. “Acer saccharum.” The Fire Effects Information System. USDA, Forest Service, Intermountain Research Station, Intermountain Fire Sciences Laboratory, Missoula, Montana, 1991. Web. October 24, 2016. <http://www.fs.fed.us/database/feis/plants/tree/acesac/>.