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Does location within the forest affect leaf colour change in Sugar Maple (Acer saccharum)?

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Acer saccharum, commonly known as the Sugar Maple, is a deciduous tree native to North America. Its genus ‘’acer’’ is latin for maple, and its species name ‘’saccharum’’ comes from the Greek word “sakcaron” meaning ‘’sweet juice distilled from bamboo’’ or simply ‘’sugar’’. (Acer saccharum 2013). This tree is probably most well known because its leaf appears on our national flag (The life of sugar maple 2013).

Sugar maples can grow up to about 25-35 meters in height . Their lifespan can be anywhere from 200 to 400 years , which is very impressive by our standards. The leaves are simple opposite, and can grow from 7 to 20 cm long.They are composed of 5 lobes that are separated by U-shape sinus, meaning the dips between the tips are rounded, not pointed. The leaves are a yellow-green to green colour during the summer and in fall, they can turn yellow, orange or red . The twigs are reddish-brown colour and have small openings on the surface of the bark . The monoecious flowers are greenish to yellowish and form in clusters on long stalks. The bark of the tree is light to dark gray. When the tree is young, the bark is smooth but with age it becomes scaly. The tree produces a fruit called samara that is about 30-35 mm long (Ontario 2013, The life of sugar maple 2013,Maple Sugar 2013,Sugar Maple 2013, Acer saccharum 2013,Arboreal Emblem 2013).

The tree is common in the Northeastern North America. It can be found in most Canadian provinces and in Northern States of the United States (Ontario 2013,The life of a Sugar Maple tree 2013). This tree prefers to live in moist, rich soil with plenty of sunlight although it can tolerate shade (Ontario 2013,The life of sugar maple 2013,Maple Sugar 2013, Acer saccharum 2013).

There are 10 other species of maple tree in Canada (Arboreal Emblem 2013), however the most economically important is the sugar maple for two reasons: maple syrup and timber. Maple syrup has been discovered a long time ago by the Native Americans and is now used widely in the food industry as a sugar source. The sugar maple is important for timber because it is strong, hard, and durable wood for making furniture, floors, paneling, etc (Acer saccharum 2013).

Sugar maple is an important component of an ecosystem. Animals such as white-tailed deer, moose, snowshoe hare, red squirrel, gray squirrel and flying squirrel feed on seeds, buds, twigs and leaves of this tree. Birds are known to nest in them as well (Acer saccharum 2013).

Why study this species?
As we can see, this species is economically and ecologically vital to us here in Quebec. Studying this species and learning more about it will allow us to better protect it. This is the reason why our team decided to study this species. Few studies have been made to explain the variations in leaf coloration. Lee & al. 2003 conducted a study to evaluate the dynamics of different pigments in the leaf, while Taylor & al. 2007 and Norby & al. 2000 talks about the effect of carbon dioxide and nitrogen on leaf senescence.

Photo credit: Julie Hamel

Photo credit: Julie Hamel

Description of our project
The objective of our research project is to track the change in the colour of the leaves in Sugar Maples (Acer saccarum). Our collected data includes the GPS coordinates of each tree, for identifying them week to week; the diameter of each tree, for a rough estimation of the age of the tree and an estimation of the percentages of the leaf colour. The way we make our estimations is by standing at the base of a tree, looking at the assemblage of leaves and cooperatively agreeing on their colour proportions i.e. 40% green, 50% yellow, 10% brown. We understand that this is not the most objective way of judging the colour but since many of them are continually falling and there can be hundreds to count it makes sense to take a estimate. The fact that we are 4 headstrong youths means that we have active debate over the proportions of the colours and always come to a consensus. The coordinates are taken with a digital GPS device and recorded in order to not mix up trees since the forest is not planted in uniform rows. The diameter is determined by simply measuring the circumference with a measuring tape and using the rule D=C/2pi where D=diameter and C=circumference. We used the transect method to chose which trees we would track. This means all the trees form 2 rough lines parallel to the edge of the forest, one about 10 metres from the nearest clearing and another 45 metres deeper into the forest. We have 2 sets of these 2 rows in different parts of the Morgan Arboretum meaning the total number of rows of trees in 4 and all 4 rows are about 100 metres in length.

Photo credit : Aurore Hernandez

Photo credit : Aurore Hernandez

We want to compare data from trees located on the edge of the forest with trees that are deeper inside the forest because the light exposure is different. The trees growing on the edge of the forest probably receive a higher amount of light than the trees growing inside the forest, which, as is usually the case, only have an upper layer of leaves exposed to sunlight. Since the recession of chlorophyll tends to be accelerated by environmental conditions such as bright sunlight and shorter day length (Coder 2008), our main goal is to observe the rate at which leaves from the edge/interior of the forest lose their green chlorophyll pigments. We will do so by making graphs comparing data from four different locations of the Morgan Arboretum collected on a weekly basis during a three week study period. Also, the same environmental factors that stimulate the loss of chlorophyll in leaves are known to increase the amount of carotenoids and generate the production of anthocyanins. (Coder 2008) Carotenoids are pigments distinguishable by their yellow and orange color and become noticeable when the chlorophyll starts to decrease. They give leaves a yellowish-green color. Anthocyanins are pigments that are generated due to environmental changes during Fall and are responsible for the red color in autumnal leaves.

Of course the rate of the chlorophyll breakdown in deciduous tree leaves is induced by several other changes in the environment such as moisture and the drop in temperature (Archetti & al 2013). We assume, under our research, that these factors affect all the sugar maples equally since they are all in close proximity to each other. It is also important to know that anthocyanins can be produced in the sugar maple leaves under various conditions where the leaves are weakened such as in the cases of deficiencies, wounding, pathogenic infections and ozone exposure. (Schaberg et al. 2008) A leaf’s quantity of red pigments depends on many factors other than the light exposition which is why we will focus on the withdrawal of the green color instead of on the apparition of the various, photogenic colors that the fall season is so well known for.

Websites:

(1) Ontario, Ministry of Natural Resources [Internet]. 2013. Ontario: Ministry of Natural Resources. [July 16th 2013; October 27th 2013]. Available from: http://www.mnr.gov.on.ca/en/Business/ClimateChange/2ColumnSubPage/267334.html

(2) The life of a Sugar Maple tree [Internet]. 2013. United States: Cornell University; [October 27th 2013]. Avaible from: http://maple.dnr.cornell.edu/pubs/trees.htm

(3) Sugar Maple [Internet]. 2013. United States : Cornell University; [October 27th 2013]. Available from: http://maple.dnr.cornell.edu/kids/tree_sug.htm

(4) Arboreal emblems [Internet]. 2013. Canada: Canadian Forestry Association; [October 27th 2013]. Available from: http://www.canadianforestry.com/html/forest/arboreal_emblems_e.html

(5) Maple Sugar [Internet]. 2013. United States: Arbor Day Foundation; [October 27th 2013]. Available from: http://www2.arborday.org/treeguide/treeDetail.cfm?ID=14

(6) Acer saccharum [Internet]. 2013. United States: Rook; [March 4th 2006, October 27th 2013]. Available from: http://www.rook.org/earl/bwca/nature/trees/acersac.html

Scientific articles:

(1)  Coder KD. 2008. Autumn Leaf Colors. Warnell School of Forestry and Natural Ressources. 1-7.

(2) Schaberg PG, Murakami EPF, Turner EMR, Heitz HK, Hawley EGJ. 2008. Association of red coloration with senescence of sugar maple leaves in autumn. NRS.1-6.

(3)  Archetti M, Richardson AD, O’Keefe J, Delpierre N. 2013. Predicting Climate Change Impacts on the Amount and Duration of Autumn Colors in New England Forest.PLOS ONE. 8(3): 1-8.

(4)  Norby R, Long TM, Hartz-Rubin JS, O’Neilli EG. 2000. Nitrogen resorption in senescing tree leaves in a warmer, CO2-enriched atmosephere. Plant and Soil. 224:15-29.

(5)  Taylor G, Tallis MJ, Giardina CP, Percy KE, Miglietta F, Gupta P, Gioli B, Calfapietra C, Kubiske M, Scarasciamugnozza GE, Kets K, Long SP, Karnosky. 2007. Future atmospheric CO2 leads to delayed autumnal senescence. Global Change Biology. 14:1-12.

(6)  Lee DW, O’Keefe J, Holbrook M, Feild TS. 2003. Pigment dynamics and autumn leaf senescence in a New England deciduous forest, eastern USA. Ecological Research. 18:677-694.

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About Crystal Ernst

Hakai Institute postdoctoral scholar at Simon Fraser University (B.C.)

4 comments on “Does location within the forest affect leaf colour change in Sugar Maple (Acer saccharum)?

  1. Good post! I wonder how latitude fits into thinking about leaf colour change – is any latitudinal gradients in colour change simply related to the same latitudinal changes related to light / temperature gradients? Could there be other large-scale geographic influences on leaf colour change?

    • Interesting! I wonder about even smaller scale variations like available nutrients in the soil, or tree health in general. Are all the trees in your study perfectly healthy? do some have cavities, rot, structural anomalies? These might vary the amount of nutrients reaching the leaves.
      It might also be interesting to think about your view of the leaves. Depending on how you look at them, with regards to the suns rays, you might see different shades of color. Also, you are looking from under the tree – what’s the color variation from the top (sky view)?

      • The soil nutrients definitely play a role in the timing of leaf colour change. According to a study, if there is a deficiency in Nitrogen concentration, the leaves will start to change earlier however temperature and light exposure remain the most influential factors. http://www.fs.fed.us/ne/newtown_square/publications/other_publishers/OCR/ne_2003schaberg01.pdf

        The effects of sun rays on our perception of colour became evident upon our second week of data collection. Week 1 was overcast and week 2 was bright and sunny. We did our best to look at the leaves that were in relatively shaded areas of the canopy so as to eliminate the brightening effects of the sun. It should also be noted that often times, a tree can have clusters of red/yellow leaves in areas with more sun exposure, because they are the first leaves to sense the change in diurnal light. If those leaves are at the top of the canopy, it can be hard to see them, which is why we took extra care to look around as many angles as possible so as not to miss this highly relevant piece of data.

    • There would most likely be variation in large scale geographical distances because the further north you go (in the Northern Hemisphere) the shorter the day length and the lower the incident angle of the sun, meaning there is overall less sunlight and winter arrives sooner. If the winter season arrives earlier in some regions, it would make sense for the trees in those regions to draw in their chlorophyll sooner rather than leave their leaves exposed to the cold. Our study area was far too small to observe these regional differences but when I was in the Adirondacks a few weeks ago, I noticed that the higher I hiked, the less leaves there were left on the trees because it was much colder at the summit. So not only is there a latitudinal variation, but an altitudinal one as well.

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