It’s a brisk November day, the sky scattered with wispy cirrus clouds, and it’s a comfortable 10ºC Celsius. A collection of maple trees line Seven Lakes Drive in Bear Mountain State Park in New York, 45 minutes from campus. Gusts of wind swirl the beautiful orange and red leaves across the road and into the wooded areas where hikers take in nature’s beauty during the fall season.
Honey Maple Trees, also known as Acer Saccharin, do not always have these beautiful scarlet and mustard-yellow hues. In the spring and summer, the chlorophyll makes the leaves a vibrant green. In autumn, the daylight lessens, which means there is less solar energy for the chlorophyll in the leaves to absorb and convert into glucose and oxygen. Then the chlorophyll in the leaves break down, causing the green pigment to disappear and bringing other bright colors to the surface. Carotenoids are pigments associated with yellows and oranges, and anthocyanins are red, pink, and purple colors humans adore in the fall months.
Carotenoids are used to help chlorophyll absorb light and protect it from solar radiation damage. They also act as antioxidants to help protect energy-producing structures in plant cells. The most common carotenoids found in leaves are lutein and beta-carotene.
As for the radiant reds that scatter the mountainsides, anthocyanin accumulation is responsible for those deep reds and violets. However, they are not present in all deciduous tree species. Anthocyanins reduce the frequency and severity of photoinhibition and catalyze a photosynthetic recovery. Photoinhibition is a reduction in the photosynthetic activity of a plant. This is especially important in the autumn season because it protects the degrading chlorophyll from damaging light levels that could inhibit the resorptive process of chloroplast in the branches. The anthocyanin acts as a sunscreen for Maples, Sweetgums, Winged Sumac, and many others. This is why the leaves of maples, oaks, aspens, and all deciduous trees change color before they float to the forest floor: to reabsorb as much chloroplast and chlorophyll into the branches as possible for regeneration in the spring. The yellow, orange, and brown leaves also break from their owner’s branches to reduce water loss. The large surface area of the leaves allows for evaporation which takes away from the tree’s water retention.
When the mountainside becomes bare and the forest floors are coated with browned leaves, in the famous words of John Snow from Game of Thrones, “Winter is coming.” Deciduous trees like the Sugar Maple live up to 300 to 400 years. How do they survive winters? In freezing temperatures, tree bark provides insulation and protection against freezing and cracking. In the months leading up to the frigid temperatures of winter, temperate deciduous trees undergo dormancy induction which initiates and strengthens a tree’s cold acclimation. The diminishing hours of daylight and temperature drops cause active tissues to gradually enter a dormant state called endodormancy. On the cellular level, the tree tissue reaches maximum cold hardiness by mid-winter and exhibit freezing resistance ranging from -15 to -25°C and -30 to -50°C in twigs and stems.
Coniferous trees, trees with needles and pinecones, are hardier than deciduous trees because their needles prevent snow from accumulating and weighing them down, which can lead to branch breakage. Additionally, the small surface area of needles and their waxy coating called cutin further prevents water loss and freezing.
As the snow begins to melt and the temperature begins to warm, the Sugar Maple begins to bud. Sugar Maples can bud anywhere from March to mid-May. They only begin to flower after they are 20 years old. The older the Sugar Maple, the more flowers it will grow. During the spring months, the greenish-yellow flowers begin to bloom and are about one to three inches long. Once the flowers bloom, its fruit, the samara, begins to form, which carries one green seed that is less than half an inch long. After 16 long weeks, the samaras will bloom only to fall to the ground with their leaf companions two weeks later.
As the samaras travel from tree to ground, it is only a matter of time before the leaves turn shades of red and orange once again. Nature is hard at work during all seasons despite what is visible to the human eye.
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