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Naturalist Notes

November 18, 2018

The Best Season: Fall or Autumn?

 

As a mid-autumn morning dawns in the season most of us call fall, leaves and stems are often found on the ground rimed with frost, indicating winter is next upon us. The wind gathers strength trying valiantly to strip the fiery colors of autumn's leaves from their trees. Most of us call this time of year “fall” because leaves are drying out and fading to brown and yellow. When the winds come up, those leaves seem to fall off, thus justifying the name. But let's not dwell on the fate of leaves just yet, because those blustery winds also indicate the end of hurricane season.

 

As ocean water warms to 80 degrees in the tropics, warm, moist air evaporates from the surface. The warm air rises, cools, and condenses, releasing energy that drives the creation of thunderstorms. Our spinning earth causes storms to rotate counterclockwise. This “Coriolis effect” is fueled by continued heat and moisture which drives the rotating system into ever higher wind gusts. When these winds reach 74 mph, we have ourselves a hurricane, which is driven toward New England by our prevailing west winds. Most storms of this type reach land on south-facing coasts, thus leaving the Gulf of Maine to endure mostly heavy winds and soaking rains.[1] We have had devastating storms during the past, and the future is worrisome due to flooding and storm surge in a climate of increasing sea level.

 

We all know and observe the migrations of shore birds, song birds, raptors, and our favorite butterfly, the monarch. Unseen by us, the iconic fish species of the Gulf of Maine, the Atlantic cod, is quite active in this season as well. Spawning begins in the autumn season and, once the eggs hatch, larva float near the surface of inshore waters for several months where they are subject to predation. At one- to two-inches long, they settle to the bottom where they quickly develop into omnivorous predators in the nutrient rich colder waters of the Gulf of Maine. Like lobster and haddock, cod require the deeper, colder waters and steadily move north and east as the ocean warms. Author George Rose, in Cod: The Ecological History of the North Atlantic's Fisheries, describes the habitat of the Gulf of Maine and the Grand Banks: “these ecosystems produced an abundance of life the likes of which the world has seldom seen.”[2]

 

Back on land, the changing leaves are reflecting other colors as the dominant chlorophyll fades with the shorter amount of light available for food-making by photosynthesis. Maine author Berndt Heinrich described leaves as “solar cells”[3] because they make energy from sunlight. However, as they stop producing food, the unneeded chlorophyll begins to break down, revealing the red, orange, yellow, and gold which stipple our landscape with splashes of color as they "fall.” But do leaves really fall, thus giving us the common name for this season? Trees are actually much more proactive than that. As falling temperatures and reduced light decrease food production, trees send a chemical message to the leaves that indicates their job is done. The leaf creates a layer of cells where the stem meets the branch called the abscission layer. This layer has the same root as the word scissors, meaning they are designed to make a cut. After a week or two, this layer of cells is pushing each stem away from the branch, leaving the leaf dangling until a breeze comes along to finish the job.[4]

 

So the truth is: it is the tree, not the wind, that is making the leaves fall. This adaptation prevents the tree from freezing during the winter, as fluid would be flowing during food production if a warm snap occurred. Then, when freezing temperatures returned, the tree could be damaged by freezing and cracking. That is why deciduous trees in most parts of North America drop their leaves in the fall and grow new ones in the spring. It’s safer that way!

 

John Halloran

GOMI Naturalist

________________

1. Schmitt, Catherine, A Coastal Companion: A Year in the Gulf of Maine, 2008, Tilbury House, Gardner ME

 

2. Rose, George A, Cod: The Ecological History of the North Atlantic Fisheries, 2007, in Thurston, Harry, The Atlantic Coast: ANatural History, 2011, Greystone Books, Vancouver

 

3. Heinrich, Berndt, Mind of the Raven, 1999, Cliff Street Books, New York

 

4. Chamberland, Tom, Yardworks: Caring for What Grows in Your Yard

 

  1. John Halloran is the Director of Science for GOMI and a member of the GOMI Guide Team. John’s interests focus on the ocean environment where he pursues educational adventure travel, research, and recreation by sail, paddle, and scuba.John is the founder and director of Adventure Learning, Newburyport, MA, which has been involved with educational outreach in area schools and recreational programs for teens and adults since 1980. A long-time educator, John was at the forefront of the experiential education

movement in the U.S. for 36 years, he taught natural science in the Newburyport Public Schools.

 

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