Photo by D. Sillman
(Click on the following link to listen to an audio version of this blog … Two Fall Changes
In the Fall, two big transitions occur. One of them is driven by ecological and physiological forces, and the other is something our society has made up and, for some reason, can’t quite get rid of. The Natural event is the color change in the deciduous tree leaves. The Made-Up event is time change from Daylight Savings to Standard time.
As Fall progresses and Winter approaches, the leaves for all deciduous trees are shed primarily to help the trees to withstand the incredibly cold and dry conditions of the coming season. There are very well defined stages by which this leaf loss occurs:
First, in response to the length of the dark period of the day reaching a critical length, large numbers of cells are generated at the junction of the leaf’s stem to its branch. These cells greatly increase in number but not, at first, in their individual sizes. This layer of cells (the “abscission layer”) slowly starts to interfere with the flow of sugars out of the leaf and the flow of nutrients into the leaf.
Photo by ninjatacoshell, Wikimedia Commons
Then, the lack of nutrients causes the leaf to stop synthesizing new chlorophyll molecules. Chlorophylls are, of course, the functional pigments of photosynthesis and also the pigments that give plant leaves their characteristic green colors. Initial cessation of chlorophyll production makes the leaves appear a bit paler and less intensely green than they were during the height of summer. Continued loss of the chlorophylls starts to unmask the other pigments (the “accessory” pigments of photosynthesis: the carotenoids and xanthophylls) that have been present in the leaves all summer long. As these pigments are “revealed” the leaves then “turn” orange (from the carotenoids) or yellow (from the xanthophylls) before they finally fall.
The persisting chlorophylls in the leaves continue to carry out photosynthesis. The sugars formed by this ongoing process, though, are not able to easily exit the leaf because of the abscission layer blockage. These sugars then stimulate the synthesis of anthocyanin pigments in the leaf. These pigments generate purple or bright red colors and are thought to possibly protect the leaf (and particularly next year’s delicate leaf buds) from insect damage.
Honey locust in the fall. Photo by Kevmin, Wikimedia Commons
Sunny, warm Fall days and cold Fall nights are important drivers of these leaf-pigment changes. Also, an abundance of summer rain which enabled the trees to make and maintain a healthy crop of leaves prepares a rich canopy-canvas for the color changes. Finally, energetic weather fronts with strong winds and violent rain/snow storms must hold off until winter is closer upon us or else all the leaves will be stripped off of the trees before their display is realized.
Color is just starting to show up in the trees here in Greeley. I have heard that the aspens up near Estes Park turned a glorious gold a few weeks ago and now are scattered on the ground! It was a good year for the Fall display!
Photo by P. Seveh, Wikimedia Commons
On the first Sunday of November, we will change back over to Standard Time. This “fall behind” change in our clocks does nothing to alter the total amount of daylight we get in a day but it does change our perceptions of lengths of day and night. Supposedly we get an extra hour’s sleep on that first Sunday morning after the time change, but many of us, I am sure, just got up a bit earlier on clock time than we usually do on a Sunday.
All sorts of studies have explored the impacts of the Fall and Spring time change. The Fall, with its promise of that extra hour of sleep, seems more benign than the Spring change which takes that hour away. One researcher referred to both changes as a type of “jet lag.” Sleep pattern disruptions, headaches, and mood changes were the dominant symptoms, and like jet lag the symptoms go away within a few days. The Spring change, though, has some potentially serious consequences: for several days after the “spring back” clock change there is, an increase in work-related injuries, and, possibly (although there are conflicting studies on this) an increase in morning traffic accidents. Interestingly, according to a 2012 study published in the Journal of Applied Psychology, for several days after the Spring time change office workers also increased their on-the-job “cyberloafing” Internet time. Maybe web surfing is an adaptive way to avoid accidents and injuries!
Izzy out for a walk. Photo by D. Sillman
Mornings will be just a little more sunlit after the shift back to Standard Time, and afternoons and evenings will be a little less. When our neighbors’ take their dogs for their early, morning walks at 7 am there is a bit more daylight than under Daylight Savings Time. A flashlight, though, will soon be needed when the full darkness of the late fall and early winter mornings settles in upon us.
We are racing toward the Winter Solstice (December 21 this year) when the North Pole will be tipped as far away from the sun as it goes these days. On the Winter Solstice we will have an hour less sunlight than we do today (only 9 hours and 6 minutes). Do you remember the Summer Solstice back on June 21? We had 15 hours and 3 minutes of sunlight that day.
It’s not that Standard Time or Daylight Savings Time is better or worse than the other. It’s the shifting of our time frames twice a year to accommodate the summer Daylight Savings and the Winter’s Standard Times. Anyone with a small child is really going to suffer as bedtime and waking up tines fall into disarray.
In the U. S. Congress a bill called “The Sunshine Protection Act” has been introduced each year since 2018. This bill would establish permanent daylight savings time all across the country. There would be, then, no clock changes in the Fall or Spring. This bill was passed by the Senate in 2022 by unanimous consent with no formal vote taken. The House version of the bill, however, never made it out of committee, and, so, the bill did not become law. It does not appear at this time that The Sunshine Protection Act has enough support to get through congress in 2023, so we will continue to be saddled with the twice a year clock changes.