PORTLAND, Ore. (KOIN) – Have you noticed all the colorful treetops in the last few weeks?
The beautiful reds, golden yellows, vibrant oranges — even the brown leaves are popping. Do you have a favorite tree in your yard or a must-drive route home that brings you under the canopy of some majestic leaves? It’s a spectacular time of the year and we can tip our cap to science for the understanding of the colorful process.
It all boils down to chlorophyll and the other pigments that are embedded into the makeup of that type of leaf. The grand scheme, when the daylight starts to shed as we enter our fall months, the chlorophyll starts to breakdown and allows for other pigments to come out. You can see a list of those above.
When the leaves start to turn brown and they lose those pigments, they’re being impacted by what is called “tannins,” according to the U.S. Forest Service.
Now regardless of the year, the leaves will always change colors because of the change in daylight.
However, why do some seasons feel extra special and sparkling, while some years the leaves just turn quickly and fall? Well, those subtle differences can be influenced by the weather. There are a handful of variables that will help bring out the colors, but three important factors come down to temperature, cloud coverage and wind.
We know that those characteristics will change from year to year. Sometimes we have very cool and wet fall periods, while some years may be dry, sunny and warm. This will have a large impact on how the leaves look that season, but why?
“Sugars are trapped in fall leaves, and why chlorophyll disappears in them, is due to something called the ‘abscission layer,'” according to the University of Vermont Extension Department of Plant and Soil Science. “This is a separation layer of cork-like cells that develops between branches and leaf stems in response to shorter days (in reality it’s the longer nights) and cooler temperatures. It seals off the flow of nutrients between leaf and stems, and eventually roots, which causes the chlorophyll to not be replaced. So it disappears during early to mid-fall, leaving the yellow and orange pigments to be seen, and red pigments to be produced.”
Cool Air, which is above freezing at night, in combination with a lot of daytime sunshine will favor the anthocyanins to bloom, allowing for more reds and purples.
Freezing environments will aid in destroying the leaf’s ability to push those anthocyanins to the forefront, preventing the red tones. This is why an early frost will end the colorful foliage. We had some patchy areas this fall, which may have created a few areas of lackluster color.
Drought during the growing season can cause the abscission layer to form early and cause the leaves to drop before they change color.
Heavy wind or rain can really stunt the beautiful fall foliage just by coming in and causing the leaves to fall before they fully develop color.
Now taking all of those factors into consideration, we can process the weather that we have seen so far this month and analyze what may have helped with bringing out some of the colors this fall. We will start with the wind, of recent, we have had some windy days. A few times we had some wind gusting to the 20 mph range, but overall, sustained wind speed this month has been about 6 mph over 20 days, with three days over 10 mph. That light wind during primetime leaf changing has helped keep those leaves intact.
How about the cool temperatures overnight? Well, that has definitely occurred this month and also towards the end of September if we look a little further back. With our average overnight temperature at about 43 degrees, but we had seven nights at 40 degrees or below. Typically for the month of October, we usually sit around 46 degrees for our low temperature. That cool overnight air may have helped support the colorful reds this fall.
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