Fall Colors
In my post last year in October, I wrote about the time of the year that our trees put on a spectacular show. It starts in October and lasts until the leaves fall. The colors are unbelievable I explained the science behind it, e.g.- the leaves are green because of the presence of a pigment known as chlorophyll. It is the engine that feeds the plants as they grow in the Spring and Summer. The chlorophyll’s green color dominates and masks out the colors of any other pigments that may be present in the leaf.
The chlorophyll has the vital function of capturing solar rays, utilizing the resulting energy in the manufacture of the plant’s food, turning carbon dioxide from the air and water from the ground, into simple sugars, and exhaling the resulting oxygen so vital to animal life. During the growing season, the plant replenishes the chlorophyll so that the leaves stay green. The green pigment is broken down by the sun’s rays and the resulting energy is used to create the plant’s food.
The chlorophyll has the vital function of capturing solar rays, utilizing the resulting energy in the manufacture of the plant’s food, turning carbon dioxide from the air and water from the ground, into simple sugars, and exhaling the resulting oxygen so vital to animal life. During the growing season, the plant replenishes the chlorophyll so that the leaves stay green. The green pigment is broken down by the sun’s rays and the resulting energy is used to create the plant’s food.
Maple tree in its traditional color In late summer, as daylight hours shorten and the temperatures cool, the veins that carry fluids into and out of the leaf are gradually closed off by a new layer of special cork cells. During this time, the chlorophyll begins to decrease and the hidden pigments of Yellow and Orange are revealed. Red and Purple pigments are synthesized once half of the chlorophyll has been degraded, although why they are formed is not well understood. ( You can read more details of what else is happening in the tree in our October 2015 posting!)
So, what has happened this year? Well, locally we had a very long and very hot summer with very little rain. Of course, this has had an impact on our trees. If I look at my maple tree next to the house, I do not see an abundance of brilliant golden leaves, but only a few leaves are left, and they are yellowish and kind of shriveled. The maple tree that last year made the deep red statement next to the driveway, has lost all its leaves already. So why has our ‘leaf peeping’ season been so short and muted this year, compared to the vibrant drama of last year?
So, what has happened this year? Well, locally we had a very long and very hot summer with very little rain. Of course, this has had an impact on our trees. If I look at my maple tree next to the house, I do not see an abundance of brilliant golden leaves, but only a few leaves are left, and they are yellowish and kind of shriveled. The maple tree that last year made the deep red statement next to the driveway, has lost all its leaves already. So why has our ‘leaf peeping’ season been so short and muted this year, compared to the vibrant drama of last year?
Maple tree this year with shriveled leaves Well, temperature, sunlight, and soil moisture can greatly alter the quality of the fall foliage display. Drought is stressful for trees and lack of moisture can reduce chlorophyll production. An average sized mature tree may need up to 150 gallons of water per day. That is almost three 42 gallon oil barrels or around seven 20 gallon standard bathtubs of water! Drought can sometimes trigger the early formation of the layer of cork cells (abscission layer) we referred to in our October 2015 blog post . This layer forms naturally each Fall to block the the transport of nutrients and water in the veins of the tree, so leaves may drop before they have a chance to completely develop fall pigments. The drying out of this cork layer loosens the tree’s grip on the leaves, so heavy winds or late season rains may knock the leaves down earlier as well.
Cooler nighttime temperatures and abundant sunlight, promote the formation of the Red and Purple pigments (anthocyanins). It is not well understood yet why trees expend the energy and carbohydrates needed to create these pigments- after all, the investment is lost to the tree when the leaves are lost shortly afterwards. Some theories suggest that the brilliant hues are a defense mechanism (like so many other displays in nature) warning off egg laying harmful insects, loudly proclaiming that they are robust and healthy. (Perhaps we’ll discuss this in a future post). In any event, freezing conditions destroy the machinery responsible for manufacturing anthocyanins. An early frost may very well spell an early end to colorful foliage.
So what conditions are the best for planning your annual Fall photography and joy rides? Well that will depend on what your local conditions and location on the planet will be. An optimal Fall foliage season will have had a growing season with ample moisture, followed by a rather dry, cool and sunny Autumn. Warm days and cool frostless nights will tweak the trees’ machinery to provide the most brilliant displays. The complex recipe for this will be conjured by what nature has provided during the preceding seasons.
So if you like to plan a ‘leaf peeping’ excursion every year for the sheer joy of seeing mother nature at work, mark your calendar this year on the date that the colors begin to change! Remember, it is not the swirl of the environmental factors of temperature and moisture that begin the show. Rather it is the length of daylight in each area (latitude), that triggers the plants to start their displays, so your area should start pretty much at the same time each year.. How good a show it will be, will be determined by the wind, the rain, and the chill of the nights during the preceding year.
So if you like to plan a ‘leaf peeping’ excursion every year for the sheer joy of seeing mother nature at work, mark your calendar this year on the date that the colors begin to change! Remember, it is not the swirl of the environmental factors of temperature and moisture that begin the show. Rather it is the length of daylight in each area (latitude), that triggers the plants to start their displays, so your area should start pretty much at the same time each year.. How good a show it will be, will be determined by the wind, the rain, and the chill of the nights during the preceding year.
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