Monday, September 23rd - Marks the First Day of AUTUMN!

Submitted by George Garnett, Apache-Sitgreaves National Forests

Fall Aspen leaves

(photo credit: G. Garnett, USFS)


September 23, 2019 - Marks the first day of Autumn!

It’s happening now. Suddenly the pallet of nature is rapidly changing on and near the Apache - Sitgreaves National Forests.

Autumn marks the transition from summer to winter. For those of us who live in the Northern Hemisphere, the Autumn Equinox is the period when daylight becomes noticeably shorter and the temperature begins to cools down considerably. One of the most notable features is the shedding of leaves from deciduous trees. Traditionally, autumn lasts from September 21 to December 21. 

For a brief period, residents and visitors will experience the vivid display of autumn color that occurs before winter takes over. Prompted by shorter days and dropping temperatures, the green leaves of spring and summer transform into a vivid palette of radiant golds, autumn reds, oranges and browns before falling from the trees. 

Factors like direct sunlight cause leaves to change and fall more quickly. Another autumn beauty are aspens and oaks. Oak brush or Scrub Oak are common in the National Forest.

Oak leaves may remain on the branches until growth starts again in the spring. Environmental factors affect when the oak shed their leaves, but leaf drop occurs primarily in autumn or spring, depending on species.

Aspen trees grow all over the world, in parts of North America, Europe, Asia, and Africa. The common American variety of aspen tree, Populus tremuloides, generally grows in high-altitude areas above 5,000 feet but also exists at sea level where climate conditions are ideal. Much of the Apache-Sitgreaves National Forests is at a higher altitude so, chances are you may see some brightly colored Aspen leaves this fall (see photo).

Although rarer, the Apache - Sitgreaves National Forests is also home to mountain maple, which are tall shrubs that turn brilliant orange and red in the fall.

So, why do leaves change colors? During spring and summer, leaves serve as factories, manufacturing most of the foods necessary for a tree’s growth. This takes place in the leaf cells that contain chlorophyll, which gives the leaf its green color. But leaves also contain orange, and yellow pigments masked much of the year by green chlorophyll. Autumn’s shorter days and cooler nights stop the leave’s food manufacturing process. Chlorophyll breaks down, exposing other pigments including yellow, red, and orange, which you see in oak and maple leaves.

In addition, colors on the same tree can vary from year to year, depending upon the weather conditions. When autumns are warm and rainy, leaves are less colorful. When leaves fall to the ground and decay, they help fertilize soil, returning some of the elements borrowed by the growing tree.

So get out there and enjoy the autumn colors because, soon you will be looking for your hats and gloves, and getting ready for winter.