Autumn Leaves: Why Do They Change Color During Fall?

The foliage of fall is full of vibrant colors of orange, red, and yellow. But why exactly do leaves change color during this season? How do they know that this is the time for them to change?

Tree Leaves

Across boreal and temperate forests, shrubs and trees that drop leaves are known to be deciduous plants. These include cottonwoods, aspens, oaks, and maples. At the other side of the spectrum are those plants that do not shed leaves, such as spruces, pines, cedars, and conifer-making firs.

During winter, the energy produced by both trees is less. However, conifers are capable of adaptations that allow them to maintain their needles throughout the year.

Trees Adjust to the Environment

Supervisory forester Adam Moore from the Colorado State Forest Service notes that all kinds of trees are capable of picking up environmental cues that tell them when they should start bracing themselves for winter.

During early fall, the weather starts changing. It turns cooler and daylight duration also gets shortened. As a whole, the amount of harvestable sunlight for plants is lesser. Hence, deciduous trees start pulling back in order to stay alive.

Moore explains that like factories, trees like being efficient. They produce energy for themselves and oxygens for humans. Without sunlight, trees start to close up. When the first freezes start hitting, trees are already on the way to become dormant.

The Color of Autumn Leaves

When it comes to harvesting light, chlorophyll is the most common pigment. Green leaves have their look before chlorophyll takes in blue and red light while it reflects green light.

However, plants are also filled with secondary pigments. As the chlorophyll within the leaves of trees start waning, these secondary pigments become more visible. According to arboriculturist Kristina Bezanson, this is what is observed during the peak of fall.

Purple and red tones surface from secondary pigments known as anthocyanins, while xanthophylls and carotenoids yield yellow and orange tones.

In a single group, like maples, various species have evolved with their own unique pigments. For instance, red maples have a great scarlet color during fall, while black maples turn yellow.

Aside from offering beauty to trees, these pigments also play a vital role. Having various pigments that can aim at various light wavelengths enables plants to get more energy during the process of photosynthesis. However, not all trees follow this strategy as it could be expensive to have so many pigments invested in. Nevertheless, the trees that tend to do so are considered fast growers.

Genetics is also known to play a role in the timing of the color changes. One experiment found that several thousands of genes had different expressions during the period of color-changing. Scientists have also observed that same species members that dwell at similar latitudes will simultaneously change colors irrespective of their elevations.

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