Why do the leaves change colour?
Each fall, we see the summery green trees turn into brilliant shades of yellow, orange, red, and even deep purple. It can be stunning to witness, but why does it happen, and what determines the colour the leaves will change to? How do the trees know when it’s time to shed their leaves?
The main reason for these changes is shorter days and cooler temperatures, but other factors also affect the fall foliage. Everything you wanted to know about why the leaves change colour is below!
Shorter Days
As summer comes to a close and fall begins, the days grow shorter, and there is less sunlight. Trees are sensitive to this change and use it as a signal to prepare for winter, prompting a series of physiological processes.
Cooler Temperatures
As temperatures drop, chemical reactions within the leaves are affected. These lower temperatures, especially at night, act as a cue to start the process of senescence, the gradual aging and deterioration of the leaves.
Chlorophyll Breakdown
Chlorophyll is the green pigment in leaves that plays a main role in photosynthesis, the process by which trees convert sunlight into energy. As the days shorten and temperatures drop, trees receive less direct sunlight, and the chlorophyll in the leaves begins to break down, revealing other pigments.
Leaf Pigment
In addition to chlorophyll, leaves contain other pigments, such as carotenoids and anthocyanins.
Carotenoids
Produce yellow and orange colours and are always present in leaves. They are usually masked by the green chlorophyll, but as it breaks down, the yellow and orange pigments become more visible.
Anthocyanins
Are not part of the leaf in the growing season and are sugars that get trapped in leaves. Through a chemical process, it produces new pigments in dark red and purple, which are found only in some tree species.
Tree Species
The exact colours and timing of the change can vary depending on the tree species. Each species contains its own pigment combinations and can respond differently to environmental cues. For example, maples are known for their vibrant red and orange leaves in the fall, while certain oak species tend to turn yellow or brown. Oaks also keep their leaves much longer than other tree species and can still be green as other trees turn colour.
Other Environmental Factors
Decreased daylight and cooler temperatures are the main reasons for the changing leaves, but other factors also play a role. Soil moisture levels, rainfall, and the tree’s health also play a role in the changing leaves. Those under stress, whether due to drought or disease, may have less vibrant fall colours.
Now that you know all the basics of the brilliant colour changes, it’s time to get out and witness this once a year change for yourself! Head outside because it always seems to go quickly; one day they are lighting up the autumn forest, and the next they’ve all fallen to the ground.
Where to Peep the Leafs?
Wondering where to go? Check out our blog on where to Peep the Leafs at HCA!
