Leaves change color because deciduous trees are preparing for winter.
Shorter days trigger major chemical changes inside the leaf.
Chlorophyll creates the summer green
Chlorophyll absorbs light used in photosynthesis and strongly reflects green wavelengths.
During the growing season, trees continually replace chlorophyll as it breaks down.
In autumn, replacement slows.
The green begins disappearing.
Yellow and orange pigments were already there
Carotenoid pigments produce yellow and orange colors.
They are present during summer but are usually hidden by the much stronger green chlorophyll.
Once chlorophyll fades, those colors become visible.
Where does red come from?
Some trees make anthocyanin pigments during autumn.
Those can produce red or purple colors.
Weather, light, sugar levels, and species all affect how strong the red becomes.
Why do leaves eventually fall?
The tree forms a separation layer where the leaf stem meets the branch.
Water and nutrient movement are gradually cut off.
Eventually the leaf detaches.
That reduces water loss and protects the tree during winter conditions.
Why do pine trees stay green?
Pine needles stay green in winter because evergreens use a different strategy.
Their needles are built to conserve water and tolerate cold rather than being discarded all at once.
So the fall colors are not painted onto the leaf.
Much of the yellow and orange was already there.
Green simply stopped covering it.
And that’s the short explanation.
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