One of the best and most beautiful parts of fall, and one of the things I look forward to the most every single year is watching those leaves change color and tumble down to the ground. I’m sure you’ve been told why this happens; trees let go of their leaves to hunker down for the winter, but how does this happen?

Throughout the spring and summer, leaves act as a solar panel for the tree. They take in energy from sunlight and a green chemical called chlorophyll uses this energy to break down carbon dioxide and water into oxygen and sugars. This chemical is what colors the leaves green.

However when it starts to get colder and days get shorter, the tree notices how it’s getting less sunlight and prepares to close shop for the winter, which includes getting rid of its leaves. This happens because keeping leaves working in the cold uses more energy and resources than it’s good for.

To start this process, the tree starts reabsorbing nutrients from the leaves back into its twigs and branches. The problem here is that the chlorophyll is still creating extra energy, which can interrupt this transport. So, the tree breaks down its chlorophyll molecules to shut them down, they end up losing their green color, and then the natural orange and yellow of other pigments, carotene and xanthophyll, shines through. These other pigments are already in leaves year round, but they aren’t given a chance to show underneath the bright green chlorophyll.

That’s right! Leaves are already naturally orange and yellow to begin with, their chlorophyll just colors green over the orange and yellow. However, this doesn’t explain how some trees turn deep red.

Sometimes, when the tree is trying to evacuate nutrients out of its leaves, it starts producing anthocyanins, which give the leaves their red color. Not a whole lot is known about why this happens and what exactly it does, but one of the main theories as to why this happens is that the additional red pigment acts as a sunscreen to protect the nutrients while they’re being transported back to the tree, which helps a lot, especially if there’s still some active chlorophyll in the leaves.

There seems to be various factors to influence this; some suggest that it happens when the soil doesn’t have much nutrition, meaning that the tree needs to put more effort into keeping whatever nutrition it has in its leaves; others suggest that it happens when the autumn sunlight is too bright, so they need to block sunlight to keep the nutrients safe. It also depends on the type of tree as well, some types of trees seem to be more prone to turning red than others, but it still seems fairly random as to what trees turn what color.

Either way, there’s still plenty of mystery surrounding the color of leaves, but if one thing is for sure, they’re beautiful. Not to mention that satisfying crunch is one of my favorite parts of an autumn walk.