Rosabelle Rosario

Student biologist

Last updated: October 3, 2023

Fall is in the air! The autumn season brings brisk morning temperatures, beautiful golden evenings and cascading leaves — perhaps that’s why we call it “fall”?

We all know that the fall leaf colours turn the landscape from a green forest canopy to one of yellow, orange and red. But many are left to wonder why is it that the leaves change the palette of the landscape during this time of year.

The Science Behind the Leaves

Different coloured leaves

Throughout the spring and the summer months, deciduous trees invest energy into producing chlorophyll, a green pigment used to convert sunlight into food. The production of chlorophyll is advantageous during these months, as there is plenty of sunlight to be absorbed.

In fall and winter, the trees don’t receive enough energy due to the reduced intensity and duration of sunlight. The pigments in each leaf begin to change as chlorophyll production starts to decrease in late August and early September.

In addition, deciduous leaves become increasingly vulnerable to freezing. This is because they don’t have the same adaptations that more northerly coniferous trees have, which protect them from colder weather.

Simply put, leaves change colour due to the lack of sunlight and not because of the cooler temperatures.

Yellow and Orange Everywhere

Fall foliage with a body of water

Once the leaves loose their green pigment, their true colours become more visible, creating a palate of yellow and orange leaves. Other chemical changes also take place within the leaves, turning them a brighter or burnished red colour. These are easily seen in sugar maples, staghorn sumacs and dogwoods. Each deciduous tree species has its own distinct shade of yellow, orange or red. The deep red shades have always been my favourite.

In the National Capital Greenbelt, there are over 70 species of trees and shrubs, including 50 distinct deciduous species. There is one exception to the general rule: a northern, coniferous tree called tamarack (Larix laricina) sheds its leaves in late October and November — making it a deciduous, coniferous tree. This species is a bog specialist which turns a brilliant gold colour in late fall. Easily seen from the Mer Bleue boardwalk, these trees provide great photographic opportunities once the maples, oaks and poplars have shed their leaves.

Where to See the Leaves

A hiking trail with fall colours

The stunning landscape brings many visitors from Canada and abroad to enjoy this forest phenomenon. Fall Rhapsody is the NCC’s way of celebrating the fall colours in the National Capital Region. There are many well-maintained trails for you to experience Fall Rhapsody in the Greenbelt and Gatineau Park this fall.

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