Colour My World: 10 Reasons Why Leaves Change Colour

With the Autumnal Equinox comes a dramatic change in the look of the Boreal forests in Northwestern Ontario. What natural processes are behind all the changes? There are reasons leaves change colour and it's pretty interesting.

Fall Transitions in Northwestern Ontario

So the Autumnal Equinox happened on September 21st and that date means a new look is emerging from the Boreal forests in Ontario's Sunset Country. With the colder overnight temperatures, the changes are easy to see. But did you ever wonder what was behind this transition? What natural factors work just before and during fall that causes the big colour change? 

Read on and learn more about what nature does, as Albert Camus notes,  to make fall a second spring, where every leaf becomes a flower.

Mostly yellows here as the predominant species are poplar and birch trees
Poplar, birch, and tamaracks give a yellow splash against the evergreens.

Natural Factors Behind the Colour Change

The change in the colour of leaves during the fall is a complex process influenced by various factors. Here's a breakdown of what happens in nature to produce the magical colour change:

  1. Decreasing Daylight: Decreasing daylight plays a significant role in getting the ball rolling on fall. As the days shorten, there's less light available for photosynthesis. This signals the trees to start preparing for winter.
  2. Temperature: Cooler temperatures, especially during the night, can trigger the breakdown of chlorophyll and influence the display of colours.
  3. Chlorophyll Breakdown: Chlorophyll gives leaves their green colour. As daylight decreases and temperatures cool, chlorophyll production slows down and the existing chlorophyll starts to break down, revealing other pigments in the leaf.
  4. Carotenoids: These pigments are always present in the leaf, but they are usually masked by the green chlorophyll. As chlorophyll breaks down, carotenoids become more visible, producing yellow and orange hues. Carotenoids are responsible for the colours in carrots, bananas, and corn.
  5. Anthocyanin Production: Unlike carotenoids, anthocyanins are not always present in leaves. They are produced in response to various factors in the fall, such as cooler temperatures and increased sugar concentration in the leaf. Anthocyanins can give leaves red, blue, or purple colours. The exact shade depends on the pH of the tissues – redder in acidic conditions and purpler in alkaline conditions.
Fall colour transition on the Canadian Shield rocks
Colour changes on the Boreal shield include both shrubs and trees.
  1. Tannins: As other pigments degrade, tannins can become more prominent in some tree species, resulting in brown hues.
  2. Weather Conditions: A series of warm, sunny days followed by cool, crisp (but not freezing) nights tends to produce the most vibrant colour display. During these conditions, sugar production in the leaf is high, but the cooler nights prevent the sugar sap from flowing out of the leaf, leading to a higher production of anthocyanin pigments.
  3. Soil Moisture: Adequate rainfall in the preceding spring and summer can also influence the vibrancy of fall colours. Severe drought can delay colour change and decrease its vibrancy.
  4. Tree Species: Different tree species have different pigments, leading to a variety of colours. For instance, oaks can display deep red, brown, or russet hues, while maples can exhibit vibrant scarlet, orange, or yellow.
  5. Health and Location of Trees: Trees that are stressed due to diseases, pests, or other adverse conditions might show early or less vibrant colour changes. Additionally, the colour display can vary based on the tree's location, whether it's in a low or high area, or if it's exposed to more sunlight or shade.

While these natural factors play a major role in the fall colour change, the exact timing, duration, and vibrancy of the display can vary annually based on a combination of these factors. By having knowledge of what processes are at work and what actually happens to the trees and plants in fall, you can better understand the changes as they happen.

Smaller plants are often the brightest in colour
Small plants often show the brightest colours during the fall transition.

Fun Things to Do Outdoors in the Fall

Now that you know what is going on behind the scenes to cause this kaleidoscope of colours, the good news is that fall is one of the best times to get outdoors in Sunset Country! Here are just a few prime fall activities:

  • Hiking - With zero bugs, fall is the best time to enjoy the woods since those beautiful colour changes will be all around you. There are many great nature trails in Sunset Country.
  • Fishing - Fall fishing is spectacular as the water temperatures cool down the fish get active, looking to eat as much as possible before winter sets in.
Fall fishing in Ontario
The fish are hungry and biting in the fall months.
  • Wildlife Viewing - Wildlife also sense the coming of winter so fall is a time of year when they get much more active. You are more likely to see big mammals like whitetail deer, moose or black bears during fall.
  • Auto Touring - With the wonderful colour change, you can't beat fall when it comes to auto touring. Drive our winding roads and see the majesty of colours that define the change of season. Here is a suggested touring route where you'll see a lot of fall colours. 
Whitetail deer in Ontario, Canada
Whitetail deer bucks prepare for the rut in the fall so they are very active in their movements.
  • Hunting - Fall is the time for hunting in Ontario's Sunset Country. Try your luck pursuing moose, whitetail deer, bear, and ruffed grouse.
  • Outdoor Photography - Nature's fall colour palette is reason enough to take lots of photos, but with more animals on the move, you could capture some amazing images.
Fall in Ontario's Boreal forest
Nature offers a stunning colour palette in the fall.

Time Flies By Quickly During Fall

Sadly, the fall colour splash in northwestern Ontario lasts for 2-3 weeks then the trees go bare for 6 months. This means if you want to enjoy the majesty that is happening, you have to act quickly and decisively. On that note, hopefully, we'll see you soon.

Fall aerial view in Northwestern Ontario
Aerial view of the Boreal forest in the fall. Credit: Kevin Palmer
About Gerry Cariou

Gerry is Executive Director of Ontario's Sunset Country Travel Association and is an avid fisherman and nature photographer. Gerry has been writing about Sunset Country's varied travel experiences for over 20 years and lives these experiences year-round in Kenora, Ontario.

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