HALIFAX 鈥� The customary reds, oranges and yellows of the trees, marking the arrival of fall, may have appeared early this year, or not at all.
The dramatic summer weather that brought wildfires in some parts of the country and heavy rain in others is being reflected in fall colours across Canada, researchers say.
In Nova Scotia, where summer started with forest fires and ended with stretches of overcast and stormy days, dull brown has replaced the vibrant hues usually seen this time of year in much of the province.
Mason MacDonald, an assistant professor of environmental sciences and agriculture at Dalhousie University, said the colours he鈥檚 seen so far this autumn don鈥檛 compare to the brilliant reds and oranges Nova Scotians are used to.
鈥淲hat you're probably seeing is a lot of really dull-looking colours this year. Even the reds are probably more of a dull, darker red, or rust colour,鈥� MacDonald said in a recent interview.聽
鈥淚've heard it from a lot of people this year, especially people from the southern parts of Nova Scotia,鈥� he said.
As the nights get longer in the fall, trees receive less direct sunlight, and chlorophyll, which trees use to absorb sunlight during photosynthesis, begins to break down, displaying the natural pigments within the leaves.
One of these pigments 鈥� anthocyanins 鈥� creates the red shade in leaves, and it requires consistent sunlight through late summer to be produced. A drop in anthocyanins isn't harmful to a tree, MacDonald said, adding that if next summer is sunnier, those vibrant reds will likely be back in full force.
鈥淭his year we got more rain than is typical for us, and along with that we had a whole bunch of these dark, grey, cloudy days. That's what happened. We didn't get the sun we would normally get. Therefore, they can't make those colours,鈥� MacDonald said.
Trees in Ontario, by contrast, have begun displaying the natural pigments earlier than usual.
Sean Thomas, a professor of forest ecology at the University of Toronto, says there is anecdotal evidence to suggest that smoke from wildfires in northern Ontario this summer may have triggered trees to reveal their colours prematurely.
鈥淲ildfire smoke is a kind of chemical cocktail,鈥� Thomas said.
That cocktail of carbon dioxide, ozone, sulphur dioxide, carbon monoxide and particulate matter 鈥渋ncludes trace quantities of chemicals that play a sort of hormonal role with plants,鈥� he said, which can cause trees to drop their leaves early.
鈥淚n our case, we got those acute smoke effects earlier in the summer, but it still may be partly what鈥檚 accounting for the earlier fall colouration,鈥� Thomas said.
He said there is lots of colour in much of Ontario this season, but added there is reason to believe that ongoing impacts of climate change will see fall colours diminish in the coming years.聽
鈥淭here is good reason to think that climate change will disrupt that normal leaf colouration that we see,鈥� Thomas said.聽
The combination of warmer temperatures and delayed first frosts will potentially lead to duller fall colours, he said. This effect, he added, will likely be most acute in major cities, which are generally hotter than rural areas because of the urban heat-island effect 鈥� when structures such as roads and buildings absorb and re-emit the sun鈥檚 heat.
If climate change delays the longer, colder nights in places like Toronto, "that鈥檚 a recipe that is likely to lead to much less fall colouration right in the city, and that will be exacerbated by climate change,鈥� Thomas said.
In Cape Breton, where the Celtic Colours International Festival is underway, an event spokesperson said in an interview Thursday that trees across the region are beginning to change colour. Dave Mahalik said he鈥檇 heard that colours are less vibrant in parts of Nova Scotia this year, 鈥渁nd it made me wonder a bit about where we鈥檙e at and how we鈥檇 fare," he said.
鈥淏ut I鈥檓 in Sydney and there's trees here that are starting to pop, and they're looking like they usually do,鈥� he said.聽
Mahalik said he鈥檚 hearing from his colleagues that colours are looking bright elsewhere on the island, which bodes well for the festival that鈥檚 hosting about 50 concerts in communities across Cape Breton.聽
鈥淚鈥檓 excited as can be and I'm sure the colours will be as vibrant as ever,鈥� he said.
This report by The Canadian Press was first published Oct. 7, 2023.
鈥� With files from Fakiha Baig in Toronto.
Lyndsay Armstrong, The Canadian Press
