It’s a marvellous time of year in the Forest City as the vast canopy turns from green to vibrant shades of red, orange and yellow.
If you want to see the beautiful colours of fall from a unique vantage point, the City of London has opened its top-floor observation deck. You can visit the city’s website to reserve a time to see the fall landscape until mid-October.
To find out about the science behind the annual changes, London Morning host Andrew Brown talked to local arborist Isaac Ladore with Koala Tree Services.
The following has been edited for length and clarity.
Andrew Brown: So what’s happening out there that makes the leaves change colour?
Isaac Ladore: As the cooler seasons approach and the trees start to enter their dormant stage, the production of chlorophyll, which is a big player in photosynthesis, starts to break down. What ends up happening as it breaks down is it either creates some new compounds when those sugars break down inside of a leaf, or compounds that were already there before hidden behind the green are revealed.
AB: OK, so then what determines which colour the leaves turn?
IL: So a really cool thing about the fall colours is you can actually identify different trees vaguely from a distance based on the colour that they’ve turned. So say you’re Reds are produced from anthocyanins and that’s what’s created when the sugars and the leaf break down. So your red maples, your red oaks, those colours that have a distinct red in their common name usually show off a bright red colour. Your oranges come from carotene, which is the same thing that makes our carrots orange. The last one of the common colours is your yellow xanthophyll, your beaches, your birches, and your aspens. You’ll usually see a big stand of yellow out in the distance.
London Morning6:53The science behind the changing colours of fall
It’s a beautiful time of year with a rainbow of colours on the trees. London Morning asked local arborist Isaac Ladore with Koala Tree Services to explain the science behind leaves changing their colours.
AB: The carotene detail is interesting and surprising.
IL: Yes, and I mean your xanthophyll with the yellow, that’s in your corn and you’re squash. A lot of plants share the same compounds.
AB: So what are the trees themselves doing at this time of year?
IL: With the cooler seasons approaching, the fragile tissue of the leaves can’t handle the winter conditions. So the trees shed their leaves to conserve energy, seal off excess moisture and also shed extra weight. When those high winter winds and the weight of snow comes on, they start to seal off their leaves. They’ll eventually shrivel up and drop off.
AB: And then how long do the do the leaves typically hang on?
IL: It depends on your various species and also the age of them. So trees like Beech or oak trees will hold on to their leaves sometimes throughout the whole winter. If they’re younger, they don’t really need to let go of them, so they kind of hold on to them.
AB: What’s the situation now with oak wilt right now?
IL: So oak wilt is a really interesting but kind of terrifying disease that affects the oak trees in our country and as well as the states. It’s spread by beetles and it carries a fungal pathogen that can infect our oak trees and even spread to other oak trees via their roots. So if one tree on a city block gets it, all of those oaks could get it and die off.
Going into November is what we like to call oak season because it’s cold enough that those beetles that spread the fungal disease aren’t active anymore. So we can begin work on oak trees in November and throughout the winter. During the summer, we highly recommend, you know, don’t touch your oak trees, don’t cut them, don’t do anything because, you know, there’s a risk.
AB: And then bringing it back to leaves, once those leaves do start falling, what kind of recommendations do you give on what people should do with those leaves?
IL: Many people have probably heard of ‘No Mow May,” which is something that is encouraged to kind of help out our local pollinators. In the fall, you can do a similar thing, leaving your leaves. All this leaf cover on the ground gives vital habitat and also food for all sorts of beneficial critters, even mammals, and mostly our native pollinators, a lot of butterflies and caterpillars. The plants, the pollinators, they’ll thank you for it.