While the fall season has officially been underway for a few days, it’s still a little bit early for some trees in B.C. to be showing their fall colours.
There are a variety of factors that impact why and when the colours of leaves change on our beautiful B.C. trees.
We spoke with Scott Gardner, the district manager of the Burnaby Davey Tree Expert Co. office, who thankfully had lots of answers about fall leaves.
Gardner works with trees around the Lower Mainland.
“I dispatch the crews, work on customer service. So meeting people, visiting their houses to assess trees, and [setting] out a game plan for renovating them.”
Gardner has been doing this for 11 years, which was important to contextualize our conversation, as in recent years, we’ve seen more reports around fall colours creeping in earlier than usual. Environmental factors have also contributed to the early signs of spring in recent years.
We wanted to know how Gardner has seen autumn change in his time working with trees in the Lower Mainland. It’s also not just about colours changing, but we’re also seeing leaves drop from some trees earlier than usual.
“Specifically in the Lower Mainland, we are seeing quite a few of the trees start to turn. I know on the Mary Hill Bypass, for example, there’s a lot of alders that are turning right away, and dogwoods.”
Gardner suggested that some of the drooping of trees and the falling of leaves is a bit premature.
He said that typically, we usually see that type of behaviour around a month from now. He also advised that we’re not seeing this reality in all B.C. trees, but only in some of them.
As for the potential cause?
“The heat and the lack of water over the last two or three months are definitely taking a toll on the trees,” he said, adding that if you have trees that you water at your home, do so earlier in the season, like in June or July, as the heat starts to hit and it starts to rain less.
We’ve experienced much more intense drought conditions in previous years, which Gardner attributes to some of the causes behind this phenomenon.
“Over the last five years or so, in the summers in British Columbia, specifically in the Lower Mainland, we’ve been having droughts; three to four months with next to no rain almost every summer.”
He added that this year was actually relatively stable in comparison to the previous five years.
Why do the leaves change colour, though?
“The leaves have chlorophyll that runs through them. It gets mixed in with water and kind of goes up into the leaves, makes photosynthetic material, and then that will distribute sugars throughout the tree to put energy into different areas,” he said.
“When the trees are changing colour, they’re going into dormancy. So they’re drawing out the chlorophyll from the leaves, and in taking that out, what’s left is a variety of different colours that change as that process is happening.”
Last year, we spoke to Dr. Santokh Singh, a professor of teaching at the UBC Department of Botany, about seasonal leaf senescence. This fancy term describes the physiological reasons for the seasonal changes in tree leaf colour.
“Normally, in most of these broad-leaf trees, those leaves will only turn to yellow, red or purple at the end of September or in the fall season.”
That’s not always the case; it boils down to plant hormones called cytokinins, which Singh refers to as greening hormones. In contrast, ethylene and abscisic acid are hormones that cause senescence in plants.
“The early leaf colour change, as observed in some trees in Vancouver, could be the result of one or more of these environmental stress conditions. So that can cause the change in the production of some of these hormones,” Singh said.
“Nitrogen deficiency can also be one of the reasons.”