Fall foliage fans might be revelling in the vivid red, orange and yellow leaves currently lining Vancouver’s streets—but the city isn’t putting on as good a show as it could be, according to experts. Dr. Santokh Singh, researcher and professor of botany at the University of British Columbia, says we’re entering the “peak period” of being able to view the magnificent colour change, but the autumnal tones in most places are dimmer than what we’re accustomed to. Part of the reason why leaves are more muted lies with B.C.’s uncharacteristically balmy autumn, says Singh. September and October haven’t shown the low temperatures typical of the season, especially come nightfall, and thus the leaves are missing their annual environmental cues. The process of leaves changing colour, technically referred to as leaf senescence, occurs when cold temperatures break down chlorophyll, the lush green pigment. As the green pigment degrades, other pigments within the leaves—molecules called carotenoids that are always present but masked by the green of the chlorophyll—are revealed. Most commonly seen are the yellow xanthophyll, the red and purple anthocyanins, or the yellow, orange and red carotene. “Those low temperatures and shorter days are really very crucial for showing the crispness and the colours,” says Singh, who has been studying the biochemical and developmental changes that occur during this process for close to 35 years. He says this process is most typically seen in broadleaf trees like the Maple, a species common throughout the Lower Mainland. Some nature enthusiasts might have noticed that certain trees within B.C. looked to be in a state of confusion earlier this year, with some displaying the withered brown leaves typically associated with fall during the peak summer months. The excessively hot and dry weather the province experienced over summer has only encouraged the lacklustre fall foliage, with heat stresses causing the premature demise of the leaves long before autumn’s cold snap. “This year, in many places in B.C., there was very little rain,” says Singh. “The trees were suffering from drought, with very little water in the soil. The growth of the leaf gets impacted and the leaves start to wilt, they start to become brown, and they shed the leaves much earlier than they otherwise would.” For the fall fanatics the outlook might seem bleak, but Singh assures there is still a chance to enjoy the jewel tones of autumn despite the unprecedented weather patterns, people just have to know where to look. “There are areas in Stanley Park, Queen Elizabeth Park, and certain areas of UBC that are starting to show fairly good leaf color change,” he says, noting his favourite spots for foliage-observing as the Stanley Park seawall and Burnaby’s Central Park. Those hoping to catch a glimpse of the tones before the season comes to a close should act fast as “the window can close very quickly,” he says. Towards the end of October and in early November, the leaves, once they have changed colour, will fall and the ambers and russets that illuminate these viewing hotspots will disappear. The shedding comes after the tree has extracted as much nutrients as possible from its leaves, typically 90-95 per cent, to preserve enough energy to ensure survival during the cold winter months and the healthy development of new leaves come springtime. As the nutrients are drained the cells weaken and a gust of wind or two is enough to shed it from the tree completely, a process technically referred to as leaf abscission. “It’s a wonderful phenomenon to witness, even if this year is duller than usual,” says Singh.
