After weeks of closely observing how plant traits such as fruits and flowers have changed in quality and color throughout the season, it’s time to piece together the story they are telling. Here’s what I’m finding:
The story isn’t easy to decipher. Although a few species and traits such as fruiting in stream alders and wax currants are developing later within the cold air pool (CAP) than outside of it as expected, the majority of traits are developing at the same rate. So there’s not sufficient evidence to say that the cooler temperatures within the CAP is impacting plant phenology.
A handful of traits such as stream alder fruits (left) and wax currant fruits (right) are both developing about a week later within than outside of the CAP.
Plant phenology is also messy. Many variables besides temperature such as soil moisture and amount of sunlight can impact plant development. And just by observing phenology, we can’t tell how much each of these variables contributes to phenology. Is temperature the main factor? Or does soil nutrient levels and proximity to the river also factor in?
Many traits such as stream alder flowers (left) and lodgepine pine seed cones (right) are developing at the same rate within and outside of the CAP, though.
Finally, the cooler temperatures within the CAP may not be sufficient to elicit a phenological response in plants. We’re finding that the temperatures in the CAP are cooler at night by as much as 5 °C, and that the CAP forms almost every night. However, once the CAP dissipates, daily high temperatures in areas where the CAP used to be get as high as in areas where no CAP forms. Perhaps the CAP is not cool enough or does not last long enough to impact phenology.
A snapshot of hourly temperature across 3 days in July within and outside of the CAP. The CAP usually forms at around 8pm and dissipates at 3pm the next day.
Now what? The search for an ecological link continues. If plant phenology isn’t the best way to monitor an ecological response to CAPs, is there another indicator we could use? Insect are very sensitive to temperature shifts since they are cold-blooded, and many insects have shifted their phenology in regions that are warming. Could we compare insect phenology (e.g., when butterflies and dragonflies hatch or emerge) inside and outside of the CAP?