Spring is alive and well in southern coastal Maine! The landscape is filled with all kinds of beautiful colors: white and pink petals everywhere, and the deep reds and bright yellow-greens of baby leaves. As the days get warmer, our insect friends emerge—so far I have seen American Lady (pictured above) and Cabbage White butterflies, and the bumblebees are all over our flowering trees and shrubs!
If you feel like spring is coming earlier and earlier every year, you might be onto something. One study from 2015 (Allstadt. et al, 2015. Environmental Research Letters, 10(10)) used mathematical models to predict the start of spring for multiple decades. The authors predicted that by 2100, spring would advance by 23 days. They also assessed false spring risk, which is when plants start growing due to a random week of nice weather, but then when we jump back to freezing temperatures, new growth is damaged. Over the next 75 years, false spring risk was not predicted to increase in the northeastern U.S., but other regions such as the Great Plains and Midwest may experience a higher risk.
False springs can affect plants much further into their life cycles than just new growth at the beginning of the growing season. The phenological mismatch of spring ephemerals and bumblebee emergence was investigated by a 2019 study (Kudo & Cooper, 2019. Proceedings of the Royal Society B, 286(1904)). The authors found that while spring ephemerals begin to grow after snowmelt (see last month’s blog post here), bumblebees use soil temperature as a cue to begin foraging. Because snowmelt and warmer air temperatures can occur before the ground warms up, spring ephemerals may start flowering before the bees come out. This phenomenon decreased the bees’ ability to pollinate the wildflowers, and consequently seed production was decreased.
While Kudo & Cooper’s study used mathematical models to predict the future, another study experimentally increased temperatures to simulate global warming up to an increased 5℃ (Marchin et al, 2015. Global Change Biology, 21(8):3138-3151). These warmer temperatures advanced the budburst of some tree and shrub species by 5 to 15 days. The authors found that certain trees were affected differently: ring-porous trees (trees with vessels that start out large in spring and shrink in summer, like oaks and hickories) seem to rely on photoperiod for budburst. Diffuse-porous trees (trees with consistently sized vessels, like maples and birches) had shifted budburst timing depending on winter chilling.
Although shifting phenological events can be worrying, we can find a silver lining by taking advantage of the earlier spring weather to plant native plants! The date for last frost has passed in southern coastal Maine, so false springs are no longer a concern for planting. At our nursery, we have woody plants currently blooming such as serviceberry, chokeberry, and blueberry. Help out our early pollinators by planting trees. Order online and schedule a pick-up at shop.mainenativeplants.org.
