8 March 2023
North American wildflowers face many threats to their existence including habitat loss, deer overpopulation and pollinator declines but there is another threat we didn’t see coming until now. As the climate heats up North American spring ephemerals will have no time to bloom and store food for the coming summer. Their existence is threatened by the Too Early Springs of climate change.
Forest wildflowers bloom before the trees leaf out because they are in a race to gather as much sunshine as possible before the canopy closes. When the trees reach Full Leaf the flowers stop blooming.
Wildflowers in deciduous forests often rely on leafing out before the canopy to create 50-100% of their annual carbon budget. Lead author and Carnegie Museum of Natural History postdoctoral research associate Dr. Benjamin Lee describes it “as if a person were to eat all the calories they needed for a year in the first three weeks.”
Ideally, wildflowers would merely advance their blooming schedules and all would be well but the study published last December in Nature Communications shows otherwise. Using herbarium specimens in North America, Europe and Asia, researchers compared wildflower blooming times and tree leaf out dates for the three continents.
Blooming early works in Europe and Asia because those trees leaf out later anyway. But in North America the trees and flowers use the same temperature trigger. We had a real life example of this in Pittsburgh in March 2012 when temperatures stayed in the 60s to 70s for at least two weeks. In that Too Early Spring everything happened at once.
I visited Barking Slopes on 25 March 2012 and I found both early and late spring wildflowers in bloom: Bloodroot (Sanguinaria canadensis) which normally blooms in late March or early April and large-flowered bellwort (Uvularia grandiflora) which normally blooms in late April.
The trees were leafing out, too.
June weather in March? What could go wrong?
Fewer spring wildflowers in the future.
Read more about the Too Early Spring of 2012 below. Will it happen this year? Only time will tell.
(photos by Kate St. John, diagram from Wildflower phenological escape differs by continent and spring temperature)
p.s. The time gap between bloom-time and leaf out is called the “wildflower phenological escape” hence the study’s name.