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Flowers in the Snow

Snow this morning!  It was warm enough that the roads were merely wet, but the dusting of snow I woke up to at 6 AM was, two hours later, a half-inch covering on the cars and the colder spots on the ground.  By late morning, the last traces of snow had melted.  The day remained chilly and gray, though, well into the late afternoon.  It was quite a contrast with the previous few days of sunshine and temperatures in the 70s.

A visitor asked me yesterday, as she fled the sun to take a seat next to me in the shade near Riverside Geyser, if it was normally this hot in early June.  I gave my usual answer: almost anything is normal at this time of year.  It can be warm and sunny or it can be snowing.  She was a little surprised at that, I think.  “Snowing?  Really?”  I wonder if she was still in the park this morning to enjoy the spectacle of new-fallen snow in June.

It can snow any month of the year here, at an elevation of 7,400 feet and a latitude almost halfway to the north pole.  Historically, the frost-free growing season here is only about two months long.  The summers are so short that all the flowers seem to bloom at once, creating the colorful displays we admire along the roadsides and in the meadows of Yellowstone.  Today, the cold night and dusting of snow is testing the hardiness of the early bloomers—some flowering plants might be insufficiently frost-tolerant to survive the chill.

Historically, natural selection created good synchrony between the time at which frost-sensitive plants come into flower and the decreasing likelihood of a killing frost.  But climate change is messing with that relationship.  Though it might seem that a warming climate would simply bring about a longer growing season that would benefit plants, the picture is hardly that simple.

One of the biggest problems documented by ecologist David Inouye of the University of Maryland and the Rocky Mountain Biological Laboratory is that, while snowmelt is indeed occurring earlier, there are more damaging frosts than there used to be.  The date of the last hard freeze has remained more or less unchanged in mid-June, but with the growing season starting earlier, more plants are exposed to damage.

One victim Inouye has documented is Helianthella, a cheery yellow little sunflower.  Because Helianthella is a long-lived perennial, the frosts haven’t been bad enough to kill the plants, but they have been damaging the young, tender flower buds.  The resulting scarcity of mature flowers means that there is no pollen for insects to gather, and no seeds to feed other animals—much less to sow the next generation of sunflowers.

Inouye has recorded similar problems for a number of other species, including the larkspur Delphinium barbeyi, a favorite food source for hummingbirds; heartleaf bittercress (Cardamine cordifolia), with its exploding seed pods;and one of my favorite early-season bloomers, the glacier lily (Erythronium grandiflora).

Inouye’s research focuses on an area near Crested Butte, Colorado.  I am not aware of similar long-term phenology research here in the Greater Yellowstone Ecosystem.  Still, I worry about the long-term consequences for the plants, as the warming climate could lead to a loss of species diversity—and fewer lovely wildflower displays for us to admire.

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