Lasting impact of early spring hard to pinpoint
Research on the iconic wildflowers around Crested Butte is shedding light on the impacts of earlier springs on both the flowers and the animals that depend on them.
David Inouye has been spending his summers at the Rocky Mountain Biological Laboratory outside Gothic since 1971, but the landscape around him has started to change slightly in the past decade.
In the 1970s, Inouye, a biologist based at the University of Maryland the rest of the year, began observing the abundance and variety of wildflowers in 6-foot by 6-foot plots outside the lab, work which continues to this day.
Lab officials say this ongoing work is one of the country’s longest-running studies of phenology, or the timing of events in plants’ or animals’ life cycles, such as flowers blooming or migrating birds returning.
In recent years, these observations have yielded insights into some of the effects of climate change on mountain wildflowers and the wildlife that depend on them.
In only two of the 11 years between 1974 and 1984 did Inouye see almost no aspen sunflowers blooming in the studied plots. There were nine such years, however, in the 11 years between 1997 and 2007.
This change points to a paradoxical increase of frost damage resulting from global warming.
Inouye says wildflowers are beginning to bud and leaf out earlier in the year as warmer temperatures arrive sooner, but that the last hard frost of the year has still been falling in early June, damaging the buds and, thus, the flowers’ ability to flower and reproduce.
Another researcher, studying the Mormon fritillary butterfly, was having trouble figuring out why butterfly populations were fluctuating so much from year to year, when she mentioned to Inouye that the insects’ main nectar source was one of the flowers he had been studying.
“So we put together her data and my data,” he said.
The results showed the butterflies were laying especially low numbers of eggs in years following an early snowmelt. In other words, they suffered after early springs.
The puzzle was solved once they discovered early springs meant less wildflowers — and thus less nectar for the butterflies to drink.
“If there’s not enough nectar there’s not going to be enough eggs or caterpillars,” he said by phone from the lab.
This year, a frost hit there a couple weeks ago. Combined with the warm, early spring, he said, “it looks like this year there’s going to be very few of these flowers, so we already know that next year there will be fewer of these butterflies.”
Would there be knock-on effects of low butterfly populations for other species higher up the food chain?
Possibly, Inouye said.
He also pointed out that fewer flowers means fewer seeds, so that species that eat seeds would also be affected.
Humans are not immune from the effects of early springs, either, Inouye noted, pointing to Michigan and Pennsylvania, which lost much of their cherry crop this spring because of warm early season temperatures followed by a late frost.
“That kind of event is becoming more common, not just for wildflowers but for agriculture as well,” he said.
For now, fruit trees in the Grand and North Fork valleys seem to be safe. This spring’s late frost here came after the fruit was generally big enough that it was not damaged, he said.
Weather data for the past five decades actually shows the last frost coming earlier in the valleys.
Looking at data recorded at Orchard Mesa by Colorado State University’s Western Colorado Research Center, CSU’s Horst Capari pointed out that median day of the last spring frost was May 2 for the period between 1964 and 1988 and is April 19 for the past 24 years.
But Caspari also pointed out that growers are cultivating both more early and late peach varieties now than 20 or 50 years ago.
“Unfortunately, early-season peaches also have earlier bud break than our old standards, and thus are more at risk from spring frosts,” he said.
The impacts of early spring on orchards, then, are still hard to pinpoint and variable.
“Last year more or less all the crops ran two weeks late; this year everything is two to three weeks early,” Caspari noted.