For the past four years, plant biologist Elsa Godtfredsen has moved to a subalpine meadow in Colorado to study the interactions between wildflowers and bumblebees. The pollinators buzz among fields of purple delphinium and columbine, an iconic image of spring in the Rocky Mountains.
Godtfredsen works at the Rocky Mountain Biological Laboratory, a research center amid evergreens and jagged granite peaks in Gothic, Colorado. Each spring and summer, they track four species of wildflowers from flowering to seed set, using this data to model the impact of climate change on these plants and their pollinators.
“Subalpine and alpine ecosystems are changing rapidly,” said Godtfredsen. “We’re trying to see if these species can persist in ecosystems that are going to continue to change unless we see drastic shifts in policy.”
As winters warm, snow in alpine and subalpine regions melts earlier, causing a timing where flowers bloom before bumblebees emerge from diapause or insect hibernation. Without enough pollinator visits, plants cannot make seeds and reproduce. This will leave fewer flowers for pollinators next spring – and future springs too.
“We see a ubiquitous trend: Generally when snowmelt occurs earlier, we also see flowering earlier,” Godtfredsen said.
Scientists warn that these mountainous ecosystems portend trends that other areas may soon experience, or in some cases already face. Worldwide, spring is gradually arriving sooner. Flowers are now blooming several weeks ahead of schedule in temperate forests Japan and an average of 23 days earlier in the United States. Another study in the United Kingdom found that plants bloom a month earlier average.
Most animals and insects rely on temperature cues to initiate seasonal activities, such as migrating, breeding, or emerging from hibernation. When those signals change due to warming temperatures or earlier snowmelt, it can lead to timing mismatches that threaten populations.
For example, insectivorous early nesting tree swallows in the spring face higher chick mortality rates due to inclement weather, which reduces insect availability. Arctic plants were too emerged earlier in Greenland, and many caribou calves died when spring plant growth preceded caribou’s calving season.
Among the smallest, and possibly most worrisome, animals affected are insect pollinators, such as bees, flies, butterflies and moths. These arthropods are crucial to our food system: They help pollinate a third of the most important food crops and contribute around $15 billion annually to American agriculture. However, climate change causes 60 percent of plants and insects falling out of sync.
Chris Wyver, a postdoctoral scientist at the University of Reading, found that Bramley apples in the UK bloom earlier now due to warmer springs and increased rainfall. Their pollinators also emerge earlier, but are less sensitive to temperature cues that trigger apple blossoms. If this divergence continues to widen, it could threaten apple yields.
“We saw that in warmer sources the mismatch was slightly larger compared to cooler sources,” Wyver said.
In crops such as cranberries, Brazil nutsand passion fruitflowering times also occur weeks earlier.
If timing worsens globally, scientists warn it could also worsen the decline of pollinators. Inadequate pollination currently causes a 3 percent to 5 percent decrease in global fruit, vegetable and nut production annually, resulting in more than 400,000 deaths due to reduced access to diverse and nutritious diets.
“The impact probably won’t be felt in the UK or the US or Europe – the global North,” Wyver said. Instead, he noted, the strongest impact is likely to be felt in regions already experiencing food insecurity, where supply chains are less reliable.
In some cases, managed honey bees can compensate for pollinator losses if timing mismatches cause significant native pollinator decline. Farmers already use honey bee colonies to pollinate crops such as apples, nuts and seed crops.
However, there is supply concerns.
“If we have to turn to honeybees, the question is, will there be enough?” Wyver said. “I’m worried that it’s just going to create a bidding war for honeybees that’s going to make food more expensive.”
In early April of this year, Godtfredsen’s colleagues from the Rocky Mountain Biological Lab skied to the research meadow to lay large black shade cloths on the snow, each about 16.5 feet wide. Over time, the dark dust causes snow to melt faster than the surrounding area, mimicking pockets of earlier spring. Once the snow melts, they remove the patches so plants can grow.
“The plants need to grow to a good size and put up flower stalks, and then flower,” Godtfredsen said. “That’s when I go out.”
As soon as the plants are ready, usually in late May, Godtfredsen walks to the meadow. They and a team of research assistants spend the summer counting the number of fruits on the plants they study, observing bees as they move from one flower to the next, and collecting seeds.
“Basically, you stand up, walk two feet, crouch and look at another plant,” Godtfredsen said.
The team then compares data between the black-clad, early snowmelt plots and normal conditions, and compares flowering and pollinator activity.
“What we’re seeing is a common narrative in climate change research,” Godtfredsen said. “Some species are going to benefit from this scenario, and some will suffer.”
One of the research site’s earliest blooming flowers, Nuttall’s larkspur, or Delphinium nuttallianumhad fewer pollinator visits than the other flowers.
Another wildflower species they study, prairie smoke, or Geum triflorum, performs better under the early snowmelt manipulation. The plant has larger stems and produces the same number of seeds. But a third species, wild blue flax, or Linum lewisiitakes hits across the board, with smaller stems, lower seeds and more signs of plant stress.
“The narrative is never simple,” Godtfredsen said. Godtfredsen acknowledged that this could be because the plants they study rely on a variety of animal pollinators, including bumblebees, solitary bees, flies and hummingbirds.
Plants that rely on specialist pollinators – those with highly adapted relationships to specific plants – may be significantly more affected by seasonal shifts caused by climate change.
Lonely native squash bees, Peponapis pruinosa and Xenoglossa strenua, for example, are crucial pollinators of squash, pumpkins, and gourds in the United States, collecting pollen primarily from plants in the squash family. But a recent study revealed that squash plants produced fewer seeds in drought conditions, threatening squash plants and the bees that depend on them.
“The connections are very direct and limited between specialist bees and the plants they feed on,” said Ed Henry, an ecologist with the US Department of Agriculture’s Natural Resources Conservation Service. If those connections are broken, then “the [specialist bees] going to be in great danger.”
We also don’t know how much tolerance for change is built into our ecosystems, Henry explained, or when we will exceed that tolerance to the point where plants or pollinators decline significantly or become extinct.
“It’s like we’re walking in the dark, and we know that there are cliffs, and we don’t know where the edge is,” Henry said. “But we continue to step forward.”
One of the biggest challenges is the lack of reliable, long-term data on insect pollinators, so scientists know very little about how their populations and timing have changed.
Such a data gap – especially in the tropics, where pollinators and the farmers who depend on them is particularly vulnerable – makes it difficult to determine whether conservation efforts are needed to counteract timing.
“In some places the data is fantastic,” Wyver said, “but in others we don’t really know what’s doing the heavy lifting from a pollinator standpoint, and addressing those parts of the world has been a big challenge. ”
Through his work at USDA, Henry guides and assists state and local land managers in planning and installing pollinator forage and habitats on the nation’s working fields. Pollinator habitats on farms can improve crop yields and reduce the need for pesticides, which can help farmers with climate change adaptation.
Native plants adapted to local climate, soil and pollinator species can provide food and habitat for pollinators that are more resistant to extreme weather conditions in a specific region.
To make our food system more climate resilient, Henry noted, we need to aim for diversity and complexity, not the other way around.
“When you simplify a system,” Henry said, such as through monoculture farming, “it’s usually less resilient. Nature creates the most resilient system over time.”
