Growing up in Kent, nicknamed the “Garden of England,” Chris Wyver was surrounded by apple and pear orchards, and he always noticed the native bees that zigzagged through the orchards every year, cross-pollinating the fruit trees when they blossomed.
Now, Wyver is a Ph.D. student at the University of Reading, studying how climate change is affecting bees and their crucial role in transferring pollen between trees to help them produce robust fruit. He and his colleagues have observed that warming temperatures have prompted many wild bees to start emerging earlier in the year, timing that may no longer sync with fruit blossom cycles as closely as before. Wyver and his co-authors recently published a paper in Ecology and Evolution detailing the findings of their study.
Analyzing more than 350,000 data points covering 40 years and 88 wild bee species, they found that for every 1 degree Celsius in temperature rise, wild bees emerge from their nests an average of 6.5 days earlier. Though some species did not change their timing, others showed dramatic shifts, changing by 10 or more days.
As spring becomes warmer, bees could emerge even earlier, and they may struggle to survive if their normal food sources are not yet available. The plants, in turn, may receive suboptimal pollination, hurting the yield and quality of produce. Both the bee populations and the crops they pollinate could suffer.
The other side of the equation is how climate change could be affecting the timing of blossoms, which researchers are also studying using a website called FruitWatch, where members of the public can post observations.
Timing is everything
For bees to pollinate a crop, Wyver explained, they must be present during the right time in the plant’s cycle. The timing of important cyclical life events, like hibernation or migration, is known as phenology. The climate-driven phenological shift bees in the U.K. are experiencing is especially concerning, Wyver says: “If they’re not there at the same time, the pollination doesn’t happen.”
Native bees are highly effective at cross-pollinating flowering fruit plants across a wide area, and this cross-pollination generally leads to better quality fruit that can be more nutritious and even have a longer shelf-life. Though honey bees and other pollination methods can be used, they can be costly and may be less efficient than cross-pollination from native bees.
In addition to bees, many other animals face potential threats from phenological shifts, ranging from the timing of flowering and breeding seasons to predator-prey mismatches. In some areas, species that usually change their fur color to white to blend in with winter snow — like snowshoe hares — face a phenological mismatch when their coloring no longer syncs with the environment around them, leaving them sticking out rather than camouflaged.
“We know that it’s not just bees, but biodiversity responds to changes in climate,” says Deepa Senapathi, ecologist and associate professor at the University of Reading and a co-author on the study.
Bees around the globe are facing numerous climate-related struggles, including extreme weather, drought, heat, wildfires, and storms. Bees provide vital ecosystem services, especially through their role as pollinators. When bees suffer, it can affect the entire ecosystem — including humans.
Native bees are adept at pollination
“Apart from saying that every species has its own intrinsic value, bees are really important pollinators of plants and crops,” Senapathi says. “Both wild plants and very important crops that are needed for food security are dependent on insect pollinators, particularly bees, so understanding how bees might be responding to changing climate and what implications this might have for crop pollination and wildflower reproduction in the future is quite key if we need to put conservation management in place that actually works.”
Other pollination methods include using wind, artificial means, or managed honeybees, though each method has its pros and cons, along with costs that will be passed on to consumers when they buy produce.
Wyver says native bees are ideal for pollinating fruit crops because they are especially adept at cross-pollination — collecting pollen from different trees and spreading it all around the orchard. He says honey bees have different pollination patterns.
“Honey bees, for example, tend to stick to one row so they don’t do so well at cross-pollinating, while the native bees are a bit more haphazard all over the place where they will go around an orchard, so they actually touch all the pollinizer varieties and transfer pollen between the varieties, so they are better than honey bees at pollinating,” Wyver says.
The importance of pollination extends far beyond the bees, rippling to the human food supply and economy.
“If you’re going to lose key insect pollinators that pollinate these crops, that’s going to have an impact not just on the ecology of the system but also on the economy and on food security,” Senapathi says. “And other than just a drop in quantity in yield, good pollination is also required for quality of produce. For example, strawberries that are well-pollinated have a longer shelf life, apples that are well-pollinated have a higher market value because more of them are classified as grade-one apples. So there is an economic impact as well, and also a nutritional impact because well-pollinated fruit and veg are higher in micronutrients that are vital for human health and well-being.”
FruitWatch gathers blossom data
To learn more about any changes in blossom timing, Wyver and colleagues developed FruitWatch, a website where people can record the stages of fruit tree blossoms they are observing, creating a valuable data set for future studies. In the past two years, FruitWatch has received nearly 7,000 reports for apple, pear, plum, and cherry trees across the United Kingdom. People submit the location, tree type, and variety if known, upload photos, and submit data on the blossoms they see.
“It’s been really interesting seeing [the reports] come in and watching when things are blossoming and looking at the peoples’ pictures that they send in,” Wyver says. “We’re trying to fill the gap. With the bee data there’s great spatial coverage from all across Great Britain, whereas from the fruit blossom side, there’s very little spatial coverage.”
As they fill the data gap, Wyver and colleagues are analyzing the data they receive to observe patterns, looking at temperature, rainfall, frost, and other factors to see what role they may play. Future analysis will also focus on extreme climate-related events in addition to more gradual changes in temperature, rainfall, and other factors.
Previous studies in the U.K. have found some plants are flowering earlier due to climate change, so researchers are keeping a close watch on potential springtime patterns.
And they’re working to learn more with an eye to potential management solutions to help alleviate the negative effects of a phenological mismatch.
“We need to really delve in to see where those critical mismatches might be happening and, if they’re happening, what we can do to try and put in place management that could help mitigate that asynchrony,” Senapathi says.