Blueberries are highly coveted, but the coveted mountain fruit has been hard to find in much of northern Idaho and eastern Washington this year.
Pickers were able to locate some productive plants and beds, but often encountered healthy bushes with few or no berries.
“In general, this is not a very good year,” said Wayne Kasworm, a grizzly bear biologist for the US Fish and Wildlife Service who tracks blueberry production in the Selkirk, Cabinet, and Yaak mountain ranges.
With the changing climate, scientists like him are increasingly pursuing blueberries, which are an important food source for grizzly bears and other wildlife, and are also coveted by humans. Native Americans have harvested blueberries for thousands of years and continue to do so today. The small berries with a pleasant mix of sweet and tart are also attacked by recreational and commercial pickers. They are used to make pies, ice cream and other desserts, and added to pancakes, milkshakes and smoothies.
Grizzlies depend on the berries as their primary food source.
“I started looking at blueberries, in part because they’re a very big part of the bear diet,” said Tabitah Graves, a scientist with the US Geological Survey. “Glacier National Park, which is where most of my work is focused, blueberries make up over 50% of their diet in midsummer, so that’s a pretty big part and during the time they’re gaining fat to be able to overwinter. ”
In the course of studying plants, she learned how important they are to Native Americans and others, and how they play a small role in rural economies. Small restaurants and shops sell blueberry products, and some people make extra money by picking and selling them.
But not only humans and bears are looking for the berries.
“The other thing I learned doing this work is how many other species depend on blueberries. It’s really a key species,” Graves said. “We found coyotes, martens and weasels (with berries) and we took pictures of all kinds of birds and small mammals that also eat blueberries. I don’t know how important they are to all of these species, but I do know they are part of their diet.”
What makes a good blueberry?
Graves is studying what blueberry plants need at different stages of their development to produce berries and how the distribution of the plants might change in response to climate factors such as larger, more frequent, high-intensity wildfires.
She and a graduate student identified five species of bumblebees and other bees that help pollinate the plants. One of these, the western bumblebee, is in decline and a candidate for protection under the Endangered Species Act.
“Occupancy dropped 93% between 1998 and 2018 across the western United States. It wasn’t quite as bad up here in the Northwest, which is good, but it’s a concern,” Graves said.
Researchers like her want to know how new fire regimes may affect the facility. Blueberries need lots of sun and tend to like the types of openings that fire often creates. When tree canopies close due to plant succession, berries are often shaded.
Some Native American tribes used fire to manage the blueberry’s habitat. But these burns were usually of low intensity. Today, many fires, caused in part by climate change and a build-up of biomass resulting from earlier firefighting, burn much more intensely.
“Fire used to be used on purpose to regenerate bush fields and get them to produce more blueberries, but now we have a different system and climate,” Graves said. “We don’t really know yet what the more serious fires are – what kind of impact that will have on (berry) distribution.”
Graves developed a method to track the distribution of blueberry plants by using aerial photography to capture the plant’s seasonal color change. They turn red in late summer and fall. She and her team used the paint to map the blueberry’s habitat and then conducted field visits to determine the method’s accuracy.
Janet Prevey, another USGS scientist, has studied how the plant might respond to climate change. It could get dramatic. Plants may be less common in some lower and drier locations. That could mean that blueberries are retreating from some of the plant’s southern ranges and encroaching on northern latitudes.
Prevey found that under some carbon emission scenarios, blueberry habitat could be reduced by 5% to 40% in the Northwest and expand by 5% to 60% in northern British Columbia, Canada. The timing of flowering and fruiting could also change. She found that flowering can advance in the calendar by 23 to 50 days and fruiting can advance by 24 to 52 days.
“Where there are a lot of blueberries now, maybe we’ll see fewer blueberries growing in the future,” she said. “But all of this is based on modeling and climate projections.”
Kasworm has been tracking blueberry plant production in the mountains of northern Idaho and northwest Montana for several years. He and colleagues also use grizzly bears to identify the blueberry’s habitat.
Every summer he visits blueberry fields to measure how much fruit they produce. He drops 10-inch by 10-inch frames along a random cross-section through the patches about every 2 feet, then counts the berries within. He also uses data tractors to document climatic conditions.
“My goal is just to compare year by year,” he said. “It’s an index – is this a good year, a bad year, or an average year?”
This year the Selkirks were better than the Yaaks and the production was the worst in the Cabinet Mountains. In all places the berries were less numerous and smaller than usual. Kasworm uses a refractometer, a tool used by winemakers to track sugar levels. Although the berries were small this year, he said the sugar content was similar and often higher than previous years.
He noted that anyone who has seen bear poop full of whole berries might wonder why bears bother eating them.
“It’s the juice, the soluble sugars in that juice — that’s what bears get out of them because they turn over their stomach contents pretty quickly,” he said. “A bear’s approach to doing something is to keep eating, get what you can quickly and easily, defecate or remove it from the system and keep eating. In this way, they are trying to capitalize on a more short-term food resource and get as much out of it as possible when it is available.”
Kasworm has put tracker collars on several bears. In August, several of the bears located themselves on mid- to high-elevation southern slopes, indicating they likely found productive berry patches. He and his colleagues are now using the bears to identify productive berry areas by noting where they hang out in late summer and then visiting those locations to see if they’re good beds. Then they record conditions at those locations and use the data to predict where berries might occur elsewhere.
“We do that by looking at things like soils, slope, elevation, orientation, canopy and a whole bunch of different things that are there to ask the bears where the good spots are and use that information to do.” try to project over a larger area where similar sites are located.”
“I started looking at blueberries in part because they are a very big part of the bear diet. At Glacier National Park, which is where most of my work is focused, blueberries make up over 50% of their diet in midsummer, which is a fairly large component, and during the time when they’re gaining fat to be able to overwinter.
“The other thing I learned doing this work is how many other species depend on blueberries. It really is a key species. We found coyotes and martens and weasels (with berries) and we took pictures of all kinds of birds and small mammals that also eat blueberries. I don’t know how important they are to all of these species, but I do know they are part of their diet.”
Tabitah Graves, scientist at the US Geological Survey
“It’s the juice, the soluble sugars in that juice — that bears come out of (blueberries) because they turn over their stomach contents pretty quickly. A bear’s approach to doing something is to keep eating, get what you can quickly and easily, defecate or remove it from the system and keep eating. In this way, they are trying to capitalize on a more short-term food resource and get as much out of it as possible when it is available.”
Grizzly bear biologist Wayne Kasworm explains why bear poop is filled with unchewed berries