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Climate can vary across large areas of land, but it can also vary within much smaller areas such as farms. A new study by researchers at Penn State has examined whether these microclimates—the climate of a very small or restricted area—affect pollination by both wild and managed bees and resulting wild blueberry yields.

The study, in Agriculture, Ecosystems & Environment, took place on a 170-acre wild blueberry field in Maine.

Researchers discovered that both wild bees and honey bees found the most densely blooming areas of the fields and concentrated their foraging in these areas. Wild bees also tended to forage on plots that were warmer than average.

The researchers also found that even though managed honey bees were abundant at the site, there was no evidence of fewer wild bees near the honey bee hive locations or in the fields that had the highest honey bee foraging.

Heather Grab, assistant professor in the College of Agricultural Sciences and lead author on the paper, said the findings could be used to help inform precision agriculture approaches to help conservation efforts.

"For example, precision agricultural management approaches often suggest removing low-performing sites from production, perhaps to the benefit of increasing areas for biodiversity conservation," she said. "Remote sensing techniques could measure flower density patterns across the field and identify low-blooming regions, which may be a promising method for selecting candidate areas to convert to conservation habitats."

As pollinators decline worldwide, much research has been dedicated to finding out why, with factors such as climate change and availability of floral resources and nesting habitats identified as contributors, according to Grab. The researchers said that while these factors are important at a broad scale, finer-scale variations in these factors can also drive pollinator distributions in smaller microclimates, such as within farms.

While prior studies have shown that factors like habitat cover in the surrounding landscape and weather patterns can be important for predicting pollinator activity, diversity and health, Grab said a large amount of variability still remains to be explained.

"Much of that variation could be explained by fine spatial and temporal variation in temperature and humidity across the day and across different microclimates within a given area, which is what we sought to explore in this study," she said.

Christina Grozinger, Publius Vergilius Maro Professor of Entomology and director of the Huck Institutes of the Life Sciences, said the project was a collaboration between the Penn State Center for Pollinator Research, the University of Pittsburgh and Wyman's—one of the largest wild blueberry producers in the United States and the largest brand of frozen fruit in the U.S.

She noted that the center and Wyman's have worked together for many years, supporting pollinators and pollination services in agricultural fields.

"Our collaborators at Wyman's noted that some parts of their fields consistently produced fewer berries, but there was no obvious reason," she said. "We decided to tackle this mystery by developing new strategies for monitoring and modeling crop yield, pollinator activity and environmental variation, in collaboration with Vikas Khanna's group at the University of Pittsburgh."

Khanna, professor in the University of Pittsburgh's Department of Civil and Environmental Engineering and co-author of the paper, noted one of the strengths of the study was how tightly knit the collaboration was among all three institutions.

"The impact of climate change on farming systems and agricultural productivity involves complex dynamics," he said. "Tackling these issues demands interdisciplinary strategies that integrate knowledge from diverse fields, as demonstrated by this research team."

Undergraduate and graduate students at the University of Pittsburgh deployed temperature and humidity sensors across the 170-acre commercial wild blueberry field—which was divided into 120 sites that were one square meter in size—and measured the progression of flower blooms as well as the number and diversity of blueberry pollinators.

"We were able to leverage this data to build a model of the microclimates throughout the farm—including both temperature and humidity—that tracked environmental changes every 10 minutes across the entire field throughout the bloom period," Grab said. "We also had data on the location and number of honey bee hives and the fruit set and yield of blueberries at 100 plots across the field."

The researchers found that across the site, variations in the landscape resulted in microclimates with differences of as much as 10 degrees Celsius and 29% relative humidity. Both managed honey bees and wild bees had overlapping foraging areas and habits, with both favoring warmer microclimates, although wild bees foraged earlier in the day and during a wider range of conditions.

The team also found that flower density, which was greater in spots with a warmer microclimate, was the primary driver of both wild bee and honey bee foraging, as well as blueberry yields.

"Because warmer areas of the field also had more flowers and higher yields, changes to the climate that increase microclimate variability may contribute to increased yield variability within fields," Grab said.

In the future, additional studies could explore whether these patterns vary across different, broader regions and in different years, the researchers said.

Other co-authors of the paper were Garrett Sisk and Anaís Ostroski, of the University of Pittsburgh; Travis Dillard and Bruce Hall, of Jasper Wyman & Son; and Sarah Goslee, of the U.S. Department of Agriculture, Agricultural Research Service.