Wild Blueberry Fields in Down East Maine are Warming Faster than Previously Thought

A new study by researchers from the University of Maine on the impacts of climate change on the barrens in the last four decades reports that in Down East Maine, wild blueberry fields are warming faster compared to the state as a whole.

According to the team, the variation in increasing temperature rates indicates the need to design particular wild blueberry management plans, like irrigation and fertilizer use, to alleviate the impacts of climate change on Down East fields, instead of using approaches devised using statewide climate patterns.

Rafa Tasnim, a PhD student of ecology and environmental sciences, guided the study that examined changes in climate change patterns, specifically in precipitation and temperature, at Down East wild blueberry fields in the last four decades of growing seasons from 1980–2019, and then compared them with aggregate variations in climate quantified for the state as a whole.

Yongjiang Zhang, an assistant professor of applied plant physiology, and Francis Drummond, professor emeritus of insect ecology and pest management, collaborated on the study, which is the first to evaluate climate change patterns for a fruit spanning various fields in a single production region.

The study results were published in a special issue of the research journal Water titled “Impacts of Climate Change on Plant Water Use, Carbon Balance, Nutrient Economy, and Their Interactions.” The results also showed that increasing temperatures at Down East wild blueberry fields induced increased possible evapotranspiration, or water loss, over 40 years.

The continuation of water loss could affect the water supply for crops and the low-water holding capacity of the soil in which the crops reside. The combined effects of warming and higher probable evapotranspiration could affect the health and yield of wild blueberry, the researchers noted.

Our findings clearly show that wild blueberry fields are not immune from climate change, so growers will need to be prepared for future warming and a predicted increase in water loss. Researchers will also need to develop new and innovative solutions to make this cultural heritage sustainable under a quickly changing climate.

Yongjiang Zhang, Assistant Professor of Applied Plant Physiology, University of Maine

A major part of the 18,000 hectares of wild blueberry fields in Maine is located in the Coastal Climate zone, which has been undergoing quicker warming compared to the Interior and Northern climate zones.

Tasnim and her collaborators report that the change in climate over the three zones could lead to wild blueberry fields experiencing the impacts of climate change differently. The concept questions the efficacy of utilizing statewide climate statistics in management practices, which prompted this study.

The researchers examined four decades of annual data for minimum, average, and maximum temperature and precipitation for 26 wild blueberry fields—24 in Washington County and 2 in Hancock County—all at least measuring at least 1 km² in size.

The team used Geographic Information System (GIS) methods, remote sensing, and several tools in ArcGIS Pro Software to measure climate patterns in the study area. A comparison of the results with statewide data, gathered from the Climate Reanalyzer, showed that there was a higher increase in minimum, average, and maximum temperatures in the study area compared to overall Maine between 1980 and 2019.

The study notes that the highest temperature for the blueberry fields increased by around 1.2 °C, while it increased by around 0.95 °C for overall Maine. The minimum temperature increased in the fields by around 1.55 °C, while the state underwent a 1.25 °C increase in its minimum temperature. The state underwent an increase of 1.1 °C in its average temperature, but in Down East fields, it was 1.3 °C.

Also, the research unraveled variations in climate throughout the Down East fields. The fields situated closest to the coast had been warming the quickest and experiencing the lowest average and maximum temperatures and highest minimum temperatures.

According to the researchers, “Since wild blueberry fields closer to the coast showed significantly higher increases in growing season temperatures, growers who have fields closer to the coast need to pay more attention to the potential negative effects of warming on crop health and production.”

The team found no variations in precipitation across the 40 growing seasons throughout the Down East wild blueberry fields or in the state as a whole.

The researchers identified a positive correlation between temperature, evapotranspiration, and crop health at the time of their study. With the continuous increase in temperatures, and thus evapotranspiration, more water deficits could be experienced throughout wild blueberry fields, the team notes. Remote sensing methods that consider evapotranspiration can thus help growers determine inadequate water supplies and assess the need for irrigation.

Earlier research by Tasnim; Zhang; Drummond; Seanna Annis, a UMaine associate professor of mycology; and Lily Calderwood, an assistant professor of horticulture and University of Maine Cooperative Extension wild blueberry specialist, on wild blueberry physiology showed that photosynthesis dropped when air temperature exceeded 25 °C. Moreover, wild blueberry crops and soil underwent water loss when temperatures exceeded 22.4 °C.

As part of this study, Tasnim and her collaborators discovered that out of 26 Down East wild blueberry fields, over half experienced temperatures surpassing the 25 °C threshold between 1980 and 2019. Optimum temperatures for July and August, the peak of the growing season, have also exceeded 22.4 °C and 25 °C.

The team added that the risks posed by climate change indicate the need for wild blueberry growers to consider mitigation measures and irrigation and soil amendment methods in their plans. The development of predictive crop production models that consider the temperature and evapotranspiration thresholds examined in this study would also help them regulate their crops with the climate change.

In light of our recent studies regarding climate change and wild blueberries, starting from this summer under the supervision of Dr. Zhang, we are further going to investigate mitigation techniques for warming using biochar-compost mix and mulch in an experimental warming test in the wild blueberry field at the Blueberry Hill Farm owned by University of Maine for research.

Rafa Tasnim, PhD Student of Ecology and Environmental Sciences, University of Maine

Journal Reference:

Tasnim, R., et al. (2021) Climate Change Patterns of Wild Blueberry Fields in Downeast, Maine over the Past 40 Years. Water. doi.org/10.3390/w13050594.