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Going to Extremes at HBEF

Notice: This project page is no longer being updated as of January 2023.

There is growing concern that the frequency and severity of extreme weather events are increasing under the changing climate.

Scientists continue to study the impacts these extreme weather events can have on natural and managed ecosystems. Progress has been made in understanding the impacts of gradual changes in temperature and rainfall on forest systems. However, much less is known about the consequences of extreme weather events. This is because extreme events are unpredictable in time and space, which makes them very difficult to study.  A team of scientists at the Hubbard Brook Experimental Forest (HBEF) are taking on this research challenge. They are learning the effects of extreme weather are often equal to or greater than the more gradual shifts in temperature and rainfall patterns associated with climate change.

Explore three types of extreme weather that occur in the Northeast: ice storms, drought, and warming. Learn about the impacts these extreme events are having on northern hardwood forest ecosystems and what you can do to help make your forests more resilient in a changing climate. And don’t forget to look up!

HB_Ice Storm Control

The Hubbard Brook Experimental Forest (HBEF) is a world-renowned center for research on hydrology and forest ecosystem dynamics. The ~8,000-acre HBEF was establish in 1955 by the USDA Forest Service. Located in the White Mountain National Forest in New Hampshire, the forest is a center for hydrologic research in New England. The original focus was to better understand how forest management and forest harvest affect the timing and amount of stream flows. Since that time, hundreds of scientists from around the world have used the small watersheds at Hubbard Brook. Researchers have studied the effects of natural and human disturbance on forest nutrient cycling, soils, plants, and animals in northern hardwood forests.

Ice storms are an important natural disturbance in forest ecosystems in northern forests around the world. These glazing events (defined as a quarter inch of ice or more) are often perceived as rare occurrences. However, ice storms can be common in certain regions, such as the “ice belt,” in the United States, which is a broad area that extends from east Texas up through southern New England. Mild-to-moderate ice storms tend to happen every 2-5 years in many parts of the northeastern United States. These types of storms often present communities with economic hardship. To date, ice storms in have caused billions of dollars of insured and uninsured property losses in the US (Irland 1998, 2000). They also often cause school and business closures and disrupt road and air travel. In addition, the ice can leave thousands to millions of households without power and can result in storm-related injuries and fatalities.

Scientists expect ice storms, which can cause major disruptions to become more severe with climate change. However, not much is known about the short- and long-term effects of ice storms on forests. It is hard to study ice events since we don’t know when or where the next ice storms will occur. Instead of waiting, scientists at the Hubbard Brook Experimental Forest created experimental ice storms. Data from this experiment now give scientists a window into how forest health, vegetation growth, wildlife, and nutrient cycles (like carbon and nitrogen) are affected.

Scientists are also looking at results from the 1998 ice storm. It is hoped that the Hubbard Brook work will help answer questions about how forests respond to big ice storm disturbances and empower communities to be more prepared for the next big ice storms.

Lindsey Rustad, a research ecologist with the USDA Forest Service, discusses the first-ever ice storm experiment. Hear how the experiment is helping researchers better understand the impacts that an extreme ice event can have on forest ecosystems.

HB_Ice Storm Extreme

As winters warm, the ice storm belt that extends from Texas to southern New England is likely to move north. Fueled by warmer winters, more moisture in the atmosphere along the Atlantic coast, and arctic blasts of cold air, future ice storms may become more severe. Climate models predict that under likely climate change scenarios, we will see the same number of ice storms as we do today. However, more of these storms will fall into the class of large events like the 1998 storm (Swaminathan et al. 2018).

To create an ice storm, the research team used fire hoses to spray water over the forest canopy during winter cold snaps. There were 10 experimental plots, and each plot was about the size of a basketball court. Each plot received different treatments of ice (ranging from a quarter of an inch of ice up to three-quarters of an inch of ice) to simulate different storm severities. Some of the plots received a second treatment of ice the following winter. This allowed scientists to measure the forest’s response after back-to-back ice storms. According to the National Weather Service, the quarter inch ice treatment simulates a relatively light icing event seen in southern New England. The half inch ice treatment simulates a significant ice storm and corresponds to ice storm warnings seen in northern New England. Finally, the three-quarter inch ice treatment simulates an extreme or “epic” ice storm.

Scientists are piecing together the early results from this ice storm experiment. The experiment identified a threshold at which ice begins to seriously damage trees. It also found that the twigs and branches brought down by a single ice storm can rival the amount that normally falls in a whole year. Other effects were on soil temperature, and nutrient cycling through this ecosystem. Check out more of their findings in the research brief posted on the HBEF website.

HB_Drought by Design

The Northeast is experiencing a greater number of heavy rain events, and this increase in number of events is expected to continue. However, much of that increased amount of rain is falling in the winter, rather than in the summer. Lindsey Rustad, a research ecologist with the USDA Forest Service, discusses how this shift will likely cause more drought events, despite an increase in total rainfall.

Similar to other extreme weather events, it is difficult to study drought because researchers cannot plan for where and when one might occur. Just ask Heidi Asbjornsen, associate professor of Natural Resources and the Environment at the University of New Hampshire. Here Heidi tells about how her team took on the challenge and designed a way to study drought in a forest ecosystem.

Heidi Asbjornsen, is an associate professor of Natural Resources and the Environment at the University of New Hampshire. She shares how the research here on drought can help land managers and landowners take care of the forests they care about. By having a better understanding of the forests, land managers can make more informed management decisions.

Once the drought experiment was started at the Hubbard Brook Experimental Forest, researchers replicated the design at other sites. Sites at the University of New Hampshire (UNH) looked more closely at the impacts of drought on the State’s more southern hardwood forests. Researchers are studying the effects of altered rain patterns, less consistent snowpack, earlier snowmelt, and a longer, warmer, growing season. Data will give a bigger picture about how these changes may impact forest ecosystems into the future.

HB_Forest Drought

Drought and drought-associated forest disturbances are expected to increase under a warming climate. Drought has both direct and indirect effects on forest ecosystems. It is important to understand these effects in order to adapt and manage forests for drought uncertainty. Types of management include reducing leaf area by thinning or regenerating forests with species that consume less water.

Drought is expected to increase in frequently in the Northeast under our changing climate. However, historically much of New England has not experienced frequent extreme droughts. Because of this, many tree and wildlife species may be more vulnerable to these future conditions. Heidi Asbjornsen, associate professor of Natural Resources and the Environment at the University of New Hampshire, explains.

Did you know that there is an international drought network funded by the U.S. National Science Foundation? Drought-Net is an “experimental network aimed at advancing understanding of how and why terrestrial ecosystems across the globe may differ in their sensitivity to drought.”

In addition to drought, northern forests are also facing increased pressure from forest pests and increased competition. This is in part because more southern tree and pest species are now able to establish in northern forests due to milder winter temperatures. Boston University biology professor, Pamela Templer, tells us more about what is happening.

HB_Forest Soil Warming

The response of forests to a changing climate is complex. In the Northeast, climate change means warmer temperatures year-round, which can have a positive impact on tree growth. Warmer winter temperatures are expected to lead to smaller and patchier snowpacks. Because snow insulates the soil, less snow may mean more soil freezing, which can damage roots and offset any increases in growth resulting from warming. The Climate Change Across Seasons Experiment was designed to study these changes. This is the first experiment of its kind to examine the combined effects of soil warming during the snow-free seasons and soil freezing during the winter.

Studying climate change in mature forest ecosystems can be challenging. In this experiment, heating cables warmed the forest soil in spring, summer, and fall. In the winter, the insulating snow was shoveled off the plots, causing the soils to freeze, and then there were warmed back up with heating cables, creating a ‘freeze-thaw’ cycle. Check out the team’s publication on this experiment for more details on how it was implemented and the results they found.

At Hubbard Brook, long term records show that the climate has been warming, and researchers know from data collected at the site that snow packs are shrinking. Less snow pack is actually leading to more frost in soils. Because of this, we are actually getting colder soils in this warmer world. Listen to USDA Forest Service research ecologist, Lindsey Rustad, speak further on this topic.

“Many of us are familiar with the fact that temperatures are rising around the world, however many might not know that temperatures in winter are rising faster than the rest of the year," reports Pamela Templer, a professor in the Department of Biology at Boston University. Give a listen to this webinar, 'Climate Change Effects on New England Forests: Shorter and Warmer Winters' from the Northern Institute of Applied Climate Science which features Pamerla Templer's work.

Forests and wildlife will have to adjust to changes in climate – if they can. So will the people in the region who depend on the forest and the snowpack for their livelihood. Tourism in New England relies on the renowned fall foliage, spring sugaring season, and outdoor winter recreation such as skiing. However, these once dependable events are now changing, making many rural economies in New England more vulnerable to climate change.


Woodstock, NH

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USDA Forest Service, Hubbard Brook Experimental Forest