Pioneering UNH Study Finds Drought May Limit Tree Growth | New Hampshire Public Radio

Pioneering UNH Study Finds Drought May Limit Tree Growth

Oct 29, 2020

The drought study used barriers to keep water from reaching the ground in experimental plots of red oaks and white pines.
Credit UNH Agricultural Experiment Station

Certain New England tree species might not grow as fast after severe drought years like this one, according to new research from the University of New Hampshire.

The findings come from an ongoing study on plots of red oak and white pine trees – both key timber species – in Durham and the White Mountains.

The experiment attempts to simulate drought conditions, and has now lasted through two actual drought years as well – 2016 and 2020.

Researcher Heidi Asbjornsen says trees need to take in water from the soil for photosynthesis, where they turn carbon dioxide into carbohydrates that help trees grow.

“So if they deplete their carbohydrates during a prolonged drought, that could just have long-term consequences in terms of their overall health,” Asbjornsen says.

Her study predicts that these oaks and pines won’t grow as much wood next year due to this season's dry conditions. It also finds differences in the timing of how these species react to drought.

A UNH researcher samples a tree canopy this fall as part of the drought experiment.
Credit UNH Agricultural Experiment Station

Asbjornsen says this is one of the first drought experiments of its kind in the Northeast, where even short-term droughts have been historically rare – but could become more common, in between heavier, more sporadic rains, as the climate warms.  

"Conducting these manipulated experiments really provides a great opportunity to start to understand the degree that different tree species are able to adapt and survive droughts in the future,” Asbjornsen says.

New Hampshire’s current drought is still extreme in part of the state, and did not improve between last week and Thursday’s update from the National Drought Monitor.

The drought is moderate through most of New England, with severe and extreme patches in far Southern Maine into Southeastern New Hampshire, as well as Cape Cod and the south coast of Massachusetts into Rhode Island.