Research reveals white spruce in N.B. shows climate resilience, but warming could change that

New research shows a 25 per cent drop in growth during recent drought years, with larger trees affected the hardest. While the species-a key source of wood to the provincial forestry industry-shows resilience, current climate models suggest that within a few decades, white spruce growth may decline in N.B.

White spruce (Picea glauca), a key species in New Brunswick's forestry sector, has shown resilience to recent droughts, according to new research.

However, findings suggest that climate change may already be reshaping forest dynamics.

Katherine Tripp, who recently completed her master's degree in forestry at the University of New Brunswick, spent the past two years studying how these trees respond to drought.

Her findings revealed a 25 per cent drop in growth during the recent 2017-2021 drought years, with 2019 marking the lowest growth increase since 1968. Larger trees were hit hardest.

Tripp's research comes at a critical time, said Dr. Anthony Taylor, Tripp's co-supervisor and an associate professor in the faculty of forestry and environmental management at UNB.

He emphasized the species' economic importance.

"Most of the trees, I'd say more than half the trees, planted across the region are white spruce trees."

Tripp's study was based in the Black Brook district near St. Leonard, where she sampled white spruce trees across 32 planted sites. Using the science of tree rings (dendrochronology), she measured annual growth and compared it with drought severity.

"It's amazing how much we can learn by studying trees, particularly from their rings," she said.

"A larger tree has a bigger root and branching system, and so it has more to feed. It's harder for that tree to keep up when the resources are limited than a smaller tree of the same age."

Contrary to expectations, competition and site factors, such as slope, soil texture and water table depth, did not significantly affect drought response.

Tripp attributed this to the nature of planted areas, where trees are intentionally planted on optimal sites and often thinned to reduce density.

"We didn't find any impact of stand density on the drought response … most have received silvicultural treatments, meaning that they've been reduced in density," she said.

The study's results offer cautious optimism for forest managers. While growth declined during droughts, mortality rates remained low, suggesting that current thinning practices may help trees withstand dry conditions.

Still, thinning has its limits.

"It can only be thinned to a certain low density before it doesn't have positive effects anymore. It can turn negative," she said.

Her findings have implications for forestry operations.

Larger trees, which are typically harvested for lumber, may need to be cut earlier to avoid drought-related losses. Tripp noted that this could influence harvest rotation strategies, especially as climate models predict more frequent and severe droughts in Atlantic Canada.

Her research also highlighted the importance of studying natural stands, which were not included in this study.

"Understanding trees in a non-plantation environment would be helpful to capture the more natural range of density and site conditions that this project didn't capture," she said.

Taylor also stressed the need for similar studies in natural forests to improve predictions of climate change effects, as natural forests may provide insights into how genetic diversity and interspecies competition influence drought resilience.

He noted that this year's summer drought in New Brunswick was worse than the period Tripp studied, a point confirmed by Agriculture and Agri-Food Canada (AAFC), which has published the Canadian Drought Monitor map and associated products every month for about the past 20 years.

"Our data shows 2025 has seen the worst drought conditions for that time period," said Stéphanie Blais, senior communications advisor with AAFC.

"Looking at individual climate stations in the region, 2025 was within the top five driest July-August-September periods."

Dr. Loïc D'Orangeville, an adjunct professor at UNB and an associate professor at the faculté de foresterie, de géographie et de géomatique at Université Laval, was also one of Tripp's supervisors.

"The way this project was initially planned was to verify if the plantations in the Maritimes were vulnerable to drought. There are many concerns about drought across much of the world, especially in drier regions, including central Canada (which receives two to three times less precipitation than the Maritimes). Still, there is an ongoing debate about whether wetter areas are also vulnerable or not," D'Orangeville said.

"Given white spruce's importance for the industry and the communities as a key source of wood, [Tripp's] results show that we've not yet observed drought levels sufficient to really put white spruce plantations at risk. But climate models suggest it's going to get much warmer, which means we'll eventually start seeing declines."

Taylor warned that continued warming with climate change over the coming decades may have a negative impact on white spruce growth in New Brunswick and push its range farther north.

"It's imperative society take climate change more seriously and reduce greenhouse gas emissions and deforestation," said Taylor.

Tripp's work adds to a growing body of research aimed at helping the forestry industry adapt to climate change. She hopes it will guide future decisions in forest management and policy.

"I know white spruce is vital to the province for many reasons," she said.

"Hopefully, this research can help."