A new study in Tree Physiology highlights a paradox in Canada’s boreal forests: jack pine (Pinus banksiana) is improving its water-use efficiency as the atmosphere becomes drier, yet the same adaptation is tied to slower growth on sandy soils. Researchers measured 30 years of tree rings across three sites in western Québec, using dual isotopes to track how the trees balance carbon uptake with water conservation.
“Our results reveal a physiological tipping point, where increased efficiency no longer sustains carbon gain under intensifying climate stress,” said lead author Oloruntobi Gideon Olugbadieye of the Institut de Recherche sur les Forêts in a published statement.
The study found that vapor pressure deficit (VPD)—a measure of atmospheric dryness—was the dominant driver of these shifts. As VPD rises, trees close their stomata to conserve water, conserving resources but restricting carbon uptake.
The results suggest that while rising carbon dioxide and atmospheric demand push jack pine toward greater water-use efficiency, the trade-off may be a decline in productivity on drought-prone sites. For industries tied to forestry, pulp and paper, or carbon accounting, this means carbon storage projections could be overly optimistic in regions where soils drain quickly and moisture is limited.
At the same time, fire risk in Canada’s boreal zone is climbing, with hotter and drier summers intensifying the pressure on already stressed stands. Site-specific management—such as shorter rotations, selective thinning, or alternative planting on sandy eskers—may be needed to maintain resilience as climate stress accelerates.
