A University of Waterloo black spruce study pinpoints the three traits that let trees thrive in warmer, drier conditions — and why any one of them on its own is not enough.
New Canadian research argues that targeted tree selection — choosing species and individuals with specific biological traits — may matter more for the future of the country’s forests than simply planting greater numbers of seedlings. The study, released publicly on September 16, 2026, comes from University of Waterloo biology professor Dr. Julie Messier, MSc student Sabina Henry and their collaborators, and was published in the journal Annals of Botany.
The team set out to answer a deceptively simple question: what makes one tree grow better than another as conditions get hotter and drier? Working with black spruce, they identified three traits that, taken together, were associated with strong growth in warm, dry climates. Crucially, none of the three worked on its own.
The Three Traits Black Spruce Needed Together
According to the Waterloo researchers, black spruce trees that performed best under warmer and drier conditions shared a specific combination:
- Fewer needles: a lower overall needle load rather than dense foliage.
- Conservative water use: needles that release less water.
- Conservative carbon use: a resource-cautious rather than resource-hungry approach to carbon.
The finding the team flagged as most important is the interaction between the three. Individual traits, measured alone, did not deliver the growth advantage. “The most surprising part of this study is that individual traits weren’t sufficient for the trees to be successful in that climate,” Messier said, noting that the team had expected conservative water use to be decisive on its own. It was not.
Why Fewer Needles Was the Unexpected Result
Fewer needles came with an obvious trade-off: less leaf area means less photosynthesis. That is why the trait was not on the team’s shortlist of predicted winners.
Messier’s explanation is that water loss, not carbon gain, is the binding constraint in hot and dry conditions. “We think this trait helps because trees with fewer needles lose less water through transpiration,” she said. “The trees doing best are using a double safety strategy: they have fewer needles to lose water, and each of these needles loses less water.”
In other words, the winning black spruce were conserving moisture twice over — at the level of the whole crown and at the level of each individual needle. The trade-off in photosynthetic capacity appears to be worth accepting when heat and drought stress are the main threats.
The Carbon-Use Finding That Did Not Fit the Prediction
The team’s original expectations centred on efficient water use and efficient leaf cooling. Instead, the data showed that needles with conservative carbon use supported better growth in warmer, drier conditions — even though carbon use does not directly reduce heat stress or water stress.
The researchers interpret this as indirect selection. Needles, they suggest, tend to be conservative across all resources or acquisitive across all resources; they do not easily mix strategies. Carbon-conservative needles therefore travel together with the water-conservative behaviour that does help under drought, which is why the carbon trait shows up in the results.
That distinction matters for how the finding should be read. The paper’s title — “Selection for fewer, water- and carbon-conservative needles in black spruce trees under warm, dry climates” — describes a trait syndrome, not three independent levers a planner can pull one at a time.
What “Right Trees, Not More Trees” Means for Planting Programs
The practical argument in the Waterloo work is a shift in emphasis. Large-scale tree planting is usually measured in seedling counts. This research suggests that counting stems says little about whether those stems will still be alive and growing decades from now in a warmer climate.
The researchers position their results as a decision-making tool: information practitioners can use to choose which trees to plant, so that planted forests hold up as temperatures rise. Applied at scale, that logic points toward seed sourcing, nursery stock selection and monitoring built around measurable traits rather than volume targets alone.
It is a slower and more technical approach than mass planting, and the study itself does not prescribe policy. What it offers is evidence that the trait combination — not the trait list — is what correlates with growth under stress.
Why This Lands in a Warming Canada
The timing is relevant for readers following climate adaptation in Canada. National assessments have repeatedly described a country warming faster than the global average, with shifting precipitation patterns and longer, more volatile fire seasons — the same pressures documented in Canada’s Changing Climate Report, which maps a nation under strain.
Forests sit at the intersection of several of those pressures at once: carbon accounting, fire risk, water cycles, biodiversity and the economics of forestry regions. Seasonal variability adds another layer of uncertainty for anyone planting today for a canopy that will mature in 2080; forecasters have been tracking exactly that kind of year-to-year swing, as seen in the El Niño fall forecast pointing to a mild autumn and a late Canadian winter.
Against that backdrop, a study that narrows the question from “plant more” to “plant which” has obvious appeal to the people who have to commit budgets and seed stock years in advance.
General Context: How Species Choice Fits Into Canadian Reforestation
The following is general industry background, not findings from this study. Reforestation and afforestation programs in Canada typically involve several actors: provincial and territorial forest agencies, federal programs, Indigenous-led land stewardship initiatives, forestry companies meeting regeneration obligations, and nurseries that grow the seedlings. Decisions about what goes in the ground are usually shaped by seed zones, site conditions, harvest history and available nursery stock.
Trait-based research of the kind described here generally feeds into that chain at the front end — informing which seed sources and which stock are selected before planting crews are ever deployed. Whether that happens depends on how quickly findings reach practitioners, and on whether nurseries can supply material that matches the trait profile being sought. The study does not report any program changes, funding commitments or government adoption, and none should be assumed.
Who Conducted the Research and Where It Was Published
The work was led by Dr. Julie Messier of the University of Waterloo’s Faculty of Science, with MSc student Sabina Henry and collaborators. The institution is based at 200 University Avenue West in Waterloo, Ontario. The resulting paper appeared in Annals of Botany.
The source material does not specify the study’s field sites, sample size, funding sources, study duration or the full list of collaborating institutions. Those details are not mentioned in the material available, and readers wanting the methodology should consult the published paper directly.
For Canadian business and policy readers, the broader signal is consistent with a wider pattern of capital and attention moving toward climate resilience and infrastructure durability — a theme that also ran through the commitments announced when the Canada Investment Summit unleashed nearly $500 billion in new commitments. Forests are a slower-moving asset than a data centre or a pipeline, but the same question applies: will what is built today still function in the climate of 2060?
Frequently Asked Questions
Does this study say Canada should plant fewer trees?
No. The argument is about selection, not volume — choosing trees with the right traits rather than relying on mass planting alone. The researchers do not recommend reducing planting numbers.
What does “conservative” water or carbon use mean?
In this context, conservative means resource-cautious: needles that lose less water and use carbon sparingly, as opposed to acquisitive needles that take up and spend resources more freely.
Do the findings apply to tree species other than black spruce?
The study examined black spruce. The source material does not extend the three-trait finding to other species, so applying it more broadly would go beyond what was reported.
Why would fewer needles help if it reduces photosynthesis?
The researchers suggest the water saved through reduced transpiration outweighs the lost photosynthesis under warm, dry conditions — a “double safety” effect when combined with needles that individually lose less water.
Where can the full study be read?
It was published in Annals of Botany under the title “Selection for fewer, water- and carbon-conservative needles in black spruce trees under warm, dry climates.”
