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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →Quaking aspens can carry a measurable imprint of past drought into leaves produced in later growing seasons. In a three-year common-garden experiment, prior drought was associated with changes in leaf defense chemistry and fungal communities. The trees did not keep their old leaves or consciously remember anything: the finding is a physiological legacy, and its effects on long-term recovery remain unknown.
What “remembering” means when aspens shed their leaves
“Functional memory” is the study authors’ term for a persistent imprint of earlier environmental conditions on leaf traits. Aspen leaves are shed and replaced, but the researchers detected differences in newly produced leaves in later seasons. The phrase describes those lasting physiological effects, not conscious memory or the survival of the same foliage.
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The study, “Functional memory of drought affects leaf chemical defenses and microbial interactions in aspen,” by Aubrey M. Hawks and co-authors, appeared in New Phytologist on September 13, 2026. Read the study.
How researchers tested drought history
The researchers used clonal rootstock of quaking aspen (Populus tremuloides) collected from sites in five national forests in Utah and Colorado, then propagated it in a University of Utah common garden. The full experiment included 360 plants arranged in randomized blocks. From 2021 to 2023, watering treatments varied by year; drought-treatment blocks received reduced irrigation, and temporary rain-exclusion canopies were used in 2022 and 2023.
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The researchers compared plants with different drought histories, including continuous-control, repeated-drought, and alternating drought-and-recovery sequences. They sampled leaf chemistry and foliar fungi. Because the plants grew under controlled common-garden conditions, the comparisons show how drought history was associated with later traits in this experiment; they do not establish that every aspen population responds the same way in a natural forest.
What changed in leaves after drought
Prior-year drought was associated with higher levels of salicinoid phenolic glycosides (SPGs) and lower levels of condensed tannins (CTs). Both are classes of defensive phenolic compounds, so the response was not simply an increase in every measured defense. Genotype also explained substantial variation in chemical defenses.
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SPGs and canopy damage
In 2023, plants that had experienced drought the previous year had 8% higher total SPGs than prior-year controls (Hawks et al., 2026; P < 0.0001). Higher SPG concentrations were associated with less canopy damage: the authors estimated that each 1% increase in SPGs by dry weight corresponded to 1.8% lower expected canopy damage (95% CI: 0.8% to 2.9% lower; P < 0.001).
That is an association, not proof that SPGs alone caused the reduction in damage. Relationships between CTs or total phenolics and canopy damage also depended on drought history. The authors found no evidence that greater allocation to defensive chemistry came at the expense of growth.
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Leaf-associated fungi
Fungi classified as pathogen-capable in the analysis were more abundant under current-year drought and declined as SPG concentrations increased. Responses varied among fungal groups, however, and the community-level pattern was modest: a model including drought-treatment group, SPGs, and CTs explained 3.9% of variation in fungal community composition (R² = 0.039; P = 0.001).
These findings describe community associations; they do not show that a particular fungus caused leaf damage. The study notes that Cladosporium has varied lifestyles and that its ecological role in this setting remains uncertain.
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What the experiment does—and does not—show
The results indicate that drought history can be associated with chemical and microbial differences in newly produced aspen leaves after conditions change. They do not establish whether those shifts ultimately help or harm recovery, protect trees from future drought, or determine forest decline. The physiological or molecular mechanism behind the chemical legacy also remains unresolved.
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As study co-author Talia Karasov, assistant professor of biology at the University of Utah, put it: “We wanted to understand drought not simply as an acute stress, but as an event that may reshape how trees interact with their biotic environment long after soils have rewetted,” according to the University of Utah’s October 9, 2026 explainer.
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