Hydraulic traits reveal which mountain trees climb or retreat as warming intensifies

As global temperatures climb, mountain forests are on the move. But not all species are heading in the same direction, and a new analysis published in Nature Plants suggests that the hidden plumbing inside trees may explain why. By combining historical climate records, tree-ring measurements and detailed hydraulic trait data across dozens of species and thousands of mountain sites, researchers have uncovered a striking pattern: the way a tree transports and manages water appears to determine whether it migrates upslope in response to warming or retreats downhill as drought stress intensifies.

The scale of the underlying evidence base is considerable. The authors analysed past climate data alongside tree-ring records for 45 species, elevational-shift data covering 102 species across 3,057 mountain sites, and direct measurements of 11 distinct hydraulic traits. This combination allowed them to link long-term patterns of range movement with the physiological machinery that governs how individual trees cope with water limitation, a connection that has long been suspected but rarely demonstrated at such breadth.

The central finding is deceptively simple. Species with more efficient water transport systems, indicated by traits such as higher leaf-specific hydraulic conductivity, were more likely to shift their ranges upslope under climate warming. These trees can move water quickly through their vascular tissue, sustaining growth even as conditions change, which seems to give them the capacity to colonise higher, cooler elevations. In contrast, species adopting more conservative, drought-resistant hydraulic strategies tended to move downslope as drought stress intensified, a counterintuitive result that challenges the assumption that warming pushes all mountain species uphill.

Hydraulic efficiency did not only influence the direction of movement; it also shaped the pace. The rates of range shifts were themselves influenced by water-transport characteristics, meaning that two species experiencing essentially the same warming trend can respond at markedly different speeds. Species exhibit distinct movement patterns even under comparable warming conditions, the authors report, underscoring that climate velocity alone is a poor predictor of where forests will actually end up.

One of the most consequential discoveries concerns change over time. For nearly one-third of the species examined, the relationship between elevation and drought sensitivity shifted over the course of the twentieth century. In other words, the elevation at which a given species was most vulnerable to drought was not fixed. This points to a dynamic reorganization of climate–growth relationships across mountain gradients, with tree-ring records revealing that the physiological rules governing where trees can thrive have themselves been rewritten by a century of environmental change.

The technical significance of this reorganization is hard to overstate. Ecological models that forecast species distributions typically assume that a species’ climatic tolerances remain constant through time, an assumption known as niche conservatism. If the drought sensitivity of a population at a given elevation can change substantially within a single century, those assumptions become shaky. Incorporating hydraulic traits into distribution models offers a way to ground predictions in measurable physiology rather than in static correlations between species occurrences and climate variables.

Tree rings provide the temporal backbone of the analysis. Because each ring records the growth conditions of a particular year, ring-width series can be compared against historical climate data to reconstruct how drought sensitivity varied across elevations and decades. When this growth-climate calibration is paired with hydraulic trait measurements, such as conductivity and post-drought recovery capacity, it becomes possible to ask not just where species moved, but why some moved quickly and others lagged behind.

The conservation implications are immediate and sobering. For drought-sensitive species that are shifting upslope, suitable habitat becomes increasingly limited near mountaintops. As these species climb, they face shrinking land area, potentially heightened competition with species already occupying high-elevation zones, and an elevated risk of local extinction once there is nowhere left to go. The study’s authors note that this squeeze effect could make mountaintop communities some of the most vulnerable in the coming decades.

At the same time, the findings offer a practical tool. Because hydraulic traits could help identify the species most vulnerable to range contraction, conservation planners may be able to tailor interventions to different elevational zones, prioritising efficient water-transporters racing upslope in some areas and conservative drought-survivors sliding downslope in others. Rather than treating mountain forests as a uniform wave of upward migration, managers can begin to think in terms of species-specific trajectories shaped by water-use strategy.

What emerges from this work is a reframing of how scientists think about mountain biodiversity under climate change. Warming sets the stage, but the script is written in xylem. The routes species take and the rates at which they take them depend on hydraulic architecture, and a substantial fraction of those rules have already changed within living memory. As warming accelerates, understanding the plumbing of trees may prove as important as tracking thermometers in predicting which forests will persist, which will relocate, and which will quietly disappear.

Subject of Research: How hydraulic traits govern the direction and rate of elevational range shifts in mountain tree species under climate warming

Article Title: Routes and rates

Article References: Yan, Y. (2026). Routes and rates. Nature Plants, 12(9), 1656-1656. https://doi.org/10.1038/s41477-026-02415-4

Image Credits: AI Generated

DOI: 10.1038/s41477-026-02415-4

Keywords: climate change, mountain forests, hydraulic traits, tree rings, elevational range shifts, drought sensitivity, plant ecology, species migration, Nature Plants, conservation, xylem conductivity, montane biodiversity