Mountain forests may be moving in opposite directions at the same time, according to a new global study that links the future of montane tree species to the way they transport and manage water. As temperatures rise and drought intensifies, some trees are rapidly advancing toward cooler elevations, while others appear capable of expanding downslope into warmer areas. The difference, researchers report, can be predicted by hydraulic traits—an often overlooked set of characteristics governing how leaves and stems acquire, move and conserve water.
The findings, published in Nature Climate Change, offer a mechanistic explanation for why tree species exposed to the same mountain climate can respond so differently. Rather than treating warming-driven migration as a uniform uphill movement, the study shows that climate sensitivity and hydraulic performance can push species along contrasting geographic trajectories. This distinction could reshape forecasts of how montane forests will be reorganized during the coming decades.
The research team integrated one of the broadest datasets yet assembled to examine these changes. It combined hemispheric-scale tree-ring records from 45 species and 121,743 individual trees with global observations of elevational range shifts covering 102 species. The researchers also incorporated hydraulic trait information for 11 functional attributes, connecting long-term growth responses and observed distribution changes with the physical properties of trees’ water-use systems.
Hydraulic traits describe the architecture and operating limits of a plant’s internal water network. Water absorbed by roots travels upward through xylem, a specialized tissue that must maintain a continuous pathway from soil to leaves. During drought, declining soil moisture and rising atmospheric demand can place this pathway under intense tension. If the water column breaks, a process known as embolism, the affected tissues may lose their ability to transport water efficiently. Leaf-level traits also influence how rapidly plants lose water through transpiration and how effectively they regulate that loss.
The study found that species more sensitive to warming and drought tended to track changing conditions rapidly by shifting toward higher elevations. Higher slopes generally provide cooler temperatures and, in many mountain systems, a refuge from heat stress. For a climate-sensitive tree, moving upslope may therefore represent a race to remain within a tolerable climatic envelope. But this apparent mobility does not necessarily indicate greater ecological strength. A species may move quickly because populations at lower elevations are increasingly exposed to conditions that damage growth, reproduction or survival.
In contrast, species that showed greater resistance to heat and water stress were positioned to expand downslope. Their hydraulic systems may allow them to continue functioning under warmer or drier conditions, opening habitats that were previously too stressful. This could produce a striking reshuffling of forest communities: vulnerable species retreating toward mountain summits while more stress-resistant species spread into lower elevations. The result would not simply be forests climbing upward, but a complex reassembly in which winners and losers are determined partly by water transport strategy.
The researchers also uncovered evidence that the relationship between climate and tree growth is not fixed. For nearly one-third of the species examined, the way drought sensitivity varied with elevation changed over time. A species that once grew relatively well under a particular combination of temperature and moisture may now respond differently as climate conditions shift. Such changes suggest that trees are experiencing a dynamic reorganization of climate–growth relationships across mountain gradients, rather than responding to a single, permanent environmental threshold.
This time-dependent pattern is important for conservation planning. Elevational range limits are often used to estimate where species will occur in the future, but a static model can miss changes in acclimation, competition and stress exposure. Hydraulic traits could help improve those projections by revealing why a species is likely to persist, decline or expand in a particular direction. They may also help identify populations that are especially vulnerable before large-scale changes become visible in forest inventories.
The study does not imply that every hydraulically resistant species will automatically conquer lower elevations, or that every climate-sensitive species will successfully reach higher ground. Mountains contain fragmented habitats, abrupt changes in soil and precipitation, and barriers created by human land use. Seed dispersal, competition, pests and fire can all limit migration. Even so, the researchers’ synthesis establishes leaf- and stem-level hydraulic characteristics as a powerful biological signal of future range dynamics. As warming and drought intensify, understanding how trees move water may prove essential to predicting where montane forests will survive—and what they will become.
Subject of Research: Hydraulic traits and elevational range shifts of montane tree species under warming and drought
Article Title: Hydraulic traits govern opposing range shifts of montane trees under warming
Article References: Zhang, X., Liu, H., Manzanedo, R.D. et al. Hydraulic traits govern opposing range shifts of montane trees under warming. Nat. Clim. Chang. (2026). https://doi.org/10.1038/s41558-026-02726-6
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41558-026-02726-6
Keywords: Montane forests, climate change, warming, drought, hydraulic traits, tree-ring data, elevational range shifts, forest ecology, plant water transport, tree migration
