Hydraulic traits reveal why some mountain trees move uphill while others shift downhill

Scientists have uncovered a surprising truth about how mountain trees are responding to climate change. While many assumed that species would simply migrate uphill in search of cooler temperatures, a new study published in Nature Climate Change reveals that the picture is far more complex. Researchers found that some tree species are moving uphill, while others are actually shifting downhill.

The key to understanding these opposing trends lies in the trees' water management strategies. By analyzing tree ring records, climate data, and hydraulic traits from over 121,000 trees across 45 species, the international team of researchers identified that hydraulic traits, which regulate water transport and drought tolerance, are powerful predictors of how forests will reorganize in response to warming temperatures.

Trees with highly efficient water transport systems, which allow them to quickly track climate change, tend to shift upslope more rapidly. In contrast, species with stronger drought resistance often persist or even expand into lower elevations. These contrasting responses help explain why mountain forests are changing in unexpected ways worldwide.

The study also highlights the potential consequences for biodiversity. As uphill-moving species encounter progressively less available habitat, many climate-sensitive species may become concentrated in smaller and smaller areas at high elevations, intensifying competition and raising extinction risks. Conservation efforts must now move beyond the assumption that all species will simply move uphill and instead account for the physiological traits that determine each species' capacity to adapt.

Understanding these physiological differences is crucial for accurately forecasting future forest change and identifying the most vulnerable species that require targeted conservation measures.